HYDROCHEMISTRY OF AN ALPINE KARST SYSTEM, NORTHERN NEW MEXICO: LAS HUERTAS

Persistent drought conditions, increased water use, and anthropogenic modifications of water resources have made wetlands in the southwest vulnerable to a changing climate. Spring-fed waterbodies in mountain recharge zones, such as Las Huertas in the Sandia Mountains, New Mexico, rely on snowmelt and monsoonal input for recharge and often have intermittent groundwater inputs along flow paths. Las Huertas provides water for the surrounding community and is the primary water source for acequias and irrigation for Placitas, New Mexico. Regional climate change models predict decreased snowpack therefore increased observation of wetlands, such as Las Huertas, is a management priority for Cibola National Forest. The Las Huertas watershed is ideal for this study as spring emergence is at a high elevation in an arid land region, with CO2-rich springs actively precipitating travertine in some reaches but not others, which may be indicative of variable fluid inputs and geochemistry along the flow path. Presently, connections between surface water and groundwater and the karst aquifer (Madera Limestone) are poorly understood. Methods include major ion chemistry analysis and stable isotope analysis. Geochemical mixing models are used to identify end members and quantitatively determine the relative contributions of annual recharge and older groundwaters.

Stable isotope data indicate that both winter and summer monsoonal precipitation are contributing to the recharge of the regional aquifer feeding these springs. Field observations suggest that travertine precipitation is more active in the upper reaches of the watershed which may be indicative of equilibration of the stream with lower atmospheric CO2. Spring waters are dominantly classified as calcium bicarbonate, with some Na-Cl.

Although salinities vary from less than 200 ppm to over 1000 ppm, individual springs show limited interannual/seasonal variation. Las Huertas and Capulin Springs, headwater springs at high elevation, show some of the highest salinities. This study will fill critical gaps in understanding the flow contributions to Las Huertas Creek, one of few perennial streams in the Sandia Mountains. Our work will help identify flow contributions to the water source, with implications for its resilience for anticipated changes from climate change.