Climate is complexly linked to the soil water budget in that it controls water and heat fluxes to the soil as well as influencing soil formation and soil properties. This project will use stable isotope geochemistry combined with climatic and soil physics monitoring to investigate how the soil water budget and styles of soil water movement vary across a climate gradient. Precipitation, snow melt and soil water will be monitored at three sites in central Washington State that have annual precipitation ranging from 136 cm to 23 cm, occurring mostly as snow in the winter months. The hypothesis underlying this research is that the style in which water percolates through the soil (e.g. piston flow vs. preferential flow), the rates of evaporation versus transpiration, and the timing of deep soil water/groundwater recharge varies predictably during different hydrologic seasons across this climate gradient. To test this hypothesis, soil water will be collected and analyzed by two methods: 1) direct equilibration of soil cores with CO2; 2) suction lysimeter. Stable isotope measurements will be combined with climatic measurements and soil physics monitoring to determine amounts and residence times of mobile versus stationary soil water and to quantify evaporation rates, transpiration rates, and downward percolation fluxes. These parameters will in turn be related to site characteristics such as precipitation, soil properties, and vegetation type/density. In addition, within-site variability in soil characteristics and soil water isotopes will be assessed. This research will explore how the soil water budget in a snowmelt-dominated system is influenced by climate and fill a gap in our understanding of the detailed dynamics of water movement in the critical upper soil region. The information gained will have significant broader implications in areas such as contaminant transport, biogeochemical cycling, agricultural and forestry practices, water management, etc. In addition, the project will involve an outreach program, in which precipitation collectors and weather stations are installed at local schools and incorporated into the K-12 curriculum. This outreach program will strengthen existing partnerships between scientists at Central Washington University (CWU) and science teachers at local schools. The research activities will contribute to an already active undergraduate research environment at CWU and will take advantage of recently built Geochemistry laboratories and associated instrumentation.
