Estimation of submarine groundwater discharge (SGD) to semi-enclosed basins by Ra isotope mass balance is herein assessed. We evaluate 224Ra, 226Ra, and 228Ra distributions in surface and bottom waters of Long Island Sound (CT-NY, United States) collected during spring 2009 and summer 2010. Surface water and bottom water Ra activities display an apparent seasonality, with greater activities during the summer. Long-lived Ra isotope mass balances are highly sensitive to boundary fluxes (water flux and Ra activity). Variation (50%) in the 224Ra, 226Ra, and 228Ra offshore seawater activity results in a 63–74% change in the basin-wide 226Ra SGD flux and a 58–60% change in the 228Ra SGD flux, but only a 4–9% change in the 224Ra SGD flux. This highlights the need to accurately constrain long-lived Ra activities in the inflowing and outflowing water, as well as water fluxes across boundaries. Short-lived Ra isotope mass balances are sensitive to internal Ra fluxes, including desorption from resuspended particles and inputs from sediment diffusion and bioturbation. A 50% increase in the sediment diffusive flux of 224Ra, 226Ra, and 228Ra results in a ∼30% decrease in the 224Ra SGD flux, but only a ∼6–10% decrease in the 226Ra and 228Ra SGD flux. When boundary mixing is uncertain, 224Ra is the preferred tracer of SGD if sediment contributions are adequately constrained. When boundary mixing is well-constrained, 226Ra and 228Ra are the preferred tracers of SGD, as sediment contributions become less important. A three-dimensional numerical model is used to constrain boundary mixing in Long Island Sound (LIS), with mean SGD fluxes of 1.2 ± 0.9 × 1013 L y–1 during spring 2009 and 3.3 ± 0.7 × 1013 L y–1 during summer 2010. The SGD flux to LIS during summer 2010 was one order of magnitude greater than the freshwater inflow from the Connecticut River. The maximum marine SGD-driven N flux is 14 ± 11 × 108 mol N y–1 and rivals the N load of the Connecticut River.

中文翻译：

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半封闭盆地海底地下水流量估算的镭质量平衡敏感性分析：以长岛声为例

本文评估了通过 Ra 同位素质量平衡对半封闭盆地的海底地下水排放 (SGD) 的估计。我们评估了 2009 年春季和 2010 年夏季在长岛海峡（美国 CT-NY）地表水和底水中的 224Ra、226Ra 和 228Ra 分布。地表水和底水 Ra 活动表现出明显的季节性，在夏天。长寿命 Ra 同位素质量平衡对边界通量（水通量和 Ra 活性）高度敏感。224Ra、226Ra 和 228Ra 近海海水活动的变化 (50%) 导致全盆地 226Ra SGD 通量变化 63-74%，228Ra SGD 通量变化 58-60%，但只有 4- 224Ra SGD 通量变化 9%。这突出表明需要准确地限制流入和流出水中的长寿命 Ra 活动，以及跨越边界的水通量。短寿命 Ra 同位素质量平衡对内部 Ra 通量敏感，包括重新悬浮颗粒的解吸和沉积物扩散和生物扰动的输入。224Ra、226Ra 和 228Ra 的沉积物扩散通量增加 50% 会导致 224Ra SGD 通量降低约 30%，但 226Ra 和 228Ra SGD 通量仅降低约 6-10%。当边界混合不确定时，如果沉积物贡献受到充分限制，224Ra 是 SGD 的首选示踪剂。当边界混合受到很好的限制时，226Ra 和 228Ra 是 SGD 的首选示踪剂，因为沉积物的贡献变得不那么重要。三维数值模型用于约束长岛海峡 (LIS) 中的边界混合，2009 年春季的平均 SGD 通量为 1.2 ± 0.9 × 1013 L y–1 和 3.3 ± 0。2010 年夏季为 7 × 1013 L y–1。2010 年夏季到 LIS 的 SGD 通量比来自康涅狄格河的淡水流入量大一个数量级。海洋 SGD 驱动的最大 N 通量为 14 ± 11 × 108 mol N y–1，可与康涅狄格河的 N 负荷相媲美。