Stable isotope composition of waters in southeastern California: 2. Groundwaters and their relation to modern precipitation

Abstract

We compare isotopic data on modern groundwater recharge, estimated from a 7‐year collection of precipitation samples, with the isotopic compositions of 82 samples from wells and perennial springs collected in southeastern California. Over half the samples represent recharge that is considerably more depleted in deuterium (δD) than the lightest (winter) precipitation δD values now precipitating in nearby areas. Wells in the vicinity of irrigation canals fed from the Colorado River contain water whose δD resembles that of the irrigation canals, and wells adjacent to the Mojave River are recharged by Mojave River water. The remainder of the samples from the 17 hydrologic units discussed in this paper include one or more whose δD values are depleted in deuterium by at least 10‰ compared to recharge estimated from modern winter precipitation. A plot of δ18O versus δD for 56 wells and 22 springs shows substantial scatter (R2=0.66) and defines a slope of 4.9, which is lower than the slope of the Meteoric Water Line. This slope and the scatter of the data suggest these diverse waters were evaporated to different degrees before recharge, and they may also have exchanged oxygen with solid mineral phases. We interpret the fact that many groundwaters in this region have lower δD values than modem precipitation to indicate that recharge of many of the groundwater basins occurred during an earlier period, probably the late Pleistocene, when winters were colder, evaporation rates were lower, and precipitation was quantitatively greater and isotopically lighter.

Synoptic and mesoscale controls on the isotopic composition of precipitation in the western United States

“…A persistently shallow slope or individual data that fall well below the mean LMWL represent potentially problematic samples (Clark and Fritz 1997). The LMWL at each of the sites is comparable to that of previous studies from the western US (Benson and Klieforth 1989;Friedman et al 2002;Ingraham and Taylor 1991;Smith et al 1992) and the slopes are not statistically different between the Sequoia (SEKI), Pinnacles (Pinn) and Joshua Tree (JT) sites. Although we cannot entirely rule out bias associated with evaporation from the precipitation collector at these sites, we infer based on the consistency between the LMWL calculated for these samples and that reported from previous studies that the influence is likely minimal and therefore did not significantly influence the integrity of samples from the SEKI, PINN or JT sites.…”

Physical and Temporal Isolation of Mountain Headwater Streams in the Western Mojave Desert, Southern California1

“…Although the quantity of water from these sources is small, it is locally important. Similar processes have resulted in isotopically heavy ground water in the eastern part of the study area near San Gorgonio Pass (Figure 10), and along the western edge of Antelope Valley (not shown in Figure 1) where the altitudes of the San Gabriel Mountains are lower (Smith et al ., 1992).…”

Interbasin flow revisited: The contribution of local recharge to high-discharge springs, Death Valley, CA

“…The apparent 14 C ages of Furnace Creek waters (Table 2) suggest there is a significant component of late-Pleistocene water, at which time an episode of the recharge of valley-fill aquifers has been documented in the Death Valley region (Quade et al, 1998;Smith et al, 1992). Under a local recharge scenario, water discharging at Furnace Creek has been in storage in near-surface fractured bedrock, the damage zones of the Furnace Creek and Greenwater fault zones, and especially the semi-consolidated materials of the Furnace Creek and Funeral Formations for a considerable period of time.…”