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

这项提案寻求对华盛顿州三个地点的土壤水、土壤二氧化碳和降水进行稳定的同位素研究。这项研究的主要目的是(1)限制从土壤到大气的二氧化碳通量的氧同位素组成。(2)从时间和空间上评价土壤CO2和土壤水分之间的氧同位素平衡程度。(3)树木年轮研究场地土壤水稳定同位素系统学特征。为达到这些目标，当局会定期从土壤剖面的不同深度抽取土壤和土壤气体样本，并会在每个地点安装雨水收集器，每两星期抽取样本一次。将测定土壤水分、降水和土壤二氧化碳的稳定同位素组成(H、C和O)，并将土壤剖面数据与一维模型进行比较，该模型考虑了入渗、蒸发、土壤呼吸产生的二氧化碳、土壤二氧化碳和水之间的同位素交换以及含有D、18O和13C的分子的差异扩散。拟议中的研究的一个独特方面是，它将与树轮中的稳定同位素及其保持气候记录的能力的研究(NSF资助的冯夏宏博士的项目)相结合。在解释树木年轮中的同位素时，最大的不确定性之一是降水的同位素组成在被并入木材纤维素之前是如何被修改的。为了解决这个问题的一个方面，来自土壤水、雨水、树液水和树轮的同位素数据将在奥林匹克半岛的两个地点收集，冯博士在那里开始了她对树轮的研究。这将是第一次同时收集树木年轮、降水、土壤水和树液水的同位素数据。在全球范围内，土壤二氧化碳同位素体系的定量模型可以限制从土壤进入大气的二氧化碳的通量和同位素组成(土壤呼吸的二氧化碳)。在高纬度地区，大气中二氧化碳的~(18)O/~(16)O比低于与海水的平衡预测值，这一差异归因于植物和土壤中较低的~(18)O二氧化碳大量流入大气。然而，人们对土壤呼吸的二氧化碳的氧同位素组成知之甚少，很难进行直接测量。对土壤二氧化碳18O/16O的测量和定量描述可以限制土壤呼吸二氧化碳的18O/16O，从而改进全球大气二氧化碳模型。这是她职业生涯中的关键时期，因为她正在努力建立一个实验室，并建立一个研究计划。POWRE计划的支持将为这一过渡提供重要的推动，从而极大地促进她的科学发展。

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.