Impact of nitrogen fertilizers on the natural weathering-erosion processesand fluvial transport in the Garonne basin

Knowledge of the impact of N-fertilizers on the weathering-erosion processe s of soils in intensively cultivated regions is of prime importance. Nitrif ication of NH4- fertilizers produces HNO3 in the basin of the Garonne river , enhancing soil degradation. Their influence on the weathering rates was d etermined by calculating the consumption rate of atmospheric/soil CO2 by so il weathering and erosion, and its contribution to the total dissolved rive rine HCO3-. This contribution was found to be less than 50% which correspon ds normally to a complete carbonate dissolution by carbonic acid, suggestin g that part of the alkalinity in the river waters is due to carbonate disso lution by an acid other than carbonic acid, probably HNO3. (C) 2000 Elsevie r Science Ltd. All rights reserved.