Coastal lagoons face anthropogenic pressures worldwide, and understanding groundwater discharge to these sensitive environments can enable better management of water budgets and nutrient inputs. The main objective of the study was to quantify groundwater seepage into a large and shallow coastal lagoon using a detailed radon (²²²Rn, a natural groundwater tracer) mass balance. To assess and reduce uncertainty, three wind-speed scenarios were modelled in two seasons using two ²²²Rn-in-groundwater endmembers. Groundwater discharge to the lagoon ranged between 5.2 ± 5.8 m³/s to 18.7 ± 19.6 m³/s during summer and 0.9 ± 2.2 m³/s to 8.1 ± 10.5 m³/s during winter. Wind-driven radon evasion was the most influential component of the radon mass balance. Higher summer wind speeds resulted in groundwater discharge estimates 3.5 times greater than those during winter. We carried out an in-depth uncertainty analysis of the radon mass balance results, which confirmed the importance of accounting for individual uncertainties, particularly the most sensitive parameters of the model. Overall, results from the radon mass balance revealed groundwater discharge to the lagoon was 1-2 orders of magnitude greater than previous localised seepage meter estimates. This is likely because radon tracer approaches quantify both one-directional discharge and bi-directional porewater exchange at a larger spatial scale than traditional seepage meter methods. In spite of large uncertainties, the possible range of reasonable estimates revealed groundwater seepage as an important component of the water budget at this site. This study highlights the benefits of broad-scale tracer-based mass balances for quantifying groundwater discharge to coastal lagoons and the value of in-depth uncertainty analysis to increase confidence in seepage flux estimates.

沿海泻湖在全球范围内面临着人为压力，了解地下水向这些敏感环境的排放可以更好地管理水的预算和养分输入。该研究的主要目的是使用详细的ra（²²² Rn，天然地下水示踪剂）质量平衡来定量分析渗入大而浅的沿海泻湖的地下水。为了评估和减少不确定性，在两个季节中使用两个²²² Rn的地下水终端构件对三种风速情景进行了建模。夏季排入泻湖的地下水范围为5.2±5.8 m ³ / s至18.7±19.6 m ³ / s，夏季为0.9±2.2 m ³ / s至8.1±10.5 m ³/ s在冬季。风驱ra逃逸是the质量平衡中最有影响力的组成部分。夏季较高的风速导致地下水排放量估计是冬季的3.5倍。我们对don质量平衡结果进行了深入的不确定性分析，这证实了考虑单个不确定性（尤其是模型中最敏感的参数）的重要性。总体而言，from质量平衡的结果表明，地下水向泻湖的排放量比以前的局部渗流计估计值高1-2个数量级。这可能是因为ra示踪剂方法在比传统的渗透仪方法更大的空间尺度上量化了单向排放和双向孔隙水交换。尽管存在很大的不确定性，合理估计的可能范围表明，地下水渗漏是该站点水预算的重要组成部分。这项研究强调了基于示踪剂的大规模质量平衡对量化向沿海泻湖的地下水排放的好处，以及深入不确定性分析的价值，以增加对渗流通量估计的信心。