Residence Time

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Science  19 Nov 2004:
Vol. 306, Issue 5700, pp. 1263
DOI: 10.1126/science.306.5700.1263b

Agricultural and industrial activity has increased the amount of N added to rivers far above natural levels. This N, added mostly as nitrate, is a major pollutant that contributes to eutrophication and produces anoxia in water bodies of all sizes; it also is a source of the greenhouse gas nitrous oxide (N2O). The magnitude of the impact of riverine N is hard to judge, however, because of large gaps in our knowledge about its removal during transport through the river system.

Donner et al. use an aquatic transport model to investigate in-stream N removal and N2O emissions in the Mississippi River system and how they may be affected by interannual climate variability. Their results show that the fraction of N removed in the river system can vary by nearly a factor of 2, with a threefold range in the associated N2O emissions, depending on precipitation. The lowest fraction of N removal and the greatest N2O emissions occur in the wettest years, when river flow is greatest and the residence time of the water in the rivers is shortest. — HJS

Geophys. Res. Lett. 31, L20509 (2004).

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