XVI INQUA Congress

Paper No. 9
Presentation Time: 11:10 AM

INCREASE IN THE EXPORT OF ALKALINITY FROM NORTH AMERICA’S LARGEST RIVER: CLIMATE AND LAND-USE CONTROLS ON ALKALINITY EXPORT FROM THE MISSISSIPPI RIVER


RAYMOND, Peter, School of Forestry and Environmental Studies, Yale, 205 Prospect St, New Haven, CT 06511 and COLE, Jon, IES, Millbrook, NY, peter.raymond@yale.edu

Chemical weathering and the subsequent export of carbonate alkalinity (HCO3- +CO3-2 ) from soils to rivers is a significant fate of terrestrially-sequestered atmospheric CO2 . We show here that during the past half-century the export of this alkalinity has increased dramatically (59%) from North America’s largest river, the Mississippi. This increased export is in part the result of increased flow resulting from higher rainfall in the Mississippi basin. Global change models predict a continuation in the alterations to the global water balance over the following decades with a general increase in precipitation. Thus it appears that the rate of alkalinity export and terrestrial CO2 sequestration through weathering could continue to increase in future years.

Sub-catchment data of the Mississippi suggest that the increase in the export of alkalinity is also strongly linked to land cover. Croplands, which make up >30% of the Mississippi watershed, export 4 to 9 times more alkalinity per unit area than forests. The direct mechanism is unclear, but sub-catchment observations indicate that cropland systems respond differently to rainfall events than forested systems. These observations have important implications for potential management of C sequestration in the United States and suggest that reconverting abandoned cropland fields to forest will decrease terrestrial carbon sequestration through weathering at a rate comparable to above ground forest biomass accumulation.