GroMoPo Metadata for Nassau County SEAWAT model

A methodology is proposed to define indices for quantifying risks under the threat of reducing in groundwater levels, the existence of saltwater intrusion (SWI), and an increasing nitrate contamination load in submarine groundwater discharge (SGD). The proposed methodology considers coastal regions under geological heterogeneity and it is tested on a groundwater system in Nassau County of Long Island, New York (USA). The numerical model is constructed with the SEAWAT code. The parameter uncertainty of this model is evaluated by coupling the Latin hypercube sampling method (as a sampling algorithm) and Monte Carlo simulation to consider the uncertainty in both hydraulic conductivity and recharge rate. The indices are presented in spatial maps that classify areas of risk to potential threats. The results show that two of the water districts have a high risk under conditions of decreasing groundwater level. Salinity occurs in the southern and southwestern parts of the Nassau County aquifer and a considerable area of high risk of SWI is identified. Furthermore, the average SGD rate with the associated fluxes of nitrate is estimated as 81.4 million m(3)/year (average 0.8 tons of nitrate through SGD per year), which can adversely affect the quality of life in the local coastal ecosystems. The framework developed in this study could help the water district managers to identify high-risk areas for short-term and long-term planning and is applicable to other coastal settings.

本研究提出了一种方法，旨在量化地下水位下降、海水入侵（SWI）以及海底地下水排放（SGD）中硝酸盐污染负荷增加等潜在威胁下的风险指标。该方法考虑了地质异质性的沿海地区，并在纽约长岛纳骚县（美国）的地下水系统中进行了测试。数值模型采用SEAWAT代码构建。通过将拉丁超立方抽样法（作为一种抽样算法）与蒙特卡洛模拟相结合，评估了该模型的参数不确定性，以考虑水力传导率和补给率的随机性。风险指标以空间地图的形式呈现，用于对潜在威胁的风险区域进行分类。结果显示，在地下水位下降的条件下，有两个供水区域存在高风险。纳骚县含水层南部和西南部出现盐分，并确定了相当面积的高风险SWI区域。此外，估计平均SGD速率为8140万立方米/年（平均每年通过SGD排放0.8吨硝酸盐），这可能会对当地沿海生态系统的生存质量产生不利影响。本研究开发的框架有助于供水区域管理者识别短期和长期规划中的高风险区域，并可适用于其他沿海地区。