Anthropogenic activities involving nitrogen (N) are contributing to eutrophication in marine and fresh waters. Because headwater streams are the primary interface between terrestrial and aquatic systems, they are an important link in the transport of N from enriched landscapes. However, N may be retained or removed through ecological processes occurring within streams. We will investigate the effects of enrichment on the ability of streams to retain N by comparing retention in study streams that span a gradient of N use and concentration. Retention will be measured by tracking the fate of N tracers experimentally released into study streams. We will quantify changes in ecosystem structure (biotic standing stocks) and function (metabolic activity) associated with enrichment and evaluate the influence of environmental factors (e.g., hydrology) on N retention. This approach to linking N enrichment and retentitive efficiency will increase understanding of theoretical and managerial aspects of N loading to lotic systems.
