TRACE ELEMENT SALINIZATION OF THE JEMEZ RIVER, NEW MEXICO: GEOTHERMAL SPRING AND MAJOR TRIBUTARY INPUTS

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). We focus on the northern portion of the JR, spanning a segment 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. Generally, there is a net ~500 ppm increase from above the thermal springs to the end of the study reach.

Concentrations of twenty-four trace metals from recent Fall 2017 sampling are detected through inductively coupled plasma mass spectrometry. The range of relative abundance is defined by ‘ultra-trace’ levels (0.1-1 ppb) and measurements as much as 1 ppm. A group of elements (e.g., As, Li, Rb, Ba, Ti) follows the same downstream behavior of major ions, wherein there is an increase in concentrations at each inflow and the greatest contribution (as much as 10¹) is observed at Soda Dam. Another set (e.g., U, Al, Fe, Mn, Se) shows complex downstream patterns, which may be a result of non-conservative processes, such as sorption, precipitation/dissolution, and complexation. Some metals (e.g. Pb, Cd, Be, Tl) appear below detection. To better understand local in-stream geochemistry and potential secondary reactions, spatial profiles of pH, dissolved oxygen, temperature, oxidation-reduction potential, and turbidity are sampled with regular 1-km spacing and finer (50-m) resolution along sites with complete aqueous chemistry. We present initial processing and correlation with more discretely spaced water sampling of these surveys.