Baget

The Baget 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, in collaboration with BRGM (Occitania regional agency), the laboratory Geosciences and Environment Toulouse (GET) and the Station of Theoretical and Experimental Ecology (SETE) in Moulis (Ariège, France).

The Baget catchment (Pyrénées, Ariège) is a mountain ecosystem of middle altitude (Alt.= 1000 m) receiving around 1000mm of precipitation per year. Located close to Balagué village at 10 km West from Saint-Girons, the Baget catchment (13.25 km2) is drained by a karstic network which supplied the surface runoff of Lachein stream (specific discharge: 36 l.s-1.km-2). It is a tributary of the Lez which joins the Salat River, right tributary of the Garonne River.

From 1968, this experimental site was intensively equipped by the CNRS underground Laboratory of Moulis (today SETE). The device is composed of one main weir at the outlet, 3 full excess controls, 3 piezometers of which one inside the abyss, and one subterranean loss.

This karstic watershed has been surveyed since 1968 for some hydro-climatic parameters, particularly air temperature, precipitations and stream discharge at the outlet. Some geochemical parameters (pCO2, chemical and isotopic compositions of waters) and some hydro-biological and ecological data (invertebrates, particularly Crustacea) have been surveyed for periods during the last 40 years by the CNRS underground Laboratory of Moulis.

Since 2011, Baget catchment belongs to the French Network of Catchments (RBV) and it is included in the certified National Observatory Service SNO Karst. Then, new parameters are measured twice a month or with higher frequencies during some flood events (major cations and anions, alkalinity, pH, conductivity, dissolved organic carbon, total suspended matter, H, O, C isotopes…). Since 2014, a multi-parameter probe has been installed with different sensors to measure continuously water level, pH, conductivity, turbidity, dissolved oxygen, nitrate and chloride. These continuous measurements are calibrated twice a month with laboratory analyses. The water discharge is measured by BRGM-Occitania because the Baget karst is part of the French patrimonial network of ground-waters and it belongs to the piezometric network managed by BRGM.

The Baget catchment is very sensitive to limit conditions of surface drainage and to land covers. It offers the possibility to develop an eco-systemic survey, which integrates the hydrology, the geochemistry and the ecology of a mountain ecosystem in the SW of France. In this region, climate and land use changes will have significant impacts on biodiversity, ecosystem functioning and biogeochemical cycles for the next decades

The objective is to follow on the long term the response of this karstic hydro-system to hydro-climatic changes, and to anthropogenic perturbations and land use changes, with particular focus on their impact on water cycle, carbon and nitrogen biogeochemical cycles.