Evaluation of mean residence time in subsurface waters using oxygen-18 fluctuations during drought conditions in the mid-Appalachians
Evaluation of mean residence time in subsurface waters using oxygen-18 fluctuations during drought conditions in the mid-Appalachians
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DOI：
10.1016/s0022-1694(02)00006-9
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发表时间：
2002-04-15
影响因子：
6.4
通讯作者：
Gburek, WJ
中科院分区：
文献类型：
--
作者：
McGuire, KJ;DeWalle, DR;Gburek, WJ
利用稳定同位素氧-18 （O-18）的季节变化，估算了宾夕法尼亚州中部山谷和岭省两个流域水的平均停留时间（MRTs）。通过将O-18输入降水特征应用于描述地下系统流动条件的响应函数模型来估计MRT。降水O-18通常是季节性的；然而，在1998年3月至1999年6月的研究期间，异常的天气条件和严重的干旱导致了O-18降水的异常季节性特征。非典型输入降水量和O-18特征要求使用补给因子和扩展的过去输入函数进行调整，以表示在研究期间促成流域内周转量的输入水的不同比例。研究了张力和零张力土壤溶水仪、浅井和溪流输出水中氧-18的变化。土壤水分O-18特征对降水O-18变化的响应强于径流O-18特征。基于指数活塞流和弥散流过程的理论模型比其他地下水年龄分布模型（即纯活塞流或纯指数模型）更适合数据。分析表明，在干旱条件下，更大比例的老水主导了径流O-18组成，并且当年降水O-18特征在地下流系统中变得更加衰减。在14和100 ha流域，每个站点的流量MRT分别为9.5和4.8个月，100 cm深度的土壤水分MRT约为几个月；表明浅层地下水对降水的反应相对较快。(C) 2002 Elsevier Science B.V.版权所有
Seasonal variations of the stable isotope, oxygen-18 (O-18), were used to estimate mean residence times (MRTs) of water in two Valley and Ridge Province watersheds in central Pennsylvania. MRT was estimated by applying O-18 input precipitation signatures to response function models that describe flow conditions in the subsurface system. Precipitation O-18 is usually seasonally periodic; however, during this study period (March 1998 to June 1999), unusual weather conditions and severe drought caused an abnormal seasonal signature in precipitation O-18. The atypical input precipitation amounts and O-18 signatures required that adjustments be made using recharge factors and an extended past input function to represent the varying fraction of input water that contributed to turnover within the watershed during the study period. Oxygen-18 variations were investigated in output waters from tension and zero-tension soil water lysimeters, shallow wells, and streamflow. Soil water O-18 signatures were more responsive to precipitation O-18 variations than streamflow O-18 signatures. Theoretical models based on exponential piston-flow and dispersion flow processes fit data better than did other groundwater age distribution models (i.e. pure piston flow or pure exponential models). Analysis suggested that during drought conditions, larger portions of older water dominated streamflow O-18 composition, and that the current year's precipitation O-18 signature became more attenuated in the subsurface flow system. MRTs obtained for streamflow at each site were 9.5 and 4.8 months for a 14 and 100 ha watershed, respectively, and soil water MRT at 100 cm depth was on the order of a couple months; indicating a relatively rapid response of shallow groundwater to precipitation. (C) 2002 Elsevier Science B.V. All rights reserved.