AN INTERDISCIPLINARY ASSESSMENT OF EXPOSED WOODEN SHIPWRECK STRUCTURAL STABILITY IN A SHALLOW-WATER TIDAL-FRESH ECOSYSTEM

Abstract

Wooden shipwrecks are found in diverse aquatic systems worldwide, filling critical niches in these systems as ‘islands of life.’ Within these systems, wooden shipwrecks exhibit different properties. Some are intact and have a structure sitting high above the seafloor. Others have no exposed structure, with the remaining structure buried in the seafloor. While the intact, proud structures do exist, archaeologists and resource managers will at some stage interact with and seek to protect buried structures. These shipwrecks have been exposed to a series of site formation processes that have broken down or covered any exposed shipwreck structure. Such processes include microbial degradation by delignifying and lignocellulose-degrading bacteria, as well as chemical breakdown driven by local hydrological conditions. Furthermore, these buried wooden shipwreck structures have undergone a series of anthropogenic processes that have contributed to their degradation, both during their use and within the archaeological context. While these processes cannot be characterized or evaluated for buried wooden shipwreck structures, they can be measured in those with exposed, extant structures. This project characterized and evaluated the relationship between in situ preservation of the exposed wooden shipwreck structure and environmental conditions in a tidal-fresh, shallow-water context. Using Aowa, a wooden steamship of the United States Shipping Board Emergency Fleet Corporation in the Mallows Bay-Potomac River National Marine Sanctuary, this study developed a methodology that integrated historical, archaeological, microbial, and hydrological data to assess and quantify the degradation of exposed wooden shipwreck structures. This study is a first attempt at linking degradation across a shipwreck’s systemic use life and its archaeological context. First, this study reconstructed the systemic use context of the case study site, including the development of its historical narrative and the construction of a digital model of the vessel. Archaeological data collected at the site were used to analyze the systemic behaviors that led to degradation prior to 2022. Beginning in 2022, two years of seasonal monitoring were conducted at the site, including the collection of wood density data using a Resistograph micro-drilling device, bacterial community data from the shipwreck and the surrounding environment, and local water chemistry data. The wood density, identified microbial community (both whole community and delignifying and lignocellulose-degrading community members), and water chemistry data were correlated to assess the presence and strength of relationships across a spatiotemporal scale. While these relationships were weak, this project represents the first step toward correlating the site-formation processes that contribute to the degradation of the exposed wooden structure. Furthermore, the findings suggest these relationships are reciprocal and, thereby, cyclical. The methodology combines novel techniques with analytical approaches to integrate data from distinct site-formation processes in innovative ways, drawing connections among processes and ultimately providing a means to calculate the rate of degradation of exposed wooden shipwreck structures. For resource managers, the presented findings and methodologies serve as tools to adjust management plans for the holistic management of natural and cultural resources. For archaeologists, this study provides one of the first to explore the interlinkage of site formation processes on an exposed wooden shipwreck structure and to quantify degradation across systemic and archaeological contexts. This study lays the groundwork for further analysis of these processes in tandem, supporting holistic, integrated site management.