Spatio‐temporal patterns of evapotranspiration from groundwater‐dependent vegetation

Abstract

Understanding hydrological processes in water-limited systems requires consideration of temporal and spatial vegetation water use patterns at the landscape scale. We used data derived from the MODerate Resolution Imaging Spectroradiometer (MODIS) satellite instrument and interpolated climate data covering a ten-year period to contrast the spatio-temporal patterns of actual evapotranspiration (AET) from known phreatophytic and non-phreatophytic vegetation overlying a large superficial aquifer. We assessed shallow to deeper groundwater habitats and compared AET responses to seasonal and inter-annual variation in precipitation. Overall, vegetation in shallow groundwater habitats had higher AET rates during the growth season (spring and summer) than vegetation growing in deeper groundwater habitats, suggesting that the former was not physiologically constrained by water deficit. Vegetation in areas of consistently high (ground-)water availability maintained higher AET, reaching a peak of 95 mm in mid-summer. In contrast, plantation maritime pines had the highest AET rates at deep groundwater habitats. Inter-annual variability in AET correlated with rainfall and AET rates peaked two months after the majority of effective rainfall had fallen. During low rainfall years, maximum AET peaked one month earlier relative to higher rainfall years. The results of this study suggest that remote sensing of AET can give a conditional indication of where groundwater is important in supporting vegetation and can be a valuable tool in identifying management focus areas where vegetation is variably sensitive to water deficit. Copyright © 2016 John Wiley \u26 Sons, Ltd. Copyright © 2016 John Wiley \u26 Sons, Ltd

Spatiotemporal variations in groundwater and evaporative demand drive ecophysiological functioning of a phreatophyte in drylands

“…The spatial variability in DTGW might explain the response patterns of gas exchange throughout the growing season. Increasing DTGW negatively affected carbon assimilation and water loss, as has been previously observed in a variety of GDEs (Butler et al, 2007;Carter and White, 2009;Osuna et al, 2015;Sommer et al, 2016). Thus, deeprooted species, particularly from arid and semiarid regions, can face physiological constraints fostered by deep water sources (Nardini et al, 2014).…”

“…Coupled with DTGW and salinity gradients, temporal groundwater depletion might induce water-de cit stress, particularly in the late summer (Naumburg et al, 2005;Sommer et al, 2016). Our results revealed a signi cant decrease in both Ψ pd and Ψ md from spring to summer, although DTGW did not substantially decline during the growing season.…”

“…Here, A, g s , and E decreased with the increase in DTGW as consequence of such constraints. In summer, the importance of groundwater availability increased, as shown by the rise in these gas-exchange rates as consequence of higher net radiation and temperature (O'Grady et al, 1999; Sommer et al, 2016), and this rise in gas-exchange rates was more pronounced in plants at shallower DTGW. On the contrary, plants at deep water tables did not experience such noticeable increase in ecophysiological activity.…”

“…In this sense, an understanding of the connection between morpho-functional and hydraulic traits with groundwater characteristics (i.e., groundwater depth, conductivity, and temperature) will be crucial for predicting climate change effects upon GDEs. Zolfaghar et al, 2014; Osuna et al, 2015;Sommer et al, 2016;Nolan et al, 2017a). Hydraulic traits such as water potential are strongly correlated with DTGW gradients, as shown in phreatophytic oaks, eucalyptus, and acacias from California and Western and Central Australia (Carter and White, 2009;Osuna et al, 2015;Nolan et al, 2017a).…”

Estimating groundwater evapotranspiration by phreatophytes using combined water level and soil moisture observations

“…Given the significance of groundwater for ecosystems, efficiently quantifying vegetation‐induced groundwater evapotranspiration ( ET g ) is very important for arid and semiarid environments (Doody & Benyon, ; Sommer, Boggs, Boggs, Dijk, & Froend, ). One classical method for estimating groundwater ET, which was initially introduced by White (; hereafter called the White method), uses diurnal water table fluctuations (WTFs).…”