Nitrogen fluxes from large watershed to coastal ecosystems controlled by net anthropogenic nitrogen inputs and climate
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Howarth, R. W.; Swaney, D. P.; Billen, G.; Garnier, J.; Hong, B.; Humborg, C.; Johnes, P.; Morth, C.; Marino, R. M.
The flux of nitrogen (N) to coastal marine ecosystems is strongly correlated with the net anthropogenic nitrogen inputs (NANI) to the landscape across 154 watersheds, ranging in size from 16 km 2 to 279 000 km 2, in the US and Europe. When NANI values are greater than 1070 kg N km -2 yr -1, an average of 25% of the NANI is exported from those watersheds in rivers. Our analysis suggests a possible threshold at lower NANI levels, with a smaller fraction exported when NANI values are below 1070 kg N km -2 yr -1. Synthetic fertilizer is the largest component of NANI in many watersheds, but other inputs also contribute substantially to the N fluxes; in some regions, atmospheric deposition of N is the major component. The flux of N to coastal areas is controlled in part by climate, and a higher percentage of NANI is exported in rivers, from watersheds that have higher freshwater discharge.
Funding was supplied in part from the National Oceanic and Atmospheric Administration (NOAA) through the Coastal Hypoxia Research Program, the US Department of Agriculture through the Agriculture, Energy, and Environment Program at Cornell University, and David R Atkinson through an endowment given to Cornell to support a professorship awarded to RH. This paper resulted from workshops held in Sigtuna, Sweden, and Paris, France, funded by Baltic Nest and Nine-ESF. This is Contribution #CHRP 138 from the NOAA Coastal Hypoxia Research Program.
Abee meteorite; anthropogenic effect; atmospheric deposition; climate effect
Previously Published As
Frontiers in Ecology and the Environment, 10: 37-43.