Linkages of nitrate losses in watersheds to hydrological processes

A variety of factors can affect NO3 concentrations in surface waters, including atmospheric nitrogen (N) deposition, fertilizer N inputs, wastewater N contaminants, internal N cycling processes (e.g. plant uptake, mineralization, nitrification, denitrification) and hydrological flowpaths. Elevated levels of N inputs to ecosystems due to anthropogenic influences may have profound effects, including alterations of biotic diversity and N cycling (Vitousek et al., 1997). The dominant N solute in surface and ground waters for those systems experiencing ‘N saturation’ is often NO3, with NH4 and dissolved organic N (DON) generally being of lesser importance. In contrast, DON often predominates in systems with lower total N (TN) concentrations. ‘Nitrogen saturation’ can be defined as an increase in NO3 when N sources exceed the biotic demand for this element. Stages of ‘N saturation’ in catchments have been described as a continuum with increasing NO3 concentrations and changes in the seasonal patterns of NO3 in surface waters (Stoddard, 1994). Elevated NO3 can contribute to freshwater acidification and coastal eutrophication.