Predicting the impact of land use on the major element and nutrient fluxes in coastal Mediterranean rivers:: The case of the Tet River (Southern France)

This study presents a detailed discrimination between the natural and anthropogenic sources of dissolved major elements in the Tet River, a typical small coastal river in the south of France. The main objectives were to quantify the materials that were released by human activities in the basin, and to determine the specific element inputs for the major land use forms. The dissolved material fluxes were estimated by weekly monitoring over a hydrological year (2000-2001) along the major water gauging stations, and the flux relationships were examined in the context of anthropogenic and natural basin characteristics as determined by a Geographical Information System (GIS). Intensive agricultural land use in the form of fruit tree cultures and vineyards has a strong control on the dissolved element fluxes in the river. Area specific element releases for these cultures are greatest for SO4, with an estimated average of about 430 +/- 18 keq km(-2) a(-1). This is >= 11 times the natural SO4 release by rock weathering. Also for K, NO3, PO4 and Mg, the specific releases were >= 6 times the natural weathering rates (respectively about 44, 60, 4 and 265 keq km(-2) a(-1)). Waste-waters are the other major source of anthropogenic elements in the river. They have an important role for the fluxes of inorganic P and N, but they are also a considerable source of Cl and Na to the river. For example, the average annual release of Cl is around 150 moles/ inhabitant in the rural basin parts. Further downstream, however, where population density strongly increases, industrial effluents can enhance this value (> 300 moles/inhabitant). The waste-waters contribute more than 70% of the dissolved inorganic N export to the sea, although their contribution to the average DOC export is almost negligible (3%). (c) 2006 Elsevier Ltd. All rights reserved.