DELINEATION OF COMPLEX NITROGEN DYNAMICS IN NATURAL AND MANMADE POND SYSTEMS

Stormwater ponds feature prominently in coastal South Carolina and perform important functions, including flood control and stormwater pollution reduction.These ponds accumulate and process high concentrations of nutrient elements, such as nitrogen (N), before discharging them into downstream natural water bodies. However, our knowledge of specific hydrological and biogeochemical processes, or in other words, the dynamics of such nutrient chemicals are poorly understood. In this study, we focused on delineating specific nutrient dynamic pathways, particularly that of N, a nutrient that significantly contributes to the degradation of coastal aquatic ecosystems. In addition to being transported in dissolved and particulate-bound forms, N undergoes a variety of hydrogeochemical transformations in pond environments as a result of factors such as seasonal temperature, dissolved O₂ content, pH, redox chemistry, and microbial structure. The focus of this study is a freshwater pond located within the lower coastal plain of South Carolina and is characterized by a humid environment, mild temperatures, low topography, and widespread fresh and estuarine wetland systems. This pond serves as an analog for stormwater ponds common to the region, and is driven by accessibility as well as the existing research and monitoring infrastructure. Groundwater, pond water, and bed sediment were sampled and analyzed for various forms of N. We observed high concentrations of reduced forms of N in the shallow groundwater down-gradient from the pond compared with up-gradient of the pond. In this presentation, we will present a conceptual and quantitative model to describe the dynamic pathways of N in such systems. We expect that these models will be applicable for use in stormwater ponds used widely across the southeastern US.