Geochemical analysis of calcium carbonate cementation and its role in reducing loss rates along Snake Creek, southern Snake Valley, White Pine County, Nevada.

摘要

Geochemical analysis of Snake Creek was initiated as a result of the Southern Nevada Water Authority's request for the export of water from rural Nevada basins. The creek is important because of ecologically sensitive springs and caves along the creek, and flow in the creek is used by the Nevada Department of Wildlife (NDOW) for a fish rearing station. The hydraulic connection between Snake Valley and the southern Snake Range is provided by two main aquifers, a basin-fill aquifer underlain by a regionally extensive carbonate aquifer. A previous study by Elliott et al. (2006) indicated that Snake Creek is connected to the carbonate aquifer within and adjacent to Great Basin National Park and might be adversely affected by groundwater pumping.;Downstream of the fish rearing station, flow in the creek shows little loss, even though heads decrease with depth beneath the streambed and gradients are more than 0.6 m/m. Water chemistry and geochemical modeling was used to determine if calcite precipitates may have clogged the streambed along the creek. Inverse modeling and isotopic analysis also were used to determine if groundwater in limestone at a USGS well next to Snake Creek is geochemically connected to groundwater in Quaternary and Tertiary basin-fill deposits at the NDOW fish rearing station well.;Modeling results indicate that calcite precipitation along the streambed is likely, and is primarily caused by the mixing of Spring Creek Spring and Snake Creek at a confluence downstream of the fish rearing station, as well as evaporation and CO2 off-gassing. Inverse modeling shows that water in the USGS well is geochemically connected to the underlying limestone and less than 10 percent can be from shallow groundwater in the basin-fill deposits represented by water in the NDOW well. These results suggest that groundwater discharging from limestone into streams in the mountains of eastern Nevada, where outcrop of limestone is prevalent, could result in the clogging of streambeds from calcite precipitates and a reduction in loss rates farther out on the alluvial fans.