Urban Water Environment Research Articles

Unraveling the synergistic mechanisms of coagulation combined with oxidation for the treatment of sewer overflow: The interaction between iron species and NaClO

During wet weather, sewer overflow pollution can pose a serious threat to surface water. In order to reduce the impact of overflow discharge on receiving waters, ferric chloride (Fe(Ⅲ))/potassium ferrate (Fe(Ⅵ))/polyacrylamide (PAM) coagulation (Fe(Ⅲ)/Fe(Ⅵ)/PAM) combined with sodium hypochlorite (NaClO) oxidation was proposed. Different combinations were constructed, including pre-oxidation coagulation (NaClO-Fe(Ⅲ)/Fe(Ⅵ)/PAM), pre-coagulation oxidation (Fe(Ⅲ)/Fe(Ⅵ)/PAM-NaClO), and synchronous coagulation oxidation (NaClO+Fe(Ⅲ)/Fe(Ⅵ)/PAM). The combined processes achieved efficient removal of conventional contaminants, and the produced byproducts were controlled, especially in the NaClO-Fe(Ⅲ)/Fe(Ⅵ)/PAM. The obvious discrepancy in the sulfamethoxazole (SMX) removal was observed in different processes. NaClO affected the distribution of hydrolyzed iron species, and the proportion of active iron in the NaClO-Fe(Ⅲ)/Fe(Ⅵ)/PAM significantly increased. More complexation sites were generated in the NaClO-Fe(Ⅲ)/Fe(Ⅵ)/PAM, which can complex with the coagulant and then effectively transfer to the flocs. The composition of the flocs further confirmed the differences in coagulation characteristics. The generated·OH played a crucial role in SMX removal in the NaClO+Fe(Ⅲ)/Fe(Ⅵ)/PAM, and ClO·was responsible for partial removal of ammonia nitrogen (NH4+-N). The contribution of high-valent iron species was confirmed, and the introduction of NaClO promoted the generation of iron species. This study may provide an ideal for overflow treatment to improve the urban water environment.

Novel drainage pipeline breakages detection based on MEMS inertial sensor: From mechanism to application

Urban water environment pollution is a global concern, in developing countries, sewage infiltration resulting from urban drainage pipelines breakage is an essential element in the urban groundwater pollution and the recurrence of black odor water bodies, it is crucial to accurately and efficiently detection and localisation of urban drainage pipelines breakage to protect the urban water resources. In this paper, a device for detecting defects in drainage pipelines was developed and assembled using microelectromechanical systems (MEMS) inertial sensors as the core components, and the improved cumulative sum (CUSUM) model was used for anomalous detection of the pitch angle of the device's movement along the course of the pipeline as a method of detecting pipeline breakage. In the laboratory simulation of drainage pipeline tests, the CUSUM peaks (0.709, 1.102, 3.038, 7.990) for the case of external water infiltration rates into the pipeline at the point of pipe breakage (2.9%, 4.6%, 5.8%, 9.2%), and for the cases of sewer exfiltration rates in the pipeline of 4.2% and 6.4% (0.760, 1.382). CFD simulations of the water flow in the laboratory pipeline show a high degree of overlap between the trend of the water surface near the point of breakage and the anomalous fluctuations in the pitch angle of the device motion in the laboratory tests. Finally, the authors tested the device on municipal drains in the city of A. The results demonstrated the reliability and high accuracy of the device. The device enables to improve the ecological quality of urban water environment by accelerating the rate of defect detection in urban drainage pipelines and reducing the detection expenses.

Coupling coordination relationship between urbanization and water environment in China

The intensification of urbanization (U_UR) in China exacerbates the pressure on the water environment (U_WE). The U_UR and U_WE exhibit incredibly intricate and intertwined interactions. The coordination between U_UR and U_WE is crucial for the sustainable development of cities. Hence, a comprehensive evaluation index system was developed to analyze the coupling coordination relationship and spatial effects between the U_UR and U_WE in China, based on the entropy weight method, the coupling coordination degree (CCD) model, and the spatial autocorrelation analysis method. The data was collected from the China Statistical Yearbook (2013–2023), the China Urban Construction Statistical Yearbook (2012–2022), and provincial statistical yearbooks. The results indicated that the overall trend of CCD in China showed an upward trajectory, increasing from 0.44 to 0.55 in 2012 to 0.56–0.66 in 2022. The average values of CCD for 31 provinces rose from 0.51 in 2012 to 0.61 in 2022, with a growth rate of 19.61%. The regional development level of CCD exhibited spatial heterogeneity, characterized by East > North > South > Northeast > Northwest > Southwest. However, the development of the U_WE subsystem lagged behind the U_UR subsystem, and there was a significant spatial imbalance in the CCD between the U_UR subsystem and U_WE subsystem in China from 2012 to 2022. The High-High Cluster areas of CCD were concentrated in the eastern part of China, while the Low-Low Cluster areas were concentrated in the western part. The research can provide theoretical and technical support to promote the sustainability of urban development and water environment protection.

Identifying the fate of dissolved organic matter in wastewater treatment plant effluent-dominated urban river based on fluorescence fingerprinting and flux budget approach

Effluent organic matter from wastewater treatment plants (WWTPs) is an important source of dissolved organic matter (DOM) in urban rivers worldwide and is an important water quality factor. Identifying the fate of DOM in urban river is crucial for water quality management. To address this concern, a fluorescent flux budget approach was conducted to probe the fate of DOM in WWTP effluent-dominated urban river, in combination with field measurement and fluorescence fingerprinting. An urban river receiving two WWTP effluents in Hefei City, China was chosen as the study site, where longitudinal measurements of river hydrology and water quality were performed. The fluorescence fingerprinting revealed the presence of two humic-like components (C1, C4), one fulvic-like component (C2) and one protein-like component (C3) in this investigated river, among which C2 and C4 were indicative of anthropogenic influences, closely associated with treated effluents. For each fluorescent component, the WWTP effluent contributed over 80 % of the total fluorescent dissolved organic matter (FDOM) input in this river. Using the developed FDOM flux budget model, it was found that the C1 and C3 were almost conserved within the waterbody, while the C2 and C4 experienced losses due to biogeochemical reactions. The decay rates of C2 and C4 were estimated to be 0.109–0.174 d−1 and 0.096–0.320 d−1, respectively. Spatial heterogeneity of decay rates for C2 and C4 were associated with the varied chemistries of the lateral input sources including two treated effluents and one tributary flow. Our study highlights that after treated effluent is released into the receiving waterbody, the FDOM would undergo loss from the waters particularly for anthropogenic fulvic-like substance C2 and humic-like substance C4. Additionally, the quantified FDOM decay rate in actual urban water environment provides insights for river water quality management, especially when using DOM as the surrogate indicator of organic pollutants.

Sustainable Stormwater Management for Different Types of Water-Scarce Cities: Environmental Policy Effect of Sponge City Projects in China

With high-speed urbanization, ecological space is seriously shrinking, and lagging drainage facilities contradict the ecological needs of citizens. In particular, water-scarce cities are faced with frequent stormwater disasters, such as excessive accumulation of rainwater, peak runoff and water pollution, which threaten the safety of the urban water ecological environment. This paper combined the actual construction content of the sponge city project with a whole process policy evaluation framework to examine whether the projects solve these problems and to find different approaches to the results. Utilizing entropy fuzzy comprehensive evaluation provides a systematic standard for the evaluation system. The research shows that the sponge city project can achieve a good governance effect, including constructing a suitable scheme for urban hydrological characteristics, effectively improving the rainwater treatment level of different types of water-scarce cities, and alleviating the ecological contradiction of urban water environment. The stages of policy formulation, policy implementation and policy results achieve a good degree of completion. On one hand, sponge city projects transform the infrastructure at key locations, aiming at improving the rainwater interception capacity of the streets; on the other hand, restoring original natural waters improves the capacity of water conservation and forms a sustainable ecosystem between the city and nature.

Intelligent optimal layout of drainage pipe network monitoring points based on information entropy theory

The rapid expansion of urban drainage pipe networks, driven by economic development, poses significant challenges for efficient monitoring and management. The complexity and scale of these networks make it difficult to effectively monitor and manage the discharge of urban domestic sewage, rainwater, and industrial effluents, leading to illegal discharges, leakage, environmental pollution, and economic losses. Efficient management relies on a rational layout of drainage pipe network monitoring points. However, existing research on optimal monitoring point layout is limited, primarily relying on manual analysis and fuzzy clustering methods, which are prone to human bias and ineffective monitoring data. To address these limitations, this study proposes a coupled model approach for the automatic optimization of monitoring point placement in drainage pipe networks. The proposed model integrates the information entropy index, Bayesian reasoning, the Monte Carlo method, and the stormwater management model (SWMM) to optimize monitoring point placement objectively and measurably. The information entropy algorithm is utilized to quantify the uncertainty and complexity of the drainage pipe network, facilitating the identification of optimal monitoring point locations. Bayesian reasoning is employed to update probabilities based on observed data, while the Monte Carlo method generates probabilistic distributions for uncertain parameters. The SWMM is utilized to simulate stormwater runoff and pollutant transport within the drainage pipe network. Results indicate that (1) the relative mean error of the parameter inversion simulation results of the pollution source tracking model is linearly fitted with the information entropy. The calculation shows that there is a good positive linear correlation between them, which verifies the feasibility of the information entropy algorithm in the field of monitoring node optimization; (2) the information entropy algorithm can be well applied to the optimal layout of a single monitoring node and multiple monitoring nodes, and it can correspond well to the inversion results of the tracking model parameters; (3) the constructed monitoring point optimization model can well realize the optimal layout of monitoring points of a drainage pipe network. Finally, the pollution source tracking model is used to verify the effectiveness of the optimal layout of monitoring points, and the whole process has less human participation and a high degree of automation. The automated monitoring point optimization layout model proposed in this study has been successfully applied in practical cases, significantly improving the efficiency of urban drainage network monitoring and reducing the degree of manual participation, which has important practical significance for improving the level of urban water environment management.

Analysis of rainwater utilization technology and current situation in the roof garden

The urban water environment has been deteriorating over the last decade due to land development and climate change, increasing the pressure on urban stormwater drainage systems. With economic development, the value of buildings has also been challenged at a higher level. Roof garden, as a new form of roof treatment, can effectively increase the urban greening area and compensate for the ecological and water environments that have been damaged by building development and utilization. This paper analyzes the advancement of roof garden by comparing it with the traditional sloped roof. The analysis finds that roof gardens can store water and control drainage, and have significant advantages in reducing rainwater discharge, reducing building water demand, and improving the urban water cycle. Roof gardens not only have the ability to utilize rainwater efficiently, but also come with a series of economic, ecological, and social benefits, such as improving the urban heat island effect, saving the amount of water demanded by buildings, and energy consumption. By analyzing domestic and international cases of roof gardens, it is verified that roof gardens are designed as a combination of utility and aesthetics.

Optimization of LID Strategies for Urban CSO Reduction and Cost Efficiency: A Beijing Case Study

Combined sewer overflow (CSO) can lead to serious urban water environment pollution and health risks to residents. Low Impact Development (LID) facilities are one of the important measures to alleviate CSO and have been widely applied. The rational selection of LID facility types, locations, and scales is the most important task, which can effectively improve resource utilization efficiency. Based on the NSGA-II multi-objective optimization algorithm and coupled with the SWMM sewer network hydraulic model, this study takes the combined sewer overflows and the construction cost of LID facilities as optimization objectives and optimizes the types and scales of LID layout in the study area, including eight different return periods. By using the Pareto frontier and visualizing the results of the model, the effects of different rainfall return periods on the CSO control and investment cost of LID layout schemes are compared. The results show the following: (1) the optimization model can demonstrate the relationship between CSO control volume and LID construction cost under different LID layout schemes through the Pareto frontier, showing three different trends, indicating that the relationship between overflow volume and investment cost is nonlinear; (2) with the increase in rainfall intensity, higher requirements are proposed for LID schemes to meet CSO control targets, leading to a decrease in the number of Pareto frontier solution sets. Under larger rainfall intensities, it is difficult to achieve the same overflow control effect by increasing the scale of LID construction. Therefore, considering constraining the LID construction cost between RMB 5.3 and 5.38 million is helpful to determine the most suitable solution; (3) in the optimal layout schemes under different return periods, 87.3% of the locations where LID is deployed have similar scales. Based on these locations with a relatively large proportion of deployment, it can be determined that special attention should be paid to spatial positions in LID planning and construction. This study provides valuable insights for solving combined sewer overflow problems and optimizing urban drainage management and provides guidance for future planning and decision-making processes.

Progress in Sponge City Research in Yunnan Province

As urbanization accelerates, the challenges faced by traditional urban drainage systems are becoming increasingly prominent. The concept of the "sponge city" has emerged as a new urban development paradigm, playing an increasingly important role in sustainable urban development, alleviating water disasters, and improving the urban water environment. This paper takes Yunnan Province as the research subject and delves into the progress of sponge city research in the region, as well as conducting a comprehensive assessment of the environmental conditions for implementing sponge city construction in Yunnan. The unique geographical and climatic characteristics of Yunnan Province make it an ideal area for implementing the sponge city concept. The paper not only examines in detail the pilot sponge city projects that have been initiated in the province, analyzing the implementation effects of these projects, but also proposes strategies and suggestions for future development based on these case studies. In terms of research methodology, this paper employs a variety of research methods, including literature review, field investigation, and data analysis, to ensure the scientific rigor and comprehensiveness of the research findings. The results show that the sponge city construction in Yunnan Province has achieved certain effects, such as significant progress in urban flood control, rational utilization of water resources, and improvement of the ecological environment. However, the study also identified some problems and challenges, such as gaps between the implementation of some projects and the expected outcomes, as well as difficulties in technology, funding, and policy encountered during the promotion process. Based on these findings, the paper provides targeted suggestions from multiple perspectives, including technological innovation, funding, and policy support, aiming to further promote the development of sponge city construction in Yunnan Province and nationwide. The study emphasizes that Yunnan Province should leverage its unique advantages and formulate appropriate sponge city construction standards and technical guidelines that align with local conditions. It also recommends enhancing interdisciplinary and interdepartmental cooperation to foster a deeper integration of scientific research with urban planning practices, maximizing the benefits of sponge city construction. Overall, this paper's research not only provides valuable experience and insights for the construction of sponge cities in Yunnan Province and other regions of China but also makes an important contribution to the theoretical research and practical exploration of sponge cities. Through an in-depth analysis and systematic study of sponge city construction in Yunnan Province, the paper showcases the tremendous potential and challenges faced by the sponge city concept in specific Chinese practices, holding significant theoretical and practical significance for guiding future urban development planning and management.

Study on financial cost evaluation of urban water environment management and pollution prevention and control

Abstract Nowadays, water pollution has become a major factor restricting social development. To address this, the government has issued a series of policy documents to control water environmental pollution and achieved certain results. However, on the whole, the prevention and control of the pollution of water environments requires a large amount of capital investment, but the corresponding results and benefits are not significant. Hence, this paper takes Shanghai, Nanjing, Hangzhou, and Hefei as examples to study the financial cost-effectiveness of the governance of urban water environments from the two dimensions of time and space. It is concluded that the cost of water environmental treatment has a negative effect on the comprehensive benefit of environmental treatment in the region in the short term and a positive effect in the long term, which indicates that water environmental pollution treatment is work that needs to be adhered to for a long time, and long-term planning is also needed for cost input. On this basis, strategies to improve the cost efficiency of water pollution treatment are presented.

Retracted: Comprehensive Treatment of Urban Landscape Water Environment Based on Aquatic Plants Purification and Restoration

Retracted: Comprehensive Treatment of Urban Landscape Water Environment Based on Aquatic Plants Purification and Restoration

Multi-source data-driven estimation of maximum carrying capacity of urban water storage facilities under extreme conditions

Abstract With the deepening of urbanization and rapid economic development, urban water storage systems face increasing challenges. In this paper, the behavioral mechanism of urban water storage system is deeply analyzed by using the system dynamics method, and a system dynamics model of the carrying capacity of urban water storage equipment is established. Further, based on the gray correlation theory, a prediction model of the carrying capacity of urban water storage equipment is constructed and accuracy is examined. The study estimated the maximum carrying capacity of urban water storage equipment through performance analysis. The results show that the relative error of the fitted data is deficient, indicating that the model is highly accurate. The empirical Analysis of the carrying capacity index of the urban economy and water environment pollution is high. The prediction results for 2030 show that the carrying capacity of water storage facilities in City M is 0.22, which is already slightly overloaded and faces a severe risk of overloading. The model proposed in this study can not only accurately predict the trend of the carrying capacity of water storage equipment, but also effectively predict the overloading problem of urban water storage equipment, which provides a scientific basis for the optimization and improvement of urban water storage equipment, and an essential support for the formulation of the city’s sustainable development strategy.

Probing the microbiome in stormwater pipeline sediments: Co-occurrence patterns and novel functionalities

Stormwater pipeline is an essential pathway to transfer stormwater runoff into nearby receiving water bodies. Understanding the composition, co-occurrence patterns, and function of the microbial communities in stormwater pipeline sediments can help to provide management and control strategies for stormwater runoff pollution to safeguard water safety and ecological health of the urban water environment. This study employs 16S rRNA gene amplicon sequencing to probe the microbial communities in stormwater pipeline sediments of a highly urbanized area in Guangzhou, China. Results show that the sediment bacterial community is rich in Listeria, Prevotella, Stenotrophomonas, and Pseudomonas, which all pertain to pathogens. Methanogens (Methanobacterium, Methanosaeta, Methanosarcina, and Methanobrevibacter) and ammonia-oxidizing archaea (Ca. Nitrosopelagicus, Ca. Nitrososphaera, and Ca. Nitrosotenuis) dominated the archaeal community in stormwater pipeline sediments. These microbial functions are further validated by the function prediction of the overall microbial community. The co-occurrence network and microbe-environment correlation analyses suggest that particulate C-N-P components play a more crucial role, in comparison to dissolved ones in regulating the sediment microbiome, although not all samples follow this mechanism. These findings are expected to contribute to the pollution control of stormwater runoff in stormwater pipeline systems and provide valuable guidance for improving the environmental well-being of urban water ecosystems.

Purification of runoff pollution using porous asphalt concrete incorporating zeolite powder

Purification of urban runoff is of great significance for reducing the pollution of receiving water bodies and protecting the urban water environment. Zeolite powder is added to porous asphalt mixture in this study to improve the purification effect. The influence of zeolite powder on the road performance was evaluated to determine its optimal content. The effects of air void content, suspended solid (SS) concentration, heavy metal concentration, and rainfall intensity on the purification effect were studied and the purification durability was also analyzed. The experimental results show that the addition of zeolite powder has no obvious impact on road performance of porous concrete and can increase the removal rates of SS, chemical oxygen demand (COD), Zn2+, and Pb2+ by 6.4%, 25.2%, 20.6%, and 23.5%. The removal rates of SS, COD, Zn2+, and Pb2+ increase with the increase in SS concentration while the removal rate of heavy metals decreased with the increase in heavy metal concentration. Large air void content and rainfall intensity result in a decrease in the adsorption and purification effect. The removal rate shows a rapid decline since the sixth year, especially for SS, indicating that maintenance should be conducted at this time.

Research on the Water Environment Governance of Hangzhou Bay Based on the DEA–Tobit Model

With rapid urbanization and industrialization, Hangzhou Bay faces significant pressure in water environment governance. This study, based on panel data from 2011 to 2021 in Zhejiang’s Hangzhou, Jiaxing, Shaoxing, and Ningbo, employs the Super-Efficiency DEA model to assess water environment governance performance. The Tobit model analyzes external environmental factors. Findings reveal fluctuating water governance efficiency during the study period, with inefficiencies from 2012 to 2019, followed by significant improvement from 2019 to 2021. Key factors impacting governance include urban water environment performance in Hangzhou, urban residents’ disposable income, population density, and secondary industry GDP development. A higher urban income enhances environmental awareness and governance performance, while population density and industrial GDP intensify resource use, energy consumption, and wastewater discharge, worsening governance pressures and performance. This research offers insights for enhancing water environment governance in Hangzhou Bay, aiding in the formulation of protection plans and management policies. Additionally, it provides valuable experiences for watershed governance globally.

Analyzing the response distribution of DO concentration and its environmental factors under the influence of typhoon rain events with remote sensing

Typhoon rain events are important factors that trigger changes in dissolved oxygen concentrations in watersheds. The direction of the typhoon driving force is clear, but the mode of action and mechanism are complex. Moreover, quantifying the relationship between these actions and dissolved oxygen is challenging. This study collected measured data from water quality monitoring and remote sensing during the 2022 typhoon rain events. By analyzing the changes in typhoon driving factors and dissolved oxygen (DO) concentrations in water under various typhoon storms, extended MOORA plus the full multiplicative form (MULTIMOORA), Multiscale Geographic Weighted Regression (MGWR), and spatial autocorrelation analysis were used to evaluate the response of DO concentration. Furthermore, the effects of the atmospheric environment under the influence of human activities on the response distribution of the urban water environment were analyzed. The results of the study showed that under the effect of a typhoon with higher rainfall intensity, the response of DO concentration in the water body of the river in the center of the city was better. However, the response of DO concentration in the water body at the mouth of the sea had a tendency to become worse. Under the influence of typhoon rain events with smaller intensity, the scouring effect of rainwater dominated, and the DO concentration response in the water body had a tendency to become worse. The analysis of spatial heterogeneity under the influence of human activities showed that the ranking values of DO concentration response in rivers in the city area of Zhongshan, under the influence of typhoon rain events, were positively correlated with the distribution of ozone (O3) concentration and sulfur dioxide (SO2) concentration in the eastern, central, and western parts of Zhongshan. Conversely, it was negatively correlated with the distribution of O3 concentration and SO2 concentration in the northern and southern parts of Zhongshan. Based on the research results, we constructed a technique to evaluate the response of dissolved oxygen concentration during the typhoon transit period, which can provide an indicator reference for urban managers in water environment management.

A 1D-2D dynamic bidirectional coupling model for high-resolution simulation of urban water environments based on GPU acceleration techniques

Urban water pollution is an important issue of global concern. An integrated model that can be employed to efficiently and accurately simulate the whole system of urban surfaces, underground drainage systems and river and lake water environments is an important tool for comprehensively treating urban water pollution. Therefore, we developed a 1D-2D dynamic bidirectional coupling model for high-resolution simulation of the entire urban water environment (GAST-GCSE) comprising the graphics processing unit (GPU)-accelerated surface water flow and transport (GAST) model and the storm water management model (SWMM). The SWMM and GAST model were used for coupled simulation of hydrological and hydrodynamic quantities and water quality in 1D and 2D regions, respectively. The time steps of the two models are the same. Compute Unified Device Architecture (CUDA) parallel architecture programming and advanced model algorithms were adopted to improve the simulation accuracy and efficiency of the GAST model. The two models were dynamically coupled by calling the dynamic link library (DLL) in the SWMM and adding external functions. Two test cases were considered to verify the performance of the proposed model. The results showed that the proposed model provides high simulation accuracy. Compared with the results obtained by commercial software and theoretical values, the relative errors of the water quantity and water quality simulation results were less than 3%. The whole water environment of the main urban area of Changzhi city in North China was evaluated by the GAST-GCSE model, and the simulation results were compared with monitoring data and pure SWMM simulation results. The simulation errors at three waterlogging points were less than 14%, and the Nash efficiency coefficients (NSE) of the NH4+-N concentration in the three river sections were 0.77, 0.56 and 0.64, respectively. Notably, the model needed only 4.39 h to simulate rainfall production and confluence on a 2D surface, a river flood in complex terrain and its accompanying pollutant evolution process involving 3,849,428 cells over 4 h. This study provides new insights, ideas and tools for urban water environment simulation and change mechanism study.

Constructing Urban Building Water Environment Governance through Digital Art-Enhanced Big Data Visualization

Constructing Urban Building Water Environment Governance through Digital Art-Enhanced Big Data Visualization

Significant Dynamic Disturbance of Water Environment Quality in Urban Rivers Flowing through Industrial Areas

The urban water environment is seriously affected by human activities. Rivers in highly industrialized areas, which often carry various types of industrial pollutants, such as metals and nutrients, are especially affected. In this study, the water quality of the Pi River, an industrial base that flows through Chengdu, a large city in Southwest China, was tested for one year. Heavy metal concentrations in the water, sediment, and macrobenthic and algal communities in the river were examined. The water pollution index (WPI) and trophic level index (TLI) were employed to measure the water pollution degree and eutrophication status, respectively. The Shannon—Wiener index (H’) and Margalef’s index (dM) were determined to represent the diversity and richness of macroinvertebrates. The principal component analysis (PCA) was employed to define the main heavy metal influencing factors in the Pi River. Our study showed that the eutrophication status increased with spatial change, and the eutrophication status was the most serious in the downstream reach, which was moderately eutrophic. The water body of the Pi River was seriously polluted by heavy metals, and the content of chromium (Cr) in the sediment and cadmium (Cd) in the water/sediment was far beyond the prescribed limit. In addition, we found that Cd had a serious impact on both the benthic and algal communities, and the benthic community structure was completely changed, destroying the original aquatic environment. We explored the mechanisms of the influence of Cd on aquatic fauna, and this information is of great significance for the future conservation of industrial urban rivers. In this study, the spatial–temporal variations in water quality and aquatic communities revealed the pollution status of a river flowing through industrial areas, which provided a basis for future river conservation and restoration.

Temporal and spatial changes of water quality in intensively developed urban rivers and water environment improvement: a case study of the Longgang River in Shenzhen, China.

The water quality status, spatial and temporal change processes, and water environment improvement process of urban rivers are valuable lessons to be learned under the sustainable development strategy. This study aims to reveal the water environment improvement process of intensively developed urban rivers, elucidate the spatial and temporal distribution characteristics of major pollutants, and provide recommendations for their water environment management. Water quality data from eight monitoring sites (2007-2020) in the Longgang River basin in Shenzhen, China, and comprehensive pollution index method (CPI), modified comprehensive pollution index method (M-CPI), and Pearson correlation analysis method were used for comprehensive analysis. The study shows that TN, TP, NH3-N, and COD have the greatest influence on the water quality of Longgang River, with the average pollution contribution of 53.39%, 14.49%, 11.66%, and 4.92%, in order. In 2015-2020, the water quality of the main stream of the Longgang River in the wet season was worse than that in the dry season, while the water quality of the tributaries Dingshan River and the Huangsha River in the dry season was worse than the wet season. The spatial distribution characteristics based on M-CPI indicate that the water quality of the lower reaches of Longgang River, the tributaries Dingshan River and Huangsha River, is relatively poor. In addition, the water environment improvement process of Longgang River can be divided into 3 stages: engineering stage (2007-2013, rating changed from heavily polluted to basically qualified), bottleneck stage (2013-2017, rating fluctuated slightly above and below basically qualified), and ecological restoration stage (2017-2020, rating reached qualified in 2019).