Groundwater transit time distribution and mean from streambed sampling in an agricultural coastal plain watershed, North Carolina, USA
Groundwater transit time distribution and mean from streambed sampling in an agricultural coastal plain watershed, North Carolina, USA
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美国北卡罗来纳州农业沿海平原流域的地下水渡越时间分布和河床采样平均值
DOI：
10.1002/2015wr017600
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发表时间：
2016
影响因子：
5.4
通讯作者：
John E. Solder
中科院分区：
文献类型：
--
作者：
T. Gilmore;D. Genereux;D. Solomon;John E. Solder
我们使用点尺度采样和渗流毯（一种新型渗流仪）测量了桑迪河床中的地下水表观年龄（τ）和渗流速率（v）。我们发现非常相似的MTT估计从河床点采样在58米达到（29年）和2.5公里达到（31年）。地下水排放到流的TTD是最好的伽玛分布模型拟合，并在两个河段的河床点采样非常相似。在相邻的点尺度和渗流毯样本之间，来自渗流毯的水通常较年轻，主要是因为毯样本含有一小部分“年轻”的河水。校正河流含水率的覆盖层数据使大多数覆盖层样本的τ估计值更接近于相邻点样本的τ估计值。从修正的毯子数据的MTT估计值与从邻近毯子的采样河床点的那些一致。总的来说，年龄测定示踪剂之间的一致性，示踪剂数据和活塞流模型曲线之间的一般雅阁，以及河床中的大地下水年龄梯度，表明活塞流表观年龄是大多数样品的地下水渡越时间的合理估计。总的来说，我们从两个现场活动的结果表明，在河床中收集的地下水可以提供合理的估计地下水排放的表观年龄，MTT可以通过不同的年龄测定示踪剂和不同的地下水收集设备采样来确定。耦合河床点测量地下水年龄和地下水渗透率是一种新的，可重复的，有效的方法来估计含水层TTD和MTT。
We measured groundwater apparent age (τ) and seepage rate (v) in a sandy streambed using point‐scale sampling and seepage blankets (a novel seepage meter). We found very similar MTT estimates from streambed point sampling in a 58 m reach (29 years) and a 2.5 km reach (31 years). The TTD for groundwater discharging to the stream was best fit by a gamma distribution model and was very similar for streambed point sampling in both reaches. Between adjacent point‐scale and seepage blanket samples, water from the seepage blankets was generally younger, largely because blanket samples contained a fraction of “young” stream water. Correcting blanket data for the stream water fraction brought τ estimates for most blanket samples closer to those for adjacent point samples. The MTT estimates from corrected blanket data were in good agreement with those from sampling streambed points adjacent to the blankets. Collectively, agreement among age‐dating tracers, general accord between tracer data and piston‐flow model curves, and large groundwater age gradients in the streambed, suggested that the piston flow apparent ages were reasonable estimates of the groundwater transit times for most samples. Overall, our results from two field campaigns suggest that groundwater collected in the streambed can provide reasonable estimates of apparent age of groundwater discharge, and that MTT can be determined from different age‐dating tracers and by sampling with different groundwater collection devices. Coupled streambed point measurements of groundwater age and groundwater seepage rate represent a novel, reproducible, and effective approach to estimating aquifer TTD and MTT.