Human influence on nitrogen export: a comparison of mesic and xeric catchments

Human impact on export of nitrogen in rivers is of great concern because increases in nitrogen export can dramatically increase primary productivity and decrease water quality in the coastal zone. Most research on this has been done for mesic catchments and not the xeric catchments that cover a large fraction of the earths surface. This paper uses river data to compare whole-catchment nitrogen export from xeric and mesic areas and human impact on this export. Results suggest that although nitrogen export is lower from xeric catchments than from mesic catchments, human impact on export acid forms of nitrogen being exported may be similar. In both xeric and mesic catchments with low population density (<20 humans km(-2)) the export of nitrate averages only 30% of export from catchments with populations 20 humans km(-2). For organic N export there is little effect of human population in either xeric or mesic catchments. Thus, for both xeric and mesic catchments human activity is associated with a shirt in dominant form of N being exported. On average, organic N is the dominant form of nitrogen being exported at low human population densities, whereas inorganic N export tends to dominate at higher population densities.