Stable Isotope Hydrometeorology of a Semi-Arid Catchment

Stable isotopes of hydrogen and oxygen, the two elements that make up water molecules, tell us where water comes from and how water moves through the subsurface. Stable isotopes are effective tools for studying the water cycle in catchments such as Dry Creek Experimental Watershed (DCEW), located just north of Boise, Idaho. DCEW consists of complex terrain and is dominated by seasonal snowpack. Precipitation and stream water samples were collected at multiple sites and multiple elevations in DCEW, and these samples were analyzed using a Los Gatos Research Liquid Water Isotope Analyzer. Further statistical analysis was completed on the data to determine any trends. Additionally, we analyzed the stable isotope compositions of hydrogen and oxygen of snowpack samples at multiple depths to further understand the complexity of snowmelt contributions to the watershed. Snow plays an important role in catchments such as DCEW because it does not enter the water cycle of the catchment until melt occurs. Each snow event has its own unique isotopic composition, and processes such as ablation, vapor diffusion, storage time sublimation, and melting as temperatures warm affect these compositions. Our results suggest that due to the orographic effect and fractionation of isotopes, the higher elevation precipitation is depleted isotopically with respect to deuterium and oxygen-18; however, this is not always the case, and possible reasons require further discussion