High-frequency water vapor isotope measurements with a laser spectrometer in a paddy field during growing season and application for evapotranspiration partitioning
Abstract
Knowledge of the partitioning evapotranspiration (ET) into evaporation (E) and transpiration (T) components is crucial to improve water use efficiency in irrigated land, especially in paddy field. However, much less is known about the relative contribution of each component owing to difficulties in field observations. In this study, we estimate the fractions of evaporation and transpiration contributing to the total evapotranspiration flux in a paddy field of Tuskuba, Japan (36° 03' 14.3" N, 140° 01' 36.9" E) using high-frequency laser spectrometer (Picarro L2120-i Analyzer). The isotopic composition of evapotranspiration flux (δET) is determined by Keeling plot method based on water vapor isotope measurements of 1-minute interval on a diurnal time scale. The surface water isotope ratios is used to estimate the isotopic compositions of transpiration flux (δT) and evaporation flux (δE) with Craig-Gordon model. The results indicate that the transpiration is highly related to the leaf area index and drastically increase in growing season. The transpiration is the strongest in June and July, representing more than 90% of the total evapotranspiration flux. However, evaporation is dynamically controlled by water temperature at nighttime and appears to predominate the total nighttime evapotranspiration flux. These results are well consistent with those calculated from eddy correlation method and suggest the importance of nighttime evaporation in estimating diurnal flux. This finding may contribute to solving the closure energy imbalance problem in foregoing experimental studies in paddy field. Our present study provided a simple method for investigating water balance of paddy field and corroborated that water isotope is a powerful diagnostic tool in understanding the water exchange processes.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.B21A0456W
- Keywords:
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- 1818 HYDROLOGY Evapotranspiration;
- 1843 HYDROLOGY Land/atmosphere interactions