DROUGHT SENSITIVE MONTANE SPRING RELIABILITY AND HYDROLOGIC CONTROLS IN MOJAVE NATIONAL PRESERVE, CA

A limited number of springs sourced from basin-scale aquifers provide perennial flow and habitat for wildlife in the Mojave Desert, however over a broad expanse of the region, more abundant small montane springs provide the only source of water. A comprehensive inventory in Mojave National Preserve and an annual survey by citizen scientists indicates that many such springs occur in canyons and ravines along the slopes of mountain ranges associated with small, locally recharged, perched aquifers. Over nine years of surveys, nearly all springs were observed dry due to drought conditions, but on variable temporal scales and drought severity. In this study we ask, what is the pattern of spring persistence and what are potential controls on spring reliability? Within the 643,112 ha study area 135 spring systems consisting of 238 distinct surface water expressions were monitored. Through the GeoCorp America program, GIS data were collected on all springs and field data were collected on 39 springs including: spring colluvial sediment area, hydraulic conductivity, and phreatophyte vegetation area. Stable oxygen isotope analysis was also conducted for 49 springs to assess recharge area. Statistical analysis with a generalized linear model showed watershed catchment area and spring brook length accounted for 28% of the variation in persistence. In the subsample of 39 visited springs, colluvial sediment area was correlated with spring persistence (P = 0.020), but phreatophyte vegetation area and hydraulic conductivity were not. Stable isotope results indicate the springs have a local source area with ratios similar to precipitation. These results support the conceptual model that many montane springs in the Mojave National Preserve occur in stream channels where bedrock and lateral channel constrictions force groundwater from local perched aquifer systems to the surface. The better understanding of montane springs and the statistical correlation of catchment area and stream brook length to spring reliability will assist resource managers with spring assessments elsewhere and with preparation for reduced water availability due to climate change.