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

POWRE：华盛顿州选定地点土壤水和土壤二氧化碳的稳定同位素系统学

• 批准号: 9806178
• 负责人: Carey Gazis
• 金额: $ 7.5万
• 依托单位: Central Washington University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1998
• 资助国家: 美国
• 起止时间: 1998-10-15 至 2001-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9806178&HistoricalAwards=false
• 关键词: POWRE; Stable; Isotope; Systematics; Soil

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.

[806178]本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同位素研究的支持。本研究的主要目的是：(1)对土壤到大气CO2通量的氧同位素组成进行限制。(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)研究树木年轮同位素研究点土壤水分稳定同位素系统特征。为了达到这些目标，我们会定期从土壤剖面的不同深度取样土壤和土壤气体，并在每个地点安装集雨器，每两周取样一次。测定土壤水分、降水和土壤CO2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，其中包括入渗、蒸发、土壤呼吸产生的CO2、土壤CO2与水之间的同位素交换以及含有D、18O和13C的分子的微分扩散。这项拟议研究的一个独特之处在于，它将与一项关于树木年轮稳定同位素及其保留气候记录能力的研究（冯夏红博士资助的nsf项目）结合起来进行。在解释树木年轮的同位素时，最大的不确定因素之一是降水的同位素组成在被纳入木质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，将在奥林匹克半岛的两个地点收集土壤水、雨水、树液水和树木年轮的同位素数据，冯博士在那里开始了她对树木年轮的研究。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系统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”二氧化碳）。在高纬度地区，大气二氧化碳的18O/16O比率低于与海水平衡时的预测值，这一差异归因于植物和土壤向大气输送了大量低18O的二氧化碳。然而，人们对土壤呼吸二氧化碳的氧同位素组成知之甚少，而且很难进行直接测量。土壤CO2的18O/16O的测量和定量描述可以约束土壤呼吸CO2的18O/16O，从而改进全球大气CO2模型。首席研究员凯里·加齐斯博士最近在中央华盛顿大学地质系开始了一个终身职位，该系的研究生和本科课程正在活跃和不断增长。这是她职业生涯的关键时刻，因为她努力建立一个实验室，建立一个研究项目。power项目的支持将极大地促进她的科学发展，为这一转变提供重要的推动作用。