Use of stable water isotopes in the understanding of soil vegetation - atmosphere - interactions
Utilisation des isotopes stables de l'eau dans la compréhension des interactions sol - végétation - atmosphère
Résumé
Evapotranspiration from continental surfaces is one of the most important components of the global water cycle. Its determination, especially at larger scales, remains largely a challenge. Traditional measuring methods include the Bowen ratio, the eddy correlation and the water balance estimation (micro lysimeter, sap flow), but they are applicable only at the field scale. The challenge is even higher when trying to identify the partition of evapotranspiration between its components: bare soil evaporation, transpiration by the plants and evaporation of intercepted water. However, most of the widely used Soil Vegetation Atmosphere Transfer models (SVATs) provide estimates of these components and a proper validation of this partition is often difficult. To progress in a better quantification of this partition, the use of isotopic biogeochemistry can provide useful information. Assuming specific hypotheses of stationarity, it is possible to identify and quantify the different sources of the atmospheric water vapour (local and regional, vegetation and soil) Analysis of the heavy stable isotopic ratios of water in both the liquid and vapour phases : 18O and 2H can allow to determine the « history » of the water in the soil since the last rainfall event (infiltration, re-evaporation) or the root extraction depths.