Assessing Near Surface Hydrologic Processes and Plant Response over a 1600 m Mountain Valley Gradient in the Great Basin, NV, U.S.A.

Abstract

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-Juniper West 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 (ET ref) 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 ET ref 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.

Differing Fine-Scale Responses of Vegetation and Bare Soil to Moisture Variation in a Pinyon-Juniper Woodland Underlie Landscape-Scale Responses Observed from Remote Sensing

“…Forest canopies are dynamic living surfaces. Spectral reflectance of such surfaces have been shown to detect the ebb and flow of plant available water and associated vegetation responses, reflecting an ecological response to environmental variation (Pettorelli et al, 2005;Devitt et al, 2018) In addition, spectral reflectance can detect spring green up and leaf development and senescence associated with deciduous species (Kaye & Wagner, 2014;Park et al, 2015;Xu et al, 2019). Climate change has the potential to significantly alter these oscillations occurring at the plant and stand level, especially in the American southwest where growth and productivity of plants is strongly coupled to water availability (Bunting et al, 2017).…”

“…An important aspect of understanding landscape and regional responses of semiarid ecosystems to precipitation and soil moisture variation is determining the ecosystem components that shape spatial signals obtained from satellite remote sensing. Pinyon-juniper ecosystems may be an ideal ecosystem type for doing this in Nevada because water use of these plant communities has been documented to be intricately coupled to precipitation, which at some sites has led to a zero recharge component in the water balance (Devitt et al, 2018).…”

Effects of groundwater fluctuations on the distribution and population structure of two cyprinid fishes in a desert spring complex

“…A pattern of annual fluctuations in shallow GWLs in response to seasonal cycles in evapotranspiration has been observed elsewhere in Snake Valley, as well as other regions of the Great Basin (Welch et al 2007;Gardner and Heilweil 2014;Hurlow and Kirby 2014). Recent trends toward increasing temperatures and decreased snowpack in the Great Basin and other regions of western North America have the potential to reduce shallow GWLs and spring discharge rates by increasing evapotranspiration and reducing runoff and groundwater recharge (Weissinger et al 2016;Udall and Overpeck 2017;Devitt et al 2018). The influence of increased evapotranspiration at the Leland Harris Spring Complex due to warmer temperatures is likely to be minimal during winter, when water loss caused by evapotranspiration is negligible, but would be expected to accelerate the contraction of ponds during late spring and summer and could potentially impact core spring habitats as well.…”

Seasonal Analysis of the 2011–2017 North American Monsoon near its Northwest Boundary

“…This is supposed to happen even in areas, such as ours, where cool-season precipitation may be equal, or even less, than warm-season precipitation. It should be noted that our study site is the only location within the northwest NAM region where in situ data can be used to test the distinction in sources of groundwater recharge that has been derived from isotopic studies (see also [62]).…”