STREAM RESTORATION FOR NITROGEN REMOVAL: A WATERSHED PERSPECTIVE

Many stream restoration projects to date are implemented on an opportunity basis, rather than strategically planned in response to specific problems. Since stream restoration is an expensive enterprise, the selection of project sites should involve a rigorous process in which the history and characteristics of the landscape setting, watershed location, and feasibility are carefully considered. We use stream restoration for nitrogen (N) reduction in Coastal Plain watersheds as an example to illustrate the use of a heuristic framework for prioritizing site selection. At the regional scale, the identification of locations where N loadings are highest is imperative. High loading rates of N to streams can result from large sources and/or efficient hydrologic pathways into river networks and factors associated with each of these can be relatively easily identified. Physiographic province delineations within North America integrate many geologic and hydrologic factors relevant to N transmission. Sub-units of the provinces (geomorphic districts) provide finer detail of the landscape relief, lithology and history, which influence hydrologic pathways and stream water chemistry. Within geomorphic districts, patterns of land use influence loadings as well as transmission so they should be considered next followed by stream size. All things being equal, small headwater streams have the highest nutrient uptake rates. At the reach and sub-reach scales, identifying local factors that contribute to large N exports and reduced N removal can narrow the pool of potential restoration targets and influence the restoration approach.