Intrinsic Isotopic Tracers as Independent Evaluators for China Lake Basin, CA

Abstract

This study evaluates the usefulness of intrinsic isotopes for investigating the processes controlling the chemical evolution of groundwater in the China Lake Basin, CA. This was done broadly for the entire basin and more specifically along a flow path in the shallow aquifer of township 26S/40E. In addition to general mineralogy, radioactive and stable isotopes were determined for 24 samples (δD, δ18O, δ11 B, δ13C, 14C3H and 87Sr/86Sr); these data were evaluated along with a compilation of chemical and isotopic data from other studies. The data provide insight on a number of processes occurring in the basin. In the deep aquifer, radiocarbon, boron and strontium support the presence of Pleistocene groundwater. The strontium and boron isotopes further indicate that water in the shallow aquifer originates from the deep aquifer in the west, following a west-to-east transect. In the shallow aquifer the evolution of chemical data along a flow path suggest ion exchange, sulfate reduction, and ion concentration processes. There is evidence that density flow may play a significant role as a concentration mechanism. Also in this area, infiltration from local sewage ponds is observable in the trends of δD and δ18O. Finally, the radiocarbon and tritium data demonstrate that recharge to the shallow aquifer from precipitation occurs only at the playa.