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Evaluating the spatial and temporal variability of groundwater uptake by riparian vegetation in a humid southeastern US catchment

Jeffrey W. Riley·Luke A. Pangle·Brent T. Aulenbach
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Abstract

In environments with shallow water tables, vegetation may use groundwater to support transpiration (T G ). This process has been carefully studied in some arid climates but rarely in humid climates—even those with severe droughts and seasonal water deficits. As such, the role of T G in humid-catchment hydrology is poorly constrained. We analysed water table fluctuations from nine monitoring wells along three transects in a second-order forested catchment to estimate T G at plot and whole-riparian zone scales. Average T G estimated around all well locations ranged from 1.06 to 4.95 mm d −1 and did not change systematically as a function of distance from stream channel or with plot-scale tree basal area. Counter to some previous studies, we found that T G was greater when the water table depth was deeper. Furthermore, the pattern of T G with water table depth was not monotonic at all locations. The ratio of T G to potential evapotranspiration tended to increase over the growing season, reflecting the progressive decrease in soil moisture storage and a greater reliance by vegetation on groundwater. Due to the lack of consistent spatial patterns in T G , we explored the number of monitoring wells needed to consistently estimate average T G within the 95% confidence bounds of the true mean. Based on this analysis, six or more wells were needed to consistently fall within the 95% confidence interval of the true mean. While this is based on the observed variability at a single site, it provides information for others considering this approach in similar upland forested catchments in humid regions.

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Jeffrey W. Riley, Luke A. Pangle, Brent T. Aulenbach. 2023-01-21. Evaluating the spatial and temporal variability of groundwater uptake by riparian vegetation in a humid southeastern US catchment. https://doi.org/10.1002/eco.2520

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