科学家报告在西班牙马尔梅诺尔（Mar Menor）潟湖下方发现一条隐蔽的海底地下水排放通道网路，将含汞地下水渗入潟湖，估算每年约输入2.2磅汞。马尔梅诺尔为浅、超盐度的沿海潟湖，面积约52平方英里，与地中海之间由狭长沙洲分隔。测得地下水汞浓度与大气相近，且约为阿尔布洪河（Albujón River）的70倍，指向过去采矿与农业留下的「历史汞」污染。

当地下水（包含淡水与回渗水）在近岸与高盐、低氧且富含有机质的潟湖水混合时，环境有利于微生物把无机汞转化为甲基汞。甲基汞会沿食物网生物累积，通常使大型掠食鱼类浓度更高。研究人员在近岸水域发现较高甲基汞浓度，显示地下水入海区可能成为甲基汞生成热点；虽然目前潟湖水体与鱼类汞含量尚不被视为「令人警觉」，但额外的甲基汞生成可能随时间改变风险评估。

团队采集潟湖水、海滩沉积物孔隙水、钻孔地下水与阿尔布洪河水样，并同时量测溶解态汞/甲基汞与镭同位素（用作地下水入流速率的放射性示踪），再结合水文地质模型估算不同地下水组分的年度贡献。结果显示，潟湖水在沉积物中的长尺度回渗循环主导汞负荷，淡水地下水仅占较小比例。研究发表于《Environmental Science & Technology》，并指出全球多处潟湖可能正默默承受「自下而上」的汞输入；未来更暖的夏季与更频繁热浪可能加剧低氧，进一步增加甲基汞生成机会。

On Dec 25, 2025, scientists reported a hidden submarine groundwater discharge network feeding Spain’s Mar Menor lagoon with mercury, estimated at about 2.2 pounds per year. Mar Menor is a shallow hypersaline lagoon (~52 square miles) separated from the Mediterranean by a sandbar. Measurements found groundwater mercury levels comparable to air and ~70× the Albujón River, pointing to legacy contamination from past mining and farming.

Where fresh or recirculated groundwater mixes with salty, low-oxygen, organic-rich nearshore water, microbes can convert inorganic mercury into methylmercury, a form that bioaccumulates up food webs. Researchers detected high methylmercury nearshore hotspots, though current water and fish levels are not considered alarming; added production could raise risk over time, especially given recent algal blooms and oxygen-loss events driven by nutrient runoff.

The team sampled lagoon water, porewater, borehole groundwater, and the Albujón River, pairing dissolved mercury/methylmercury with radium isotopes and a hydrogeological model to apportion sources through the year. Long-scale recirculation through sediments dominated the mercury load, with fresh groundwater a smaller share. The study (Environmental Science & Technology) suggests many coastal lagoons may receive under-recognized mercury from below, and that warming and heatwaves could intensify low-oxygen conditions that favor methylmercury formation.