Department of Earth Sciences, Pondicherry University, Puducherry 605 014, India; Department of Geology, Khajamalai Campus, Bharathidasan University, Trichy 620 023, India.
Department of Earth Sciences, Pondicherry University, Puducherry 605 014, India.
J Contam Hydrol. 2020 Aug;233:103660. doi: 10.1016/j.jconhyd.2020.103660. Epub 2020 May 23.
Groundwater contributed nutrients aided with increasing population threaten the global coastal ecosystems. In this study, attempt has been made using major ions and nutrients to evaluate the significance of submarine groundwater discharge (SGD) in a semi-arid estuary of south India. Surface, seepage and groundwater chemistry altered from fresh (NaK-CaMg-NOCl) to mixed (NaK-NOCl) to saline water (NaCl) type from upstream to outlet that connects Bay of Bengal. We predicted abundant nitrate (NO) along upstream and towards the bay due to application of fertilizers and aquaculture activities, respectively. Elevated ammonium (NH) observed in the recirculated groundwater/sea water suggests contribution from sea water intrusion and higher phosphate (PO) noted at the outer bay suggests sources from phosphatic nodules. Decreasing Redfield ratio towards the bay suggests anoxic aquifer condition due to salinization. The SGD driven nutrient fluxes were 40.0-47.0% for NO, 43.0-51.0% for NH and 9.0-32.0% for PO from the total input fluxes. The estimated nutrient fluxes showed that NO and PO discharges to the sea due to SGD and NH removed from the coast due to consumption by microorganisms that creates toxic algal blooms in the study area.
地下水带来的营养物质和不断增长的人口威胁着全球沿海生态系统。本研究试图利用主要离子和营养物质来评估印度南部半干旱河口区地下水排泄（SGD）的重要性。地表水、渗流和地下水的化学性质从上游到连接孟加拉湾的出水口逐渐由淡水（NaK-CaMg-NOCl）变为咸水（NaCl）类型。我们预测，由于化肥和水产养殖活动的应用，硝酸盐（NO）会在上游和海湾地区大量存在。在循环地下水/海水（recycled groundwater/sea water）中观察到的铵（NH）升高表明海水入侵的贡献，而在外部海湾中观察到的较高磷酸盐（PO）表明磷结核的来源。由于盐化作用，向海湾方向的 Redfield 比值（Redfield ratio）降低表明缺氧含水层条件。由 SGD 驱动的营养物通量分别为总输入通量的 40.0-47.0%用于 NO、43.0-51.0%用于 NH 和 9.0-32.0%用于 PO。估计的营养物通量表明，由于 SGD，NO 和 PO 排放到海中，而 NH 由于微生物消耗而从海岸去除，这在研究区域中产生了有毒藻类水华。
