The Aurade observatory includes the Montoussé watershed in Auradé (3.28 km²), sub-tributary of the Save river, located 40 km west of Toulouse, on the Gascogny hillsides of Southwestern France. It is an agricultural catchment, with crops (wheat/sunflower rotation) occupying 90% of its surface. The climate is temperate oceanic with an average temperature of 13.9°C and an average rainfall of 620 mm/year (based on data from 1985-2018). The flood period occur in winter (December/January) and spring (May/June), with a low water period from the end of June to October, with occasional dry periods. This catchment is characterized by a strong evapotranspiration (500-600 mm/year). It is developed on a Miocene clay-limestone molasse derived from the erosion of the Pyrénées. The soils belong to the sequence calcareous-calcic-leached brown soils.
Starting year: 1983
Location: 40 km West of Toulouse, in Gascogne hillsides of Southwestern France
Keywords: oceanic climate, calcareous-clayey molassic deposit, agricultural systems, hydrology, biogeochemistry
Database: work in progress (OMP-SEDOO)
The scientific question that led to the establishment of the Auradé observatory is the impact of the agricultural activities (land use, agricultural practices, fertilizer inputs, phytosanitary products) and climate change on soil and water quality. Dissolved and particulate matter balances from natural and anthropogenic origins. Corresponding transfer models of these materials are established in order to:
- Analyze and evaluate the impact of agri-environmental measures on the physical and chemical weathering of soils and molasse, on the quality of water, soils, sediments and aquatic ecosystems in the context of climate change;
- Simulate water quality and aquatic environment scenarios in response to climate change, changes in land use and agricultural practices;
- Define relevant biological indicators on the health of aquatic ecosystems and the response of ecosystems to anthropogenic pressures.
Sites and measured variables
Instrumentation consists of:
- Within the watershed: 1 complete meteorological station, 2 rainfall collectors for chemistry (major elements) and stable water isotopes (2H et 18O), 4 lysimetric plates to collect soil solutions at different depths at mid-slopes, 3 piezometers (along a slope);
- At the outlet of the basin: a gauging station with a water level sensor, 2 multiparameter probes for continuous measurements of physicochemical parameters and suspended matter, 2 sediment traps (bottom and surface), 2 automatic samplers (one collecting water daily and the other one, according to water level variation) in order to sample floods. This instrumental park allows the collection of hydro-geochemical data: major anions and cations, alkalinity, dissolved silica, nutrients, pH, conductivity, dissolved organic carbon, turbidity, and suspended matter, water and carbon isotopes.
A flux tower from the the Observatoire Spatial Régional (OSR, CESBIO) is installed near the watershed. In addition, since 2006, similar hydrochemical monitoring are carried out on the Save river at the outlet of the basin (1,100 km2), at the Larra station within the framework of ZA PYGAR.
Partners and further information
The Auradé observatory is led by the Laboratoire Écologie Fonctionnelle et Environnement, CNRS-Toulouse University, in collaboration with GPN/TOTAL until May 2011, and with other Toulouse (CESBIO, GEODE) and Bordeaux (EABX, ETTIS from INRAE) laboratories. Close links also exist between the Groupement des Agriculteurs de la Gascogne Toulousaine (GAGT), as well as socio-economic partners (agricultural cooperatives, Chambers of Agriculture) and local authorities (Auradé Commune, Gers Department, Occitanie Region). These collaborations facilitate the development of research and operational management for the improvement of soil, sediments and water quality and ecosystems preservation.