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Assessing Near Surface Hydrologic Processes and Plant Response over a 1600 m Mountain Valley Gradient in the Great Basin, NV, USA
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This study investigated near surface hydrologic processes and plant response over a 1600 m mountain-valley gradient located in the Great Basin of North America (Nevada, U.S.A.) as part of a long-term climate assessment study. The goal was to assess shifts in precipitation, soil water status and associated drainage with elevation and how this influenced evapotranspiration and plant cover/health estimated by a satellite-derived Normalized Difference Vegetation Index (NDVI), all to better understand how water is partitioned in a mountain valley system. Data were acquired during a three-year period from meteorological stations located in five plant communities ranging in elevation from 1756 m (salt desert shrubland zone) to 3355 m (subalpine zone). The analysis also included groundwater depths measured at the Salt Desert Shrub West site, mine water flow near the Pinyon-JuniperWest site and drainage estimates using drainage flux meters at the four higher elevation sites. Annual precipitation increased with elevation in a linear fashion (R-2 = 0.93, p < 0.001) with an average increase of 2.9 cm for every 100 m in elevation. Reference evapotranspiration (ETref) declined in a highly linear fashion with elevation (R-2 = 0.95, p < 0.001) with an average 4.0 cm decline for every 100 m rise in elevation. Drainage occurred only at the Montane West and Subalpine West sites and not at the lower elevations. No drainage occurred after Julian day 160. Growing degree days were found to be negatively associated with the time of peak drainage (R-2 = 0.97, p < 0.001), the date drainage first occurred (R-2 = 0.90, p < 0.001), drainage duration (R-2 = 0.79, p < 0.001) and total drainage volume (R-2 = 0.59, p < 0.001). It was estimated that 27% of precipitation at the Montane West site (years 1, 2 and 3) and 66 % at the Subalpine West site (40% without year 1) contributed to drainage at the local site level, indicating possible strong recharge contribution from the higher elevation plant communities. Percent vegetation cover and ETref accounted for 94% of the variation in NDVI and 90% of the variation in ET totals when data from all sites were combined. Such data will be extremely valuable to collect and compare over time to assess shifts associated with potential climate warming and/or basin water diversion.