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Isolated Spring Wetlands in the Great Basin and Mojave Deserts,USA: Potential Response of Vegetation to Groundwater Withdrawal 总被引:3,自引:0,他引:3
Desert springs, often the sole sources of water for wildlife and cattle, support wetland and wetland/upland transition ecosystems
including rare and endemic species. In the basin and range province in Nevada, USA, springs in the Great Basin and Mojave
deserts are sustained by interconnected deep carbonate and shallow basin-fill aquifers which are threatened by proposed groundwater
withdrawal to sustain rapidly expanding urban areas, a common problem in arid regions worldwide. This paper draws on historic
groundwater data, groundwater modeling, and studies of environmental controls of spring ecosystems to speculate on the potential
effects of groundwater withdrawal and water table decline on spring-supported vegetation. The focus is on springs in the Great
Basin and Mojave deserts representative of those that may be affected by future, planned groundwater withdrawal. Groundwater
withdrawal is expected to reduce spring discharge directly through reduced flows from the shallow basin-fill aquifer or through
reduction of the hydraulic head of the deep carbonate aquifer. This flow reduction will truncate the outflow stream, reducing
the areal cover of wetland and wetland/upland transition vegetation. Lowering the local water table may also reduce the amount
of upland phreatophytic vegetation by causing water levels to drop below plant rooting depths. Percolation of salts to surface
soils may be reduced, eventually altering desert shrub cover from halophytes to nonhalophytes. The extent of these effects
will vary among springs, based on their distance from extraction sites and location relative to regional groundwater flow
paths. On-site monitoring of biotic variables (including cover of selected hygrophytes and phreatophytes) should be a necessary
complement to the planned monitoring of local hydrologic conditions. 相似文献