SALT MARSH MOSQUITO DITCH ALTERATIONS: ECOLOGICAL IMPACTS AND PERSPECTIVES IN MANAGEMENT DECISIONS
Nolan, Casey B
Salt marsh ecosystems are prized for the numerous ecological and economic services that benefit society. On the U.S. east coast, virtually all salt marsh habitat from Maine to Virginia has been hydrologically degraded by the creation of mosquito ditches. In the 1930s, mosquito ditches were excavated throughout marshes to drain standing water and reduce mosquito breeding habitat. Investigations of mosquito ditches found that ditching had including lowered water tables and salinities, changed plant communities, and reduced habitat for fish and waterfowl species. A large scale effort to fill mosquito ditches and restore natural hydrology is on-going at Assateague Island National Seashore, Maryland. I investigated the impact of ditch filling at Assateague on plant species Spartina alterniflora and Salicornia. The percent cover and occupancy of Spartina alterniflora and the occupancy of Salicornia species were similar between ditched and unditched salt marshes before ditch filling was conducted. Following ditch filling, there was little evidence that ditch filling altered percent cover and occupancy in an ecologically meaningful way. I also tested the hypothesis that ditch filling would lower salinities in unvegetated marsh panne habitat and facilitate the establishment of S. alterniflora using transplants. Ditch filling did not appear to alter porewater salinities and though transplant survivorship was generally low across all marsh types, transplants in ditch-filled marshes exhibited 20% greater annual survivorship compared to ditched marshes. In a broader context, filling ditches is one of several ways to alter mosquito ditches for a desired hydrological impact. Ditch plugging, Open Marsh Water Management, and ditch remediation have also been used to alter marsh hydrology in order to achieve management desires. However, each technique involves uncertainty in outcome and impacts both in the short and long term. Practitioners of these techniques were interviewed to describe their approach towards this uncertainty and how they evaluated risk-versus-reward scenarios. Practitioners expressed similar responses towards approaching the ecological uncertainty of these techniques. Each championed the notions of starting pilot studies before larger efforts were initiated, the importance of ecosystem processes (such as vertical accretion), and that uncertainty in outcome should not inhibit trial-and-error approaches to restoring salt marsh hydrology.
Nolan, Casey B. (December 2018). SALT MARSH MOSQUITO DITCH ALTERATIONS: ECOLOGICAL IMPACTS AND PERSPECTIVES IN MANAGEMENT DECISIONS (Doctoral Dissertation, East Carolina University). Retrieved from the Scholarship. (http://hdl.handle.net/10342/7077.)
Nolan, Casey B. SALT MARSH MOSQUITO DITCH ALTERATIONS: ECOLOGICAL IMPACTS AND PERSPECTIVES IN MANAGEMENT DECISIONS. Doctoral Dissertation. East Carolina University, December 2018. The Scholarship. http://hdl.handle.net/10342/7077. February 17, 2020.
Nolan, Casey B, “SALT MARSH MOSQUITO DITCH ALTERATIONS: ECOLOGICAL IMPACTS AND PERSPECTIVES IN MANAGEMENT DECISIONS” (Doctoral Dissertation., East Carolina University, December 2018).
Nolan, Casey B. SALT MARSH MOSQUITO DITCH ALTERATIONS: ECOLOGICAL IMPACTS AND PERSPECTIVES IN MANAGEMENT DECISIONS [Doctoral Dissertation]. Greenville, NC: East Carolina University; December 2018.
East Carolina University