On groundwater fluctuations, evapotranspiration, and understory removal in riparian corridors

Abstract

[1] This study utilizes 7 years of continuously monitored groundwater-level data from four sites along the Río Grande riparian corridor in central New Mexico to calculate evapotranspiration from groundwater and assess impacts of understory vegetation removal during a restoration project. Diurnal groundwater fluctuation measurements were used to compare the well-known White method for estimating evapotranspiration from groundwater (ET g ) to colocated measurements of total riparian evapotranspiration (ET) measured using the eddy covariance method. On average, the two methods were linearly correlated and had similar variability, but groundwater hydrograph estimates of ET g tended to be larger than tower ET estimates. Average ET g estimates for two wells at one site ranged from 91.45% to 164.77% of measured tower ET estimates, but were also shown to range from 57.35% to 254.34% at another site. Comparisons between the methods improved with deeper water tables, reduced groundwater and river connectivity, and where soil profiles were dominated by coarse-sized particles. Using a range of texturebased estimates of specific yield (S y ) with water table position improves the field application of the White method. River-induced fluctuations in groundwater increased the variability of ET g measurements. Removal of understory vegetation at one site resulted in a small but significant reduction in diel groundwater fluctuation amplitude of 19-21%. Caution is required when understory vegetation removal is used as a means to decrease overall riparian ET. Diel groundwater fluctuation amplitudes can be useful in gauging the hydrological effects of vegetation removal. Riparian groundwater hydrographs are critical to investigating the hydrologic connectivity between river and shallow groundwater, the temporal patterns of vegetative consumption, and monitoring changes to the vegetation community.

Groundwater-dependent ecosystems: recent insights from satellite and field-based studies

“…In some circumstances groundwater uptake by vegetation can be seen as a diel fluctuation in the depth-to-groundwater , as first identified in groundwater hydrographs by White (1932). These daily fluctuations in depth-to-groundwater cease when the water table falls below the rooting zone (Butler et al, 2007) or when vegetation is dormant (Lautz, 2008;Martinet et al, 2009;Miller et al, 2010). However, changes in the density of water with temperature can cause expansion and contraction of an aquifer (Post and von Asmuth, 2013), leading to the erroneous conclusion that the vegetation is accessing groundwater.…”

“…This approach has been successfully applied in the Okavango Delta in Botswana (Bauer et al, 2004), an upland grassland catchment in central Argentina (Engel et al, 2005), an oak/grassland site on the Great Hungarian Plain of eastern Hungary (Nosetto et al, 2007), the Sopron Hills of western Hungary (Gribovszki et al, 2008), the Gobi desert of northwestern China (Wang et al, 2014), and various sites in the USA (Butler et al, 2007;Lautz et al, 2008;Martinet et al, 2009). The White method tends to over-estimate ET g (Loheide et al, 2005;Martinet et al, 2009). A major source of error is estimation of S y , to which this method is very sensitive (Loheide et al, 2005;Gribovszki et al, 2008;Lautz, 2008;Logsdon et al, 2010;Miller et al, 2010).…”

“…Furthermore, representative measurements of the readily available S y are difficult to make and are complicated by capillary flux, trapped air, hysteresis, and departure of the soil-water ecosystem from an equilibrium (Logsdon et al, 2010). The value of S y is dependent upon soil texture (Loheide et al, 2005); thus, Martinet et al (2009) applied a value of S y that varied with the soil texture in contact with the capillary fringe of the water table. With a measure of ET g (e.g.…”

Scaling down hyporheic exchange flows: from catchments to reaches

“…species) and water consumption (i.e. ET) drive nonlinear spatial variations in shallow GSE and vertical and lateral hyporheic flow patterns (Martinet et al, 2009;Wondzell et al, 2010;Larsen et al, 2014).…”

Estimating groundwater evapotranspiration by a subtropical pine plantation using diurnal water table fluctuations: Implications from night-time water use

“…In recent years the method has been further developed to account for variations in diurnal groundwater inflow and enabling sub-daily estimates of ET g (Gribovszki et al 2008;Loheide, S. P. 2008). Several studies have applied the methods in a variety of ecosystems ranging from wetlands (Mazur et al 2013;McLaughlin & Cohen 2013), savannah (Miller et al 2010) and forests (Vincke & Thiry 2008) to riparian corridors where most studies have been conducted (Butler Jr. et al 2007;Schilling 2007;Lautz 2008;Martinet et al 2009). One of the main assumptions behind the method is that groundwater inflow from the background to the point of measurement representative for the inflow at both day and night can be calculated from predawn behaviour in the groundwater water table, commonly defined from midnight to 4 am when vegetation water use is assumed negligible (Loheide, S.P.…”