Using Distributed Temperature Sensing (DTS) as a Means to Understand Evaporative and Transpirative Processes in Shallow Groundwater Basins.

Evapotranspiration (ET) is important to both the surface energy balance and hydrologic cycle, particularly in arid and semi-arid regions where ET can dominate the loss of water from ground surface. Closer inspection and better understanding of these processes are crucial for closing the water budget. Of practical importance for understanding ET processes is the direct connection to groundwater resources, mainly through recharge. Decreasing groundwater levels within a shallow groundwater basin from either overpumping and/or climate change could decouple the connection between phreatophytes and groundwater, and change water distribution between the phreatic and vadose zones. Correlating soil moisture, water potential, and thermal gradients to the ET rates could provide critical understanding when assessing the movement of mass and energy through the vadose zone. To further our understanding of these gradients and its relation to changes in ET rates, distributed temperature sensing (DTS) was used to measure temperature along a vertical gradient by wrapping fiber optic (FO) cable around a PVC pipe providing temperature changes caused by near-surface water gain or loss and changes in groundwater level. Soil moisture and water potential were measured using TDR and HDU sensors, respectively. The nested measurement technologies, coupled with FO DTS, were used in Spring and Snake Valleys, NV, where the water table is known to be shallow and available for phreatophytic shrubs. This presentation provides preliminary data analysis of the DTS wrapped pipe and the comparison of the different technologies in shallow groundwater basins.