New Mexico Geological Society Annual Spring Meeting — Abstracts

The Saguache Creek watershed located in the northern San Luis Valley has been selected for an intensive hydrological study including research into the chemical evolution of spring water. The watershed has an abundant distribution of springs with respect to elevation and these springs have been sampled for chemical analysis. Samples of snow and snowmelt runoff have also been collected and analyzed. All samples were analyzed for sodium, potassium, magnesium, calcium, chloride, fluoride, nitrate, phosphate, sulfate, silica, temperature, pH, and conductivity. Preliminary data revealed encouraging trends in the chemical compositions of spring water from high to low elevations. Snowmelt runoff showed minimal increases in cation concentrations as compared with the cation concentrations of the snow samples. However, there were more pronounced increases in the anion concentrations of snowmelt runoff, especially with respect to potassium, magnesium, and calcium. Many of these constituents show linear increases in concentration with decreasing elevation (i.e. small concentrations in the high elevation springs trending toward higher concentrations in low elevation springs). It also appears that snowmelt runoff rapidly acquires a silica concentration which is nearly 25 percent of the silica concentration observed in spring waters. The snowmelt runoff was observed as overland flow and the rapid acquisition of silica appears to occur within a few minutes of contact with the soil. Electrical conductivity and temperature both increase linearly with decreasing elevation. These trends are encouraging; yet, further research is needed to gain an understanding on the origin of the chemical compositions observed in these springs. Thus, NETPATH, a model used to calculate net geochemical reactions along a flow path, was used to predict the amount of reacted minerals needed along a flow path to acquire the observed chemical composition. NETPATH requires that the user provide chemical constraints and mineral phases based on the geology of the study area through which the geochemical reactions are modeled. This poster will present the findings determined by NETPATH on the origin of the chemical composition of springs in the Saguache Creek watershed of Saguache, Colorado.