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)