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Paper No. 40-3
Presentation Time: 2:10 PM
ION CHROMATOGRAPHY ANALYSIS OF GROUNDWATERS FROM THE COAST RANGE OPHIOLITE MICROBIAL OBSERVATORY (CROMO) WATER MONITORING WELLS.
In California, USA, the Coast Range Ophiolite Microbial Observatory (CROMO) is a subsurface research laboratory where ultramafic rocks are reacting with through-going water in the subsurface. Here, the process of serpentinization produces highly reducing (strongly negative oxidation-reduction potential) and highly alkaline (pH up to 13) aqueous fluids with unusual and unique chemistry. In order to understand biogeochemical interactions in groundwaters from the CROMO site, eight groundwater monitoring wells were established in 2011 near Lower Lake, CA in the McLaughlin Natural Reserve, administered by the University of California-Davis. These wells were installed at two sites in the Reserve, the Quarry Valley site (Wells QV1_1, QV1_2, QV1_3) and the Core Shed Well site (Wells CSW1_1, CSW1_2, CSW1_3, CSW1_4, CSW1_5), and each well reaches a different depth in the shallow subsurface. For this study, we collected groundwaters and simultaneously recorded key environmental parameters (temperature, pH, conductivity, oxidation-reduction potential, and dissolved oxygen). Using ion chromotography (DIONEX ICS5000+ instrument at the University of Rhode Island, courtesy S. Pradhanang), aqueous ions were separated based upon their affinity with the ion exchange column, and concentrations were quantified. Patterns in major cation and anion data reflect changing Mg2+ and Ca2+ concentrations as signals of surface-derived and deeply-sourced groundwaters in this region, and highlight interactions between different subsurface groundwater flow regimes.