Watershed N inputs

Increases in river N export over time often correlate relatively well with increases in N inputs to watersheds. However, the response of river N export to decreases in watershed N inputs is not necessarily as rapid or well understood. In at least one case, the Patuxent River (MD, USA), point source reductions in N resulted in rapid reductions in N export (Boynton et al., 1995 Jordan et al., 2003). However, N export is generally dominated by non-point sources, not point sources (Carpenter et al., 1998 Dumont et al., 2005 Seitzinger et al., 2005b others), so substantially reducing N export often requires a reduction in non-point N inputs. Reductions of non-point nutrient inputs have been attempted in a number of systems, but response of river N export to these reductions is often much slower and less predictable than responses to reductions in point sources (Stalnacke et al., 1999). 

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