Ganga River Ecology Research Laboratory, Environmental Science Division, Centre of Advanced Study in Botany, Institute of Science, Banaras Hindu University, Varanasi 221005, India.
Ganga River Ecology Research Laboratory, Environmental Science Division, Centre of Advanced Study in Botany, Institute of Science, Banaras Hindu University, Varanasi 221005, India.
Ecotoxicol Environ Saf. 2019 Apr 30;171:709-720. doi: 10.1016/j.ecoenv.2019.01.039. Epub 2019 Jan 16.
Dissolved oxygen (DO) plays a major role in sustaining aquatic communities; its concentration and regulatory determinants are considered a key node predicting eutrophy, ecosystem health, and biogeochemical feedbacks. Here we report the status of dissolved oxygen deficit (DOD; hypoxia), and its mechanistic links with sediment oxygen demand (SOD) in the Ganga River. We conducted two independent but interlinked studies during summer low flows of three consecutive years (2016-2018) considering: 1) a 518 km middle segment of the Ganga River between Kanpur upstream and Varanasi downstream; and 2) trajectory analyses downstream two point sources, one flushing industrial effluents (Wazidpur drain) and the other with urban sewage (Assi drain). The concentration of DO at sediment-water interface (DO) did appear < 2.0 mg L (hypoxia) at Jjmu; and up to 600 m and 800 m downstream Assi and Wazidpur drain respectively. The DOD at sediment-water interface (DOD) was highest at Jjmu and did not show a significant decrease up to 300 m downstream to point sources. The SOD which varied between 2.03 and 13.16 (main river stem); 4.39 and 16.81 (Wazidpur drain); and between 2.00 and 13.50 g O m d (Assi drain), was found to be a major contributor of DOD. Principal component analysis (PCA) and non-metric multi-dimensional scaling (NMDS) separated DO and alkaline phosphatase (AP) opposite to oxygen-consuming processes and sediment-P release. Using a dynamic fit model, we tested the dependence of sediment-P release on DO and DOD. A large increase in the sediment-P release with increasing DOD and decreasing DO indicated that the system may compromise its resilience in long-term future in terms of self-fertilization and P-eutrophy if the similar magnitude of anthropogenic pressure is continued. The study advances our understanding towards DOD associated habitat fragmentation, ecosystem resilience and niche opportunities useful for recovery and management of the Ganga River.
溶解氧（DO）在维持水生生物群落方面起着重要作用；其浓度和调节决定因素被认为是预测富营养化、生态系统健康和生物地球化学反馈的关键节点。在这里，我们报告了恒河的溶解氧亏缺（DOD；缺氧）的现状，以及它与沉积物需氧量（SOD）之间的机制联系。我们在连续三年（2016-2018 年）夏季低流量期间进行了两项独立但相互关联的研究，考虑了：1）恒河的一个 518 公里的中游段，位于坎普尔上游和瓦拉纳西下游之间；2）在两个点源下游进行轨迹分析，一个是冲洗工业废水的（瓦济德布尔排水沟），另一个是城市污水的（阿西排水沟）。沉积物-水界面的 DO 浓度（DO）似乎在 Jjmu 处<2.0mg/L（缺氧）；在阿西和瓦济德布尔排水沟的下游分别达到 600m 和 800m。沉积物-水界面的 DOD 在 Jjmu 处最高，在到达点源 300m 之前没有显著下降。SOD 变化范围在 2.03 和 13.16（主河干）之间；4.39 和 16.81（瓦济德布尔排水沟）之间；以及 2.00 和 13.50g O m d（阿西排水沟）之间，是 DOD 的主要贡献者。主成分分析（PCA）和非度量多维标度（NMDS）将 DO 和碱性磷酸酶（AP）与耗氧过程和沉积物-P 释放分开。使用动态拟合模型，我们测试了沉积物-P 释放对 DO 和 DOD 的依赖关系。随着 DOD 的增加和 DO 的减少，沉积物-P 释放量大大增加，这表明如果继续承受类似的人为压力，该系统在长期内可能会损害其自我受精和 P 富营养化的恢复能力。该研究增进了我们对与 DOD 相关的栖息地破碎化、生态系统恢复力和生态位机会的理解，这些机会有助于恒河的恢复和管理。
