Abstract Sulphur Springs Cave is an extensive phreatic cavity that produces a large, historic spring in the middle of metropolitan Tampa, Florida, USA. The city of Tampa extracts groundwater from the spring to supplement municipal water supply and to support low-salinity habitat in the estuarine Hillsborough River. Extraction at this site has occurred for many decades, but has intensified since the early 2000s, rapidly increasing the salinity of the spring and cave water. The purpose of this study was to address the potential sources and mechanisms of saltwater intrusion at this site using historical and current hydrochemical data published in the literature and online by government agencies. We also explored the cave to identify point-sources of intrusion, and collected water and biological samples from inside the cave to identify potential ecosystem impacts of increasing cave salinity. From 1946 to present, Sulphur Springs water shifted from being fresh (specific conductance −1 ) and of calcium-sulfate type to being brackish (specific conductance ∼5000 µS cm −1 and higher) and of sodium-chloride type. We found numerous vents in the cave that issue saline, thermal, sulfidic water and host distinct microbial mat communities. These vents are likely connected to bedrock fractures that provide preferential flow-paths along which confined, deep-sourced saline water enters the freshwater portion of the aquifer, probably originating from the coastal mixing zone. Salinity increased at the spring during dry-season pumping activity and after wet-season recharge events, which likely increased artesian pressure in confined saline aquifer units. Salinization of Sulphur Springs may disrupt the cave microbe and stygobite communities and eventually make the spring unsuitable to maintain low-salinity habitat in the Hillsborough River.

中文翻译：

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城市泉水的命运：潜水洞穴中抽水引起的海水入侵

摘要 Sulphur Springs Cave 是一个巨大的潜水洞，在美国佛罗里达州坦帕市的中部产生了一个历史悠久的大型泉水。坦帕市从泉水中提取地下水以补充市政供水并支持希尔斯伯勒河河口的低盐度栖息地。该地点的开采已经进行了几十年，但自 2000 年代初以来一直在加强，迅速增加了泉水和洞穴水的盐度。本研究的目的是利用政府机构在文献和网上发布的历史和当前水化学数据来解决该地点咸水入侵的潜在来源和机制。我们还探索了洞穴以确定入侵的点源，并从洞穴内部收集水和生物样本，以确定洞穴盐度增加对生态系统的潜在影响。从 1946 年至今，硫磺泉水从新鲜（电导率 -1 ）和硫酸钙类型转变为微咸水（电导率 ∼5000 µS cm -1 或更高）和氯化钠类型。我们在洞穴中发现了许多喷口，这些喷口发出盐水、热水、硫化水，并拥有不同的微生物垫群落。这些喷口很可能与基岩裂缝相连，基岩裂缝提供了优先的流动路径，沿着这些路径，受压的深层咸水进入含水层的淡水部分，可能来自沿海混合区。春季旱季抽水活动和雨季补给活动后盐分增加，这可能会增加封闭盐水含水层单元的自流压力。硫磺泉的盐碱化可能会破坏洞穴微生物和柱状菌群落，最终使泉水不适合维持希尔斯伯勒河中的低盐度栖息地。