Exchange-Corrected CFC Dating of Stream Flow

交换校正的溪流 CFC 测年

• 批准号: 0309212
• 负责人: D. Kip Solomon
• 金额: $ 23.1万
• 依托单位: University of Utah
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-08-15 至 2007-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0309212&HistoricalAwards=false
• 关键词: Exchange; Corrected; CFC; Dating; Stream

0309212..SolomonThe mean transit time of groundwater is a fundamental and robust characteristic of a subsurface flow system. In unconfined aquifers, the mean groundwater transit time is related to (1) the volume of water stored in the aquifer and (2) the flux of water into or out of the aquifer. Environmental tracers such as tritium have been used to estimate the mean transit time, but generally require a time series of measurements from the early 1960s to approximately 1980 and such data sets are very rare. Precise groundwater dating using dissolved gases such as chlorofluorocarbons (CFCs) has become relatively common. If CFC groundwater ages were preserved in the base flow of streams it might be possible to obtain flow-weighted mean transit time estimates even when long-term time series are not available. Although one might think that CFCs in streams would equilibrate with the atmosphere, samples collected from a variety of streams during base flow conditions are NOT in equilibrium with atmospheric CFCs (at the temperature and elevation of the stream) suggesting that exchange with the atmosphere is sluggish.The central hypothesis of the proposed research is that gaining streams will not equilibrate with CFCs in the atmosphere provided that the flux of non-modern groundwater can offset the rate of exchange with the atmosphere. It is further hypothesized that by quantifying the rate of gas exchange in a particular stream, the mean concentration of CFCs in groundwater can be estimated. If these hypotheses can be validated, a new tool will exist for obtaining integrated hydrologic properties in the subsurface. Such integrated values can then form the basis for transforming properties measured at the scale of boreholes to the scale of a groundwatershed (i.e. upscaling.)This research will be conducted primarily in the Red Butte watershed in the Wasatch Mountains, Utah, along with an application of the results to regional streams draining the Colorado Plateau. Gas exchange mechanisms, including the effects of bubble formation, will be evaluated by conducting gas tracer tests in streams. The spatial variability of aquifer properties (thickness, specific yield, etc.) and preferential (macropore) flow will be considered by comparing groundwater ages in short-screen piezometers with integrated values obtained in stream baseflow.The development of a tool to evaluate the mean transit time of a subsurface watershed will provide the basis for developing new paradigms for the regulation and protection the Nation's water resources that are based on measurable values for the average transit time of water and solutes in the subsurface.

0309212..地下水的平均渡越时间是地下水流系统的一个基本的和鲁棒的特性。 在非承压含水层中，平均地下水运输时间与（1）含水层中储存的水量和（2）进出含水层的水通量有关。 氚等环境示踪剂已被用于估计平均渡越时间，但通常需要从20世纪60年代初到大约1980年的时间序列测量，这样的数据集非常罕见。 使用溶解的气体如氯氟烃（CFCs）进行精确的地下水定年已经变得相对普遍。 如果氟氯化碳地下水的年龄保存在河流的基流中，即使没有长期的时间序列，也有可能获得流量加权平均过境时间估计数。 虽然有人可能认为溪流中的CFC会与大气平衡，在基流条件下，从各种水流中采集的样品与大气中的CFC不平衡（在溪流的温度和海拔）这表明与大气的交换是缓慢的。拟议的研究的中心假设是，获得流将不会与大气中的CFC平衡，前提是非现代地下水可以抵消与大气的交换率。 进一步假设，通过量化特定水流中的气体交换率，可以估计地下水中CFC的平均浓度。 如果这些假设能够得到验证，一个新的工具将存在获得综合水文特性的地下。 这样的综合价值，然后可以形成的基础上转换的属性测量的规模钻孔的地面流域的规模（即放大）。这项研究将主要在犹他州瓦萨奇山脉的红巴特流域进行，并将研究结果应用于沿着排放科罗拉多高原的区域溪流。 气体交换机制，包括气泡形成的影响，将进行气体示踪剂测试流进行评估。 含水层特性的空间变异性（厚度、单位产量等）和优惠（大孔隙）流量将被认为是通过比较地下水年龄在短-开发一种评估地下流域平均过境时间的工具，将为开发新的规范和保护国家水资源提供基础，这些规范是基于水和溶质在地下流域中的平均过境时间的可测量值。地下。