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1 April 2012 Response of an Intermountain Groundwater-Dependent Ecosystem to Water Table Drawdown
Daniel Pritchett, Sara J. Manning
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Groundwater-dependent ecosystems (GDEs) that do not meet the legal definition of wetlands are important for sustaining regional biodiversity, livestock grazing, and outdoor recreation in the Intermountain West. Such GDEs in Owens Valley, California, are also used to produce 11,225 hectare meters (91,000 acre-feet) of water annually from about 100 water wells. We used 21 years of Landsat data and 18 years of field monitoring data to analyze responses of 2 adjacent-meadow GDEs to different groundwater management practices. The northern meadow, which was subject to continuous water table drawdown below the rooting zone of phreatophytic grasses, experienced decline in total live cover from 42.7% to 30.2%, decline in grass cover from 27.5% to 14.1%, transition from grass to shrub dominance, and change from groundwater dependence to precipitation dependence. These responses had been predicted by managers in 1976. The southern meadow, which was managed with cycles of water table drawdown and recovery, experienced neither cover decline nor dominance-type conversion and remained groundwater dependent. Variation in depth-to-water table (DTW) explained 83% of the pooled variance in total live cover in both meadows. Results showed that nonwetland, nonriparian GDEs are vulnerable to water table decline, as are wetland and riparian GDEs. Managing groundwater extraction through imposing one- to several-year cycles of water table drawdown and recovery may avoid further cover decline and type conversion in GDEs already affected by groundwater withdrawals.

© 2012
Daniel Pritchett and Sara J. Manning "Response of an Intermountain Groundwater-Dependent Ecosystem to Water Table Drawdown," Western North American Naturalist 72(1), 48-59, (1 April 2012).
Received: 24 February 2011; Accepted: 11 October 2011; Published: 1 April 2012

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