POWRE: Stable Isotope Systematics of Soil Water and Soil CO2For Selected Sites in Washington State

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9806178GazisThis proposal seeks support for a stable isotopic study of soil water, soil CO2, and precipitation from three sites in Washington State. The principal objectives of this study are (1) to place constraints on the oxygen isotope composition of the CO2 flux from soils to the atmosphere. (2) To assess the degree of oxygen isotope equilibrium between soil CO2 and soil water, both temporally and spatially. (3) To characterize the stable isotope systematics of soil water in sites where tree ring isotope studies are being done. To achieve these objectives, soils and soil gas will be sampled at regular intervals from different depths in the soil profile and rain collectors will be installed at each site and sampled every two weeks. The stable isotope compositions (H, C, and O) of soil water, precipitation and soil CO2 will be determined and soil-profile data will be compared to one-dimensional models which account for infiltration, evaporation, production of CO2 by soil respiration, isotopic exchange between soil CO2 and water, and differential diffusion of molecules containing D, 18O and 13C.One unique aspect of the proposed study is that it will be done in conjunction with a study of stable isotopes in tree rings and their ability to retain climate records (NSF-funded project of Dr. Xiahong Feng). One of the greatest uncertainties in the interpretation of isotopes in tree rings is how the isotopic composition of precipitation is modified before it is incorporated into wood cellulose. To address one aspect of this question, isotope data from soil water, rain water, sap water and tree rings will be collected at two sites in the Olympic Peninsula where Dr. Feng has begun her study of tree rings. This will be the first time that isotopic data for tree rings, precipitation, soil water, and sap water are all collected at the same time.On a global scale, a quantitative model of the isotopic systematics of soil CO2 can constrain the flux and isotopic composition of CO2 that enters the atmosphere from soils ("soil-respired" CO2). At high latitudes, the 18O/16O ratio of atmospheric CO2 is lower than that predicted for equilibrium with ocean water, a difference that has been attributed to substantial flux of lower-18O CO2 to the atmosphere from plants and soils. However, the oxygen isotopic composition of the soil-respired CO2 is poorly understood and direct measurements are difficult to make. Measurements and quantitative descriptions of the 18O/16O of soil CO2 can constrain the 18O/16O of soil respired CO2, and will thus improve global models of atmospheric CO2.The PI, Dr. Carey Gazis, has recently begun a tenure-track position in the Geology Department at Central Washington University, with active and growing graduate and undergraduate programs. This is a critical time in her career as she strives to build a laboratory and establish a research program. Support from the POWRE program will greatly enhance her scientific development by providing an important boost for this transition.