Increase in extreme rains stimulates larger erosional N and P fluxes to the northern Gulf of Mexico in recent decades

Abstract:

Soil erosion yields enormous amounts of macro-nutrients including nitrogen (N) and phosphorus (P) that are transported from land to rivers and oceans, potentially sustaining water column soluble reactive nutrient levels for decades. In this study, we represented erosional N and P fluxes in the Energy Exascale Earth System Model and applied the model to the continental US. We estimated that during 1991–2012 soil erosion yielded 614 Gg yr^-1 of particulate N and 261 Gg yr^-1 of particulate P (1 Gg = 10⁹ g) on average to the drainage basins of the northern Gulf of Mexico. We further estimated that particulate P was the dominant P constituent in these large rivers and over 55% of P export by erosion came from soil P pools that could be biologically available within decades. More importantly, we found that erosional N and P fluxes have increased at significant rates of 10 Gg N yr^-1 and 4 Gg P yr^-1, respectively, due to an increase in extreme rains in the Mississippi/Atchafalaya river basin, despite no significant increase of mean annual rainfall. With extreme rains projected to increase dramatically with warming, erosional nutrient fluxes in the region would likely continue to rise in the future.