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Ash Meadows, Nevada, USA is a site of major groundwater discharge (similar to 38,000 L/min) in the arid Mojave Desert, and hosts a number of endemic and threatened wetland species. In addition to these resources, Ash Meadows may also represent the future discharge location of radionuclide-laden waters from nuclear weapons testing at the Nevada Test Site. More importantly, however, Ash Meadows provides the opportunity to understand the controls on water transfer between basins through fractured bedrock.

4000+ solute analyses were assembled from the literature into a single database. The data were screened for spatial distribution, completeness, charge balance, and elevated temperatures (>= 20 degrees C and within regional flow systems), with 246 candidate up-gradient water remaining distributed among six potential source areas in addition to and Ash Meadows itself. These potential sources include both carbonate, volcanic and perhaps valley-fill aquifer systems. These waters were characterized by cluster analysis in order to sort similar waters in an objective fashion into potential flow paths and to establish representative endmember waters for inverse geochemical models and other modes of analysis.

Isotopic tracers, both conservative and those reflecting water-rock interaction, all suggest that waters at Ash Meadows are derived by southward flow from volcanic terranes, parallel to the preferred permeability structure induced by active regional east-west extension. Solute balances support this conclusion. However, this runs counter to the prevailing model that waters at Ash Meadows are derived from easterly and northeasterly flows from the Spring Mountains and Pahranagat Valley areas by interbasin flow through a continuous fractured carbonate aquifer. This work suggests that carbonate aquifer systems in extended terranes are more compartmentalized than previously appreciated and that anisotropy in fracture permeability is key to compartmentalization and the control of flow directions. (C) 2010 Elsevier B.V. All rights reserved.