River ecosystem resilience risk index: A tool to quantitatively characterize resilience and critical transitions in human-impacted large rivers

Nonlinear and spatial spillover effects of urbanization on air pollution and ecological resilience in the Yellow River Basin

Based on Panel data collected from 2011 to 2020 targeted to 50 prefecture-level cities in the Yellow River Basin, this paper adopted standard deviation ellipse and spatial Dubin model to explore the nonlinear effects and spatial spillover effects of urbanization on air pollution and ecological resilience in the Yellow River Basin. The results show that the degree of air pollution in the southeast of the Yellow River Basin is higher than that in the northwest of the Yellow River Basin, the distribution range of air pollution is shrinking, the concentration of ecological resilience is enhanced, and the ecological environment is developing for the better. There is a significant U-shaped relationship between urbanization and air pollution in the Yellow River Basin, and an inverted U-shaped relationship between urbanization and ecological resilience. For every 1% increase in urbanization, air pollution decreases by 0.0873%, ecological resilience increases by 0.4046%. For every 1% increase in the square term of urbanization, air pollution increases by 0.2271%, ecological resilience decreases by 0.1789%. The urbanization of the Yellow River Basin has a spatial spillover effect on air pollution and ecological resilience, and urbanization has a significant negative impact on the ecological environment of neighboring cities. The robustness of the above conclusions is verified by introduce an inverse distance weight matrix replacing the spatial weight matrix.

Effects of COVID-19 lockdown on water quality, microbial extracellular enzyme activity, and sediment-P release in the Ganga River, India

This study investigates possible improvement in water quality and ecosystem functions in the Ganga River as influenced by COVID-19 lockdown in India. A total of 132 samples were collected during summer-2020 low flow (coinciding COVID-19 lockdown) for water (sub-surface and sediment-water interface) and 132 samples separately for sediment (river bottom and land-water interface) considering 518-km main river stem including three-point sources (one releases urban sewage and the other two add metal-rich industrial effluents) and a pollution-impacted tributary. Parameters such as dissolved oxygen deficit and the concentrations of carbon, nutrients (N and P), and heavy metals were measured in water. Sediment P-release was measured in bottom sediment whereas extracellular enzymes (EE; alkaline phosphatase, FDAase, protease, and β-D-glucosidase) and CO₂ emission were measured at land-water interface to evaluate changes in water quality and ecosystem functions. The data comparisons were made with preceding year (2019) measurements. Sediment-P release and the concentrations of carbon, nutrients, and heavy metals declined significantly (p<0.05) in 2020 compared to those recorded in 2019. Unlike the preceding year, we did not observe benthic hypoxia (DO <2.0 mg L^-1) in 2020 even at the most polluted site. The EE activities, which declined sharply in the year 2019, showed improvement during the 2020. The stability coefficient and correlative evidences also showed a large improvement in the water quality and functional variables. Positive changes in functional attributes indicated a transient recovery when human perturbations withdrawn. The study suggests that timing the ecosystem recovery windows, as observed here, may help taking management decision to design mitigation actions for rivers to recover from anthropogenic perturbations.

Multitemporal Total Coliforms and Escherichia coli Analysis in the Middle Bogotá River Basin, 2007–2019

Currently, one of the main environmental problems that need to be addressed is the pollution inflicted upon different ecosystems by anthropic activities. One example of this problem can be seen in the Bogotá River, a major river in the Cundinamarca department of Columbia and the main water source supplying the Bogotá savannah, which reaches the Colombian capital city. The Bogotá River is highly affected by effluents and wastewater of domestic and industrial origin, among others. These pollutants are generated and accumulated throughout the entire basin, without ever receiving any type of treatment. The pollution levels to which the Bogotá River is subjected can be determined with the calculation of environmental indices, including microbiological contamination indicators such as total coliforms (TC) and fecal coliforms, which include Escherichia coli, Enterobacter, Klebsiella, Serratia, Edwardsiella, and Citrobacter bacteria, living as independent saprophytes. This paper assesses the quality of the water in the Bogotá River, using microbiological indicators and data provided by the Regional Autonomous Corporation (CAR) of Cundinamarca to assess water samples, extracted based on the climatic bimodality exhibited in the basin in dry and wet seasons. The scope of this study was limited to the 35 monitoring Regional Autonomous Corporation of Cundinamarca (CAR) stations located throughout the middle basin. For these purposes, a multitemporal analysis of the TC and Escherichia coli variables was conducted for the 2007–2019 period, which evidenced the contamination levels in this section of the water body. In broad terms, the current state of the middle section of the Bogotá River basin is unacceptable, due to the different activities occurring within its riparian buffer zone, such as uncontrolled domestic, industrial, and/or commercial wastewater discharges. To optimize water treatability, the continuous improvement of existing treatment plants is expected, as well as the implementation of new sustainable treatment alternatives aimed at improving water quality.

Integrating resilience with functional ecosystem measures: A novel paradigm for management decisions under multiple-stressor interplay in freshwater ecosystems

Moving beyond monitoring the state of water quality to understanding how the sensitive ecosystems "respond" to complex interplay of climatic and anthropogenic perturbations, and eventually the mechanisms that underpin alterations leading to transitional shifts is crucial for managing freshwater resources. The multiple disturbance dynamics-a single disturbance as opposed to multiple disturbances for recovery and other atrocities-alter aquatic ecosystem in multiple ways, yet the global models lack representation of key processes and feedbacks, impeding potential management decisions. Here, the procedure we have embarked for what is known about the biogeochemical and ecological functions in freshwaters in context of ecosystem resilience, feedbacks, stressors synergies, and compensatory dynamics, is highly relevant for process-based ecosystem models and for developing a novel paradigm toward potential management decisions. This review advocates the need for a more aggressive approach with improved understanding of changes in key ecosystem processes and mechanistic links thereof, regulating resilience and compensatory dynamics concordant with climate and anthropogenic perturbations across a wide range of spatio-temporal scales. This has relevance contexting climate change and anthropogenic pressures for developing proactive and adaptive management strategies for safeguarding freshwater resources and services they provide.

An integrated model to predict and prevent hypoxia in floodplain-river systems

Hypoxia can occur following rewetting of floodplains and cause severe impacts on aquatic biota and biogeochemical processes. The likelihood of such events is influenced by a number of factors including temperature, the mass of plant litter on the floodplain (which is influenced by the duration between inundation events), the volume of water available for dilution of oxygen-demanding dissolved organic matter, and the exchange of water to dilute and disperse that material. Using constructed infrastructure to generate managed inundations on floodplains increases the likelihood of hypoxic "blackwater" events relative to unregulated floods, as larger areas of floodplain are inundated at lower flow rates. A model (the "DODOC plugin") was developed for the Source hydrological modelling software to inform risk mitigation strategies for these managed inundation events. This development enables the interaction between complex hydrology and floodplain inundation on the resulting release of dissolved organic carbon (DOC), and subsequent consumption of dissolved oxygen (DO), to be represented. Key functionality of the plugin includes the ability to represent (i) spatial variability in organic litter build up and degradation, (ii) DOC leaching from litter when inundated, (iii) DO consumption arising from microbial decomposition of the DOC, and (iv) reaeration processes from autotrophic productivity and turbulence as water passes over water level regulating structures. The model is configurable on both river channels (links) and floodplains (storages) to represent changes in DO from both natural and managed inundation events at the scale of an individual floodplain up to multiple floodplains and river reaches. The plugin was parameterised to successfully simulate DOC (R² = 0.84-0.93) and DO (R² = 0.74-0.92) along an approx. 100 km study reach of the River Murray in South Australia, once the different behaviour of the labile and refractory components of the DOC was represented in the model. A number of hypothetical operational scenarios were tested using the model to demonstrate parameter sensitivity and to inform planning of managed inundations. The development of the DODOC plugin demonstrates that complex water quality processes can be integrated into the Source (or other) hydrological software, to represent cumulative implications of floodplain inundation events and to minimise the risk of hypoxia.