Auradé observatory

Auradé observatory

Scientific context

The Aurade observatory includes the Montoussé watershed in Auradé (3,28 km²), tributary of the  Save river. It is located 40 km West of Toulouse, in Gascogne hillsides of Southwestern France. It is an agricultural basin, with crops (wheat/sunflower rotation) occupying 90 % of its surface. The climate is temperate oceanic with average temperature of 13,9°C, average rainfall of 621 mm/year for the period 1985-2018. Flood periods 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 basin is characterized by a strong evapotranspiration  (500-600 mm/year). The basin is developed on a Miocene clay-limestone molasse which comes from the erosion of the Pyrenees. The soils belong to the sequence of leached brown soils.


Starting year: 1983

Localisation: 40 km West of Toulouse, in Gascogne hillsides of Southwestern France

Keywords: oceanic climate, marlo-chalk formations, agricultural systems, hydrology, biogeochemistry

Database: work in progress (OMP-SEDOO)

Web site:

PIs: Jean-Luc PROBST et Anne PROBST

Vue d'ensemble du bassin versant d'Auradé
Overview of the Auradé catchment © aprobst

Scientific questions

The scientific question that led to the establishment of the Auradé observatory is the impact of the agricultural activities (land use, agricultural practices, fertilizing inputs, phytosanitary products) and climate change on water and soil quality. Dissolved and particulate matter balances from natural and anthropogenic origin and transfer models of these matter are established in order to:

  • Analyze and evaluate the impact of agri-environmental measures on the physical and chemical erosion of soils and molasse, water quality, soils and 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:

  • Inside the watershed: one complete meteorological station, two collectors for chemistry (major elements) and rainfall stable water isotopes (2H et 18O), four lysimetric plates to collect soil solutions at different depths at mid-slopes, three piezometers (along a slope);
  • At the outlet of the basin: a gauging station with a water level sensor, two multiparameter probes for continuous measurements of physicochemical parameters and suspended matter, two sediment traps (bottom and surface), two 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 hydrogeochemical data: major anion, 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 at the outlet of the basin (1 100 km2), at the Larra station in the framework of ZA PYGAR.

Exutoire du bassin versant (station de jaugeage, sonde multiparamètre, préleveurs automatiques, pièges à sediments)
Catchment outlet (gauging station, multiparameter probe, automatic samplers, sediment traps) © jlprobst
Collecte des solutions de sols gravitaires par plaques lysimétriques en milieu de versant
Collection of gravity soil solutions by lysimetric plates in the middle of the slope © aprobst
Station météorologique et collecteur de précipitations pour l'analyse chimique et isotopique (réseau RENOIR)
Meteorological station and rainfall collector for chemical and isotopic analysis (RENOIR network) © aprobst

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, ETBX from INRAE) laboratories. Close links exist also between the Groupement des Agriculteurs de la Gascogne Toulousaine (GAGT), as well as socioeconomic partners (agricultural cooperatives, Chambers of Agriculture) and local authorities (Auradé Commune, Gers Department, Region Occitanie). These collaborations allow the development of research and operational management aimed at improving soil and sediments conditions, water quality as well as preserving the health of the ecosystems.