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.
Environ Pollut. 2021 Jan 1;268(Pt B):115771. doi: 10.1016/j.envpol.2020.115771. Epub 2020 Oct 6.
Riverine ecosystems can have tipping points at which the system shifts abruptly to alternate states, although quantitative characterization is extremely difficult. Here we show, through critical analysis of two different reach scale (25 m and 50 m) studies conducted downstream of two point sources, two tributaries (main stem and confluences) and a 630 km segment of the Ganga River, that human-driven benthic hypoxia/anoxia generates positive feedbacks that propels the system towards a contrasting state. Considering three positive feedbacks-denitrification, sediment-P- and metal-release as level determinants and extracellular enzymes (β-D-glucosidase, protease, alkaline phosphatase and FDAase) as response determinants, we constructed a 'river ecosystem resilience risk index (RERRI)' to quantitatively characterize tipping points in large rivers. The dynamic fit intersect models indicated that the RERRI<4 represents a normal state, 4-18 a transition where recovery is possible, and >18 an overstepped condition where recovery is not possible. The resilience risk index, developed for the first time for a lotic ecosystem, can be a useful tool for understanding the tipping points and for adaptive and transformative management of large rivers.
河流生态系统在达到临界点时可能会突然转变为另一种状态，尽管定量描述极其困难。通过对两个不同的河段尺度（25 米和 50 米）的研究进行批判性分析，这些研究分别位于两个点源、两个支流（干流和交汇点）以及恒河的 630 公里河段下游，我们发现人为导致的底层缺氧/无氧会产生正反馈，推动系统向相反的状态发展。考虑到三个正反馈因素——反硝化作用、沉积物磷和金属释放作为水平决定因素，以及胞外酶（β-D-葡萄糖苷酶、蛋白酶、碱性磷酸酶和 FDA 酶）作为响应决定因素，我们构建了一个“河流生态系统弹性风险指数（RERRI）”，以定量描述大河中的临界点。动态拟合相交模型表明，RERRI<4 代表正常状态，4-18 代表可能恢复的过渡状态，而>18 代表不可恢复的超越状态。该弹性风险指数是首次为流动生态系统开发的，可以作为理解临界点和进行大型河流适应性和变革性管理的有用工具。
