NOT DEAD YET! Mesquite Bosques in Borrego Valley, Part 2
Last updated 12/21/2024 at 8:45am
Note: This article summarizes research done so far by researchers at UC Irvine, with Proposition 68 grant monies from the state Department of Water Resources. The project is called the “Groundwater Dependent Ecosystems (GDE) Identification, Assessment, and Monitoring Program.” It’s important to note that this research is ongoing and has not been reviewed by the Watermaster Board, which oversees the sustainable management of water in Borrego.
An earlier article explained what a GDE (groundwater dependent ecosystem) is, and named the mesquite bosque near the Borrego Sink as the primary example in our valley. This continuation describes in more detail the work done by UC Irvine researchers on GDEs that began in 2022 and is continuing still.
A March 2023 report by UCI provided several indications that GDEs are much more extensive here than had been suggested in the 2020 draft Groundwater Management Plan for Borrego (https://borregospringswatermaster.com/wp-content/uploads/2022/10/Exhibit-1_GMP.pdf, Appendix D4). It includes data showing deeper mesquite roots and shallower groundwater than cited in the GMP – both of which would enable more use of groundwater (vs. rain) by the plants. Analysis done by UCI also found that the map used in Appendix D4 mistakenly excludes much of the area in the Subbasin covered by the mesquite bosque, because it evaluated only ABDSP land, and large swaths of the bosque are located on parcels of private and other non-State Park land. And finally, the data used to analyze trends in the greenness of vegetation was averaged over a long period of time, and hence did not allow identifying dry periods when greenness could not be ascribed to rain – that is, when the mesquite were most likely using groundwater.
These indications of the presence of a significant GDE at the Sink led to performing further research under this grant: updated vegetation mapping, in depth field research, and expanded remote sensing analyses to better assess groundwater use in the mesquite bosque. Results of that work will be reported in the next article in this series.