BIOGEOCHEMISTRY OF SMALL HEADWATER WETLANDS IN THE SOUTH CAROLINA PIEDMONT

With the rapid urbanization of the Atlantic Piedmont ecoregion, headwater stream systems and small associated wetlands face increasing risk of degradation and loss. These wetlands provide valuable ecosystem services including nitrate removal and sediment storage that are critical in an urban landscape but often remain overlooked because of their small sizes and transient nature. Many of these wetlands are a product of ecosystem engineering by beaver (Castor canadensis), which can increase habitat diversity and alter nutrient cycling in stream systems. The main objective of this study was to investigate biogeochemical transformations taking place in four headwater wetland systems in the Piedmont of northwestern South Carolina, including three beaver-associated wetlands. Land cover in the watersheds of these four wetlands ranged from mostly forested to heavily urbanized. Water samples were collected from the wetland sites and sites upstream and/or downstream of the wetlands in June-August 2022. Samples were analyzed for major anions and cations, ammonium, dissolved organic carbon, and total dissolved nitrogen (TDN). Relative to upstream sites, wetland sites displayed variable concentrations of bicarbonate (-10% to +85%) and dissolved organic nitrogen (-72% to +30%), higher concentrations of iron (+8% to +435%), manganese (+69% to +2672%), and ammonium (+33% to +3700%), and lower concentrations of nitrate (-71% to -97%), TDN (-39% to -99%), and sulfate (-9% to -69%). In wetlands, dissolved organic nitrogen and ammonium accounted for higher proportions of TDN and nitrate accounted for lower proportions of TDN than in flowing stream reaches, indicating altered nitrogen cycle processes in wetlands. These changes occurred alongside lower concentrations of dissolved oxygen in wetlands. The transformations occurring in these wetlands, only one of which was listed in the US Fish and Wildlife Service’s National Wetland Inventory, indicate that small wetlands can play a role in the biogeochemical cycles of headwater ecosystems, including urbanized headwaters. The largest proportional changes in chemical parameters were observed in wetlands formed by beaver activity, which emphasizes the importance of including beaver wetlands into studies of wetland conservation in the southeastern Piedmont.