Determining the importance of seasonality on groundwater recharge and streamflow in the Sangre de Cristo Mountains using stable isotopes
— D. G. Tolley, M. D. Frisbee, and A. R. Campbell

In western states like New Mexico, where nearly all surface-water is derived from mountainous watersheds, it is becoming increasingly important to determine the sources that contribute to surface-water and provide recharge to groundwater, both spatially and temporally. The stable isotopes ¹⁸O and ²H were used to determine the influence of seasonal inputs of precipitation on groundwater recharge and streamflow in the Rio Hondo watershed, which is believed to be broadly representative of the Sangre de Cristo Mountains for similar climatic and orographic conditions. Precipitation collected during the winter and spring months showed δ¹⁸O ranged from about -19 to -12‰, while summer and monsoon precipitation ranged from about -8 to -5‰. Surface-water, spring-water, and groundwater samples collected on a monthly to sub-monthly basis had mean δ¹⁸O values of -14.3 ±0.7‰ (n=115), -13.9 ±1.2‰ (n=54), and -14.1 ±0.9‰ (n=56), respectively, which all fall within the winter and spring precipitation range. Using a simple two-component mixing model to determine the fractions of seasonal precipitation in samples, winter and spring precipitation account for about 68–88% of groundwater recharge and streamflow in the Rio Hondo while it only makes up about 45–55% of total annual precipitation. Therefore, reduction in the amount and duration of snowpack predicted by climate change will result in a disproportionate reduction of groundwater recharge and ultimately streamflow in the Rio Hondo watershed, and by extension similar watersheds in the Sangre de Cristo Mountains.