Estimating Nutrient Exports to Estuaries

Abstract Nutrient export coefficients for Long Island Sound were estimated by relating measured concentrations of N and P in 33 Connecticut lakes to land use in their watersheds. This approach does not require that watersheds represent a single category of land use, but rather uses the lake to integrate contributions from all sources. These estimates were then compared with those obtained from an extensive review of the literature. The results suggest that current models with a sediment transport component tend to overestimate N and P exports from agricultural land and underestimate exports of N and P from wooded and urban land. These differences are likely attributable to greater transport of nutrients in the soluble phase than predicted by such models. Moreover, efforts to reduce erosion may not be effective in preventing losses of nutrients, particularly N, where increased infiltration may actually increase N exports. In conclusion, it appears that more emphasis should be placed on management strategies to reduce leaching losses of N, with less emphasis on structural practices to reduce erosion.