Isotope hydrology and sustainability of High Plains groundwater in northeastern New Mexico
1 online resource (117 pages) : PDF
University of North Carolina at Charlotte
Observable increases in depth to water in wells throughout the High Plains Aquifer have led to growing concerns regarding the sustainability of groundwater in the High Plains region. Previous studies have pointed to overuse and the presence of paleowaters as factors contributing to the rapid declines that have been recorded. Because the High Plains Aquifer is not present or is too thin to be a productive hydrostratigraphic unit in most of northeast New Mexico, little research has been conducted on the status of groundwater there. This study aimed to fill an existing knowledge gap by analyzing 85 groundwater samples from a four-county study area in northeast New Mexico. Samples were anlalyzed for δ18O, δD, DIC, δ13C-DIC, and major ion concentrations to evaluate geochemistry and the possibility that paleowaters are present. With the exception of one sample (M8), samples in this study did not exhibit characteristics of potential paleowaters. Therefore, a unique isotopic signature of paleowaters was not identified within the study area. Isotopic composition seems to be driven instead by the elevation effect, calculated to have a lapse rate of -0.31‰ per every 100m of elevation increase for all samples. Isotopic composition also appears to match seasonal patterns observed in nearby studies (winter-dominated recharge), but seasonal contributions could not be definitively determined by this study. Four main hydrostratigraphic units were identified throughout the study area, three of which exhibit typical groundwater evolution behavior. The shallower, younger, alluvial unit contains enriched, high salinity groundwater, indicating high rates of evaporation after precipitation, but prior to recharge. Major ion analysis yielded 42 samples of the Ca2+ Mg2+HCO3- type, making this the most common type in the study area, followed by the Na+ HCO3- type with 25 samples. Evidence of modern recharge was found by way of high nitrate concentrations in three locations in the western and southwestern portion of the study area. Three locations were selected for tritium analysis to test the hypothesis that recharge occurs along watercourses and focused points at the mountain front. This data was combined with previously unpublished data to expand the discussion of modern recharge in this region. Locations along watercourses were found to contain tritium, but locations along the mountain front were not. Ultimately, locations that do not have detectable amounts of tritium were deemed to be unsustainable and are representative of groundwater mining. The finding of this study that tritium is not present in mountain front waters, where recharge is expected to occur in this setting, highlights the need for further research investigating recharge processes in northeastern New Mexico.
Allan, CraigZeigler, Kate
Thesis (M.S.)--University of North Carolina at Charlotte, 2018.
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