|
|||||
|
|
Geochemistry and Provenance of Springs in a Baja California Sur Mountain Catchment |
|
| Authors: | Jory C Lerback Brenda B Bowen C E Humphrey Diego P Fernandez Jeremiah A Bernau Shane J Macfarlan Eric Schniter J J Garcia |
| Institution: | 1. Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, Los Angeles, CA, 90095 USA;2. Global Change and Sustainability Center, University of Utah, Salt Lake City, UT, 84112 USA;3. Department of Geology and Geophysics, University of Utah, Salt Lake City, UT, 84112 USA;4. Department of Anthropology, University of Utah, UT, 84112 USA
Center for Latin American Studies, University of Utah, UT, 84112 USA;5. Division of Anthropology, California State University, Fullerton, CA, 92831 USA Economic Science Institute, Chapman University, CA, 92866 USA;6. Department of Education, Culture, and Society, University of Utah, Salt Lake City, UT, 84112 USA |
| Abstract: | Fractured rock aquifers cover much of Earth's surface and are important mountain sites for groundwater recharge but are poorly understood. To investigate groundwater systematics of a fractured-dominated aquifer in Baja California Sur, Mexico, we examined the spatial patterns of aquifer recharge and connectivity using the geochemistry of springs. We evaluate a range of geochemical data within the context of two endmember hypotheses describing spatial recharge patterns and fracture connectivity. Hypothesis 1 is that the aquifer system is segmented, and springs are fed by local recharge. Hypothesis 2 is that the aquifer system is well connected, with dominant recharge occurring in the higher elevations. The study site is a small <15 km2 catchment. Thirty-four distinct springs and two wells were identified in the study area, and 24 of these sites were sampled for geochemical analyses along an elevation gradient and canyon transect. These analyses included major ion composition, trace element and strontium isotopes, δ18O and δ2H isotopes, radiocarbon, and tritium. δ18O and δ2H isotopes suggest that the precipitation feeding the groundwater system has at least two distinct sources. Carbon isotopes showed a change along the canyon transect, suggesting that shorter flowpaths feed springs in the top of the transect, and longer flowpaths discharge near the bottom. Geochemical interpretations support a combination of the two proposed hypotheses. Understanding of the connectivity and provenance of these springs is significant as they are the primary source of water for the communities that inhabit this region and may be impacted by changes in recharge and use. |
| Keywords: | |