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Groundwater Regulates Interannual Variations in Evapotranspiration in a Riparian Semiarid Ecosystem
Author(s) -
Missik Justine E. C.,
Liu Heping,
Gao Zhongming,
Huang Maoyi,
Chen Xingyuan,
Arntzen Evan,
Mcfarland Douglas P.,
Verbeke Brittany
Publication year - 2021
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1029/2020jd033078
Subject(s) - eddy covariance , riparian zone , evapotranspiration , environmental science , water table , hydrology (agriculture) , groundwater , ecosystem , streamflow , surface water , dry season , ecology , drainage basin , geology , geography , cartography , environmental engineering , geotechnical engineering , habitat , biology
Abstract Drylands are an important component of Earth's carbon, water, and energy budgets. Changes in hydroclimatic conditions can significantly alter land surface fluxes in these ecosystems. In regions with groundwater‐river water exchange, land surface fluxes are strongly modulated by groundwater table fluctuations in response to river stage variations; however, interactions between fluxes and groundwater remain poorly understood in drylands. Here, we use eddy covariance data collected in paired upland and riparian semiarid ecosystems (AmeriFlux sites US‐Hn1 and US‐Hn2) during 4 years with contrasting river flow conditions to examine interactions among river stage, water table dynamics, meteorological drivers, and ecosystem fluxes. Elevated groundwater availability resulting from groundwater‐surface water exchange at the riparian site enhanced the latent heat flux (LE, the energy form of evapotranspiration), which was sustained longer in the growing season. Interannual variation of dry season LE was small at the upland site, while at the riparian site contrasting river flow conditions resulted in large interannual variability in LE, with June LE of high‐flow years being 2.3 times that of low‐flow years. The 4‐year mean summer LE at the riparian site was 2.1 times larger than that at the upland site. Carbon uptake (NEP) and LE were well correlated at the upland site at the monthly and annual timescales, but at the riparian site enhanced LE due to shallow water table depth did not correspond to enhanced NEP. Our results demonstrate that enhanced groundwater availability modulated by river stage is a critical driver of land surface fluxes in semiarid riparian ecosystems.