A novel comprehensive risk assessment method for sudden water accidents in the Middle Route of the South-North Water Transfer Project (China)

Influences of lower pH on phytoplankton growth in alkaline lakes after water transfer: Insights from a coupled hydrodynamic-algal ecological model and experimental analysis

Alkaline lakes with high pH and unique ecological communities often face water-level drawdown and ecological degradation problems due to climatic and hydrologic factors. Water transfer is becoming a popular method for solving these problems. However, a high pH is often considered the key to maintaining the stability of alkaliphilic algal communities, and a lower pH induced by water transfer from a neutral-pH river may threaten ecosystems in alkaline lakes. To explore the response characteristics of phytoplankton in alkaline lakes to pH changes, we conducted cultivation experiments on one species of dominant Cyanobacteria and one species of dominant Chlorophyta from alkaline lakes under different pH conditions. Subsequently, we constructed a coupled hydrodynamic and algal mathematical model considering the effect of pH to predict the dynamic changes in phytoplankton in a typical alkaline lake under water-transfer conditions. Both species are basophilic, and pH has a "low-inhibition and high-promotion" effect on their growth. A lower pH is detrimental to cyanobacterial growth and competitiveness, which may cause Cyanobacteria to lose their dominance in weakly alkaline environments with a pH < 8.5; additionally, water transfer causes a decrease in the total biomass and proportion of Cyanobacteria in Lake Chenghai, with decreases induced by pH changes accounting for 13.4% and 70.1%, respectively. The decrease in pH is the main reason for the decrease in dominance of Cyanobacteria after water transfer. These results provide a basic summary of the effects of pH changes on the algal growth in alkaline lakes and are a useful for formulating ecological water-transfer strategies for alkaline lakes.

Failure probability analysis of high fill levee considering multiple uncertainties and correlated failure modes

Such complex causative factors in current failure probability models are represented by simply random uncertainty and completely independent or correlation of failure modes, which can often limit the model utility. In this study, we developed a methodology to construct failure probability models for high fill levees, incorporating the identification of uncertainties and an analysis of failure modes. Based on quantification of stochastic-grey-fuzzy uncertainties, probability analysis involved with overtopping, instability and seepage failure modes was implemented combined with probability and non-probability methods. Given that the interaction among failure modes typically exhibits nonlinear behavior, rather than linear correlation or complete independence, a simple methodology for the binary Copula function was established and implemented in MATLAB. This methodology was applied to the high fill segments of a long-distance water transfer project characterized by high population density. It shows that the failure probability of a single failure mode is overestimated when uncertainties are not considered, because of the randomness and fuzziness of some parameters and the greyness of information. Meanwhile, it is found that the magnitude of failure probability related to levee breach is overestimated without respect to failure modes correlation, especially when the probabilities of seepage and instability are both significant and closely aligned.

Assessment of the spatiotemporal water quality variations in the Middle Route of China's South-to-North Water Diversion Project by multivariate analysis

As an important drinking water source for North China, the Middle Route of China's South-to-North Water Diversion Project (MRP) must provide high-quality water to maintain the health and safety of more than 60 million people. However, different water transfer operation modes may affect the water quality status, and the spatiotemporal characteristics of water quality in the MRP, with high water transfer volumes, remain poorly understood. In this study, the differences in water quality in the MRP between the initial stage (Nov. 2015 to Oct. 2017, low transfer volumes) and the current stage (Nov. 2017 to Oct. 2020, high transfer volumes) were compared, and the spatiotemporal water quality variations in the current stage were evaluated using multivariate statistical methods. For this purpose, approximately 12,528 observations, including the datasets of 12 water quality parameters collected from 29 monitoring sites, were used. The results showed that the water quality status improved significantly during the current stage. Based on principal component analysis (PCA), physical parameters (natural), nutrients, organic matter and microbes (anthropogenic), and heavy metals (natural and anthropogenic) were the key factors influencing water quality variations. Based on hierarchical cluster analysis, 12 months were classified into two groups: the high-flow period (HFP, Jun.-Oct.) and the low-flow period (LFP, Nov.-May). Additionally, 29 sampling sites were grouped into three sections: the Henan section (HN; S1-S16), Hebei section (HB; S17-S24), and Tianjin-Beijing section (TB; S25-S29). From the perspective of water quality regulation, the total nitrogen concentration and permanganate index in the HB and TB sections of the MRP should be considered throughout the year, and the faecal coliform concentrations in these two sections should also be considered during the HFP. The results of this study could be helpful for local administrations to understand and control pollution and better protect the quality of water in the MRP.

Modelling of pH changes in alkaline lakes with water transfer from a neutral river

While water transfer from rivers to alkaline lakes has been proposed to solve lake water level drawdown and ecological degradation problems, its effectiveness for achieving ecological goals is often questionable. A sudden pH decline in alkaline lakes due to water transfer is considered likely to harm the lake ecology. However, it remains unclear to what extent water transfer affects alkaline lake pH. Thus, a three-dimensional numerical model coupling a pH calculation method considering the carbonate balance with the MIKE3 hydrodynamic model was developed to predict pH changes in an alkaline lake. Laboratory and field measurements verified the model reliability. The model accurately simulated the mixed-water pH during water transfer, with a root mean square error of 0.03-0.07 and a coefficient of determination of 0.894-0.998. The model was then applied to predict the pH response to water transfer in Lake Chenghai. The results showed that the pH response to water transfer demonstrated spatial and temporal variability, and a low-pH diffusion zone (pH ≤ 9) formed in the northern parts of the lake during annual water transfer; the effects of water transfer on the pH in the lake were cumulative over time, and the average pH in Lake Chenghai after five years decreased by 0.2 units; strong wind and low inflow could effectively reduce the low-pH diffusion area; and daily thermal stratification of the plateau region threatened the low-pH diffusion area control in Lake Chenghai. Our results provide a new reference for formulating ecological water transfer strategies for alkaline lakes and similar water bodies.

Regional water pollution management pathways and effects under strengthened policy constraints: the case of Tianjin, China

In recent years, China has attached great importance to pollution control, and national and many provinces have introduced water pollution management policies in the hope that improvements can be made. However, there is currently a lack of objective and adequate assessment of the effectiveness of water pollution management (WPM) at the regional level, especially a lack of in-depth research on the causes of improvement, key measures, and pathways of action. This paper constructs an evaluation index system based on the driver, pressure, state, impact and response (DPSIR) model and evaluates the WPM performance of Tianjin based on the five aspects comprising the DPSIR model. The results show that WPM performance in Tianjin has been commendable, improving from 76.15 points out of 100 in 2014 to 90.93 points out of 100 in 2018. The score increased more rapidly from 2016 to 2018 after the regional policy was implemented. The main reason for this encouraging phenomenon is the significant improvement in water quality. From 2016 to 2020, the closure of high pollution industrial enterprises and the regulatory management of aquaculture have significantly reduced pollutant emissions. At the same time, under the constraints of the river chief system, pollutant discharge permits, discharge standards, ecological compensation agreements on water pollution and other policies in Tianjin, the effect of pollution source control is obvious, with improved water quality and high public satisfaction.

Safety assessment of drinking water sources along Yangtze River using vulnerability and risk analysis

Recently, the safety of drinking water sources along Yangtze River Basin is received much attention. But few works have carried out large-scale and all-round safety assessment of drinking water sources on the main stream of the whole Yangtze River Basin. In this work, 97 drinking water sources in 8 provinces of the main stream of the Yangtze River were selected as the objects to clarify the spatial distribution of the safety risk levels of drinking water sources in the whole basin and analyze the causes of drinking water source risks. The results showed that 13.4%, 55.7%, 25.8%, 5.1%, and 0% of the 97 drinking water sources were classified as low, moderate, considerate, high, and very high respectively, according to the safety risk level. This indicated that the safety risk of drinking water sources in the mainstream of Yangtze River is generally low, but there are also a number of high safety risk drinking water sources. And the safety risk degree of the lower and upper reaches in the mainstream of Yangtze River is generally higher than that of the middle reaches. The current situation of drinking water sources along the mainstream of Yangtze River could be attributed to the superposition of human activities and natural background factors. This study could contribute to the government's targeted management and control of safety risk sources for drinking water sources along the Yangtze River Basin.

Conceptual model to analyze the effects caused by technological disaster on the physical-chemical state of the lower Doce River waters, Brazil

Research has shown the effort to develop conceptual models that relate anthropic stressors to changes in aquatic environment state. Several of these models come from the structure Drivers, Pressures, State, Impact and Response (DPSIR), which has been used since the 1990s. However, there is a lack of conceptual models that consider in its structure the connection between the damages caused in the aquatic environment and technological disasters. This research develops a general conceptual model based on the DPSIR structure incorporating technological disasters. Based on the general conceptual model guidelines and the methodological procedure associated with it, a model was developed to assess the Lower Doce River waters' state, by considering Fundão's iron-ore dam failure scenario, which took place in November 2015, in the municipality of Mariana, state of Minas Gerais, Brazil. The relevant aspects of this adaptation of the DPSIR structure were: I) it considers the combined effect of drivers and pressures that already existed in the study area with those originated from the technological disaster; and II) the causal relationships among elements of the model were explicited through a systemic conceptual map, allowing a more holistic and integrated view of the problem. The application of the conceptual model to Doce River's scenario before the disaster allowed us to verify that a set of environmental pressures was already acting in a way to stress it, making the river vulnerable. For the post-disaster scenario, it was possible to determine that the already existing vulnerability condition, caused by urbanization, agriculture¹ and mining, had been intensified by adding new pressures due to the tailings dam failure.

Identification of source information for sudden hazardous chemical leakage accidents in surface water on the basis of particle swarm optimisation, differential evolution and Metropolis-Hastings sampling

A quick and accurate identification of source information on sudden hazardous chemical leakage accident is crucial for early accident warning and emergency response. This study firstly regards source identification problem of sudden hazardous chemical leakage accidents as an inverse problem and presents a source identification model based on the Bayesian framework. Secondly, a new identification method is designed on the basis of particle swarm optimisation (PSO), differential evolution (DE) and the Metropolis-Hastings (M-H) sampling method. Lastly, the designed method, i.e. PSO-DE-MH, is verified by an outdoor experiment analyses in a section of the South-North Water Transfer Project. Results show that the number of iterations, the average absolute error, the average relative error and the average standard deviations of the identification results obtained by PSO-DE-MH are less than those of PSO-DE and DE-MH. Moreover, the relative error and the sampling relative error of the identification results under five different measurement errors (MEs) (σ = 0.01, 0.05, 0.1, 0.15, 0.2) are less than 9.5% and 0.2%, respectively. The designed method is effective even when the standard deviation of the ME increases to 0.2. Therefore, the designed method can effectively and accurately obtain the source information of sudden hazardous chemical leakage accidents. This study provides a new idea and method to solve the difficult problems of emergency management.

Rapid prediction of pollutants behaviours under complicated gate control for the middle route of South-to-North water transfer project

Many crossing hydraulic structures have been constructed in the Middle Route of the South-to-North Water Transfer Project (MR-SNWTP), which increases the likelihood of sudden water pollution accidents. After an accident, managers need to assess the extent of pollution under conditions of gate control, and it's necessary to make suitable emergency control decision under this assessment. Therefore, we researched the rapid prediction of pollutants behaviours under conditions of complicated gate control in this paper, by presenting three characteristic parameters of pollutant migration and diffusion. According to the simulation results, the influencing reasons and rapid prediction formulas for the characteristic parameters (peak transport distance, pollutant longitudinal length and peak concentration) after a sudden water-soluble pollution accident are proposed. Also, the approval results show that the formulas can accurately predict the location and range of the pollutant after the emergency accident. Finally, the rapid prediction formulas for the characteristic parameters played a fundamental role in the decisions involved in the Emergency Environmental Decision Support System is proved by two application examples.

Selection of water source for water transfer based on algal growth potential to prevent algal blooms

Water transfer is becoming a popular method for solving the problems of water quality deterioration and water level drawdown in lakes. However, the principle of choosing water sources for water transfer projects has mainly been based on the effects on water quality, which neglects the influence in the variation of phytoplankton community and the risk of algal blooms. In this study, algal growth potential (AGP) test was applied to predict changes in the phytoplankton community caused by water transfer projects. The feasibility of proposed water transfer sources (Baqing River and Jinsha River) was assessed through the changes in both water quality and phytoplankton community in Chenghai Lake, Southwest China. The results showed that the concentration of total nitrogen (TN) and total phosphorus (TP) in Chenghai Lake could be decreased to 0.52 mg/L and 0.02 mg/L respectively with the simulated water transfer source of Jinsha River. The algal cell density could be reduced by 60%, and the phytoplankton community would become relatively stable with the Jinsha River water transfer project, and the dominant species of Anabaena cylindrica evolved into Anabaenopsis arnoldii due to the species competition. However, the risk of algal blooms would be increased after the Baqing River water transfer project even with the improved water quality. Algae gained faster proliferation with the same dominant species in water transfer source. Therefore, water transfer projects should be assessed from not only the variation of water quality but also the risk of algal blooms.

An inverted U-shaped curve relating farmland vulnerability to biological disasters: Implications for sustainable intensification in China

Sustainable farmland intensification is necessary in order to harmonize relationships between food security, socioeconomic development, and ecological civilization. However, the degradation of farmland sustainability because of biological disasters represents a major challenge if we are to achieve this intensification. Our understanding of farmland vulnerability to biological disasters (FVBD) remains relatively rudimentary and subjective, limiting its effectiveness as a tool for farmland sustainability analysis. Limited research has also been carried out on FVBD changes taking into account human decisions on farmland use. The aim of this study is to achieve a novel understanding of FVBD change and its implications for sustainable intensification using evidence from Chinese farmland use. A theoretical framework based on an inverted U-shaped curve that depicts FVBD as well as an assessment framework for FVBD were established using induced substitution of agricultural production. Across China and considering 15 provincial districts with scarce farmland, the relationship between FVBD and socio-economic development was identified as consistent with an inverted U-shaped curve at both national and provincial levels. FVBD values in 2016 across Southern China, on the Huang-Huai-Hai Plain, and on the middle-lower Yangtze Plain were 45.44, 40.58, and 37.22, respectively. These values also decreased in provinces on the middle-lower Yangtze Plain between 1995 and 2016, but increased markedly across provinces in Southern China and on the Huang-Huai-Hai Plain. Contributions to FVBD changes during stages of growth and decline were also analyzed between 1995 and 2016. An inverted U-shaped curve was effective in investigating the responses of farmland sustainability to a range of alternative future socioeconomic development pathways. Thus, in the Chinese settings, a typical country with scarce farmland, policies on FVBD control are essential if we are to promote sustainable farmland intensification. The findings of this work are important and present us with a new way to understand FVBD from a human perspective.