THE ROLE OF A PERMEABLE SAND COLUMN IN MODIFYING TIDAL CREEK GEOCHEMISTRY AND LAND-DERIVED INPUTS TO THE COASTAL OCEAN

Myrtle Beach, South Carolina is the fastest growing metropolitan area on the east coast. It is undeniable that as land use changes, not only are there a greater amount of pollutants entering our water bodies but the path to the coastal ocean becomes more efficient. In highly permeable and sandy environments these land-derived inputs are transformed through complex biogeochemical processes. To sustain healthy ecosystems, we must understand the mechanisms which alter land-derived inputs as water passes into marine systems. The purpose of this study is to investigate how permeable sands underlying estuarine tidal creeks, known as swashes, act as natural filters and modifiers of land-derived materials before they reach the coastal ocean.

Our study site is Singleton Swash, one of fifteen major estuarine swashes located along the Grand Strand that drains 613 hectares (ha) of watershed into Long Bay. Discharge into the coastal ocean is through one primary tidal creek, whose main channel is heavily influenced by nearshore processes and is ever-changing. Erosion-deposition patterns dictate the main types of benthic interfaces across which sediment-water exchange occurs and, consequently, the rates of biogeochemical modification of land-derived inputs before they reach the ocean.

Our hypothesis is that estuarine swashes may mitigate land-derived inputs into the coastal ocean by exchanging matter across the sediment-water interface and incorporating the remineralized constituents into microphytobenthic primary producers. We are currently assessing the non-conservative behavior of materials which are subject to enhanced exchange across a permeable sediment-water interface. We are also documenting the role of microphytobenthic communities, assimilating inorganic nutrients regenerated in porewater and transported upwards. Upon completion of this project we hope to demonstrate whether interaction through exchange between the sediment and overlying water affects tidal creek geochemistry. If so, swashes should be considered as a filter for land-derived pollutants transported through the regional watersheds, and thus mitigating the impact of land-derived substances on the coastal ocean.