Chapter 24 Relations among land cover, vegetation index, and nitrate concentrations in streams of the Enoree River Basin, piedmont region of South Carolina, USA

Abstract

Abstract Globally, high nitrate concentrations and fluxes in rivers are correlated with human population density and can lead to eutrophication of estuaries and coastal oceans. Although elevated nitrate concentrations often are associated with agricultural land cover, urban land cover also can contribute substantially to elevated nitrate concentrations in streams and rivers. In the piedmont region of the southeastern United States, urban areas typically are located in the headwater areas of watersheds. Because headwaters account for the majority of stream channel length in a watershed, the effect of urbanization on the biogeochemical cycling of nitrogen is magnified. We examined the relations between stream nitrate concentrations, land cover, and vegetation density in watersheds of nineteen tributaries of the Enoree River in northwestern South Carolina, USA. Based on data from 134 sample localities, stream nitrate concentrations generally increased with increasing urban land cover and decreased with increasing forest cover and vegetation density (normalized density vegetation index). Although watersheds with the highest percent urban land cover typically had the highest nitrate concentrations, nitrate concentrations were most variable spatially in drainage basins with 5 to 20% urban land cover. The relations between land cover, vegetation density, and nitrate concentrations are complicated by variation in the intensity of urbanization and spatial location of urban and forested land within the drainage basin of each sample locality. Artificial ponds in urban areas appear to play an important role in lowering stream nitrate concentrations and contribute to the spatial variability of nitrate concentrations.