BIOGEOCHEMICAL GRADIENTS AND TRANSFORMATIONS ALONG A SANDY TIDAL CREEK IN LONG BAY, SOUTH CAROLINA

The nearshore zone is the focus of the interface between land and ocean and the location where land-derived matter can ultimately be modified before interacting with the marine environment for the first time. Sandy shores have the potential of significant biogeochemical transformation because of the high permeability of sand and substantial exchange of water under strong physical forces such as waves, currents and tides. In coastal South Carolina, sandy beaches are frequently sculpted by meandering outlets of tidal creeks referred to as swashes which discharge considerable amounts of freshwater and dissolved matter from land into the coastal ocean. The path of swashes is frequently modified by coastal communities to manage the free flow of water and to mitigate possible erosion of coastal properties. In doing so, the path length and the resulting time that flowing water has to interact with the sandy floor change and possibly alter the rate and impact of biogeochemical transformations that could occur in both the water column and sand. Our study investigates White Point Swash, a sandy tidal creek in Long Bay, South Carolina, that empties two small marsh systems surrounded by extensive developments. Our focus is on the macronutrients nitrogen and phosphorus and how their concentrations can be influenced by the path length and discharge patterns to the ocean. The degree to which this influence is detectable may demonstrate the importance of swashes as biogeochemical filters and contribute to our understanding of their complex role as mitigation features of land-derived inputs to the coastal environment.