Aridland spring response to mesoscale precipitation: Implications for groundwater-dependent ecosystem sustainability

Aridland springs maintain groundwater-dependent habitats for aquatic and terrestrial species. San Solomon Spring (Texas, USA) is part of a regional karst spring complex in the Chihuahuan Desert that supports several species of federal and state conservation interest. However, drought, climatic variability, and groundwater abstraction threaten discharge and water quality. In the surrounding Delaware Basin, expansion in unconventional oil and gas development using hydraulic fracturing may increase demands on aquifers that also provide flows to the springs. A critical knowledge gap limiting habitat conservation and sustainable groundwater abstraction is that the flow system is not well understood. While the source of most spring discharge is from a Pleistocene-recharged regional flow system, evidence suggests that a modern local flow component provides fresh water influx. However, the exact sources, mechanisms, and timing of localized recharge are unknown. To address these questions, this study combined long-term in-situ spring water quality monitoring (specific conductance, turbidity, and temperature) data with weather station-corrected 4 km gridded precipitation data to quantify the lag response at San Solomon Springs to mesoscale storm events and to delineate potential local recharge zones. Between April 2011 and March 2012, 26 event-flow responses were documented, with an average lag of 43 days between storm event and spring response. Response time varied depending on storm magnitude, spatial extent, and antecedent soil moisture conditions. Cross-correlation analysis of spatially distributed precipitation indicated zones of potential local recharge in the mountain block/mountain front zones and alluvial channels issuing from the Davis Mountains. Some local flow paths appear to cross known watershed boundaries, suggesting that groundwater abstraction in sensitive capture zones should be managed carefully to maintain spring flows and conserve habitats.