Geochemistry and Origins of Thermal Springs Waters of the Olympic Peninsula and Cascade Range, Washington

The state of Washington contains 98 low temperature (surface temperatures between ~ 20 - 50 oC) geothermal springs, which are powered by the convective circulation of groundwater that is heated by the natural heat of the Earth. These systems operate in a cycle that begins when precipitation percolates downward into the subsurface and comes in contact with a heat source. Subsequently the heated water returns to the surface, in most cases, having interacted chemically with rocks in the reservoir and/or along its ascent path. Surveys done by the USGS between the 1970s – early 1990s show there is significant chemical variation amongst these thermal springs. The objective of this research is to investigate the origins of this chemical diversity. Using water chemistry and isotopic data, the study has been able to suggest the following: Estimated subsurface water temperatures are indicative of low-temperature geothermal systems The dominant component of spring waters is meteoric in origin The springs are most likely representative of outflow-type structures Geothermal systems in Cascade Arc are volcanically hosted while systems in the Olympic Peninsula are presumed to be fault-controlled convective cell

Natural trace element salinization of the Jemez River, New Mexico by geothermal springs and major tributaries

The Jemez River (JR), a tributary of the Rio Grande, is in north-central New Mexico within the Jemez Mountains, which houses the active, high-temperature (≤ 300 oC), liquid-dominated Valles Caldera geothermal system (VC). This work focuses on the northern portion of the JR, spanning a reach from the East Fork JR to the town of San Ysidro. Previous decadal work during low-flow or baseflow conditions (~10-20 cfs) has identified and characterized significant major-solute contributions from two outflow expressions of the VC, Soda Dam Springs and Jemez Hot Springs, and two major tributaries, Rio San Antonio and Rio Guadalupe. There is generally a net ~500-ppm increase from below Soda Dam to the end of the study segment. The distribution of concentrations of twenty-four trace metals from recent Fall 2017 sampling are defined by range from \u27ultra-trace\u27 levels (0.1-1 ppb) to measurements as much as 1 ppm. A set of elements (e.g., As, Li, Rb, Ba, Ti) follows the same downstream behavior of major ions, which is characterized by an increase in concentrations at each inflow and the observed greatest contribution (as much as an order of magnitude) is at Soda Dam. Another group (e.g., U, Al, Fe, Mn, Se) shows complex downstream patterns, which may be a result of non-conservative processes, such as precipitation/dissolution, sorption, and complexation. We attempt to resolve these potential in-stream processes with high-resolution (regular 1-km spacing with interspersed 50-m intervals around sites with complete chemistry) spatial surveys of temperature, dissolved oxygen, pH, oxidation-reduction potential, and turbidity

Natural Salinization of the Jemez River, New Mexico: An Insight From Trace Element Geochemistry

The Jemez River, a tributary of the Rio Grande in north-central New Mexico, receives thermal water input from the geofluids of the Valles Caldera, an active, high-temperature, liquid-dominated geothermal system. We focus on a ∼50-km portion of the northern Jemez River. This research extends previous decadal work (Crossey et al., in prep., 2013) on major chemistry in the river by characterizing the response of 16 trace elements to geochemical contributions from geothermal waters (McCauley, Spence, Soda Dam, and Jemez Springs springs and San Ysidro mineral waters), an area with copious hydrothermal degassing (Hummingbird), and two major tributaries (Rio San Antonio and Rio Guadalupe) during a low-flow event (∼425 L/s). The greatest known loading (as much as 101 concentration increase) of trace elements to the Jemez River is from Soda Dam ([TDS] = 4700 ppm). Seventy-five percent of analyzed trace elements are coupled with major ions and resemble mostly conservative downstream behavior. Correspondent to their inherently low ionic potential, the alkali (Li, Rb, Cs) and alkali earth (Sr, Ba) metals remain abundantly dissolved. The relative non-reactivity of some transition metals (Fe, Ni, Co, U, V, Cu, Pb), which are sensitive to redox changes and susceptible to sorption, is facilitated by transport as complexed species (predominantly as Fe(OH)30, HCoO2-, UO2(OH)20, VO3OH-2, CuCO30, PbCO30). There is no common sink for the latter 25% (As, Al, Mo, Mn), as each is potentially scavenged at different sections of the river by different processes, like oxidation-enhanced adsorption and co-precipitation. The inflowing H2S and CO2 gases at Hummingbird impart unique physiochemical conditions that allow some solutes to become non-conservatively solubilized (Cu, Pb, Al) and removed (U, Mo)

Subsurface weathering signatures in stream chemistry during an intense storm

International audienceLong-term relationships between stream chemistry and discharge are regulated by watershed subsurface structure and biogeochemical functioning. The extent to which these mechanisms are expressed and may be explored in the geochemical response of streams during storm events remains an open question. Here, we monitor an intense storm as it infiltrated an upland hillslope draining into a small steep canyon stream that is typified by chemostatic concentration-discharge relationships in rock-derived solutes. Our approach couples a high-frequency record of stable lithium isotope ratios (δ7Li) in the stream with novel sampling of rock moisture within the hillslope. At peak discharge, lithium-sodium ratios (Li/Na) increased from 0.58 μM/mM to 0.82 μM/mM and δ7Li decreased from + 28.9 ± 0.1‰ to + 26.4 ± 0.4‰ in the stream. Hillslope hydrologic monitoring reveals that the rainwater infiltrated the subsurface, yet attenuated breakthrough of the heavily depleted δD signal of this storm (as low as -86‰) only reached the upper 3-4 meters of the vadose zone. These δD data show that the storm water mixed with previously stored rock moisture and displaced stored fluid to deeper depths, causing an observable rise in the water table. Groundwater 87Sr/86Sr and δ7Li demonstrate consistency in the fluid-rock interactions that occur below the water table prior to and during the storm. In total, these observations indicate that the transfer of fluid and generation of solutes through the interior of the hillslope produce the variability of Li/Na and δ7Li within the stream during the storm, and support application of a previously established 1-D reactive transport model framework developed for the evolution of lithium within the hillslope to this extreme hydrologic event. Based on the model, both Li/Na and δ7Li versus discharge relationships reflect an overall shorter transit time of fluid through the interior of the hillslope. These model results are consistent with our hydrologic observations and indicate that Li from further upslope (where the vadose zone becomes thicker) contributes to stream solute chemistry at the height of the storm. We conclude that in this system, stream lithium isotope signatures record the routing of water and generation of solutes within the hillslope even during intense storm events