The Thane Creek-Ulhas estuary confluence region acts as a naturally active infiltration system, crucial for altering water quality in the area and Arabian Sea. Particle-water exchange, hydrodynamics, and anthropogenic discharge influence nutrient transfer and transformation, highlighting the need for effective water quality management in this urbanized ecosystem. We analyzed monthly hydrography and nutrient data in water, and particulates from April 2021 to March 2022, including period of Cyclone Gulab at four locations along the inflow and outflow sectors. Our results revealed prevalent hypoxic conditions in the confluence waters, driven by microbial oxygen demand that surpassed the chemical load due to indiscriminate sewage inflow. Phosphorus emerged as the limiting nutrient, inhibited by adsorption/desorption equilibrium. Dissolved phosphate was transformed into particulate form under intermediate suspended load, with further transform into organic phosphorous during non-monsoon season. Excessive ammonium from sewage during the cyclone and elevated urea during non-monsoon indicated regenerated nitrogen forms, rendering the region eutrophic and hyper-eutrophic, with intermittent organic pollution. Engineering interventions may help mitigate water quality alterations that pose significant ecological risks in this mangrove-dominant confluence ecosystem.

中文翻译：

---

城市化小溪-河口汇合处的溶解和悬浮营养物复杂性：对水质改变的影响


Thane Creek-Ulhas 河汇区域是一个自然活跃的渗透系统，对于改变该地区和阿拉伯海的水质至关重要。颗粒水交换、流体动力学和人为排放会影响营养物质的转移和转化，突出了在这个城市化生态系统中进行有效水质管理的必要性。我们分析了 2021 年 4 月至 2022 年 3 月期间水中的月度水文和营养物数据，以及颗粒物，包括流入和流出扇区四个位置的飓风古拉布时期。我们的结果揭示了汇流水中普遍存在的缺氧条件，这是由微生物需氧量驱动的，由于不加选择地涌入污水，微生物需氧量超过了化学负荷。磷成为限制性营养物质，受到吸附/解吸平衡的抑制。溶解的磷酸盐在中等悬浮负荷下转化为颗粒形式，在非季风季节进一步转化为有机磷。气旋期间污水中铵含量过高，非季风期间尿素升高表明氮再生形式，使该地区富营养化和超富营养化，并伴有间歇性有机污染。工程干预可能有助于缓解水质改变，这些改变对这个以红树林为主的汇流生态系统构成重大生态风险。