Data_Sheet_1.zip

Abstract

Salt marshes serve as zones of intense groundwater mixing and reaction between freshwater uplands and estuaries. This raises the question of whether the impacts of upland development on nutrient and carbon species can be transmitted through salt marshes via groundwater, or whether salt marshes can buffer estuarine waters from coastal development. We sampled groundwater from fifteen tidal creek basins in South Carolina to test for compositional differences associated with development and marsh width. Groundwater samples from near creekbanks and below freshwater uplands were analyzed for salinity, total dissolved nitrogen and phosphorus, and dissolved organic carbon. In aggregate, including creekbank and upland samples, groundwater concentrations of total dissolved phosphorus were significantly higher in the summer in developed watersheds than in undeveloped watersheds. Significant differences in total dissolved nitrogen were noted in the winter, but differed between uplands and creekbanks. In fresh groundwater below the uplands, concentrations of dissolved organic carbon were lower in developed watersheds than in undeveloped watersheds, and upland concentrations were lower in the winter than in the summer. These results support the hypothesis that development can affect groundwater compositions in coastal groundwater and therefore may affect coastal nutrient and carbon fluxes. However, results also revealed significant linear correlations between marsh width, salinity, and nutrient concentrations in some marshes. These results suggest that salt marshes can act as buffers for development, and specifically suggests that the buffering capacity of salt marshes increases with width. Narrow or trenched salt marshes are far less likely to be effective buffers.