<p> Altered waters impacted by serpentinization of Coast Range Ophiolite (CRO) ultramafic units have been reacting with trapped Cretaceous seawaters, meteoric waters, and other surface derived waters since tectonic emplacement of this ophiolite. In 2011, groundwater monitoring wells of various depths were established near Lower Lake, CA, USA in the McLaughlin Natural Reserve, administered by the University of California-Davis, in order to understand ongoing low temperature alterations and biogeochemical interactions taking place. Wells were installed at two sites in the Reserve. There are three Quarry Valley area wells (QV1-1 [23m depth], QV1-2 [14.9m], QV1-3 [34.6m]) and five Core Shed area wells (CSW1-1 [19.5m], CSW1-2 [19.2m], CSW1-3 [23.2m], CSW1-4 [8.8m], CSW1-5 [27.4m]). Water samples were collected from all installed wells, as well as from an older well drilled near the historic core shed (Old Core Shed Well, or OCSW [82m]), and an upper (TC1) and lower (TC2) site sampling a nearby groundwater-fed alkaline seep, at Temptation Creek. Key environmental parameters (temperature, pH, conductivity, oxidation-reduction potential, and dissolved oxygen) were collected in the field using YSI-556 multiprobe meter, and total concentrations for major cations (Ca⁺², Na⁺, Mg⁺², K⁺) were analyzed using Thermo Scientific iCAP 7400 Inductively Coupled Plasma-Atomic Emission Spectrometry, and anions (F^&ndash;, Cl^&ndash;, SO₄^&ndash;2, NO₃^&ndash;) on Dionex Modular DX 500 Ion Chromatography. </p><p> Principal component analysis was conducted to determine key factors and processes controlling water chemistries at CRO. Geochemist&rsquo;s Workbench software was used to model the low temperature alteration of a serpentinization-influenced model water volume passing through serpentinite over a period of 100 million years. Modeling provided insight into the changing pH, Eh, evolving water chemistries, stepwise mineral assemblages, appearance of marker minerals at geochemical transitions in the system, and supported evidence of pervasive impacts of low temperature, oxidative weathering of serpentinites. This work supports the case of incremental dilution and transformation of a deeply sourced Ca²⁺-OH^&ndash; Type II water in this environment, and constrains reaction status of present day CRO waters and those of similar sites, in terms of the progress of serpentinite weathering reactions. Further, the study informs our understanding of serpentinization-related geological environments present on other celestial bodies (<i>e.g.</i>, Mars, Europa, Enceladus) in our Solar System and beyond.</p><p>

Hydrological and geochemical data was collected from a small area within the 7.32-km$\sp2$ Cadwell Creek drainage basin in west-central Massachusetts for a period of one year. The hydrologic monitoring network included a tipping-bucket rain gauge, soil-moisture and soil-temperature probes, and continuous water-level recorders to measure changing groundwater levels and stream stage. The geochemical sampling network consisted of precipitation and throughfall collectors, soil water collectors, shallow and deep groundwater monitoring wells, and stream sampling locations. Water samples were collected on a weekly or bi-weekly basis for the entire study period. Both the hydrologic and geochemical information collected during the study period indicated that the majority of water reaching the stream, both during periods of high water level and storm flow and during baseflow periods in the summer months, was derived primarily from the top meter or two of the shallow water-table aquifer. Deeper groundwater exhibited a substantially different chemistry from that in the top 1-2 meters of the aquifer. The geochemical evidence clearly indicated that deep groundwater never entered the stream, even during baseflow periods. Instead, the stream in the vicinity of the study site became dry in the summer. Comparison of groundwater and stream chemistry during periods of high water level clearly indicated that the water in the stream was derived almost solely from the shallow groundwater, with little or no contribution from more dilute precipitation and soil water. Silica concentration, as well as alkalinity and pH values, proved to be an important indicator of the origin of water entering the stream. Specific factors affecting the degree to which acidic precipitation is neutralized before entering surface water within this watershed are primarily hydrologic in nature. The amount of time that precipitation water is in contact with the geologic materials prior to entering the stream appears to determine the degree to which it is neutralized. In this case, the depth to the top of the water table is a controlling factor. Silicate weathering dominated cation exchange as a neutralization mechanism in this watershed, at least in the vicinity of the instrumented site.