Microbial nitrogen removal in a developing suburban estuary along the South Carolina coast

The conversion of undisturbed coastal regions to commercial and suburban developments may pose a threat to surface and groundwater quality by introducing nitrate-nitrogen (NO3−-N) from runoff of land-applied wastewater and fertilizers. Microbial denitrification is an important NO3−-N removal mechanism in coastal sediments. The objective of this study was to compare denitrification and nitrate conversion rates in coastal sediments from a golf course, suburban site, undeveloped marsh, and nonmarsh area near rapidly developing Hilton Head Island, South Carolina. Nitrous oxide was measured using gas chromatography and nitrate and ammonium concentrations were measured using a flow injection autoanalyzer in microcosms spiked, with 50 μg NO3−-N gdw−1. The two marsh sites had the greatest ammonium production, which was correlated with fine sediment particle size and higher background sediment nitrate and surface water sulfate concentrations. The golf course swale had greatest denitrification rates, which were correlated with higher total carbon and organic nitrogen in sediments. Nitrate was consumed in golf course sediments to a greater extent than in the undeveloped marsh and upland freshwater sites, suggesting that the undeveloped sites and receiving estuaries may be more susceptible to nitrate contamination than the golf course swale and marsh under nonstorm conditions. Construction of swales and vegetated buffers using sediments with high organic carbon content as best management practices may aid in removing nitrate and other contaminants from runoff prior to its transport to the receiving marsh and estuary.