Evapotranspiration Partitioning with Sub-Daily Isotopic Measurement in a Sub-Humid Grassland Ecosystem

Abstract:

Evapotranspiration (ET) interweaves water, energy, and biogeochemical interactions between the land surface and atmospheric system. Stable isotopic measurement, especially field deployable laser absorption spectrometers, provides a promising tool for ET partitioning with its direct and efficient measurement on isotopic components of water vapor. This isotopic approach, however, is still facing some uncertainties in quantifying ET and its constituents according to assumptions and empirical formula involved. In this study, we combined high-time resolution measurement with laser absorption spectrometers and eddy covariance techniques to quantify ET and its two components, namely soil water Evaporation (E) and plant transpiration (T) for a sub-humid grassland in southern US. Direct chamber measurement on these two end-members was compared with revised Craig-Gordon model for the quantification consistency assessment. Our results indicate the daily ratio of T/ET and its sub-daily dynamics for different soil moisture and micro-climate conditions. We investigated the controlling factors for ET and its partitioning dynamics for this grassland ecosystem. The uncertainties involved in the quantification were also assessed by comparison between direct chamber and empirical approaches.