Groundwater Reliance
Last updated 12/2/2024 at 8:02am
Borrego Springs, November 19, 2024 – In a breakthrough study led by UC Irvine researchers, new findings have confirmed that mesquite trees near the Borrego Sink rely o groundwater to survive. This revelation confirms the presence of a groundwater-dependent ecosystems (GDE) in the Borrego Springs Groundwater Subbasin, challenging prior assumptions contained in Borrego’s current Groundwater Management Plan (GMP).
The study, funded by the Proposition 68 Sustainable Groundwater Management Grant Program, provides crucial data for sustainable management of the Borrego Springs Subbasin. GDEs, ecological systems reliant on groundwater, are officially recognized as beneficial users under California’s Sustainable Groundwater Management Act (SGMA).
Key Findings
Researchers used stable isotope analysis to determine the water sources used by mesquite trees. By examining oxygen isotopes in plant tissue, soil, and well water, they found that groundwater accounts for 55–83% of the water in mesquite tissues near Borrego Sink. The percentages varied slightly across sites and seasons, with groundwater reliance increasing during dry spells, but the data confirms that the mesquite bosque (the 1800-acre assemblage of mesquite trees around the Borrego Sink) depend upon access to groundwater for their survival. “This is the most direct evidence yet of groundwater use by mesquite in the region. This is the smoking gun.” said lead researcher Travis Huxman, Chair of the Department of Ecology and Evolutionary Biology at UC Irvine.
In addition, water potential measurements revealed that mesquite trees near Borrego Sink experienced similar water availability as those at the reference site near Clark Dry Lake, an undisputed GDE where there is no doubt about groundwater accessibility. This finding underscores the reliance on groundwater of mesquite around the Borrego Sink, especially during periods of limited rainfall.
The study also documented the ecological richness of these mesquite habitats. Surveys documented 195 native plant species near Borrego Sink, including 17 threatened, endangered, or rare species. The habitat also supports over 45 animal species, five of which are considered species of special concern.
Technology in Action
To enhance monitoring, the team deployed state-of-the-art evapotranspiration sensors at key sites in the mesquite bosque. These instruments provide real-time data on water movement through the ecosystem, offering insights into mesquite groundwater use during droughts. Remote sensing techniques, including satellite imagery, were also used to map vegetation health and detect groundwater reliance during extended dry periods.
Implications for Sustainability
The study’s findings have significant implications for groundwater management in Borrego Springs. Historically, Borrego’s Groundwater Management Plan dismissed the existence of GDEs in the basin, citing insufficient evidence. This new data calls for a reassessment of water allocations to ensure the long-term survival of these now confirmed GDE’s. Mesquite bosques play a vital role in desert ecosystems, providing habitat for numerous species and stabilizing soil. Groundwater depletion threatens not only these trees but also the biodiversity they support. “These findings underscore the urgency of sustainable water management,” Huxman noted. “We now have the tools and evidence to protect these critical ecosystems.”
Looking Ahead
The research team plans to release a comprehensive final report in March 2025. In the meantime, they continue refining remote sensing methods and analyzing additional data to better understand the dynamics of groundwater use of the GDE around the Borrego Sink. Local stakeholders, including the Borrego Springs Watermaster and environmental conservation groups, are expected to use these findings to guide policy. As California grapples with the challenges of groundwater sustainability, this study serves as a reminder of the delicate balance between water use and ecosystem health. The mesquites of Borrego Sink stand as a testament to the resilience of nature – and the pressing need for informed stewardship.
For more information on the study and ongoing updates, visit the Steele/Burnand Anza-Borrego Desert Research Center website.
