METAL AND WOODEN SHIPWRECKS: UNDERSTANDING THE RELATIONSHIP BETWEEN HEAVY METALS, ENVIRONMENTAL FACTORS, AND MICROBIAL COMMUNITIES

Abstract

Just 30 miles south of Washington D.C., Mallows Bay is an estuarine area housing nearly 200 shipwrecks, most of which have been in the area for close to 100 years and could be leaching contaminants from residual fuel and ship materials. This study examines how the wrecks, environmental factors of the estuary, and the microbial community interact and ultimately may impact the surrounding ecosystem. Sediment samples were collected in three distinct time periods around Accomac, a metal wreck site, and Aowa, a wooden wreck site over a three-year period along transects up to 200 meters. The 100 samples were analyzed for 18 heavy metals and nutrients, including chromium, lead, iron, and copper, and DNA was sequenced using the V4-V5 region of the 16S rRNA gene to identify the microbial communities. Of the tested variables, distance had the greatest impact on the heavy metal concentrations with an associated variance of 13% (PERMANOVA, p-value=0.005) Additionally, Kruskal-Wallis tests identified ship material as influential to the concentrations of chromium and lead levels, while copper and iron seem to only be influenced by distance from ship (p-value >0.05). Microbial results show a high diversity of communities and clustering by ship construction material (i.e. wood vs. metal) and sample year with some similarity by distance for the metal wreck. Environmental factors showed the greatest combined influence of factor groups (pH, season, temperature; R² = 0.117, p = 0.006), while ship material factors and heavy metals showed little to no variation. Together this suggests that these shipwrecks may be a cause of metal contamination in the surrounding sediment but have a limited effect on the microbial community structure and diversity. Based on EPA standards, the heavy metals to be concerned about at are chromium and lead and people interacting with this environment should limit time spent directly inside or around the wrecks to less than eight hour a day, five days a week.