Surface Temperatures, Groundwater Recharge Temperatures, and Noble Gases: An Investigation in the Wasatch Mountains, Utah

To understand better the systematics of noble gases in tracing groundwater recharge, we monitored dissolved noble gases in surface water and groundwater as well as temperature of the air, ground, and surface water in a high alpine basin in the Wasatch Mountains of Utah. Temperature probes were installed in local recharge and discharge areas to continuously monitor ground temperatures at 5 depths down to 1 m. Water temperatures are continuously being monitored in a small stream and a shallow well (depth ~1.5 m) located in the discharge area. Air temperatures are recorded at a meteorological station located within the basin. Noble gas and tritium samples were collected approximately every other week from February 2007 to present from both the stream and the well. Preliminary noble gas results show that groundwater recharge temperatures for samples taken from the well warmed by as much as 1.5 °C over a one month period from February to March, indicating that noble gases dissolved in groundwater exhibit temporal effects. When snow cover is present, ground and surface water temperatures are not influenced by fluctuations in air temperature. While ground temperatures at the recharge site did not record the spring snow melt event as expected, ground temperatures at the discharge site cooled by ~1 °C throughout the month of May, indicating possible movement of snow melt through the shallow aquifer. Following the snow melt event, ground and surface water temperatures mimicked the same warming and cooling trends found in the air temperatures, but were on average 5 °C to 10°C cooler than the air. We anticipate that continuous monitoring of temperatures and noble gases will offer insight into the dynamic interplay between air/soil temperatures, movement of water through the vadose zone, and recharge events in high alpine environments.