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Evapotranspiration partitioning using a simple isotope‐based model in a semiarid marsh wetland in northeastern China
Author(s) -
Zhang Shichun,
Zhang Jing,
Liu Bo,
Zhang Wenguang,
Gong Chao,
Jiang Ming,
Lv Xianguo
Publication year - 2018
Publication title -
hydrological processes
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.222
H-Index - 161
eISSN - 1099-1085
pISSN - 0885-6087
DOI - 10.1002/hyp.11430
Subject(s) - phragmites , evapotranspiration , wetland , environmental science , transpiration , marsh , hydrology (agriculture) , stable isotope ratio , ecology , geology , biology , photosynthesis , botany , geotechnical engineering , physics , quantum mechanics
Partitioning evapotranspiration ( ET ) into evaporation ( E ) and transpiration ( T ) in wetlands is important for understanding the hydrological processes in wetlands and the contribution of wetland ET to local and regional water cycling and for designing effective wetland management strategies. Stable water isotopes are useful in the application of ET partitioning through the evaluation of the isotopic compositions of E ( δ E ), T ( δ T ), and ET ( δ ET ) obtained from observation or modelling methods. However, this approach still suffers from potentially large uncertainties in terms of estimating the isotopic endmembers. In this study, we modified the traditional isotope‐based ET partitioning methods to include leaf‐level biological constraints to separately estimate the relative contributions of T from Scirpus triqueter and Phragmites australis and the relative contributions of E from the standing surface water in a semiarid marsh wetland in northeastern China. The results showed that although the δ T values of S . triqueter and P . australis were rather similar, the mean δ T values of the 2 species were different from the values of δ E , making it possible to distinguish the relative contributions of E and T through the use of isotopes. The simulation of leaf water using a non‐steady‐state model indicated obvious deviations in leaf water enrichment ( δ Lb ) from isotopic steady states for both species, especially during early mornings and evenings when relative humidity was highest. The isotopic mass balance showed that E accounted for approximately 60% of ET , and T from S . triqueter and P . australis each contributed approximately 20% to ET ; this implied that the transpiration of one reed was equivalent to that of 5.25 individuals of S . triqueter . Using the estimated ratio of T to ET and the measured leaf transpiration, the total ET was estimated to be approximately 10 mm day −1 . Using the NSS‐ T r method, the estimated ET was higher than the water loss calculated from the water level gauge. This indicated that the river water and surrounding groundwater were the sources of the marsh wetland, with a supply rate of 8.3 mm day −1 .