The Aurade catchment is managed by the Laboratory of Functional Ecology and Environment (EcoLab), a joint Research Unit between the Institute of Ecology and Environment (INEE) of CNRS, the National Polytechnic Institute of Toulouse and the University Toulouse III-Paul Sabatier.

The Aurade catchment (328 ha, SW France) is representative of Gascony hill watersheds. It is drained by the Montoussé stream which is a sub-tributary of the Save river (1110 km2), a left tributary of the Garonne river. It is mainly cultivated (94% of wheat and sunflower in rotation). The soils are clayey and carbonated since they are developed on Miocene molassic deposits (impermeable substratum) originating the erosion of the Pyrénées mountains. The climate is continental oceanic (P=700-800 mm.y-1; Q= 80-120 mm.y-1), with a strong evapotranspiration, severe drought periods and flash flood events, like in Mediterranean semi-arid climates.

The hydrochemical monitoring has been set up in 1982 by AZF Company, today Grande Paroisse Azote (GPN), to follow the impact of agricultural practices on nitrate loss fluctuations in the stream at the outlet of the catchment. Then 35-years series of data are today available, particularly for precipitation and discharge, nitrate concentrations and agricultural practices.

By 2004, the catchment monitoring was managed by EcoLab, in collaboration with GPN (agreement until 05/2011) and since 2011, it is supported by the INEE-CNRS. Then, new parameters are measured weekly or with higher frequencies during flood events (major cations and anions, alkalinity, dissolved silica, nutrients, pH, Conductivity, dissolved organic carbon, total suspended matters, trace elements, pesticides, H, O, C, N isotopes…). Since 2006, the same monitoring is conducted on the Save river at Larra station. Since 2010, a multi-parameter probe has been installed with different sensors to measure continuously water level, pH, conductivity, turbidity and nitrates The continuous measurements are weekly calibrated with laboratory analyses.

From 2001 to 2007, this catchment belonged to the national catchment network GRAPPE (Groupes Régionaux d’Action contre la Pollution par les produits Phytosanitaires dans l’Environnement). Consequently, 7-years of pesticides monitoring are also available. Since 2011, Aurade catchment is a Regional Platform for Research and Innovation in the French Occitania region and it is part of the French Network of Catchments (RBV).

Aurade experimental catchment is dedicated to the long term observations of the impacts of agricultural practices and climatic changes on the quality of waters, soils, sediments and aquatic ecosystems, chemical rock weathering, physical soil erosion, carbon and water fluxes and transfers of contaminants.

The scientific objectives are (i) to establish the balance of matter fluxes (suspended matters, major elements, nutrients and pollutants) in response to hydro-climatic fluctuations and anthropogenic pressures (agricultural practices); (ii) to understand and to model the mechanims which control their transfers; (iii) to determine the impact of pollutants on biology, going from the organisms to the communities.

The operational objectives are (i) to follow the impact of the agri-environmental devices and measures on water quality and aquatic ecosystems; (ii) to set up scenarios in response to change in climate, land cover and agricultural practices; (iii) to determine relevant biological indicators to survey the aquatic ecosystem health.

The originality of this experimental agricultural catchment is the strong link with the local farmer association (GAGT) and the interactions with different regional socio-economic partners (Agricultural Cooperative Corporations, Chambers of Agriculture, Occitania Region) and national water and biodiversity agencies (ONEMA, Adour-Garonne water agency). All these partnerships allow to develop both fundamental research and research and development, for operational management in order to improve the quality of soils, sediments and waters and to preserve the ecosystem health.

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