Donald R. Belk. EVALUATION OF HYDROLOGIC RESTORATION IN THE
ALLIGATOR SWAMP: A WATER BALANCE APPROACH. (Under the
direction of Dr. Jonathan D. Phillips) Department of
Geography and Planning, November, 1990.
Measurement of the water balance is essential to
evaluating the hydrologic component of a wetland ecosystem.
Furthermore, water budgets can provide an estimation of
inputs and outputs as a basis for predicting impacts to the
wetland.
This thesis attempts to evaluate the impact of
hydrologic changes that occurred after the installation of
drainage control structures in canals within the Alligator
Sv/ainp . Three categories of study sites were evaluated. The
first category consisted of former Atlantic white cedar
(Chamaecyparis thyoides) wetlands that were logged during
the mid-1980s. These logging sites were denoted as
"post-altered" because they were located within an area
where drainage control structures and canal backfilling were
being used to restore the hydrology to pre-disturbance
conditions. Tiie second category, "altered", consisted of
similar logging sites where drainage canals remained
unimpeded. The third category, an existing stand of white
cedar, represented a "natural" area. Comparisons were made
of the water balances from each category. Changes in soil
moisture and water table elevation fluctuations were the
components of the water balance measured in the field.
The research goal was to determine whether the
hydrologic regime in the post-altered area was more similar
to the natural or to the altered study areas. A hydrologic
model that forecasts changes in the water balance following
artificial drainage was used in conjunction with the field
measurements to assess the impact of the hydrologic
restoration.
Results of the model revealed that the hydrology of the
post-altered area closely approximated that of the natural
area. This was attributed to the model's incorporation of
surface subsidence and the loss of surface moisture from
drainage. However, results of the water balance
measurements showed that no significant differences existed
between the altered and post-altered sites. Abnormally
high precipitation during the study period and the loss of
drainage canal conveyance capacity were two factors
responsible foi' the lack of differences between the two
hydrologically-distinct study area. Furthermore, the loss
of conveyance capacity resulting from the natural
deterioration of drainage canals within the study area has
led to ttie recovery of the natural hydrologic regime.
EVALUATION OF HYDROLOGIC RESTORATION
IN THE ALLIGATOR SWAMP:
A WATER BALANCE APPROACH
A Thesis
Presented To
the Faculty of the Department of
Geography and Planning
East Carolina University
In Partial Fulfillment
of the Requirements for the Degree
Master of Arts in Geography
by
Donald R. Belk
November 1990
EVALUATION OF HYDROLOGIC RESTORATION
IN THE ALLIGATOR SWAMP:
A WATER BALANCE APPROACH
by
Donald R. Belk
APPROVED BY:
DIRECTOR OF THESIS
Jonathan D. Phillips, PhD,
CHAIRMAN OF THE DEPARTMENT OF GEOGRAPHY AND PLANNING
Leo E . Z oTm, PhD.
DEAN OF THE GRADUATE SCHOOL
Jacobs, PhD
ACKNOWLEDGEMENTS
Promises made while knee-deep in the muck of the
Alligator Swamp on a 100-degree July afternoon shall not be
broken; therefore, I gratefully thank Joy Anne Schmertmann
without whose assistance the fieldwork for this thesis would
not have been accomplished. Robert E. Noffsinger of the
ARNWR staff provided everything I needed to complete the
fieldwork, including much of his free time. It was Mr.
Noffsinger who initially presented to me the opportunity to
do research on the refuge. I owe Bob a debt of gratitude
and my heartfelt thanks.
My thesis committee members were a strong foundation on
which to build this document. Dr. Jonathan D. Phillips, my
advisor, confidant, and cajoler, provided the tremendous
patience and base of support I needed. Jonathan gave his
confidence when my own was waning. His research focus,
coupled with his love of wetlands, was an inspiration
throughout this effort. Dr. Richard A. Stephenson made life
easier during graduate school. Dick was the Great Provider.
His USGS grant supplied most of my income, and he gave open
access to his office spaces and equipment. Dick bailed me
out of more than one tight situation. Dr. Mark Brinson
allowed me to freely graze his extensive library. His
incisive critiques of my drafts provided much-needed
clarity.
I wish to thank my friend James Barnett, with whom I
shared the rewards and frustrations of graduate school.
I must acknowledge many others. From the Refuge Staff:
Bonnie Strawser, John Taylor, Jim Beasley, and Thomas B.
Sumner, ECU intern. Also, Dave Hodges of the Dare County
ses office. From the Department of Geography and Planning:
Dr. Edward Leahy, who was a role model to his graduate
students during his final graduate seminar during fall 1987;
Dr. Leo Zonn , department chairman, who praised my writing
during that critical first semester; Dr. William Buckler;
Dr. Fred Day; Dr. Charles Ziehr; Dr. Simon Baker; Dr. Doug
Wilms; Dr. Pia Leahy; Dr. Phil Shea, Graduate Coordinator
and my first contact at ECU; and Becky Moye and Shirley
Evans, the next two people I met at ECU, who lifted my
spirits on numerous occasions. Other ECU faculty: Dr. Lee
Otte; Dr. Holly Matthews; Dr. Vince Beilis; Ms. Ann Beilis;
Mr. Jim Watson. Fellow graduate students: Lynn Muter and
Kyle Schick, with whom I share fond memories during my first
year; David Hunt, who provided invaluable assistance on the
Atlas software; Scott Wade; Mike Smith; Kevin Madden; Aaron
Russell .
Lastly, but most of all, thanks to my dear wife,
Sharon for her love and understanding during everything of
the last ten years, and to Arren and Ashley for the
brightest shining moments of my life.
TABLE OF CONTENTS
PAGE
LIST OF TABLES v
LIST DF FIGURES vi
CHAPTER I. INTRODUCTION I
CHAPTER II. PURPOSE STATEMENT 3
CHAPTER III. GEOGRAPHICAL CONTEXT A
Hydrology 4
Human-Environment Interaction 7
CHAPTER IV. BACKGROUND II
Location and Context of the Study. ... II
Pocosin Communities: Successional
Relationships 19
Atlantic White Cedar 24
Organic Soils 27
Effects of Logging on Soil Properties. . 34
Wetland Hydrology 35
Wetland Evaporation Studies 38
Recovery of Artificially Drained
Wetlands 46
CHAPTER V. METHODOLOGY 50
CHAPTER VI. EXPECTATIONS OF THE STUDY 62
CHAPTER VII. RESULTS 67
NAG Calculations 67
Soils 72
Water Tables 75
Calculation of Water Balances 76
CHAPTER VIII. DISCUSSION 85
Research Needs 92
CHAPTER IX. SUMMARY AND CONCLUSIONS 96
BIBLIOGRAPHY 99
V
LIST OF TABLES
TABLE PAGE
1 SUMMARY OF NAG CALCULATIONS 69
2 SUMMARY OF NAG CALCULATIONS (CONT'D) 70
3 SUMMARY OF SOIL DATA 73
A RESULTS OF T-TESTS, SOIL DATA 74
5 SUMMARY OF WATER TABLE DATA 77
6 RESULTS OF ANALYSIS OF VARIANCE, WATER TABLE DATA
SITE COMPARISONS 78
RESULTS OF ANALYSIS OF VARIANCE, WATER TABLE DATA
GROUP COMPARISONS 79
WATER BALANCE SUMMARY 81
V i
LIST OF FIGURES
FIGURE PAGE
1 NORTH CAROLINA, SHOWING LOCATION OF
ALBEMARLE-PAMLICO PENINSULA 12
2 ALBEMARLE-PAMLICO PENINSULA, WITH SELECTED
FEATURES 13
3 STUDY AREA, SHOWING LOCATION OF SITES AND
TEST WELLS 51
4 WATER TABLE FLUCTUATIONS, POST-ALTERED SITES. . 82
5 WATER TABLE FLUCTUATIONS, ALTERED SITES .... 83
6 WATER TABLE FLUCTUATIONS, CEDAR STAND 84
7 MEAN WATER TABLE FLUCTUATIONS FOR EACH STUDY
GROUP 89
CHAPTER I
INTRODUCTION
Scientific research into wetland functions and values
has changed the public's perception of wetlands. Once
viewed as miasmatic wastelands, these areas are now highly
regarded for their economic, aesthetic, and biological
properties (Greeson et al, 1979; Bardecki, 1984; Farber and
Costanza, 1987). As the study of wetlands has progressed,
the need persists for further research into wetland
hydrology. Hydrologic processes are the primary influence
on wetland ecology and maintenance, yet the interactions
between hydrology and wetland functions are not fully
understood (Carter, 1986; Mitsch and Gosselink, 1986).
Measurement of the water balance is essential to
evaluating the hydrologic component of any ecosystem.
Furthermore, water budgets provide a first approximation of
inputs and outputs as a basis for hydrologic models and
predictions of impact (Carter, 1986). Wetland water budgets
are particularly important since investigations of
sedimentary inputs and outputs to wetlands are dependent
upon water movement. Despite this need, many previous
evaluations of wetland water budgets have either failed to
meas LI re all components, or have not used site-specific data
(LaBaugh, 1986). The need exists, therefore, for a
field-oriented hydrologic study in which care is taken in
measuring all components of the water balance. This is
concurrent with the need for expanded research and basic
data collection which focusses upon wetland hydrology and
its relation to other functions (Carter, 1986).
This thesis involves the compilation of water budgets
for the purpose of examining the impact of hydrologic
restoration in the Alligator Swamp of North Carolina.
CHAPTER II
PURPOSE STATEMENT
The purpose of this thesis is twofold. First, it will
compare the variations in water table fluctuations and soil
moisture within a regenerated, second growth stand of
Atlantic white cedar and both canalized (altered) and
hydrologically restored (post-a 11ered) clear-cut white cedar
bogs. Secondly, changes in water table levels will provide
data for the compilation of water balances to determine the
impact of hydrologic restoration on the water availability
in post-altered wetlands. The goal of this research is to
determine whether the hydrologic regime in the post-altered
wetlands is more similar to the undrained or to the altered
(canalized) study areas.
Additionally, this thesis will be the foundation of
long-term research on the effects of hydrologic restoration
and the success or failure of the regeneration of Atlantic
white cedar (Chamaecvparis thyoides) in the Alligator Swamp
(Noffsinger and Belk, 1989).
CHAPTER III
GEOGRAPHICAL CONTEXT
The analysis of changes in water regimes associated
with natural, altered, and post-altered wetlands can be
placed in the context of at least two major traditions or
subdisciplines of geography. First, the project is a study
in hydrology, which is an important subdiscipline of
physical geography (Gregory, 1985). Second, the setting of
the study - wetlands altered by human activity - places this
work in the tradition of man-land or man-environment studies
in geography (Goudie, 1986).
Hydrology
Hydrology is the study of the occurrence, distribution
and movement of water over, on, and under the earth's
surface. Knowledge of hydrology is essential in the fields
of agriculture, botany, forestry, soil science, geology,
geomorphology, and ecology. The realm of geography
encompasses or overlaps all of these; hence, specialists
from many fields have contributed to the development of
hydrology as a distinct discipline. Consequently, according
to Ward (1967), hydrology has grown "from the outside
towards a center".
5
The hydrologic cycle has long fascinated humankind.
With its inherent elegance, this cyclical movement was seen
as a great principle of order, inexorably linked to the
success of agriculture and, ultimately, to human survival.
Philosophers and theologians from medieval to modern times
have viewed the hydrologic cycle as irrefutable evidence of
the "wisdom of God" (Tuan, 1968). Geographers remain
intrigued by its conceptual elegance. R. J. Cborley, one of
the world's most influential geomorphologists, defined the
hydrologic cycle as a "natural manifestation of great
pervasiveness, power, and beauty that transcends man's
territorial and intellectual boundaries" (Chorley, 1969).
Biswas (1970) traced the history and development of
hydrology from antiquity (the first recorded evidence of
water resources work occurred in 3200 B.C.) through the
nineteenth century, when many of the theoretical foundations
of modern hydrology were began. Some of the most important
achievements included work in groundwater hydrology by the
British geologist William Smith (1769-1839), who is credited
with combining the disciplines of hydrology and geology, and
by the Frenchman Henri Darcy (1803-1858), who developed the
theoretical basis of soil and groundwater flow (Darcy's
law). The work of John Dalton (1766-1846), who first
recognized the relationship between evaporation and vapor
pressure, led to a generalized theory of vapor pressure
(Dalton's law of partial pressures) as well as to a method
6
for the estimation of evaporation (Dalton's equation).
Other significant achievements included the 1862 publication
of the first "modern" hydrology manual by Nathaniel
Beardmore, and the beginning of systematic gaging of streams
in representative watersheds of the United States (Biswas,
1970). Chow (1966) traced the development of hydrology
through periods of observation (1600-1600 A.D.), measurement
(1600-1700), experimentation (1700-1800), modernization
(1800-1900), empiricism (1900-1930), rationalization
( 1930-1950), and theorization ( 1 950-present) .
One of the most important contributions made to the
understanding of hydrologica1-c1imatic relationships evolved
from the work of the distinguished geographer C. W.
Thornthwaite, who was concerned with practical problems of
crop irrigation. He developed a system of climate
classification based on water surplus and deficiency, where
climatic boundaries were determined rationally by comparing
precipitation and evapotransporation, rather than by the
vegetative regimes adopted by the Koppen classification.
Thornthwaite calculated water need based on air temperature,
latitude, and seasonality. (Thornthwaite, 1968). His
climate classification system has been discussed in many
physical geography textbooks (for example, Strahler and
Strahler, 1983). The practicality of Thornthwaite's system
was confirmed when the United States Department of
Agriculture adopted the soil-water balance as the
7
fundamental criterion in the U.S. system of soil
classification (Soil Survey Staff, 1975).
The water balance concept was further refined by
Thornthwaite and his associate, J. R. Mather (Thornthwaite
and Mather, 1955; 1957; Mather, 1978) and is now accepted as
a basic tool in environmental analysis, including
hydrological studies in wetlands (Dooge, 1972; Carter et al,
1979; Carter, 1986; LaBaugh, 1986).
Human-Environment Interaction
Human - enVironment interaction is a fundamental theme in
geography. The environmental crises besetting modern
society have lead some geographers to reexamine this theme
as one of overriding importance in the discipline. Ronald
F. Abler, in a presidential address to the Association of
American Geographers, declared that geographers "should
speak of physical geography and of human-environment
interactions in the same way we should speak of the world's
human geography...(with a) discourse rooted in places,
regions, and interconnections.." (Abler, 1987).
Guelke (1989) advocates adopting human-environment
interaction as geography's fundamental concern. This would
provide a basis for a stronger and more coherent discipline.
Although physical geography and the study of physical
8
processes are often viewed as entities that are quite
separate from human geography, Guelke states that
"scientific knowledge of physical processes is human
knowledge, and is relevant in human geography to the degree
that people incorporate this knowledge in the way they
relate to their environment...in dealing with problems
relating to human activities on the earth, geographers would
not ignore spatial and locational factors, but these factors
would be incorporated within the human-environment theme."
Guelke adopts a strict environmentalist viewpoint by stating
"few people have integrated the possible consequences of
their present actions with future prospects of their own
survival . . .how people see themselves in a global context,
and how these understandings are reflected in their
lifestyles becomes a question for geographical analysis."
For Guelke, this idea means that the coherence of the
environmental-determinist approach to geography could be
regained without "readopting its discredited causal thesis"
(Guelke, 1989).
The theme of human-environment interaction has a rich
tradition in geography. The influence of human impact on
the environment was first explored in detail by George
Perkins Marsh, who in 1864 published the monumental work Man
and nature; or physical geography as modified by human
action . This book was probably the most important landmark
in the history of the study of human-environment interaction
9
(GoUdie, 1986). Marsh, who drew his inspiration from the
great generalist Alexander von Humboldt, defined geography
as "the science of the absolute and relative conditions of
the earth's surface and of the ambient atmosphere and the
investigation of the relations of action and reaction
between man and the medium he inhabits" (Lowenthal, 1958).
Elisee Reclus, the prominent French geographer of the
late nineteenth century, drew from the ideas of Marsh in his
two-volume work The Earth (1871). Carl 0. Sauer
(1889-1975), the great historical-cultural geographer, was
strongly influenced by Marsh, especially while developing
his concept of destructive exploitation. Sauer is credited
with reintroducing the American public to the work of Marsh
(Speth, 1977). Today, George Perkins Marsh is considered
the nation's first conservationist and the "father of the
environmental movement" (Curtis et al, 1982).
The discipline of geography, with its focus on the
analysis of human-environment interaction, is
well-positioned to address the myriad of concerns about the
present state of the environment. Alteration of wetlands
has been a significant human activity since the beginning of
colonial settlement. For three hundred years, the wetlands
of the Albemarle-Pamlico peninsula have undergone change or
destruction as the nature of land-use has shifted from
plantation agriculture to widespread logging to large-scale
10
corporate farming activities (McMullan, 1984). Yet, only in
the last 30 years have the inherent values of wetlands and
the human impact of wetland destruction been recognized.
Prudent management of North Carolina's last remaining
wetlands is thus a question for geographical analysis, as
the issues of growth, development and the preservation of
wetland values must be resolved. As such, this thesis may
appropriately be viewed in the broader context of the
man-enVironment tradition of geography.
CHAPTER IV
BACKGROUND
Location and Context of the Study
The Alligator Swamp, sometimes known as the Little
Dismal Swamp, lies on the mainland of Dare County in
northeastern North Carolina (Figure 1). The Dare County
peninsula is bordered by the Alligator River to the west,
the Albemarle Sound to the north, and to the east by the
Croatan and Pamlico Sounds. Mainland Dare County is the
easternmost part of the low-lying Albemarle-Pamlico
peninsula (Figure 2). It contains a mosaic of wetland
ecosystems, including large areas of pocosins. Pocosins are
found on the lower coastal plain of the southeastern United
States and are concentrated in North Carolina. They
comprise more than 50% of North Carolina's freshwater
wetlands (Richardson et al, 1981). According to the United
States Fish and Wildlife Service's wetland classification
system (Cowardin et al, 1979) pocosins are of the palustrine
system, with two vegetational classes: (1) Scrub-shrub, with
a shrub understory and scattered pond pine (Pinus serótina),
and (2) Broadleaf evergreen shrubs such as titi-bush
(Cyrilla racemiflora), sweet bay (Magnolia virginiana), and
red bay (Persea borbonia). Pocosins are associated with
several other wetland vegetation communities (Kologiski,
1977). Pocosins are frequently saturated and are also
Figure 1
NORTH CAROLINA
showing location of Albemarle—Pamlico Peninsula*
ro
?Dore, Hyde, and Tyrrell County mi Albennorle—Pomlico Península
Figure 2
ALBEMARLE-PAMLICO PENINSULA
with selected features
study Area
14
subject to periodic burning. These fires are a crucial
factor in the structure and composition of pocosin
vegetation (Christensen et al, 1981). Pocosins are
evergreen shrub bogs characterized by an extended
hydroperiod, with ombrotrophic (nutrient-poor) and
predominately organic soils of high acidity. The term bog
is defined as a peat-accumulating wetland that has no
significant inflows from the surrounding area and supports
acidophilic mosses such as sphagnum (Dooge, 1972; Mitsch and
Gosselink, 1986).
Pocosins generally occur in four topographic settings:
(1) blocked drainage systems; (2) Carolina bays; (3) ridge
and swale systems associated with ancient dune or beach
ridges on the lower Coastal Plain terraces; and (4) seeps,
springs and slow-flowing streams in the Sandhills region
(Christensen et al, 1981; Otte, 1981). Blocked drainage
systems, in which most pocosins occur, developed 10,000 to
15,000 years ago during the Wisconsin glaciation (the last
major ice advance during tlie Pleistocene) as sediment and
organic debris settled and clogged streams. The stream
valleys became filled with the accumulation of peat, which
spread laterally over the entire interstream divide and
formed a peat dome (hence the derivation of the term
'pocosin' from the Algonquian term for "swamp on a hill")
(Otte, 1981). These organic deposits lie atop the Pamlico
morphostratigraphic unit (msu), a Pleistocene formation of
15
arenaceous clays and argillaceous sands that lies east of
the Suffolk Scarp (Daniels et al, 1978). Carolina bays,
which are characterized by elliptical, peat-filled
depressions, occur abundantly in a broad band across the
Coastal Plain of the southeastern United States. They vary
in size from less than 50 meters in length to more than 8
kilometers long (Lake Waccamaw in Columbus County, North
Carolina). Other freshwater lakes associated with Carolina
bays are White Lake and Black Lake in Bladen County. The
geologic origin of Carolina bays is uncertain, and many
controversial theories have been proposed. Ridge and swale
and sandhills pocosins are relatively small in total area,
and have not received a great deal of attention in the
literature (Sharitz and Gibbons, 1982).
The pocosin wetlands of North Carolina, which in 1962
comprised nearly 70% of the nation's pocosins, once covered
more than 890,000 hectares (2.2 million acres) in the lower
Coastal Plain (Wilson, 1962). Today, however, only 31%
(281,000 ha, or 695,000 acres) of North Carolina pocosins
remain in a natural state. The remaining 607,000 ha (1.5
million acres) have been partially or totally altered by
human activities. As recently as 198A, the pocosins of
North Carolina were being lost at the rate of 17,600 ha
(A3,500 acres) per year (Tiner, 198A).
16
Pocosins remain the least known of wetland ecosystems.
The relative isolation and inaccessibility of these wetlands
have caused them to be largely ignored by the scientific
community until recently (Richardson, 1983). Commercial
interest in peat mining, logging, and agriculture, countered
by a national interest in wetland preservation brought
pocosin wetlands to the attention of the general public
(DeBlieu, 1987). Pocosins are now recognized as unique,
vital ecosystems of great importance to the economy of North
Carolina, especially for their roles in maintaining
estuarine water quality, and for providing habitat for
wildlife species.
The Alligator Swamp, located on the Dare County
peninsula between the Alligator River and the Pamlico Sound,
contains large areas of pocosins and associated wetland
ecosystems, which comprise more than 50% of the county's
total area. Natural pocosins in Dare County were estimated
at 55,850 ha (138,000 acres) by Wilson (1962). Richardson,
et al. (1981) estimated 5% of this area had been altered by
human activities, including logging. Logging of baldcypress
(Taxodium distichum) and Atlantic white cedar (Chamaecvparis
thyoides) (commonly known as 'juniper') was a major
enterprise in the late nineteenth and early twentienth
century (Earley, 1987). Logging continues to be the major
impact on Dare County wetlands, most of which were owned by
Prulean Farms, a subsidiary of the Prudential Life Insurance
17
Company. Another large portion of natural pocosins lies in
the southern part of the Dare peninsula within the Dare
County Bombing Range, which is owned by the federal
government for the purposes of training military pilots in
bombing techniques.
Prudential subsequently sold its holdings in Dare
County (and some adjacent land in Tyrrell County) to the
Nature Conservancy, a conservation organization based in
Virginia. Negotiations between the Nature Conservancy and
the federal government resulted in the establishment of the
Alligator River National Wildlife Refuge in March, 198A.
The refuge encompasses more than 55,600 ha (137,411 acres)
of coastal plain ecosystems, primarily pocosin and mixed
pine and hardwood swamp forest (Dean, 1984). The refuge is
perhaps best known for research into the réintroduction of
the red wolf (Canis rufus) into a natural habitat. The
species is presently extinct in the wild (Venters, 1989).
Most of the refuge area exists in an undeveloped condition,
but many sections throughout the refuge have been recently
logged for Atlantic white cedar. Clearcutting of white
cedar, mostly second-growth stands regenerated from the
logging activities from tlie 1890's through the 1920's, began
in 1979. Some cutting is slated to continue until 1996,
because timber rights were sold by First Colony Farms prior
to ownership by Prudential and the subsequent creation of
the Alligator River National Wildlife Refuge. The United
18
States Fish and Wildlife Service, the federal service
charged with management of the refuge, will attempt to
mitigate the effects of artificial drainage through a
management plan to restore the natural hydrology of a
section of the refuge. Goals of this restoration include
the establishment of favorable waterfowl habitat and the
regeneration of Atlantic white cedar (Noffsinger, 1989).
The plan calls for the installation of water control
structures Cflashboard risers) in a canal south of Milltail
Creek (see Figure 5). The Grassy Patch canal extends from
Dry Ridge North Road and drains into the Alligator River at
Cypress Point. The proposal also includes the permanent
filling of 14 smaller, adjacent canals. Flashboard risers
will be installed each end of the Grassy Patch canal so that
water levels can be manipulated to a slight extent in order
to maintain the canal access road. This management plan
will be one of the first wetland restoration efforts
undertaken on the Albemarle-Pamlico peninsula. Furthermore,
the plan provides an opportunity to study what shall be
defined as a post-altered wetland: a recovering ecosystem
that is undergoing no further alteration from silvicultural
practices, and with drainage canals permanently closed. The
plan put forth by the Alligator River National Wildlife
Refuge staff offers a premise for the study of this
recovery.
19
Pocosin Communities; Successional Relationships
Otte (1987) defines two major pocosin types found in
the prevalent blocked drainage system setting: (1) primary
pocosins that appear to be the climax ecosystem on coastal
peat domes» with some areas that may be several thousand
years old; and (2) secondary pocosins , which exist solely
because of recent human alterations. Secondary pocosins are
at most several hundred years old. Primary pocosins are
climax communities that began as marsh systems dominated by
aquatic macrophytes and grasses, succeeded to cypress and
Atlantic white cedar swamp forests, and finally to shrub bog
pocosins (Otte, 1981).
The literature is ambiguous with regards to the climax
stage of a pocosin and whether it succeeds an Atlantic white
cedar forest or vice versa. This ambiguity exists largely
because of the complexities and uncertainties involving the
role of fire in pocosin succession. Otte (1981), when
determining the origin of peat in the Croatan National
Forest, found white cedar peat overlain by pocosin peat
(primarily consisting of shrub vegetation). Within the
pocosin peat, he found patches of marsh peat, which indicate
local, wetter conditions possibly marking areas of
relatively deep peat burns that left shallow, open pools for
some period of time. Otte based his pattern of pocosin
community development on such peat profiles. He also
20
categorized the influence of fire based on four states of
recovery which depend on the type of burn. He stated that a
fire in an area of shallow peat that is severe enough to
destroy the root and rhizome mat will be repopulated by the
same species as was present before the fire; i.e., Atlantic
white cedar.
Buell and Cain (19A3) stated that if protected from
fire, the Atlantic white cedar forest will naturally succeed
to a shrub bog. Penfound (1952) noted that evergreen shrub
bogs are formed when Atlantic white cedar is removed by
cutting or fire, but that a white cedar swamp naturally
gives way to a red bay-sweet bay community when protected
from fire.
Descriptions of North Carolina forests by Ashe and
Pinchot (1897) and Korstian and Brush (1931) indicate that
Atlantic white cedar existed in a vast range throughout the
coastal plain prior to human settlement. The presence of
white cedar logs beneath shallow peats in the Holly Shelter
and Green Swamps (Kologiski, 1977; Otte, 1981) and the
presence of white cedar stumps in peat of the Hoffman Forest
(Daniels, et al., 1977) support the contention that vast
white cedar forests once existed prior to human disturbance,
only to be replaced by pocosins that were created primarily
by chronic human disturbance of the forests.
21
N. L. Christensem (1981) contends, however, that
pocosins are stable, and except at their margins, show
little evidence of succeeding to white cedar or cypress
forests. Radiocarbon dates of white cedar stumps at the
base of 1 to 2 meters of peat in a Hoffman Forest shrub bog
show that 5,000 to 7,000 years before present, a white cedar
swamp existed. This indicates that pocosins are actually
very stable ecosystems. Christensen states that instead of
creating pocosins, human disturbance actually extends
pocosin boundaries (Christensen, et al., 1981). Activities
such as logging leave extensive areas of slash and brush
that provide fuel for fires that encourage the establishment
of fire-to1erant pocosin species. Logging, therefore, may
have increased the extent of pocosins and decreased swamp
forests (Ash, et al., 1983).
It is unrealistic to theorize on the natural succession
of pocosin communities in the absence of fire (Christensen,
et al., 1981). The accumulation of decaying organic
material on the surface, the accumulation of the peat layer,
seasonal fluctuations in the water table, and the
flammability of shrub vegetation indicate that fire is
inevitable, and eventually these areas will burn. Gnce
pocosins are established, the character of the vegetation
favors a fire regime that tends to perpetuate that
vegetation .
22
Kologiski C1977) made an extensive survey of plant
communities of the Green Swamp in Brunswick County, North
Carolina, and devised a hierarchical scheme consisting of
five major vegetation systems. Only one of his systems fits
the definition of a true pocosin as described in a community
profile of pocosins and Carolina bays by Sharitz and Gibbons
(1982). Kologiski's white cedar bog system included two
community types: one with a dense canopy over deep organic
soils, and the other with a mixed Atlantic white
cedar/loblolly pine over shallow organic soils underlain by
sandy clay loam. Kologiski speculated the white cedar
forest would succeed to an evergreen bay forest following
logging. Additionally, fire intensity would determine if
the evergreen bay forest reverts to a pocosin or white cedar
forest (shallow burn), a sedge bog (deep burn/high water
table), or deciduous bay forest (deep burn/low water table).
However, the suitability of Kologiski's classification
scheme outside of the Green Swamp has yet to be determined
(Christensen et al, 1981); thus, the successional
relationships among common pocosin community types remain a
matter of speculation (Sharitz and Gibbons, 1982).
It would appear that post-fire regeneration of an
Atlantic white cedar versus a pocosin community is
indeterminate (Frost, 1987). Time of year, height of water
table, and depth of burn are interrelated factors which will
determine the potential of a plant community to occupy a
23
site disrupted by fire. For example, white cedar will
regenerate if a fire kills the canopy but does not burn deep
enough to destroy the seed bank within the soil. A deep
peat burn, however, destroys the seeds and prevents the
reestablishment of white cedar, thus favoring other pocosin
species. Korstian (192A) stated that slash fires were
beneficial to regeneration after logging. However, a second
burn some years after would eliminate white cedar, Korstian
noted that seed bank viability was the most important factor
in Atlantic white cedar regeneration. He stated that
despite repeated logging from the period following the
American Revolution to 192A, good restocking generally
resulted. Korstian observed that if the original stand of
white cedar is destroyed, together with the seed bank,
succession would be toward a pine-dominated community.
Secondary pocosins are defined by Otte (1987) as those
areas where scrub-shrub vegetation has occurred after
documented human intervention in Atlantic white cedar
forests. Such secondary pocosins do not exhibit the
well-defined vegetation community patterns found in primary
pocosins. When Atlantic white cedar forests were destroyed
during the intense logging activity of the late 1800’s
through the 1920's, the construction of drainage ditches and
barge canals for timber removal disrupted the natural flow
of water and nutrients. This set the stage for an
ombrotrophic environment (Otte, 1987). Fires
24
that burned in the logged areas destroyed the seed bank,
allowing the pocosin species that were present in the cedar
forest to quickly regenerate. Some areas that remained wet
or did not burn completely recovered as white cedar forests.
These areas can be found today in the Dismal Swamp of
Virginia and in the Alligator River National Wildlife
Refuge. The Alligator River stands that have regenerated
constitute the previously mentioned present-day logging
sites with the refuge. Thus, the post-altered pocosin area
that will be studied in this thesis originates from a
secondary pocosin.
Atlantic White Cedar
Atlantic white cedar (Chamaecyparis thyoides) is an
evergreen aromatic tree with narrow, pointed spirelike
crowns and slender, horizontal branches. The height of
mature specimens ranges from 15 to 27 meters (50 to 90
feet). White cedar is generally found in wet, peaty, acidic
soils where it forms pure stands (Little, 1980). Atlantic
white cedar is geographically distributed along a narrow
band of the eastern coastal United States, restricted to
freshwater wetlands from Maine to Mississippi (Laderman,
1982). There are no quantifiable estimates of the
presettlement range of Atlantic white cedar, but geographic
place names may provide a rough estimate of the former
existence of Atlantic white cedar forests during the last
25
300 years (Dill et al, 1987; Frost, 1987; Belk, 1989). The
extent of Atlantic white cedar forests has been steadily
reduced since colonial times, as these forests were used for
their valuable timber. Pioneers used the durable wood for
log cabin floors and shingles, and during the American
Revolution, the wood was burned to make charcoal for
gunpowder. White cedar wood remains valuable today. It is
highly regarded as an exterior building material because of
its resistance to rot, and as an interior wood because of
its aromatic properties (Little, 1980; Earley, 1987).
The most extensive Atlantic white cedar forests extant
in North Carolina, and probably in the world, are located in
the Alligator River National Wildlife Refuge (Moore and
Laderman, 1989). White cedar in this region occurs in pure,
even-aged stands, and in lowland swamp forests where it is
mixed with lowland conifers and hardwoods. The shrub layer
in pure stands most frequently contains sweet pepperbush,
highbush blueberry, dangle huckleberry, large gallberry,
inkberry, possumhaw, fetterbush, maleberry, and evergreen
bayberry (Moore and Carter, 1987). The mixed stands contain
such species as red maple, blackgum, water túpelo, and
baldcypress, along with scattered pond pine, loblolly pine,
and occasional sweet bay (Levy, 1987).
Atlantic white cedar is very intolerant to shade. It
does not reproduce beneath its own living canopy or that of
26
a deciduous swamp forest. Fire provides the opportunity for
white cedar to repopulate a site or colonize an adjacent
site occupied by other wetland communities. An intense
fire, however, destroys the seed bank and prevents the
reestablishment of cedar. Hydrologically, the moisture
regime of white cedar appears to lie on a gradient between
swamp forest (wetter) and pocosin (drier) (Frost, 1987).
Golet and Lowry (1987) monitored water table activity in six
Atlantic white cedar wetlands in Rhode Island over a six
year period to analyze the relationships between water
regimes, tree growth, and other site characteristics. They
did not find a general relationship between water regime and
annual radial growth, but indicated that more extensive data
on soil moisture may provide more evidence for such a
relationship .
The Atlantic white cedar has been extirpated from over
90% of its presettlement range in North Carolina (Frost,
1987, 1989). Traditionally, Atlantic white cedar has
regenerated sufficiently to permit extensive logging
(Korstian, 192A). However, present-day encroachment into
environments otherwise suitable for the growth of white
cedar has diminished its natural regenerating capacity.
Several factors may account for the failure of white
cedar to regenerate. Artificial drainage in white cedar
wetlands alters the soil regime by causing dehydration.
27
compaction, and subsidence. These factors lead to the
shrinkage of the organic layer and to its eventual
replacement by mineral soil. Artificial drainage has also
altered natural fire recurrence intervals, allowing fires in
drier peats to burn intensely enough to destroy the seed
bank. Suppression of fire allows logging slash to compress
the soil, and shade out young seedlings.
Undoubtedly, many other factors influence the failure
of regeneration in logged Atlantic white cedar stands. Soil
and plant chemistry, algal and microbiotic relationships,
shade and seed bank density, the relationships of competing
vegetation, and the health and seed-bearing capability of
adjacent uncut specimens, to name a few, would be essential
elements of a detailed environmental study which is beyond
the scope of this thesis. However, an examination of soil
properties and moisture regimes could provide insight into
the soil and hydrologic conditions present in the white
cedar wetlands of the Alligator Swamp.
Organic Soils
Organic soils are characteristic of waterlogged or
poorly drained environments. They are created only in the
presence of anaerobic microorganisms which transform the
accumulated organic material into peat or muck by processes
of decomposition. Anaerobic conditions are essential for
28
the accumulation of organic soils, thus, such deposits are
formed in bogs, marshes, swamp forests, and other wetlands
(Gorham, 1957; Davis and Lucas, 1959; Moore and Bellamy,
1974) .
The physical characteristics of organic soils are
determined, to a large extent, by the degree of
decomposition of the organic material. Degree of
decomposition can be determined by measuring one of the
chemical or physical characteristics that change as
decomposition advances. Farnham and Finney (1965) used
fiber content to determine this property. Later, Boelter
(1969; 1972b; 1974) used bulk density as a measure of the
degree of decomposition.
Boelter (1964) stated that water retention and
hydraulic conductivity are important physical properties
that largely determine the hydrologic characteristics of
organic soils. These properties are related to porosity and
pore size distribution which in turn are related to the
degree of decomposition. As decomposition proceeds, the
size of organic particles decreases, resulting in decreasing
total porosity and higher bulk density. Thus, undecomposed
peat has a relatively low bulk density and contains large
pores that drain readily, while highly decomposed sapric
peats have a much higher bulk density and retain more water.
Boelter (1965) found hydraulic conductivities of various
29
Minnesota peats to cover a wide range of values which were
related to pore size distribution. While undecomposed peats
allowed rapid water movement, highly decomposed peats had
rates of hydraulic conductivity lower than clays. The
hydraulic conductivity of highly decomposed (sapric) peat
has a range of several orders of magnitude and may be as
high as some fibric peats. This large variation is caused
by such phenomena as piping, buried wood, and variations in
peat stratigraphy (Siegel, 1988).
Organic soil deposits in North Carolina have been
estimated to cover nearly 500,000 ha (Lucas, 1982). They
occupy three geographic settings. The largest deposits
occur east of the Suffolk Scarp, a relic shoreline of 75,000
years BP. These peatlands, also identified by the term
Blacklands, lie atop the Pamlico morphostratigraphic unit
(msu), which is the youngest exposed seabed that constitutes
the Lower Coastal Plain. These deposits include the Great
Dismal Swamp, The Albemar1e-Pamlico peninsula, the
Pamlico-Neuse peninsula, and the Alligator Swamp. The next
largest deposits of organic soils include the Croatan and
Hoffman Forests and the Green Swamp, which lie atop the
Talbot and Wicomico morphostratigraphic units east of the
Surry Scarp, a relic shoreline of 300,000-400,000 years BP
(Daniels et al, 1978). Carolina Bays are the third setting
for extensive organic soil deposits in North Carolina.
30
Organic soil deposits in the Lower Coastal Plain
contain primarily colloidal muck soils of two main types:
(1) an upper region of brownish-black, fine grained, highly
decomposed sapric peat that overlies (2) a dark reddish
brown, decomposed though slightly fibrous sapric peat. The
differences between these two types can be attributed to
their origin. The upper peat represents accumulation in a
swamp forest environment, while the lower, more fibrous peat
is indicative of a shallow marsh environment (Ingram and
Otte, 1981; 1982; Otte, 1981; Ingram, 1987). When
saturated, both mucks have the general appearance and
consistency of black axle grease or chocolate pudding
(Ingram, 1987). These colloidal mucks are formed in poorly
aerated, low energy environments (Dolman and Buol, 1967;
1968). Colloidal muck soils are characteristically sticky,
plastic, and very acid. They have extremely low values of
hydraulic conductivity (Boelter, 1965). Colloidal mucks do
not compress, but flow when put under pressure. Such
characteristics have made the utilization and development of
the deeper North Carolina Blacklands extremely difficult;
however, areas underlain by thinner organic deposits have
more agronomica1ly desirable properties and have been
intensively developed (Lilly, 1981a; 1981b).
Organic soils are grouped under the order Histosol, one
of ten soil orders that cover the world's soils, according
to the U.S. system of classification. Histosols are further
31
categorized by three suborders: Saprist, Hemist, and
Fibrist, which differentiate Histosols on the basis of
degree of decomposition of the organic material (Boelter,
1969; McKinzie, 1974). Most Histosols in North Carolina are
classified within the Great Group Medisaprist. The prefix
medi- indicates that the soil (1) has no significant
humilluvic horizon (material moved downward by leaching) and
(2) has a mean annual temperature of 47°F with more than a
9°F variation between winter and summer means (Soil Survey
Staff, 1975).
Peatlands have long been altered by human activities.
In the United States, and particularly in North Carolina,
organic soil deposits have been important in the development
of agriculture and timber resources. Organic soils were
especially important in the years before the widespread
availability of commercial fertilizers, because these soils
naturally release nutrients such as nitrogen and phosphorus
that are important for crop growth. The human effort at
management of these areas, which usually begins with
artificial drainage, has been the catalyst for research into
organic soil deposits. Artificial drainage in organic soils
has been historically recognized as the precursor to one of
the major problems encountered in peatland utilization:
subsidence.
32
Subsidence is the loss in elevation of the soil profile
after an organic soil is artificially drained. It is an
inherent problem in the management of Histosols for
agricultural and, to a lesser extent, silvicultural
practices (Maki, 1974,* Skaggs et al, 1980). Subsidence can
be attributed to several factors, including (1) shrinkage
and dehydration, (2) burning, (3) consolidation due to loss
of the bouyant force of groundwater, (4) compaction from
tillage or logging operations, and (5) biochemical
oxidation.
Shrinkage is characteristic of both drained and
undrained Histosols. The withdrawal of moisture from the
surface layers by évapotranspiration (or drawdown from a
drainage canal) may cause high moisture tensions in the root
zone, which results in a decrease in volume above the
groundwater level, or phreatic surface. In undrained
Histosols, however, shrinkage is a seasonal phenomenon, and
constitutes only a change in volume, not a physical change
in soil mass. Shrinkage can be the major contributor to
subsidence in an artifically drained Histosol if the surface
layer dries (Skaggs et al, 1980). Skaggs and Barnes (1976)
reported that colloidal mucks shrink to one-third to
one-half of their initial volume when air dried. The drying
process is irreversible, and results in stone-hard
aggregates of granular structure, similar to ground coffee.
Colloidal materials that have been irreversibly dried will
33
not regain their original volume and consistence even after
months of soaking.
Fire is a perennial problem in Histosols. Nearly all
Histosols in North Carolina have lost some surface elevation
due to burning. Many of the small lakes within the deep
peat regions of the Lower Coastal Plain may have originated
from peat fires. Some former areas of extensive organic
deposits have been subjected to such intense, repeated
burnings that today only the mineral soil surface remains
(Frost, 1989). Peat fires are particularly hazardous during
the dry season. They are extremely difficult to extinguish
and may smolder for months.
Consolidation and compaction are often combined in the
term "densification". When drainage occurs, the bouyant
force of groundwater is lost in the upper layers. The
deeper layers are then forced to bear an increased weight of
1 gram per square centimeter for each centimeter of
drawdown. This causes consolidation and compaction of the
soil layers below the water table. When heavy equipment is
used in farming or logging operations, the compaction of
these layers is intensified.
The primary cause of subsidence is decay of organic
matter. When an area is artificially drained, the water
table drops to allow oxygen to enter the soil, creating the
34
aerobic conditions necessary for decomposition. Over time,
this decay results in increasingly smaller soil organic
matter content, and a concentration of the mineral content
of the soil (Lilly, 1981a).
Effects of Logging on Soil Properties
A key to understanding the hydrologic characteristics
of altered organic soils is to examine the effect that
logging operations may have on soil properties. While
logging may not represent the final alteration that is
indicative of agriculture or peat-mining operations, it
nonetheless constitutes a profound change in the nature of
the underlying material and must be considered when
attempting to evaluate the hydrologic response of an altered
soil.
Harvest of Atlantic white cedar in North Carolina is
usually done with an amphibian feller-buncher, a
caterpillar-like machine that is specifically designed for
harvesting wetland timber. Large, hydraulically-operated
arms on the feller-buncher seize the erect tree and shear it
at the base. A worker on foot then removes the tops and
branches, which are used for traction for the skidder that
pulls the trunks to the road (Laderman, 1989). Cedar
harvesting leaves the immature, unharvested cedars
vulnerable to windthrow. Many shallow-rooted, windthrown
35
cedars were observed lying on the fringes of the logging
sites within the study area. Uprooting by windthrow can
disturb large amounts of material, often resulting in
complete inversion of the soil profile (Schaetzl, 1986).
The soil disturbance from the logging procedure results
in compaction and displacement of the mineral layer. The
resultant effects on the clay loams and sandy loams that
underlie the organic layer are increased bulk density,
reduced infiltration capacity, and decreased porosity.
These changes are not permanent. Research in the
Mississippi coastal plain on clay loam soils affected by
tree-length skidding showed a return to pre-disturbance
conditions in eight years. Soils disturbed by wheel ruts,
however, recovered after twelve years (Dickerson, 1976).
Wetland Hydrology
Hydrology is the primary factor in the establishment
and maintenance of wetlands and wetland processes (Gosselink
and Turner, 1978; Mitsch and Gosselink, 1986). These
processes are often disrupted by human activities, and the
Albemarle-Pamlico peninsula, with extensive areas of
pocosins, is one region that has been affected.
36
The hydrologic characteristics of hydraulic
conductivity, water table fluctuations, surface runoff and
nutrient relationships in a natural and an altered pocosin
have been examined by Daniel (1981), based upon his
instrumentation and analysis of three watersheds on the
Albemarle-Pamlico peninsula. He examined the hydrology of
three watersheds that are characteristic of the
Albemarle-Pamlico peninsula. The Van Swamp basin is a
forested wetland which exists primarily in a natural state,
although some drainage for road access has taken place. The
Albemarle Canal watershed typifies the heavily-drained
agricultural areas that are prevalent on the peninsula
(Daniel, 1978). The third watershed he analyzed was located
between Pungo Lake and Phelps Lake in the northeast corner
of the Pungo National Wildlife Refuge. This basin
exemplifies the pocosin system, with deep organic soils and
vegetation consisting of evergreen bay, shrub, and pond
pine .
Daniel (1981) states that the hydrologic regime of
pocosins is influenced by four input-output events.
Precipitation is, in most cases, the only input source. The
major outputs are évapotranspiration and runoff, with
groundwater recharge being the least significant of the four
components (Heath, 1975). Evapotranspiration is the most
important output during the late summer and early fall, with
runoff being the predominant output during months of
37
increased precipitation. Richardson (1982) reported that
évapotranspiration accounts for 60% to 70% of water output
during the summer and fall in an undisturbed pocosin.
Daniel (1981) reported rainfall to exceed potential
évapotranspiration in all but the driest years. These
conditions explain the elevated water tables within
pocosins.
Several examples show how the hydrology of pocosin
wetlands has been altered by the widespread installation of
artificial drainage systems for timber management and
agriculture. Initially, the clearing of ditch right-of-ways
and the removal of vegetative cover reduces transpiration
and increases evaporation. However, ditching will lower
water table levels in the vicinity of the drainage canals.
This reduces the length of time the ground is saturated,
thus decreasing evaporation. Transpiration will increase
somewhat as the vegetation recovers. Surface runoff, which
exists primarily as overland flow in a natural bog or
pocosin (Bay, 1969; Heath, 1975; Ash et al., 1983) is
increased when drainage canals are cut. Overland flow in a
bog ecosystem is diffuse. Discharge is spread over a wide
area because of the relatively low relief of a wetland.
When drainage canals are constructed, the discharge is
directed toward outflow points, thus concentrating runoff.
Drainage canals cause an increase in the rate of runoff
38
(increases in maximum flow events), though not a significant
increase in total annual runoff volume (Daniel, 1981).
Additionally, drainage canal construction alters the
properties of organic wetland soils. Ditching increases
decomposition, changing the physical properties of the peat,
so that bulk density increases and macro-pore space and
permeability decrease. The subsidence that results from
water table drawdown may change the surface topography by
forming slightly convex surface between ditches. This is due
to the convex water table between ditches. (Boelter, 1972a;
Verry and Boelter, 1979; Skaggs et al, 1980; Daniel, 1981;
Gregory et al, 198A).
Wetland Evaporation Studies
Sharitz and Gibbons (1982), in a community profile of
southeastern slirub bog ecosystems, stated that
évapotranspiration was the least-understood component in
determining the hydrologic characteristics of pocosins.
Two approaches are commonly employed in determining
evaporation from a water surface. The mass-balance or vapor
flux approach has its theoretical foundations in Dalton's
Equation, which states that the rate of evaporation is
proportional to the difference between the vapor pressure of
59
the water (or leaf) surface and the vapor pressure of the
air directly above the surface:
E = C(e - e ) ( 1 )
s a
where E is the rate of evaporation, C is a coefficient that
is a function of wind speed, and e and e are the
s a
saturation vapor pressures at the surface and the overlying
air, respectively.
The energy budget method involves the partitioning of
available net solar radiation into its different categories
of use at the earth's surface. The energy required for
evaporation, , is determined from the energy budget
equation
Q = Q - Q Q + Q + (2)
E s r s c — g —
where Q is the shortwave solar radiation, Q is reflected
s r s
shortwave radiation, Q is the longwave radiation from the
water body, Q is the sensible heat transfer to the air, Q
c g
is the change in stored energy, and is the energy
transfer between the water body and bed. Evaporation from
the water surface (E ), is then determined by
E
o Q^/pL in mm/sec (3)
4 0
where p is air density (g cm and L is the latent heat of
vaporization of water (590 cal g ^ or 2.47 x 10^ J g ^).
While the energy budget approach is the most accurate
(Winter, 1981; Carter, 1986), obtaining exact measurements
for the separate energy components is time-consuming and
requires expensive equipment. The following discussion
centers on two formulae which are more practical for use by
the researcher, and employ readily available meteorological
data .
Thornthwaite (1948) developed his formula from the
standpoint of the energy balance approach. His method uses
air temperature as an index of the energy available for
évapotranspiration. Thornthwaite's formula assumes air
temperature is correlated with the combined effects of net
radiation, and that a fixed relationship exists between
those portions of net radiation used for heating and those
used for evaporation (Thornthwaite, 1954; Ward, 1967; Dunne
and Leopold, 1978). The formula takes the form
PE = 1.6(lOT /I)® (4)
a
where PE is potential évapotranspiration in cm month T
a
is mean monthly air temperature in degrees Celsius, I is the
-2
annual heat index, and a = 0.49 + (1.79 x 10 )I - (7.71 x
10”^)I^ + (6.75 X 10"^)I^.
41
Penman (1948) developed a formula which effectively
combines the mass-balance and the energy budget approaches,
as well as allowing the use of easily-obtained data.
Derivation of the Penman formula is described in detail by
Ward (1967), Dunne and Leopold (1978), Lee (1980) and Shaw
( 1988) .
Both the Penman and Thornthwaite formulae have found
worldwide acceptance and applicability, and can be
considered the main tools of hydrologists and climatologists
in the estimation of évapotranspiration (Ward, 1967; Shaw,
1988) .
Measurement of évapotranspiration (ET) is a special
concern in the computation of water balances for wetlands.
A multitude of empirical formulae, including the previously
discussed Penman and Thornthwaite equations, have been
developed to determine évapotranspiration. tlowever, because
of the many physical and biological factors that affect ET,
Lee (1980) stated that no reliable method exists for
estimating ET rates based on simple weather data or
computation of potential évapotranspiration. While these
formulae are able to predict évapotranspiration of open
water, grasslands, and arable crops with sufficient
accuracy, their values are subject to doubt when applied to
wetlands. The reason for this is that the mosaic of swamp
vegetation is difficult to describe in terms of the
42
necessary parameters (Van der Molen, 1988). Stalks of dead
and decomposing vegetation left over from earlier years, and
present above or between the actively growing vegetation,
will influence the energy exchange with the atmosphere,
usually reducing ET. This situation exists in the logged
white cedar wetlands of the Alligator Swamp, although it is
compounded by the presence of logging slash and buried
timber. Van der Molen further states that such "untidy"
natural vegetation patterns are in strong contrast with the
well-defined open water and trimmed grass surfaces used to
calibrate the popular formulae; therefore, they are not
directly useful for wetland hydrology problems (Van der
Molen , 1988) .
In the past, hydrological studies in wetlands have
estimated ET as a residual in the water balance equation.
Carter (1986) and LaBaugh (1986) clearly demonstrated the
inherent problems in using residuals. More recently,
studies have been undertaken which attempt to relate wetland
ET to evaporation from a free water surface, but there has
been much disagreement as to whether the presence of wetland
vegetation increases or decreases the loss of water over
that which would occur from an open body of water (Carter,
1986; Mitsch and Gosselink, 1986; Koerselman and Beltman,
1988). Bay (1967), for example, determined that losses via
évapotranspiration from some northern Minnesota bogs were
88% to 121% of open water evaporation. Eisenlohr (1966)
43
determined ET losses from vegetated prairie potholes in
North Dakota were 10% lower than from those devoid of
vegetation.
Ingram (1983), in an extensive literature review of ET
studies in bogs, fens, and mires, stated that actual
évapotranspiration from bogs is approximately equal to
potential évapotranspiration. Ingram concluded that rates
of ET depend upon the vegetation type. Considering
évapotranspiration from wetlands is rarely limited by
inadequate water supply, such factors as species type,
stomatal openings, vegetative cover and density, and stage
of development could cause rates to vary from one wetland
type to another. Definitive studies in comparative rates of
ET from different plant types are lacking, however (Carter
et al, 1979). Linacre's 1976 review of évapotranspiration
from swamps concluded that the presence and nature of
vegetation have relatively minor influences on rates of ET,
at least during the active growing season (Linacre, 1976).
These reviews show, according to Koerselman and Beltman
(1988), that models for determining évapotranspiration have
not been calibrated with field data from peatlands.
Koerselman and Beltman's hydrological study of a fen in
the Netherlands, which measured all water balance
components, was undertaken to address this need. The
objective of the study was to relate actual ET to pan
44
evaporation and to Penman's potential evaporation from a
free water surface (Penman's E ). Evapotranspiration from
o
lysimeters filled with peat and vegetation was compared with
evaporation from lysimeters filled with water, and with
Penman's formula. They found that ET from the vegetated
lysimeters exceeded evaporation from water-filled lysimeters
by a factor of 1.7-1.9 and was 0.7-0.8 times less than
evaporation calculated by the Penman formula. They
developed a regression equation that described ET from fens
(in mm day as a function of Penman's E on a monthly
o
basis: ET = 0.73E + 0.16 (r=0.97). They concluded that
o
their equation was accurate, given the reliability of the
lysimeter technique, and furthermore, that it could provide
a model for the calculation of actual ET from potential ET
that could be determined from routine weather data. They
stated their equation may also apply to other peatlands in
the temperate zone under conditions of high water tables,
but that further calibration of such models is needed
(Koerselman and Beltman, 1988; Koerselman, 1989).
An earlier study by Dolan et al (1984) used a diurnal
water-table fluctuation technique as a method for measuring
évapotranspiration in a central Florida freshwater marsh.
They noted some particular problems with lysimeter studies
in wetlands, notably, that lysimeter studies involve the
physical isolation of individual plants or plant parts which
could possibly subject them to unrealistic micro-climatic
ż.5
conditions. Dolan et al found their technique to be more
suitable since relatively simple instrumentation could
provide long-term measurements of ET for an entire plant
community, not just an isolated patcli. They also devised a
regression formula for computing monthly évapotranspiration:
-5
ET = 6.85 X 10 BS + 0.10, where B is the average
aboveground live biomass, and S is the average saturation
deficit. They found that total ET for the study period (one
year) proved to be nearly identical to that predicted by the
Thornthwaite technique. They concluded that the close
agreement between the yearly totals for the regression model
and the Thornthwaite estimates may indicate that an
empirical relationship based principally on monthly average
air temperature is adequate for yearly estimates but not for
monthly estimates CDolan et al, 1984).
The above studies by Koerselman and Beltman C1988) and
Dolan et al (1984) illustrate the utility of both the Penman
and Thornthwaite formulae in obtaining reasonably accurate
estimates of ET. However, historical evidence suggests that
the Penman formula, which combines the mass-transfer and
energy budget approaches and employs a wider range of data
inputs, is more reliable for shorter (monthly) estimates
(Ward, 1967; Mather, 1978).
46
Recovery of Artifically Drained Wetlands
Hydrologic changes induced by artificial drainage are a
function of the time that has elapsed since draining
occurred. Previous research has shown that peatlands
drained for silviculture will eventually regain the
hydrologic characteristics that were altered by drainage.
Much of this research has been conducted in Finland. In
addition to being a leading exporter of timber, Finland
contains ten percent of the world's peatlands.
Investigation of the long-term influence of forestry
drainage on peatland hydrology is of particular importance
in a country where nearly one-fifth of the total land area
has been drained for silvicultural practices (Mustonen and
Seuna, 1972; Seuna, 1980).
2
Seuna (1980) examined the drainage trends for two 5 km
basins in southeastern Finland. He analyzed 21 years of
hydrologic data for both basins in a natural condition, then
for an additional 18 years after one basin was drained for
silviculture. During the 18-year post-drainage period,
there was a decreasing trend in the influence of drainage.
At the end of the period, Seuna found that mean annual
runoff had decreased to pre-drainage levels. He attributed
this to two factors: (1) an increase in évapotranspiration
caused by a new stand of timber, and (2) the impairment of
drainage ditches, which reduces water carrying capacity.
Impairment of drainage canals is an important
consideration in the hydrologic recovery of artificially
drained areas in eastern North Carolina. The general trend
of eastern North Carolina drainage canals is toward loss of
conveyance capacity. Because of uncontrolled vegetative
growth and loss in canal cross-sectional area due to
erosion, Swicegood and Kriz (1973) found water-carrying
capacity losses in eastern North Carolina canals ranging
from 17 to 61 percent over a six-year period. Such rates
would require complete channel modification within 8 to 10
years.
Physical processes involved in canal degradation have
been described by Stephenson and Steila (1982). They found
drainage canals in the Great Dismal Swamp to be susceptible
to such factors as slope failure or slumping, the formation
of alcoves at channel toeslopes, and the hydrostatic popout
of soil from channel slope banks, known as a "moyocker".
Such phenomena led to a 70 to 80 percent loss of
water-carrying capacity within only 2 years.
Phillips (1988) presented a preliminary model of
channel deterioration. This exponential model provides a
method for estimating the change in channel roughness
(Manning's n) over time, which corresponds to changes in the
canal bankfull discharge. Increases in the roughness
coefficient are most pronounced in highly vegetated
48
channels, which are prevalent in canals constructed for
silvicultural practices.
Phillips stresses the importance of channel degradation
in wetland hydrologic modelling. Considering that
environmental management policies are often based on such
models, the recovery of wetland hydrologic regimes based
upon channel deterioration may become a factor in policy
decisions. This is particularly relevant when a
determination of wetland status is required.
Wetland functions that are characteristic of natural
systems, such as flood retention and nutrient filtering, are
known to be disrupted when artificial drainage occurs (Ash
et al, 1983). Recovery of artificially drained wetlands
implies a return to these and other functions over time;
i.e., a return to stability. Phillips (1985a), in a
theoretical assessment of the stability of artificially
drained wetlands, determined that the rate of channel
degradation following canal construction is the key variable
determining wetland hydrologic stability. When channel
degradation is rapid, the system responds by quickly
reaching a new equilibrium. The hydrologic regime of the
wetland will remain in a metastable condition, unless the
drainage canals are periodically renovated. Rehabilitation
of canal carrying capacity, including sediment removal and
the clearing of debris, results in a recurrence of
‘49
disequilibrium, or instability (Phillips and Steila, 198<4;
Phillips, 1985a; 1985b).
The concept of artificial drainage channel degradation
inducing stability in the wetland hydrologic regime is
important in evaluating the impact of hydrologic restoration
in the Alligator Swamp. The influence, if any, of the
installation of drainage control structures will be directly
related to the viability of drainage canals within the
altered and post-altered study areas.
CHAPTER V
METHODOLOGY
The study area lies within the Alligator River National
Wildlife Refuge on the mainland peninsula of Dare County,
North Carolina (Figure 2). The specific study sites within
this area consist of timber tracts used by Atlantic Forest
Products for the logging of Atlantic white cedar from 1980
to 1984 (Figure 3). These tracts were mapped by a
registered land surveyor in 1979. These individual tract
maps contain the coordinates and distances obtained by the
surveyor and were verified in the field by use of a compass
traverse (Compton, 1962). A reference traverse was plotted
from the intersection of Pull Road and Grassy Patch Road to
the intersection of Grassy Patch Road and the Phantom-Pull
Drainage Ditch.
Eight sites were selected for the computation of water
balances. These sites were chosen because logging tracts
provide a homogeneous surface in which to examine water
table fluctuations and soil characteristics. These areas
are homogeneous in that they: (1) are clear-cut, therefore
unshaded, areas; (2) were logged during 1983 and 1984; (3)
contain logging slash throughout tlie area; (4) exhibit a
high degree of surface disturbance; (5) lie within the same
soil series (Pungo) as determined from the Dare County soil
survey (Soil Conservation Service, 1989); and (6) lie within
Figure 3
STUDY AREA
showing location of sites and test wells
Legend
© Test Well
0 Drainage Control
Structure
Altered Sites
Post-Altered Sites
Cedar Stand
52
the same wetland classification as determined from National
Wetlands Inventory maps. NWI maps delineate wetlands
according to the classification scheme adopted by the U.S.
Fish and Wildlife Service (Cowardin et al, 1979). Atlantic
white cedar wetlands are classifed as System: Palustrine;
Class: Forested; Subclass: Needle-leaved evergreen.
Sites 18, 20, and 21 are currently influenced by
artificial drainage, and thus are representative of altered
wetlands. Sites 32, 35, 36, and 37 lie within the
post-altered Grassy Patch-Phantom area. Site 36 represents
a natural area. It is an uncut white cedar stand containing
specimens ranging from approximately 70 to 90 years of age.
This range of ages was determined by taking core samples
from the largest specimens with an increment borer. This
site was located by examination of 1987 aerial photography
and has been verified in the field.
Site 36 represents one of the last remaining stands of
Atlantic white cedar that regenerated from the large-scale
logging operations of the early 20th century (Peacock and
Lynch, 1982). Site 36 lies within the Grassy Patch area.
The drainage area of each site was estimated using an
assumptive method described by Phillips (1986). These
drainage basins are delineated by existing drainage canals
53
roadbeds (which act as natural levees), and the natural
water bodies of Alligator River and Milltail Creek.
Artificial drainage practices result in changes to the
water balance components of a region, as well as changes in
the properties of organic soils which predominate in the
study area (Skaggs et al, 1980). The water availability of
an altered area must be compared to that of a morphologically
similar, undrained area for these water balance changes to
be measured.
A model was chosen that could best assess the impact of
hydrologic restoration in a canalized swamp system. Novikov
and Gonchorova (1981) developed a model (henceforth referred
to as NAG) for forecasting changes in the water balance
following drainage. Because drainage decreases groundwater
levels in a swamp, water availability (or water loss) can be
evaluated from the evaporation changes that take place when
water tables are lowered. Also, changes in runoff due to
evaporation changes can be determined as the difference
between potential evaporation from drained areas and
evaporation from a natural swamp.
The methodology applied in this thesis, particularly
the comparisons of water table fluctuations between natural,
altered and post-altered wetlands is well-suited for the use
of NAG, as evaporation is the primary mechanism for water
54
table drawdown in these areas. Therefore, NAG will allow a
assessment of the water availability in the hydrologically
restored (post-altered) site based on evaporation
differences between the canalized and natural areas.
The water availability of the altered area, R , is
a J. L
given by
R - R . (5)
alt nat t s
where R .is the water availability in a natural area, and
nat
R. represents the total decrease in water availability from
t s
the onset of artificial drainage practices. It is generally
known that drainage in peat soils causes considerable
subsidence of the surface layer, though this impact
decreases over time as well as with the depth of the peat
layer (Jongedyk et al, 1954; Slusher et al, 1974;
Yevdokimova et al, 1976; Skaggs et al, 1980; Lilly, 1981a,
1981b; Parent et al, 1982). Because of this subsidence
Novikov and Goncharova (1981) maintain that estimates of
changes in groundwater storage (a key water balance
component) cannot be made by simply comparing water table
levels before and immediately after drainage. Thus,
t s '^t ^ ^th (6)
55
where represents the water content in the surface layer
of peat lowered by subsidence. It is expressed as
R
t Ad^. X (7)na t
where Ad^ represents the change in peat thickness after
drainage (subsidence). The C . value is the mean soil
na t
moisture content within the cedar stand (Site 3<4), which
represents the Atlantic white cedar wetland in its
predisturbed condition. The term d^, peat thickness before
drainage (in meters), was calculated for values ranging from
51 to 90 inches (130 to 229 cm). This range corresponds to
depths of organic soil (Pungo muck) indicated in the Dare
County soil survey. It also coincides with observations
made in the Hoffman Forest by Maki (1974), who reported peat
thicknesses of 100-200 centimeters. The subsidence of the
altered sites (Ad^) was then determined by the empirical
equation
. nlri .0.35 .0.64
Ad^ = 0.18xKxd^ xd (8)
where d is drainage canal depth (m) and K is a coefficient
of peat density (1.0 = dense peat, 1.4 = average peat and
2.2-2.7 = loose peat; Novikov and Goncharova, 1981). To
determine if the NAG values agreed with other subsidence
data from Lower Coastal Plain organic soils, subsidence
values from Equation (8) were compared to results reported
56
by Skaggs and Barnes (1976) and Tant (1979). Tant measured
subsidence in Belhaven and Pungo soils in Washington County,
North Carolina over a six-year period. Field experiments by
Skaggs and Barnes (1976), followed by Skaggs (1980), were
also conducted in Washington County at a site near Lake
Phelps. Comparisons between their findings and the NAG
subsidence equation are given in the Results chapter.
Rt.,h represents moisture losses under artificial
drainage due to moisture reduction in the upper peat layer
after water table drawdown and is expressed by
(h. - h.) (C ". C . ) (9)
th t nat d r
where h^^ represents height of the water table before
drainage (mean water table elevation in the cedar stand.
Site 34) and h^ is water table height after drainage (mean
water table elevation of the altered or post-altered sites).
C . represents the mean soil moisture content in the altered
dr
and post-altered sites (Novikov and Goncharova, 1981).
After drainage canals are plugged, the water level in
the canal will eventually equal the level of the water
table. This assumption is based on the observations of
Gilliam and Skaggs (1981) and Daniel (1981), who observed
that the water tables in organic soils drained for
agricultural rarely fall to the depth of the canal. With
57
water table elevations constantly higher than canal water
levels, the difference in hydraulic head forces water from
the adjacent soil to the canal. Furthermore, because of the
low permeability of organic soils, drainage canals primarily
serve as surface drainage. It is the outflow function of
canals that keeps water table levels artificially low
(Gilliam and Skaggs, 1981). Thus, the plugging of a
drainage canal will serve to decrease the hydraulic gradient
between the canal and the water table. Over time, gravity
seepage into the canal will diminish, and the canal water
level will fluctuate in response to precipitation and
evaporation in the same manner as the water table (Daniel,
1981). Once the equilibrium between canal and groundwater
surface levels is reached, water availability of the
post-altered sites, R , is determined by
pa
R (E E .)xA ( 10 )
pa na t canals nat cana
,ls +R.t
where E
cana,ls is the evaporation loss from the drainage
canals, E
na^t is évapotranspiration from the natural area
(Site 54), and A
cana,ls is the surface area of canals,
expressed as a percentage of total basin area. R^ was
described in Equation (7).
R the water availability in a natural area, is
nat
given via the water balance approach (Mather, 1978). Water
balances can be computed for areas of every scale, from a
58
soil profile to a large watershed (Dunne and Leopold, 1978).
For a small watershed, the generalized water budget can be
expressed as follows:
P - ET - R + CSM + CWT = 0 (11)
where P is precipitation, ET is évapotranspiration, R is
runoff, CSM is change in soil moisture, and CWT is change is
groundwater storage. This expression of the water balance
is similar to that of Pegg and Ward (1971). They conducted
a hydrologic study for a small catchment in which CSM and
CWT were monitored to estimate ET.
Each component of the water balance was evaluated
separately, with runoff treated as a residual.
Precipitation, air temperature, temperature of the dew
point, and wind speed data were obtained from the Dare
County Bombing Range, which has recorded daily weather data
since 1986. The Range weather station is located
approximately 5.7 km (6 mi) from the study area.
Evaporation was calculated by the Penman formula, which
combines the mass transfer and energy budget methods for
calculating evaporation from open water. The mass transfer
method calculates the upward flux of water vapor from the
water surface, while the energy budget method balances
incoming and reflected solar radiation with the energy used
59
for évapotranspiration and energy transfers and storage
(Dunne and Leopold, 1978; Shaw, 1988). The basic expression
of the Penman formula can be written:
E = ah + E (12)
o ź a
where E^ is the energy for evaporation, /\ represents the
slope of the curve of saturation vapor pressure plotted
against temperature, H is net radiation, E describes the
a
contribution of mass transfer to evaporation, andY" is the
psychrometric constant (0.66 mb/degree Celsius). Data
necessary for the calculation of evaporation include mean
air temperature (T ), mean temperature of the dew point
a
(T.), hours of sunshine (n), and wind speed (u). T , T.,
Q ad
and u were collected from the bombing range weather station.
Values of n are normally obtained via the use of a
Campbe11-Stokes recorder. For this study, measurements of n
were obtained from monthly summaries of climatological data
from the National Weather Service office at Cape Natteras,
which is located approximately 76 km (66 mi) southeast of
the study area. Computation of evaporation (in mm day ^)
using the four variables mentioned above was accomplished
via the use of tables published by McCulloch (1965).
Potential évapotranspiration (PE) was calculated by the
model developed by Koerselman and Beltman (1988). Developed
specifically for calculating évapotranspiration in temperate
60
zone peatlands, this equation describes évapotranspiration
from fens (ET, mm day as a function of Penman's E (mm
o
day on a monthly basis:
ET = 0,73E +0.16 (13)
o
Change in soil moisture (CSM) was measured from samples
collected from the sites. These samples were stored in
plastic zip-lock bags (to prevent moisture loss) for
transport to the laboratory, where they were weighed, dried
in an oven for 12 hours at 105, and reweighed to determine
soil moisture content (Briggs, 1977; Shaw, 1988). Water
content was calculated on an oven-dry weight basis then
converted to a volume measure using the oven-dry weight per
unit wet bulk volume (Boelter and Blake, 1964). Samples
were collected weekly.
Changes in groundwater storage (CWT) were determined
from fluctuations in the water table. Water table levels
were determined from readings taken from test wells
installed at the sites. Maki (1974) used a similar
methodology for measuring water tables in pocosins. Each
test well was installed as near as possible to the center of
the logging site. Readings were taken twice-weekly from
June 2 through September 1.
61
The test wells were made of 3.175 cm diameter PVC pipe
cut into approximately 1.8 m (six-foot) lengths. Each end
of the pipe was capped. The pipe was perforated by slits
cut in a spiral pattern, approximately 15 centimeters apart,
in a 1.2 m section of the pipe. The pipe was sheathed in
nylon filter cloth to prevent soil from entering the pipe.
The sheathed section of pipe was placed into a hole bored
into the organic soil to a depth of approximately 2 meters
using a large-bore auger designed for use in peat soils
(Hodges, 1989). Water table levels were measured from the
top of the test well, which protruded 25 to 30 cm above the
ground. Depth from the surface was measured using a
battery-operated sensing device, which consisted of a
weighted electrode attached to a coated copper cable. The
cable was incremented into 15.24 cm (six-inch) sections.
Upon contact with water, the electrode would activate a
meter in the control box of the device.
CHAPTER VI
EXPECTATIONS OF THE STUDY
The effect of the hydrologic restoration in altered
white cedar bogs in the Alligator River National Wildlife
Refuge will be analyzed by examining water balances for the
individual clear-cut sites. As previously discussed, these
water balances will be compared to those in sites where the
drainage network remains unimpaired by control structures.
The obvious effect of installing drainage control
structures is to essentially stop runoff from the canals,
which would normally flow into the Alligator River and
Milltail Creek. Although runoff will be measured as a
residual in the water balance computations, a significantly
lower value from this residual is expected in the
post-altered sites. However, the degree to which drainage
canal conveyance capacity has deteriorated may affect this
value, and the expected difference could be considerably
less .
Changes in water table levels for both altered and
post-altered sites are related primarily to drawdown from
évapotranspiration. Water table levels in the post-altered
sites are expected to be higher because of the drainage
control structure. Because the structures will block canal
outflow, there will be an increased amount of water
65
available for evaporation. However, both groups are assumed
to have equal rates of evaporation and transpiration, as the
altered and post-altered sites are comparable in vegetation,
soils, and history of disturbance. Therefore, the altered
group is expected to show more pronounced water table
fluctuations and higher values of runoff.
Another important consideration when evaluating the
water balances of the post-altered sites will be the effects
created by roadbeds. Roadbeds in the Alligator River
National Wildlife Refuge, as in most altered wetlands in
eastern North Carolina, are constructed from the spoil
created when drainage canals are cut.
While the impact of drainage ditches are
well-documented, the effects of roadbeds on wetland
hydrology are not fully understood (Laderman, 1989; Winter,
1988). Maki (1974) described the roadbeds in the Hoffman
Forest of North Carolina as having noticeable barrier
effects. He stated that the low hydraulic conductivity of
the spoil material impedes infiltration from the canal. The
roadbed, despite being composed primarily of organic
material with an abundance of roots and buried logs,
compacts to such a degree that it effectively serves as a
dam, blocking lateral water movement.
Roadbeds certainly act as barriers to surface water
movement. On several occasions, ponding of surface water at
roadbeds was observed in the study area. With a sufficient
fetch of wind, surface water washes against the banks of the
roadbed, creating an environment for sediment deposition
when the roadbed is oriented perpendicular to the prevailing
winds .
The effectiveness of roadbed barriers is related to
both the composition of the spoil material and groundwater
hydraulics. If the water level in the canal is below the
groundwater head, the pressure of the upwelling groundwater
may move it into the canal, if the roadbed material is
permeable enough to permit transmission. The upwelling
water is also capable of lifting the colloidal mucks in the
ditch and flowing around them. There is also some gravity
drainage from the area adjacent to the canal. If the water
level in the canal is above the groundwater head, gravity
allows water to move in and out of the more permeable
material, and presses the mucks against the canal bottom,
restricting seepage (U.S. Fish and Wildlife Service, 1986).
Differences in water level fluctuations within the
post-altered sites may be attributable to the aforementioned
factors. This is particularly applicable to Sites 32, 35,
and 36. Sites 32 and 35 are adjacent to the Phantom Canal,
while site 36 is bordered by Phantom Road South.
65
Observations of water levels in the altered sites (18,
20, and 21) may also reflect the influence of roadbeds (Site
21 lies adjacent to the Dry Ridge North Canal). Because the
drainage network of the altered sites remains unimpeded by
control structures, these observations may provide a clue of
the degree to which drainage canal water levels are
stabilized with the water level of the Alligator River.
Frost (1989) speculated that drainage canals may actually
prevent extreme seasonal drawdown of water tables by
stabilizing their levels with the larger water bodies of the
Alligator River and Pamlico Sound. Uniformity in water
table fluctuations in the study area could be attributable
to this phenomenon, but drainage canal conveyance capacity
could be a factor in preventing such stabilization.
Trends in water table fluctuations for the altered and
post-altered study sites should be similar, although the
residual runoff value should be lower in the post-altered
sites. If the groundwater storage component of the water
budget equation differs significantly, such factors as the
effect of roadbeds and the physical condition of drainage
canals must be considered.
In summary, this study expects to reveal the impact of
hydrologic restoration in the Alligator Swamp through the
analysis of groundwater fluctuations and water balance
comparisons. These analyses will demonstrate that the
66
hydrologie regime of the post-altered study area is similar
to that of a natural, undrained area.
CHAPTER VII
RESULTS
NAG Calculations
The Novikov and Gonchorava (NAG) model (1981) forecasts
water balance changes after drainage (see Methodology). It
considers both the evaporation changes and surface
subsidence that occur when water tables are lowered by
artificial drainage practices. The resulting decrease in
water availability from the onset of drainage, , is given
t s
by Equation (6). Water content in the peat surface lowered
by subsidence, R^, is a product of the NAG subsidence
equation (8) and the mean soil moisture content of the
natural area. Site 34 (C .). Equation (8) includes
nat
drainage canal depth, peat thickness, and a coefficient of
peat density (K).
The dense sapric peat that is characteristic of
Alligator Swamp histosols resulted in a peat density
coefficient (K) value of K = 1.0. Pre-drainage peat
thickness (d^) ranged from 130 to 230 cm (51 to 91 in).
This range was determined from observations by previous
field researchers in eastern North Carolina swamps
(including Daniel, 1981; Ingram and Otte, 1981, 1982; Otte,
1981; Lilly, 1981; and Ingram, 1987), as well as information
68
from the Dare County Soil Survey (Soil Conservation Service,
1989).
Drainage canal depth (d) was determined by measurements
taken at various intervals along the length of the canals.
Depths averaged 2.29 m (7.5 ft); thus, = 2.29^'^*^ =
1.70. When solving for the NAG subsidence values in
Equation (8), where d^ ranged from 130 to 230 cm, subsidence
of the peat surface after drainage ranged from 0.34 to 0.41 m
(See Table 1). Given the 20-year period since the canals
were cut, this range of subsidence values (1.70 - 2.05 cm
yr ^) agrees with earlier results by Skaggs and Barnes
(1976) and Tant (1979). They estimated peat subsidence in
North Carolina blacklands to average 1.02 and 2.70 cm yr
respectively.
R^, the product of subsidence and pre-disturbance soil
moisture, ranged from 0.14 to 0.17 for the given range of
thicknesses (Table 1). The other factor in Equation (6) is
Rth> which represents the moisture loss in the upper peat
surface from water table drawdown.
The range of values for total moisture decrease as
a result of drainage, are listed in Table 1. This range
(0.107 m - 0.192 m) represents a forecast of the decrease in
moisture (as a depth per unit area) from artificial drainage.
TABLE 1
SUMMARY OF NAG CALCULATIONS
Subsidence (Ad.) for ore-drainaae neat thicknesses (d ) of
130-230 cm (51-90 in) : ^
A^ d. =0n .11o8xK1/ xd 0.35 xd 0.64 w, hered. =
2.29 m , and
Water content in subsided peat layer, , where
X
=
t A^d^t xCna^t (Cna^t =0.41)
d^ (cm) Ad^ (m)
130-141 0.34 0 . 14
142-152 0.35 0 . 14
153-165 0.36 0.15
166-179 0.37 0.15
180-191 0.38 0.16
192-206 0.39 0 . 16
207-221 0.40 0 . 16
222-230 0.41 0.17
Total moisture decrease as a result of drainage. •^ts'
site for range of (0.14 -0.17)
Water availability in the altered sites, R given as
aix
R = R
-
a1l4t- na4t- "ts’
using the mean R. value, and where R
t s na^t = 0.551
* *
Site R R
ts a1l4t-
37 0 . 143 - 0.173 -
36 0 .107 - 0.137 -
35 0 . 147 - 0.177 -
32 0 143 -. 0.173 -
21 0 . 162 - 0.192 0.374
20 0 -. 146 0.176 0.390
18 0 .142 - 0.172 0.394
Mean water availability for the
Altered Group: 0.386
Value denotes depth per unit area.
70
TABLE 2
SUMMARY OF NAG CALCULATIONS (CONT’D)
Water availability in the post-altered sites, R , qiven as
-
pa
R = R (E
na^pa t cana^ls - E na^t ) + t
where R
na^t = 0.551, E. cana,ls = 0.006, E na^t = 0.004,
and R^ = 0.155
Rpa = 0.704 m (depth per unit area)
Final Results :
R 0.386
alt
R 0.704
pa
R 0.551
nat
71
The predicted values of were applied to Equation
(5) to determine R The average water availability of a
alt
natural area, R ., was calculated from the water balance of
nat
Site 34. Results from Equation (5) are summarized in Table
1. The mean water availability for the altered group, as
the average of midpoint values for each site, was 0.386 m.
Water availability in the post-altered group was
determined from Equation (10), which reflects the water
availability in the natural area minus the mean canal
evaporation and forest évapotranspiration values for the
study period. Post-altered water availability also includes
R^, which represents water content in the layer of peat that
was lost to subsidence. The final results for the NAG model
(Table 2) showed that the water availability in the
post-altered area (0.704 m) surpassed that of the natural
area (0.551 m), with the lower mean value of the altered
group (0.386 m) reflecting the decreased water availability
expected in a drained system.
Use of the NAG model to determine water availability in
the altered and post-altered areas required supporting data
from the calculation of water balances, represented by
Equation (11). Change in Soil Moisture (CSM) and Change in
Water Table (CWT) were the field-measured components of the
water balance. The results from the soil sample analyses
72
and the test well observations and their application to the
water balance are discussed below.
Soils
Values of soil moisture at 1 m were found to be very
consistent (see Table 5). The significance of differences in
the mean soil moisture content among the post-altered and
altered sites during the sampling period was tested with the
t-test (Davis, 1973). At the 95% level of certainty, no
significant differences in soil moisture were found among
the individual altered sites or the individual post-altered
sites. Additionally, no significant difference was found
between the two groups (See Table 4). Soil samples were
analyzed for organic matter content to determine if a
difference existed for this parameter. Again, no significant
differences were found (See Table 4). As expected, t-tests
reflected significant differences between the post-altered
and natural groups and the altered and natural groups (See
Table 4). The mean soil moisture percentage of samples
collected from the cedar stand (Site 54) was 41.14% and mean
percentage of organic matter was 6.46%. Throughout the
sampling period, soil water values of the cedar stand
samples did not differ significantly.
73
TABLE 3
SUMMARY OF SOIL DATA
Percent
Percent Organic
Soil H^O Matter
Standard Standard
Mean Deviation Mean Deviation
Altered Group
Site 18 86.22% 2.81 11.10 0.15
Site 20 83.42 7.53 12.46 3.06
Site 21 89.89 1.73 9.00 1.10
Group 86.51 5.81 10.85 2.26
Post-Altered Group
Site 37 88.44 1.29 10.91 1.19
Site 36 89.13 0.62 10.27 0.49
Site 35 79.95 7.22 11.05 0.67
Site 32 88.88 0.97 10.44 1.01
Group 86.60 5.18 10.68 0.85
Cedar Stand
Site 34 41.14 8.47 6.46 1.73
^Percentage of organic matter at field H^O.
74
TABLE A
RESULTS OF T-TESTS
SOIL DATA
Percent Soil H^O
Std Si g . Grit. t
Mean Dev . DF Level Value Value
Post-Altered 16 86.60 5.18
26 0.025 2.056 I o o tfi
Altered 12 86.51 5.11
Post-Altered 16 86.60 5,18
4 0.025 2.776 -10.26
Natural 4 41.14 8.47
Altered 12 86.51 5.11
4 0.025 2.776 -10.12
Natural 4 41.14 8.47
Percent Organic Matter
Std Si g . Grit. t
Mean Dev . DF Level Value Value
Post-Altet'ed 16 10.68 0.85
13 0 . 025 2.160 0.27
Altered 12 10.85 2.26
Post-Altered 16 10.68 0.85
3 0 . 025 3.182 -4.73
Natural 4 6.46 1 . 73
Altered 12 10.85 2.26
7 0.025 2.365 -4.06
Natural 4 6.46 1.73
75
Based upon this analysis, and the fact that no changes
in soil moisture content were found during the sampling
period, the CSM component of the water balance was zero.
Water Tables
Data from field observations of water table levels were
analyzed using one-way analysis of variance, or ANOVA.
ANOVA measures both the variance among sample means and the
variance within samples. These two measures of variance
constitute a statistic called the F-ratio (Davis, 1973).
No significant differences were found between sites
within the altered group (Table 6). Within the post-altered
group, there were no statistically significant differences
among the individual sites, with the exception of Site 36.
The extreme value of mean water table elevation for this
site is attributable to the test well's close proximity to
the roadbed. The deeper water table readings at Site 36 are
indicative of the drawdown that occurs near drainage canals.
The water table elevations at Site 36 resulted in a negative
mean water table elevation for the post-altered group. This
result was not plausible considering the blockage of the
drainage canals in the post-altered area; therefore. Site 36
data were deleted for the water table elevation analysis.
76
Water table elevation data (Table 5) reveal that the
range of mean elevations is 2.01 cm. The standard
deviations for all sites in all groups are high; in most
cases the standard deviation value surpasses the mean.
Overall results from the analyses of water table elevations
did not concur with expectations. As can be seen from Table
7, no statistically significant differences exist between
groups .
Line graphs illustrating the changes in water table
elevations during the study period are shown in Figures A,
5 , and 6 .
Calculation of Water Balances
Meteorological data from the Dare County Bombing Range
were compiled for the precipitation and évapotranspiration
components of the water balance equation. Rainfall for June
totaled 18.99 cm (7.A8 in), more than 8 cm (3 in) above
normal. July rainfall of 15.06 cm (5.93 in) was slightly
above the average value of 13.51 cm (5.32 in), while August
precipitation measured 21.82 cm (8.59 in). The August
figure was over 6.68 cm (2.5 in) above the monthly norm.
Mean precipitation for each observation period was 4.65 cm.
77
TABLE 5
SUMMARY OF WATER TABLE DATA^
Water Table Elevation, in centimeters'
Standard
Altered Group Mean Deviation
Site 18 1.3 1 cm 6.89
Site 20 2.23 5.06
Site 21 5.37 7.29
Group 2.91 6.52
Post-Altered Group
Site 37 1.50 3.73
Site 36 -6.01 5.29
Site 35 2.27 A . 82
Site 32 1.61 5.29
Group -0.23 5.86
Excluding Site 36 1.81 A .59
Cedar Stand
Site 3A 0.90 5 . OA
^Figures reflect mean height of water table throughout
the study period.
2
Negative values indicate height of water table below
surface.
78
TABLE 6
RESULTS OF ANALYSIS OF VARIANCE
WATER TABLE DATA
Altered Site Comparisons
Water Table Elevation, in centimeters
Std Sig. Crit. F
N Mean Dev. DF Level Value Ratio
Site 21 12 5.37 7.29
0.05 <4.28 1.60
Site 20 13 2.22 5.06
Site 21 12 5.37 7.29
0.05 3.28 1.35
Site 18 13 1.31 6.89
Site 20 13 2.22 5.06
0.05 <4.26 0.15
Site 18 13 1.31 6.89
Post-Altered Site Comparisons
Std Sig. Crit. F
N Mean Dev. DF Level Value Ratio
Site 37 11 1.50 3.73
0.05 <4.30 0.19
Site 35 13 2.27 <4.82
Site 37 11 1.50 3.73
0.05 2.82 0.17
Site 32 13 1.60 5.29
Site 35 11 2.27 <4.82
0.05 3.28 0.23
Site 32 13 1.60 5.29
79
TABLE 7
RESULTS OF ANALYSIS OF VARIANCE
WATER TABLE DATA
Group Comparisons
Water Table Elevation, in centimeters
Std Si g . Cr i t . F
N Mean De V . DF Level Value Ratio
Post-Altered 37 1.80 A . 59
7A 0 . 05 3.95 0.71
Altered 38 2.90 6.52
Altered 38 2.90 6.52
A9 0.05 A .02 0.95
Natural 12 0.90 5 . OA
Post-Altered 37 1.80 A . 59
86 0.05 3.10 0.72
Natural 12 0.90 5 . OA
80
Evaporation (Penman's E , mm day was calculated from
O
temperature and wind speed data collected at the Bombing
Range weather station. Evaporation was highest in June
(6.07 mm day Penman's E measured 5.79 mm day ^ and
o
5.86 mm day ^ for July and August, respectively. Mean
evaporation for each observation period was 5.89 mm. The
évapotranspiration component of the water balance was
determined by Koerselman and Beltman's (1988) equation where
ET = 0.75E + 0.16. Mean ET for each observation period was
o
0.65 cm.
Change in soil moisture (CSM) was zero, and change in
groundwater storage (CWT) was computed from the fluctuation
in water table elevation for each period.
The results of the water balance computations for the
study sites correlated well (r = 0.85) with the excess
moisture conditions reflected in the analysis of the water
table elevations. Results from the water balance formula
(Equation 11) are summarized in Table 8. Each site had an
average of 6.56 centimeters of water remaining after
accounting for the components of ET and CWT. This value
represents the runoff residual. Runoff was not evident in
the form of outflow from the deteriorated drainage system;
therefore it was represented by canal storage. The range of
the mean water balance values was small (1.01 cm).
81
TABLE 8
WATER BALANCE SUMMARY
Mean Precipitation: P = 4.65cm
Mean Evapotranspiration: ET = 0.45
Mean Water Table Flux: CWT = 0.33
(P -- ET R + CSM + CWT = 0)
Mean Water Balance^ 2Sum
Altered Group
Site 18 4.81cm 57.74cm
Site 20 4.17 50.04
Site 21 4.67 55.99
Group 4.55
Post-Altered Group
Site 37 4.00 39.97
Site 36 4.41 52.90
Site 35 4.29 51.48
Site 32 4.93 59.17
Group 4.42
Cedar Stand
Site 34 5.01 55.08
All Sites 4.66
^Reflects water balance computation for each observation
during the study period
2
Total water balance for the study period.
(TDWCEAPBOTMTLEHER )
00
no
(TWDCEAPBOTMTELHRE )
00
CO
FIGURE b SITE 34
NATURAL CEDAR STAND
WATER TABLE FLUCTUATIONS
(TDWCAEABPOTMELTREH)
CHAPTER VIII
DISCUSSION
The results of the NAG model showed that the post-
altered white cedar wetland surpassed the natural white
cedar bog in terms of water availability. The NAG model
incorporated surface subsidence and the consequent surface
layer moisture loss in forecasting water balance changes
from artificial drainage practices. The water balance
computations from field data did not consider these factors;
thus, they did not reveal any significant differences
between the altered, post-altered and natural areas. In
addition, the results from water table elevation data (Table
5) showed that the mean elevation of the post-altered group
was lower than that of the altered group. Such results
clearly contradict the expectations of a higher mean water
table level in the area where drainage canals were blocked
with control structures.
The miniscule range of mean water balance values (1.01
cm) between three hydrologically distinct areas is a direct
result of the wetter than normal conditions. The lack of
differences between water balances, specifically the
component of water table elevation, appears to indicate that
a simple water budget approach to evaluating hydrologic
restoration in this environment may not be viable, at least
during periods of above-normal precipitation. However, this
86
finding is inconclusive, and a more detailed examination is
needed .
Following is a discussion of several factors that may
account for the lack of significant differences in water
balances between the three study areas, as well as the
anomaly in the results of the test well readings.
Microtopographv of the white cedar forest. The cedar
stands that once existed at the post-altered sites probably
possessed the hummocky microtopography that is
characteristic of white cedar forests. Although care was
taken to avoid the remnant hummocks during siting and
placement of the test wells, it is possible that some of the
post-altered site wells were placed in slightly elevated
locations, which would have reflected lower water table
elevations relative to the surface.
Topography of the pre-peat surface. Research by Oaks
and Coch (1973), followed by Daniel (1981) and Gtte (1981),
clearly demonstrated that the pre-peat (Pleistocene) surface
of the Albemarle-Pamlico region exhibits a well-defined
dendritic drainage pattern. Characteristics of this pattern
are broad, shallow stream valleys with corresponding
interstream divides, or "highs" (Daniel, 1981). It is
conceivable that the altered group may be located near such
a high. A sloping mineral layer underlying the peat surface
87
could cause locally higher water table levels, especially
considering the barrier effects of the roadbed network.
Loss of canal conveyance capacity. As previously
discussed, the canals within the Alligator River NWR have
not been regularly maintained. Fallen trees and other
vegetation were frequently observed in all canals. The
nearest outlet constructed to drain the altered area to the
Alligator River is a canal adjacent to Gator Road. This
road lies within one of the most inaccessible areas in the
Refuge. Gator Road has overgrown with vegetation to such an
extent that it is no longer passable by vehicle. Gn one
visit, the Gator Road canal was not seen initially because
of the dense growth. When it was finally located, saplings
and dense vegetation were thriving within the canal itself.
Clearly, this outlet no longer functions as such. Given
these conditions, the canals within the altered area are no
longer viable along their entire length. Such a situation
could result in elevated water table levels within this
area.
Conditions of excess moisture. Ordinarily, late summer
is a period of high evaporative demand and pronounced
drawdown of the water table, with relatively lower amounts
of rainfall. However, during the 5-month study period June
through August, precipitation at the Dare County Bombing
Range totaled 55.94 cm (22.02 in). Normal precipitation for
88
this period, based on long-term data from the National
Weather Service stations at Cape Natteras and Elizabeth
City, is 59.12 cm (15.<4 in). The large amounts of rainfall
resulted in standing water throughout the study area.
Because vegetation moisture requirements were fulfilled and
moisture was not limiting, actual évapotranspiration equaled
the potential rate. Thus, the similar trend in water table
elevation changes among all sites excluding Site 36 (Figure
7) is accountable primarily to losses by evaporation,
particularly if runoff is negated by loss of canal
conveyance capacity.
The loss of canal conveyance capacity may best explain
the failure to meet the expectations of this study. As
stated earlier in a discussion of the recovery of
artificially drained wetlands, the rate at which drainage
canals deteriorate may be the key variable that determines
the resumption of natural hydrologic functions. Phillips
and Steila (1984), Lilly (1981), and Phillips (1985) have
speculated that canal degradation serves as an adjustment
mechanism for artificially drained wetlands to reach a new
state of equilibrium in the years following drainage.
Results of this thesis suggest that drainage canals within
the altered and post-altered study areas have deteriorated
to such an extent that the hydrologic regime has reached a
state of stability. This condition will persist as long as
the canals are not cleared or reexcavated.
(TWDCEABPOTMTLEHER )
JUN02 JUN23 JUL11 JUL26 AUG04 AUG18 SEP01
00
CO
90
This finding is consistent with previous research in
eastern North Carolina drainage systems. Swicegood and Kriz
(1973) reported losses of conveyance capacity that were
significant enough to require complete channel modification
within 8 to 10 years following drainage. Stephenson and
Steila (1982) found conveyance capacity losses of 70 to 80
percent only 2 years after drainage.
The deterioration of drainage canals within the study
area has, therefore, led to the adjustment of a new
hydrologic equilibrium. This resumption of stability
implies a restoration of 'natural' hydrologic functions.
Furthermore, the results of this thesis suggest that natural
occurrences such as vegetative growth, sedimentation,
slumping, and debris clogs can restore hydrologic
equilibrium in an artificially drained ecosystem.
Consequently, the installation of drainage control
structures has little, if any, effect on a system where the
most significant loss of water is vertical, via
évapotranspiration, rather than the horizontal flow through
drainage canals.
The effects of artificial drainage on Atlantic white
cedar regeneration in the Dare County mainland have not yet
been documented (Moore and Laderman, 1989). However, the
drier soil conditions caused by water table drawdown from
artificial drainage will increase the likelihood of fire
91
events that favor the establishment of pocosin vegetation.
(See Chapter IV - Pocosin Communities: Successional
Relationships for a discussion of pocosin and white cedar
wetland vegetative regimes.) Historically, environmental
conditions have favored the continued presence of Atlantic
white cedar, as macrofossil evidence has indicated (Otte,
1981). However, the role that spontaneous fires, lightning,
saltwater intrusion, and hurricane windthrow played in
originally opening habitat for white cedar colonization is
completely obscured by the area's history of drainage and
logging (Moore and Laderman, 1989).
The results of this thesis suggest a restoration of
natural hydrologic functions. It is premature to speculate
as to whether this restoration is a benefit or a hindrance
to white cedar regeneration, particularly when preliminary
data show a wide variance in seedling density among the
clear-cut stands (Robert E. Noffsinger and Joy A.
Schmertmann, unpublished data, 1989). This variation
implies that different conditions existed within the
substrate of the forests prior to logging. Nonetheless,
analysis of soil samples showed that the logged stands were
nearly uniform in soil moisture and organic matter content.
Because all of these stands were logged during a one-year
period (summer 1983-1984), this uniformity can be attributed
to post-disturbance deposition of the mineral elements in
the soil. If the uniformity in soil properties exists in
92
other sites logged during the same time period, it could
serve as a starting point of investigation into the variance
in white cedar regeneration among the cut stands.
The results of this thesis will serve as a preliminary
basis for further observation of hydrologic conditions in
the Alligator River National Wildlife Refuge. The water
balance approach to evaluating hydrologic restoration can be
a low-cost, field-reliable, and successful application, and
if applied over a longer and more 'average' period, the
results should yield an accurate assessment of the effects
of drainage control in a non-agricultural setting.
Research Needs
Sampling of water table elevations should be conducted
over a longer time span to reflect periods of average
precipitation. Normally, summer and fall are the driest
months. Because the groundwater head would be below the
canal water surface, an analysis of water table fluctuations
during periods of extended drawdown may yield a more
pronounced effect from drainage canals. Canal water levels
should also be monitored during the sampling period. A
comparison of the fluctuations between canal surface levels
and groundwater levels could demonstrate how canal
conveyance capacity has been reduced. Although the
viability of drainage canals has been determined intuitively
93
from the analysis of water table fluctuations, a definitive
conclusion could be obtained by measuring flow velocity
along various reaches of the canal. Such data would
accurately determine canal outflow response to individual
rainfall events.
In addition, sampling from an expanded test well grid
would produce a more accurate assessment of water table
elevation changes. For example, test wells placed along a
traverse from the Phantom South canal to the Grassy Patch
canal to Milltail Creek would allow for an evaluation of the
water table on a larger scale, and would be especially
useful in evaluating the influence of these features.
The subsidence equation in the NAG model produced
results that were in agreement with prior eastern North
Carolina studies; however, surface subsidence should be
determined empirically over an extended period of time,
using a methodology similar to that described by Tant
C1979). In one hypothetical scenario. Site 32 would be
cleared of logging slash prior to permanent marker
installation while Sites 37 and 35 would remain uncleared.
This would allow a determination of the effect of logging
debris on subsidence.
Soil sampling should be expanded to include the
remaining logged areas within the Refuge, as well as the
94
remaining white cedar forests. Such data could enhance
current knowledge of white cedar moisture regimes,
particularly soil moisture status. More extensive soil
moisture data are needed to improve the regression models
formulated by Golet and Lowry (1987).
Evapotranspiration from extant white cedar forests and
logged areas should be determined empirically through the
use of lysimeters. The results of such a study would be a
valuable addition to literature on évapotranspiration from
bogs, and particularly North Carolina white cedar wetlands.
Additionally, such results are needed to calibrate the
Koerselman and Beltman model (Koerselman and Beltman, 1988).
CHAPTER IX
SUMMARY AND CONCLUSIONS
This thesis attempted to evaluate the hydrologic
changes that occurred after the installation of drainage
control structures in canals in the Alligator River National
Wildlife Refuge. A water balance approach was used with
changes in soil moisture and water table elevation
fluctuations being the field-measured components of the
water balance .
Three categories of study sites were evaluated. The
first category consisted of former Atlantic white cedar
(Chamaecyparis thyoides) stands that were harvested during
the summers of 1983 and 1989. These logged sites were
located within an area where drainage control structures and
canal backfilling were used in an effort by the U.S. Fish
and Wildlife Service to restore the natural hydrologic
regime. This category was denoted as post-a 11ered , since
drainage canals would no longer serve as outlets for runoff.
The second category consisted of similarly logged white
cedar stands within an area where the drainage canals
remained unimpeded. Such an area was representative of
forested wetlands where artifical drainage has altered the
local hydrology. Water balances from the post-altered and
altered study areas were compared to determine the
effectiveness of hydrologic restoration. This comparison
96
was contrasted with the water balance of an extant white
cedar stand which contained specimens ranging from 70 to 90
years of age. This natural area represented the third
category.
The goal of this research was to determine whether the
hydrologic regime in the post-altered wetlands was more
similar to the undrained or to the altered (canalized) study
areas. A hydrologic model that forecasts changes in the
water balance following artificial drainage was used in
conjunction with the water balance measurements to assess
the impact of hydrologic restoration in a canalized swamp
system.
It was expected that the installation of drainage
control structures would result in higher elevations and
less pronounced fluctuations in the water table within the
post-altered area. Final water balance computations showed
that no significant differences in the field-measured
components existed between the post-altered and altered
study areas. However, results from the hydrologic model
revealed that the water availability in the post-altered
area closely approximated that of the natural area. This
was attributed to the fact that the model incorporated
surface subsidence and the consequent surface layer moisture
loss from artificial drainage. The water balance
computations did not consider these factors.
97
Two factors were primarily responsible for the lack of
significant differences in the water balances of the altered
and post-altered groups. Abnormally high precipitation
resulted in water table levels above the surface during most
of the study period; thus, soil moisture percentages
remained constant, and the similarity in water table
elevation changes could be attributed to evaporation losses.
However, the loss of canal conveyance capacity best
explained the failure to meet research expectations. Based
upon earlier research and the fact that canals within the
study area are not maintained, it was concluded that the
natural deterioration of drainage canals has led to the
recovery of the natural hydrologic regime. Consequently,
the installation of drainage control structures had little
or no effect on a system where the most significant loss of
water is vertical, via évapotranspiration, rather than the
horizontal flow through drainage canals.
The Fish and Wildlife Service staff of the Alligator
River National Wildlife Refuge will continue the work begun
in this thesis. While management policies cannot be
implemented on the basis of the preliminary findings
presented here, some implications to refuge management have
f
become apparent. Specifically, when drainage canals are not
maintained, it has been shown that they naturally lose their
conveyance capacity over time. This degradation could
eliminate the need and expense of backfilling and control
98
structure installation in some areas. Also, the monitoring
of water table elevations will be important as the Refuge
staff continues its analysis of white cedar regeneration.
The preservation and encouragement of the Atlantic
white cedar forests of the Alligator Swamp is one of the
main objectives of the U.S. Fish and Wildlife Service.
However, this goal is overshadowed by the specter of sea
level rise. Indeed, a slight increase in the base level
could virtually eliminate the gravity drainage function of
the canals, regardless of their condition. The gradual
flooding that would result could make soil conditions
intolerable for white cedar seedling survival. Furthermore,
such flooding would lengthen the recurrence interval between
fire events which are critical to the regeneration of white
cedar .
Clearly, the future of Chamaecyparis thyoides in the
Alligator Swamp is, at best, tenuous. It is hoped that the
information presented in this thesis can make a contribution
toward assessing this threat, and be a useful tool for sound
management of the endangered species of the Alligator River
National Wildlife Refuge.
BIBLIOGRAPHY
Abler, R. F. 1987. What shall we say? To whom shall we
speak? Annals of the Association of American
Geographers 77:511-524.
Ash, A. N., C. B. McDonald, E. S. Kane, and C. A. Pories.
1983. Natural and modified pocosins: literature
synthesis and management options. United States Fish
and Wildlife Service, Division of Biological Services,
Washington, DC. FWS/aBS-83/04. 156 pp.
Ashe, W. W., and G. Pinchot. 1897. Timber trees and
forests of North Carolina. North Carolina Geological
Survey No. 6, 227 pp.
Bardecki, M. 1984. What value wetlands? Journal o f Soil
and Water Conservation 39:166-169.
Bay, R. R. 1967. Ground water and vegetation in two peat
bogs in northern Minnesota. Ecology 48(21:308-310.
Bay, R. R. 1969. Runoff from small peatland watersheds.
Journal ojf Hydrology 9:90- 102.
Belk, D. R. 1989. Geographic names as an indicator of the
historic extent of Atlantic white cedar in North
Carolina. Abstracts of the Annual Meeting of the North
Carolina Academy of Science. Journal of the Elisha
Mitchell Scientific Society 105(41:202.
Biswas, A. K. 1970. History of hydrology. North-Ho1land
Publishing Company, Amsterdam, 336 pp.
Boelter, D. H. 1964. Water storage characteristics of
several peats iji situ. Soil Science Society of America
Proceedings 28:433-435.
Boelter, D. H. 1965. Hydraulic conductivity of peats.
Soil Science 100:227-231.
Boelter, D. H. 1969. Physical characteristics of peats as
related to degrees of decomposition. Soil Science
Society o_f America Proceedings 33:606-609.
Boelter, D. H. 1972a. Water table drawdown around an open
ditch in organic soils. Journal of Hydrology
15 : 329-340 .
100
Boelter, D. H. 1972b. Methods for analysing the
hydrological characteristics of organic soils in
marsh-ridden areas. Pages 161-169 in Hydrology of
marsh-ridden areas. Proceedings of the Minsk
Symposium, June, 1972. The UNESCO Press, Paris.
Boelter, D. H. 1974. The hydrologic characteristics of
undrained organic soils in the lake states. Pages
33-46 in Aandahl, A., S. Buol, D. Hill, and H. Bailey.
Histosols; their characteristics , classification , and
use. Special Publication Series, No. 6. Soil Science
Society of America, Inc., Madison, WI.
Boelter, D. H., and G. Blake. 1964. Importance of
volumetric expression of water contents of organic
soils. Soil Science Society o f Amer ica Proceedings
28:176-178.
Briggs, D. 1977. Soils : sources and methods in Geography.
Butterworth and Co., Ltd., London, UK, 192 pp .
Buell, M. F., and R. L. Cain. 1943. The successional role
of southern white cedar, Chamaecyparis thyoides , in
southeastern North Carolina. Eco logy 24:85-93.
Carter, V. 1986. An overview of hydrologic concerns
related to wetlands in the United States. Canadian
Journal of Botany 64(21:364-374.
Carter, V., M. Bedinger, R. Novitzki, and W. Wilen. 1979.
Water resources and wetlands. Pages 344-376 in
Greeson, P., J. R. Clark, and J. E. Clark, eds.
Wetland functions and values : the state of our
understanding. Proceedings of the National Symposium
on Wetlands, Lake Buena Vista, Florida, November 7-10,
1978. American Water Resources Association Technical
Publication TPS 79-2, Minneapolis, MN.
Chorley, R. J. (ed.) 1969. Water , earth, and man. Methuen
and Company, Ltd., London, 588 pp.
Chow, V. T. 1964. Hydrology and its development. Section
1 in V. T. Chow, ed. Handbook of applied hydrology.
McGraw-Hill, New York, NY.
Christensen, N. L., R. B. Burchell, A. Liggett, and E. L.
Simms. 1981. The structure and development of pocosin
vegetation. Pages 43-61 in C. J. Richardson, ed.
Pocosin wetlands : an integrated analysis of coastal
plain freshwater bogs in North Carolina. Hutchinson
Ross, Inc., Stroudsburg, PA.
Compton, R. 1962. Manual of field geology. John Wiley and
Sons, Inc., New York, NY, 378 pp.
10 1
Cowardin, L. M., V. Carter, F. C. Golet, and E. T. LaRoe.
1979. Classification of wetlands and deepwater
habitats of the United States. United States Fish and
Wildlife Service, United States Department of the
Interior. Washington, DC, FWS/ÜBS-79/31. 103 pp.
Curtis, J., W. Curtis, and F. Lieberman. 1982. The world
of George Perkins Marsh. The Countryman Press,
Woodstock, VT, 123 pp.
Daniel, C. C., III. 1978. Land use, land cover, and
drainage of the Albemarle-Pamlico peninsula, eastern
North Carolina, 1974. Water Resources Investigation
78-134. United States Geological Survey, Raleigh, NC,
2 pp .
Daniel, C. C., III. 1981. Hydrology, geology and soils of
pocosins: a comparison of natural and altered systems.
Pages 69-108 in C. J. Richardson, ed.
Pocosin wetlands: an integrated analysis of coastal
plain freshwater bogs in North Carolina. Hutchinson
Ross, Inc., Stroudsburg, PA.
Daniels, R. B., E. E. Gamble, W. H. Wheeler, J. Gilliam, E.
Wiser, and C. Welby. 1978. Water movement in
surficial Coastal Plain sediments, inferred from
sediment morphology. Technical Bulletin No. 243, North
Carolina Agricultural Experiment Station, Raleigh, NC,
31 pp .
Daniels, R. B., E. E. Gamble, W. H. Wheeler, and C. S.
Holzhey. 1977. The stratigraphy and geomorphology of
the Hofmann Forest pocosin. Soil Science Society of
Amer ica Journal 41:1175-1180.
Davis, J., and R. Lucas. 1959. Organic soils; their
formation, distribution, utilization and management.
Special Bulletin 425, Agricultural Experiment Station,
Michigan State University, East Lansing, MI, 156 pp.
Davis, J. C. 1973. Statistics and data analysis in
geology. John Wiley and Sons, Inc., New York, NY, 550
PP .
Dean, J. 1984. Prudential giftwraps 120,000 acres.
Wildlife in North Carolina 48(7): 1.
DeBlieu, J. 1987. Hatteras journal. Fulcrum, Inc.,
Golden, CO, 181 pp.
Dickerson, B. 1976. Soil changes resulting from tree-
length skidding. Soil Science Society of America
Journal 40:965-966.
102
Dill, N., A. Tucker, N. Seyfried, and R. Naczi. 1987.
Atlantic white cedar on the Delmarva peninsula. Pages
41-55 in A. D. Laderman, ed. Atlantic white cedar
wetlands . Westview Press, Boulder, CO.
Dolan, T. J., A. Hermann, S. Bayley, and J. Zoltek, Jr.
1984. Evapotranspiration of a Florida, USA, freshwater
wetland. Journal of Hydrology 74:355-371.
Dolman, J. D., and S. Buol. 1967. A study of organic soils
(histosols) in the Tidewater region of North Carolina.
Technical Bulletin 181, North Carolina Agricultural
Experiment Station, Raleigh, NC, 52 pp.
Dolman, J. D., and S. Buol. 1968. Organic soils on the
lower coastal plain of North Carolina. Soil Science
Society o f Amer ica Proceedings 32:414-418.
Dooge, J. 1972. The water balance of bogs and fens. Pages
233-271 in Hydrology of marsh ridden areas .
Proceedings of the Minsk Symposium, June, 1972. The
UNESCO Press, Paris.
Dunne, T. and L. B. Leopold. 1978. Water in environmental
planning . W. H. Freeman and Co., New York, NY, 818
PP .
Earley, L. 1987. Twilight for junipers. Wildlife in North
Carolina 48(71:1.
Eisenlohr, W. 1966. Water loss from a natural pond through
transpiration by hydrophytes. Water Resources Research
2 : 443-453.
Farber, S., and R. Costanza. 1987. The economic value of
wetlands systems. Journal of Environmental Management
24:41-51.
Farnham, R., and H. Finney. 1965. Classification and
properties of organic soils. Advances in Agronomy
17:115-162.
Frost, C. C. 1987. Historical overview of Atlantic white
cedar in the Carolinas. Pages 257-264 in A. D.
Laderman, ed. Atlantic white cedar wetlands. Westview
Press, Boulder, CO.
Frost, C. C. 1989. University of North Carolina, Chapel
Hill. History of Atlantic white cedar in
the Carolinas. Unpublished manuscript.
Golet, F. and D. Lowry. 1987. Water regimes and tree
growth in Rhode Island Atlantic white cedar wetlands.
Pages 91-110 in A. D. Laderman, ed. Atlantic white
cedar wet lands. Westview Press, Boulder, CO.
103
Gorham, E. 1957. The development of peat lands. Quarterly
Review of Biology 32:145-166.
Gosselink, J. and R. Turner. 1978. The role of hydrology
in freshwater wetland ecosystems. Pages 63-78 in R.
Good, D. Whigham, et al, eds. Freshwater wetlands :
ecological processes and management potential .
Academic Press, New York, NY.
Goudie, A. 1986. The human impact on the natural
environment (2nd ed.) The MIT Press, Cambridge, MA,
338 pp .
Greeson, P., J. R. Clark, and J. E. Clark, eds. 1979.
Wetland functions and values : the state of our
understanding. Proceedings of the National Symposium
on Wetlands, Lake Buena Vista, Florida, November 7-10,
1978. American Water Resources Association Technical
Publication TPS 79-2, Minneapolis, MN, 674 pp.
Gregory, J., R. Skaggs, R. Broad head, R. Culbreath, J.
Bailey, and T. Foutz. 1984. Hydrologic and water
quality impacts of peat mining in North Carolina.
Water Resources Research Institute of the University of
North Carolina. Report No. 214, 215 pp.
Gregory, K. J. 1985. The nature o f physical geography.
Edward Arnold, London, 262 pp .
Guelke, L. 1989. Intellectual coherence and the
foundations of geography. Professional Geographer
41(2) : 123-130.
Heath, R. 1975. Hydrology of the Albemarle-Pamlico region.
North Carolina. A preliminary report on the impact of
agricultural development. Water Resources
Investigations 9-75, United States Geological Survey,
Raleigh, NC, 98 pp.
Hodges, D. 1989. Staff field scientist, Soil Conservation
Service, Dare County, NC. Personal communication
01/23/89.
Ingram, H. A. P. 1983. Hydrology. Pages 67-158 in Gore,
A. J., ed. Ecosystems of the World. Volume 4A: Mires:
Swamp, Bog, Fen, and Moore. Elsevier, Amsterdam.
Ingram, R. 1987. Peat deposits of North Carolina.
Bulletin 88, Geological Survey Section, Division of
Land Resources. Department of Natural Resources and
Community Development, Raleigh, NC, 84 pp.
104
Ingram, R., and L. Otte. 1981. Peat in North Carolina
wetlands. Pages 125-134 in C. J. Richardson, ed.
Pocosin wetlands ; an integrated analysis of coastal
plain freshwater bogs in North Carolina. Hutchinson
Ross, Inc., Stroudsburg, PA.
Ingram, R., and L. Otte. 1982. Peat deposits of Pamlimarle
peninsula: Dare, Hyde, Tyrrell, and Washington
counties. North Carolina. Contract DE-AC18-79FC14693,
United States Department of Energy, North Carolina
Energy Institute.
Jongedyk, H., R. Hickok, and I. Mayer. 1954. Changes in
drainage properties of a muck soil as a result of
drainage practices. Soil Science Society of America
Proceedings 18:72-76.
Koerselman, W. 1989. Groundwater and surface water
hydrology of a small groundwater-fed fen. Wetlands
Ecology and Management 1:31-43.
Koerselman, W., and B. Beltman. 1988. Evapotranspiration
from fens in relation to Penman's potential free water
evaporation (Eo) and pan evaporation. Aguatic Botany
31 : 307-320 .
Kologiski, R. 1977. The phytosociology of the Green
Swamp, North Carolina. North Carolina Agricultural
Experiment Station, Technical Bulletin No. 250, 101 pp.
Korstian, C. 1924. Natural regeneration of southern white
cedar. Ecology 5:188-191.
Korstian, C., and W. Brush. 1931. Southern white
cedar. United States Department of Agriculture,
Technical Bulletin 251.
LaBaugh, J. 1986. Wetland ecosystem studies from a
hydrologic perspective. Water Resources Bulletin
22(1): 1-10 .
Laderman, A. 1982. Community structure of Atlantic white
cedar forests. Wetlands 2:63-87.
Laderman, A. 1989. The ecology of Atlantic white cedar
wetlands: a community profile. United States Fish and
Wildlife Service Biological Report 85(7.21), 114 pp .
Lee, R. 1980. Forest hydrology. Columbia University
Press, New York, NY, 349 pp.
Levy, G. 1987. Atlantic white cedar in the Great Dismal
Swamp and the Carolinas. Pages 57-67 in A. D.
Laderman, ed. Atlantic white cedar wetlands. Westview
Press, Boulder, CO.
105
Lilly, J. 1981a. The blackland soils of North Carolina -
their characteristics and management for agriculture.
Technical Bulletin No. 270, North Carolina Agricultural
Research Service, Raleigh, NC, 70 pp.
Lilly, J. 1981b. A history of swamp land development in
North Carolina. Pages 20-'^2 in C. J. Richardson, ed.
Pocosin wetlands : an integrated analysis of coastal
plain freshwater bogs in North Carolina. Hutchinson
Ross, Inc., Stroudsburg, PA.
Linacre, E. T. 1976. Swamps. Pages 329-347 in Monteith,
J. L., ed. Vegetation and the Atmosphere. Volume 2:
Case Studies. Academic Press, London.
Little, E. 1980 . The Audubon Society field guide to
North American trees (eastern region). Alfred A.
Knopf, New York, NY, 715 pp.
Lowenthal, D. 1958. George Perkins Marsh ; Versatile
Vermonter. Columbia University Press, New York, NY,
442 pp .
Lucas, R. E. 1982. Organic soils (histosols) ; formation,
distribution, physical and chemical properties and
management for crop production. Research Report 435,
Michigan State University Agricultural Experiment
Station, East Lansing, MI, 80 pp.
Maki, T. 1974. Factors affecting forest production on
organic soils. Pages 119-136 in Aandahl, A., S. Buol,
D. Hill, and H. Bailey. Histosols ; their
characteristics, classification, and use. Special
Publication Series, No. 6. Soil Science Society of
America, Inc., Madison, WI.
Marsh, G. P. 1864. HaD. and nature : ^ physical geography
as modified by human action . Scribners, New York, NY.
Mather, J. 1978. The climatic water budget in
environmental analysis. D. C. Heath and Company,
Lexington, MA, 239 pp.
McCulloch, J. S. G. 1965. Tables for the rapid computation
of the Penman estimate of evaporation. East African
Agricultural and Forestry Journal 30:286-295.
McKinzie, W. 1974. Criteria used in soil taxonomy to
classify organic soils. Pages 1-10 in Aandahl, A., S.
Buol,D. Hill, and H. Bailey. Histosols; their
characteristics, classification . and use. Special
Publication Series, No. 6. Soil Science Society of
America, Inc., Madison, WI.
106
McMullan, P. S., Jr. 1984. Land-c1earing trends on the
Albemarle-Pamlico peninsula: 300 years of development
in a wetlands region. McMullan Consulting, Durham, NC,
131 pp .
Mitsch, W., and J. Gosselink. 1986. Wetlands. Van
Nostrand Reinhold Co., New York, NY, 539 pp.
Moore, J., and A. Laderman. 1989. A case study: Atlantic
white cedar wetlands in Dare County, North Carolina.
Pages 67-78 in Laderman, A. The ecology of Atlantic
white cedar wetlands: a community profile. United
States Fish and Wildlife Service Biological Report
85(7.21), 114 pp.
Moore, J., and J. Carter, III. 1987. Habitats of white
cedar in North Carolina. Pages 177-190 in A. D.
Laderman, ed. Atlantic white cedar wetlands. Westview
Press, Boulder, CO.
Moore, P. D., and D. Bellamy. 1974. Peat lands. Springer-
Verlag New York, Inc., New York, NY, 221 pp.
Mustonen, S., and P. Seuna. 1972. Influence of forest
drainage on the hydrology of an open bog in Finland.
Pages 519-530 in Hydrology of marsh-ridden areas .
Proceedings of the Minsk Symposium, June, 1972. The
UNESCO Press, Paris.
Noffsinger, R. 1989. Atlantic white cedar on the Alligator
River National Wildlife Refuge. North Carolina Nature
Conservancy Newsletter 44:5-6.
Noffsinger, R., and D. Belk. 1990. Analysis of hydrologic
factors in the recovery of Atlantic white cedar
wetlands. In preparation.
Novikov, S., and J. Goncharova. 1981. Forecasting changes
of water resources in large rivers following land
drainage . Hydrological Sciences Bulletin
26(4) : 393-398.
Daks, R. Q., Jr., and N. Coch. 1973. Post-Miocene
stratigraphy and morphology, southeastern Virginia.
Virginia Division of Mineral Resources Bulletin 82, 35
PP .
Otte, L. J. 1981. Origin, development, and maintenance of
the pocosin wetlands of North Carolina. Report to the
North Carolina Natural Heritage Program, Raleigh, NC,
51 pp .
Otte, L. J. 1987. North Carolina pocosins: their
developmental history. National Wetlands Newsletter
9(3):2-6.
107
Parent, L., J. Millette, and G. Mehuys. 1982. Subsidence
and erosion of a histosol. Soil Science Society o f
Amer ica Journal 46:40A-A08.
Peacock, S., and J. Lynch. 1982. Natural areas inventory
of mainland Dare County, North Carolina. North
Carolina Coastal Energy Impact Program, Report No. 27,
Department of Natural Resources and Community
Development, Raleigh, NC, 148 pp.
Pegg, R., and R. C. Ward. 1971. What happens to the rain?
Weather 26(3):88-96.
Penfound, W. T. 1952. Southern swamps and marshes.
Botanical Review 18:413-446.
Penman, H. 1948. Natural evaporation from open water, bare
soil and grass. Proceedings of the Royal
Society 193:120-145.
Phillips, J. D. 1984. Estimation of drainage areas in a
homogeneous landscape. Water Resources Bulletin
20(6) : 847-850.
Phillips, J. D. 1985a. Stability of artificia1ly-drained
lowlands: a theoretical assessment. Ecological
Modelling 27:69-79.
Phillips, J. D. 1985b. Geomorphic processes and stability
of coastal wetlands. Pages 1481-1487 in Magoon, et al
(eds.) Proceedings of the Fourth Symposium on Coastal
and Ocean Management, American Society of Civil
Engineers, New York.
Phillips, J. D. 1988. Incorporating fluvial change in
hydrologic simulations: a case study in coastal North
Carolina. Applied Geography 8:25-36.
Phillips, J. D., and D. Steila. 1984. Hydrologic
equilibrium status of a disturbed eastern North
Carolina watershed. GeoJournal 9(4) : 351-357.
Reclus, E. 1871. The earth (2 vol). Chapman and Hall,
London.
Richardson, C., R. Evans, and D. Carr. 1981. Pocosins:
an ecosystem in transition. Pages 3-19 in C. J.
Richardson, ed. Pocosin wetlands: an integrated
analysis of coastal plain freshwater bogs in North
Carolina. Hutchinson Ross, Inc., Stroudsburg, PA.
Richardson, C. 1983. Pocosins: vanishing wastelands or
valuable wetlands? Bioscience 33:626-633.
108
Schaetzl, R. 1986. Complete soil profile inversion by tree
uprooting. Physical Geography 7:181-188.
Seuna, P. 1980. Long-term influence of forestry drainage
in the hydrology of an open bog in Finland. Pages
141-149 in The influence of man on the hydrological
regime with special reference to representative and
experimental basins. Proceedings of the Helsinki
Symposium, June, 1980. International Association of
Hydrological Sciences, Publication No. 130.
Sharitz, R., and J. Gibbons. 1982. The ecology of
southeastern shrub bogs (pocosins) and Carolina bays : ^
community profile. Division of Biological Services,
United States Fish and Wildlife Service, United States
Department of the Interior. Washington, DC.
FWS/OBS-82/04. 93 pp.
Shaw, E. 1988. Hydrology in practice (2nd edition). Van
Nostrand Reinhold (International) Company, Ltd.,
London, 539 pp.
Siegel, D. 1988. Evaluating cumulative effects of
disturbance on the hydrologic function of bogs, fens,
and mires. Environmental Management 12(5) : 621-626 .
Skaggs, R., and J. Barnes. 1976. Drainage and water table
control on colloidal muck soils. Paper No. 76-2041 of
the 1976 annual meeting, American Society of
Agricultural Engineers.
Skaggs, R., J. Gilliam, T. Sheets, and J. Barnes. 1980.
Effect of agricultural land development on drainage
waters in the North Carolina tidewater region. Water
Resources Research Institute of the University of North
Carolina, Report No. 159, 161 pp.
Slusher, D., W. Cockerham, and S. Matthews. 1974. Mapping
and interpretation of histosols and hydraquents for
urban development. Pages 95-109 in Aandahl, A.,
S. Buol, D. Hill, and H. Bailey. Histosols : their
characteristics > classification , and use. Special
Publication Series, No. 6. Soil Science Society of
America, Inc., Madison, WI.
Soil Conservation Service. 1989. Interim soil survey. Dare
County, North Carolina. Dare County Soil and Water
Conservation District Office, Manteo, NC, 46 pp.
Soil Survey Staff. 1975. Soil taxonomy : a basic system
of soil classification for making and interpreting soil
surveys. Agricultural Handbook No. 436, Soil
Conservation Service, United States Department of
Agriculture, Washington, DC, 754 pp.
109
Speth, W. 1977. Carl Ortwin Sauer on destructive
exploitation. Biological Conservation 11:145-160.
Stephenson, R., and D. Stella. 1982. Anthropic drainageway
failure near Moyock, North Carolina. Abstracts of the
Annual Meetings, Southeastern Division, Association of
American Geographers 37:70.
Strahler, A. N . , and A. H. Strahler . 1983. Modern physical
geography (2nd ed) . John Wiley and Sons , Inc . , New
York, NY, 532 pp.
Swicegood, W., and G. Kriz 1973. Physical effects o f
maintaining drainage channels in North Carolina's
coastal area. Journal of Soil and Water Conservation
28(6): 266-269.
Tant, P. 1979. Blackland subsidence study. Soil Science
Society of North Carolina Proceedings 22:75-80.
Thornthwaite , C. W. 1948. An approach toward a rational
classification of climate. Geographical Review
38 : 55-94.
Thornthwaite, C. W. 1954. A re-examination of the concept
and measurement of potential évapotranspiration.
Laboratory of Climatology, Publicat ion No . 1_,
Centerton, NJ.
Thornthwaite, C. W. and J. R. Mather. 1955. The water
balance. Laboratory of Climatology, Publication No . ^,
Centerton , NJ.
Thornthwaite, C. W. and J. R. Mather. 1957. Instructions
and tables for computing potential évapotranspiration
and the water balance. Laboratory of Climatology,
Publication No. 10, Centerton, NJ.
Tiner, R. 1984. Wetlands of the United States: current
status and recent trends. National Wetlands Inventory,
United States Fish and Wildlife Service, United States
Department of the Interior, Washington, DC, 58 pp.
Tuan, Y. 1968. The hydrologic cycle and the wisdom of God.
University of Toronto Department of Geography Research
Publication No. 1, University of Toronto Press,
Toronto, Ontario, 160 pp.
U. S. Fish and Wildlife Service. 1986. Draft environmental
impact statement for the Great Dismal Swamp National
Wildlife Refuge Master Plan. U. S. Fish and Wildlife
Service Region Five, Newton Corner, MA.
lio
Van der Molen, W. 1988. Hydrology of natural wetlands and
wet nature reserves. Agricultural Water Management
lA : 357-364.
Venters, V. 1989. Return of the red wolf. Wildlife in
North Carolina 53(9):19-23.
Verry, E. S., and D. H. Boelter. 1979. Peatland hydrology.
Pages 389-402 in Greeson, P., J. R. Clark, and J. E.
Clark, eds. Wetland functions and values ; the state o f
our understanding. Proceedings of the National
Symposium on Wetlands, Lake Buena Vista, Florida,
November 7-10, 1978. American Water Resources
Association Technical Publication TPS 79-2,
Minneapolis, MN.
Ward, R. 1967. Principles of hydrology. McGraw-Hill,
London , 403 pp.
Wilson, K. 1962. North Carolina wetlands: their
distribution and management. North Carolina Wildlife
Resources Commission, Raleigh, NC, 169 pp.
Winter, T. 1981. Uncertainties in estimating the water
balance of lakes. Water Resources Bulletin 17:82-115.
Winter, T. 1988. A conceptual framework for assessing
cumulative impacts on the hydrology of non-tidal
wetlands. Environmental Management 12(51:605-620.
Yevdokimova, N., M. Mostovyy, and Y. Malyy. 1976.
Subsidence and biochemical destruction of peat in the
Ukrainian Poles'ye. Soviet Soil Science 8:345-347.