Changes in groundwater oscillations, soil water content and evapotranspiration as the water table declined in an area with deep rooted phreatophytes
Groundwater in remote valleys of the Great Basin (NV, USA) has been approved by the State Engineer for pumping and export. Deep rooted shrubs such as greasewood (Sarcobatus vermiculatus) are partially dependent on this groundwater to meet plant water needs. To assess the impact of a falling water table on greasewood, we monitored evapotranspiration, reference evapotranspiration and precipitation, along with daily groundwater levels for 6·2 years. Groundwater levels declined 130 cm in a highly linear fashion (p < 0·001) over this period. Groundwater oscillations ceased in 2007 followed by a 2225-day quiescent period but then returned to daily oscillations late in 2013 for a 32-day period. The oscillation signature in 2013 coincided with the water level transitioning from sediment with 89% sand to a new horizon with only 8% sand. In 2013, we detected a soil water content depression at both 800 and 900 cm starting in early May that lasted 137 days, ending prior to the groundwater oscillation period when significant rainfall occurred in late August and early September. Soil water storage increase in the surface zone during the active growing period of 2013 was highly correlated (R2 = 0·77, p < 0·001) to changes in the lower unsaturated zone, suggesting a link between soil water storage zones based on precipitation and plant water extraction. Although the water table declined below 10·7 m and groundwater decoupling did not occur, the current rate of decline driven solely by groundwater pumping for the irrigation of alfalfa fields would suggest extensive pumping for diversion outside of the basin would not be sustainable with regard to maintaining healthy greasewood plants that have a finite rooting depth. Copyright © 2015 John Wiley & Sons, Ltd. Copyright © 2015 John Wiley & Sons, Ltd.
Changes in groundwater oscillations, soil water content and evapotranspiration as the water table declined in an area with deep rooted phreatophytes.