CHARACTERIZING NUTRIENT DYNAMICS IN LAKE ENVIRONMENTS

Freshwater lakes feature prominently in the built and natural settings of coastal South Carolina and perform important functions, including nutrient processing and transport (N, P, C), flood control, pollution reduction, and carbon sequestration. These lakes accumulate and process high concentrations of nutrients before discharging them into downstream natural water bodies and groundwater. However, knowledge of the biogeochemical dynamics of such nutrients is poorly understood in these environments. In this study, we focused on delineating specific nutrient dynamic pathways as water travels through a manmade lake and discharges into downstream saltmarsh. The focus of this study is the freshwater lake located at the Stono Preserve, which is in a lowland coastal physiographic setting and serves as an analog for thousands of freshwater lakes and ponds common to the region. Groundwater from up and downstream, lake water, and sediment were sampled and analyzed for various forms of nutrient concentrations. On average, we observed higher concentrations of N and P, and similar concentrations of C in the shallow groundwater downgradient of the lake compared with upgradient. This could be driven by the release of trapped P in lake sediment and the presence of denitrifying bacteria in the lake. Data and knowledge on biogeochemical lake processes were used to create an algorithm that describes the dynamic pathways and transformations of nutrients in such an environment. This algorithm can then be developed further to create a conceptual and quantitative model that can be applied to assess lakes and ponds across the southeastern US and help better understand their functions and impacts to the surrounding ecosystem.