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首页> 外文期刊>Marine Chemistry >An evaluation of the efficacy of radium isotopes as tracers of submarine groundwater discharge to southern Rhode Island's coastal ponds
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An evaluation of the efficacy of radium isotopes as tracers of submarine groundwater discharge to southern Rhode Island's coastal ponds

机译：评价镭同位素作为示踪剂向南罗德岛州沿海池塘排放海底地下水的有效性

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Submarine groundwater discharge (SGD) represents a significant flux of water and chemical constituents to coastal regions. Because ~(226)Ra and ~(228)Ra are highly concentrated in groundwater relative to surface water, and their signal is well-integrated throughout coastal surface waters, these isotopes have been increasingly utilized to quantify SGD over the past several decades. In this study, a combined radium and salt balance is used to yield estimates of fresh and saline SGD to four of Rhode Island's coastal ponds (Winnapaug, Quono-chontaug, Ninigret, and Point Judith Ponds). Fresh SGD rates determined for each pond range between 0 and 17 Lm~2 d~1. These values largely fall in line with previous estimates made using hydrologic models. The uncertainty of saline SGD estimates for each pond is high; minimum and maximum saline SGD estimates dif-fer by as much as three orders of magnitude. These results echo the discrepancy between two previous radium-based studies from this location. The variability of dissolved radium in the Rhode Island coastal aqui-fer plays a large role in the uncertainty of these saline SGD estimates. Groundwater dissolved radium activity is dependent upon many different factors, including groundwater salinity and redox conditions, sediment thorium and radium activities, and the amount of time to which the sediment has been exposed to saline groundwater. Due to the heterogeneous nature of glacial outwash sediments, none of these parameters are likely consistent throughout the aquifer in this location. Groundwater ~226Ra and ~228Ra activities in the coastal ponds vary significantly both laterally and with sediment depth. For example, groundwater samples collected in Ninigret Pond separated by a vertical distance of only 5 cm differ by as much as 3 x 103 dp, 100 L ~1 for both ~(226)Ra and ~(228)Ra. The results from this study indicate that a single groundwater sample or suite of sam-ples may not accurately reflect the average radium activity of the groundwater actually discharging into each pond. Targeted sampling in areas where SGD is qualitatively observed can potentially remedy this problem.
机译：海底地下水排放（SGD）代表大量的水和化学成分流向沿海地区。由于〜（226）Ra和〜（228）Ra相对于地表水高度集中在地下水中，并且它们的信号在整个沿海地表水域中都得到很好的整合，因此在过去的几十年中，这些同位素已越来越多地用于定量SGD。在这项研究中，使用了镭和盐的组合平衡来估算罗德岛州四个沿海池塘（温纳帕格，库诺-春陶格，尼尼格雷特和朱迪思角池）的新鲜和盐水SGD。每个池塘确定的新鲜SGD率介于0和17 Lm〜2 d〜1之间。这些值在很大程度上与以前使用水文模型所作的估算相符。每个池塘的盐分SGD估算值的不确定性很高；最小和最大盐水SGD估算值相差多达三个数量级。这些结果呼应了该地点先前两次基于镭的研究之间的差异。罗德岛沿岸含水层中溶解的镭的变异性在这些盐类SGD估算值的不确定性中起着重要作用。地下水溶解的镭活性取决于许多不同的因素，包括地下水盐度和氧化还原条件，沉积物and和镭的活性，以及​​沉积物暴露于盐水中的时间。由于冰川冲积沉积物的非均质性质，这些参数在该位置的整个含水层中都可能不一致。沿海池塘的地下水〜226Ra和〜228​​Ra的活动在横向和沉积深度上都有很大的不同。例如，在Ninigret池塘中收集的地下水样品之间的垂直距离仅为5 cm，相差3 x 103 dp，〜（226）Ra和〜（228）Ra均为100 L〜1。这项研究的结果表明，单个地下水样品或一组样品可能无法准确反映实际排入每个池塘的地下水的平均镭活性。在定性观察到SGD的区域进行有针对性的采样可能会解决此问题。

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