Determining the Role of Estuarine ‘Swashes’ on Water Quality Impairment Along the Grand Strand of South Carolina: Impacts of Land Use and Stormwater Runoff

Determining the role of estuarine ‘swashes’ on water quality impairment along the Grand Strand of South Carolina: Impacts of land use and stormwater runoff. Recently, the occurrence of episodic hypoxia has been documented in the nearshore waters of Long Bay, South Carolina. These events have occurred directly off the Grand Strand, an urbanized beach-front resort community encompassing the greater Myrtle Beach metropolitan area, located along the central portion of Long Bay. Evidence suggests discharges from a series of estuarine tidal creeks (locally known as swashes) play a prominent role as sources of organic matter and nutrients which fuel oxygen demand leading to hypoxia in these waters. Effective management and mitigation of hypoxia formation in Long Bay requires understanding the extent and means by which swashes serve as sources of enhanced organic matter loading to the coastal ocean. This, in turn, requires a mechanistic understanding of the extent to which current land use and stormwater practices alter the terrestrial nutrient and organic loading to swashes and the impacts these have on internal swash dynamics and subsequent material export. The state and local intended users that we are working with recognize the potential impacts hypoxia could have on the region’s tourism-based economy and have acknowledged that there is a lack of data available for the swashes, such that they are forced to make management decisions without complete scientific information. The proposed research will address this knowledge gap by focusing on four representative swashes along the Grand Strand to: quantify terrestrial inputs of nutrients and organic matter associated with surface stormwater runoff and groundwater inputs under both dry weather and stormflow conditions; establish the link between terrestrial nutrient loading under contrasting flow conditions and the net organic matter production occurring within swashes; and determine the subsequent net tidal export of material (magnitude and forms) from these swashes. Through a collaborative effort between researchers and decision-makers (intended users), the results of this project will provide the scientific justifications necessary for enabling the development of effective management strategies that improve and protect estuarine and coastal water quality, in Long Bay.