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Nitrogen (N) and phosphorus (P) concentrations are the fundamental factors affecting the nutrient status and productivity of lakes, and extrinsic inputs of N and P primarily cause eutrophication of lakes. In this essay, taking Hongze Lake as the study area, a two-dimensional hydrodynamic and water quality mathematical model of Hongze Lake was constructed, and based on calibration and verification of parameters, numerical simulation was performed on the changes in N and P concentrations in this lake after water transfer. The study results exhibited that before and after project construction, the absolute values of rates of changes in the annual average concentrations of ammonia nitrogen (NH4+-N), total phosphorus (TP), total nitrogen (TN), and permanganate index (CODMn) in Hongze Lake were all lower than 20%, which demonstrates marginal changes in the annual average concentrations. By analyzing the seasonal and spatial distribution characteristics of the concentrations of N, P and other pollutants in the lake area before and after the project operation, it is found that the main reasons that affect the water quality change in the lake area after the project operation are the newly added water transfer volume, water transfer location, and water transfer quality.

This article discusses the issues caused by traditional water resource development and utilization, as well as policy issues in China that have led to a water crisis. The article proposes a theoretical approach along with a quantitative accounting of water resources, in order to solve these problems. To improve the value accounting method for water resources, the study focuses on a unified accounting perspective of water quantity and quality, allowing for an evaluation of water use efficiency and quality. The study uses prefecture-level cities in Hubei Province as a case study and finds that the water use efficiency of these cities has constantly improved, while water quality has shown an annual improvement. Water resource assets, liabilities, and net assets have increased, but with fluctuations. The study shows differences in water resource assets, liabilities, and net assets in the eastern, central, and western regions of Hubei Province. The unified accounting perspective of water quantity and quality provides a new idea and method for the preparation of water resource balance sheets and will effectively improve the management level and efficiency of water resources.

Sustaining food production, water quality, soil retention, flood, and climate regulation in agricultural landscapes is a pressing global challenge given accelerating environmental changes. Scenarios are stories about plausible futures, and scenarios can be integrated with biophysical simulation models to explore quantitatively how the future might unfold. However, few studies have incorporated a wide range of drivers (e.g., climate, land-use, management, population, human diet) in spatially explicit, process-based models to investigate spatial-temporal dynamics and relationships of a portfolio of ecosystem services. Here, we simulated nine ecosystem services (three provisioning and six regulating services) at 220 × 220 m from 2010 to 2070 under four contrasting scenarios in the 1,345-km² Yahara Watershed (Wisconsin, USA) using Agro-IBIS, a dynamic model of terrestrial ecosystem processes, biogeochemistry, water, and energy balance. We asked (1) How does ecosystem service supply vary among alternative future scenarios? (2) Where on the landscape is the provision of ecosystem services most susceptible to future social-ecological changes? (3) Among alternative future scenarios, are relationships (i.e., trade-offs, synergies) among food production, water, and biogeochemical services consistent over time? Our results showed that food production varied substantially with future land-use choices and management, and its trade-offs with water quality and soil retention persisted under most scenarios. However, pathways to mitigate or even reverse such trade-offs through technological advances and sustainable agricultural practices were apparent. Consistent relationships among regulating services were identified across scenarios (e.g., trade-offs of freshwater supply vs. flood and climate regulation, and synergies among water quality, soil retention, and climate regulation), suggesting opportunities and challenges to sustaining these services. In particular, proactive land-use changes and management may buffer water quality against undesirable future climate changes, but changing climate may overwhelm management efforts to sustain freshwater supply and flood regulation. Spatially, changes in ecosystem services were heterogeneous across the landscape, underscoring the power of local actions and fine-scale management. Our research highlights the value of embracing spatial and temporal perspectives in managing ecosystem services and their complex interactions, and provides a system-level understanding for achieving sustainability of the food–water–climate nexus in agricultural landscapes.

The Northwest Arid Region faces the most serious resource-based water shortage in China, with challenges from engineering-, structural- and management-based water shortages. This water scarcity critically limits the socio-economic development of the region. Rational allocation of scarce water resources to achieve sustainable development of the ecological environment and economy has become a key issue in water resources research in the Northwest Arid Region. South-Central Ningxia, part of the Northwest Arid Region, exemplifies these challenges. This paper examines the urban and rural water supply projects in South-Central Ningxia. The current scheduling scheme focuses primarily on the distribution of water demand, with inadequate attention paid to water-quality requirements. Localized exceedances of water-quality standards indicate the existing scheduling scheme has failed to effectively control water-quality issues while ensuring water quantity. This study is the first to systematically evaluate the impact of the South-Central Ningxia Water Supply Project on water quality alongside field surveys and data analysis and propose an optimized scheduling scheme that addresses both water quantity and quality needs. The main findings are as follows: 1. Overall water quality is good, except for consistently high total nitrogen levels. 2. The optimized scheme significantly reduced total nitrogen levels, achieving a maximum reduction rate of 78.81%, and met all Class III standards.

With the rapid process of urbanization, water conflicts between different water use industries and areas are increasing. Therefore, China has implemented the three-cordons system of water resources management since 2012, when how to make more reasonable regulation of water resources became an urgent problem in most areas of China. In this study, taking the Yuanhe River Basin as an example, an integrated model for the simulation and regulation of water resources considering water quantity and quality from a river basin perspective was proposed, where the water supply was constrained by requirements of water resources management. First, the water resources system was conceptualized into a topologically hydraulic network in the form of point, line, and area elements, including 80 water use units and 79 water supply units. Then, taking the water quantity and quality as constraint conditions in the water supply for corresponding water use sectors, a management-oriented integrated model was established, which highlights the cordon control of the total water use and the pollution load limits of a basin. Finally, through a model simulation, the total water supply was controlled by regulating the water resources, while the pollutant loads into rivers depended on the discharge of water users. Based on the model, strategies for the utilization of water resources and achieving emission reductions of pollution loads were provided. The results of the proposed model in the Yuanhe River Basin showed that benchmarked against the total water demand of 1.705 billion m3, the water shortage was 212 million m3 with a rate of 13.5%, and the loads of COD (Chemical Oxygen Demand) and NH3-N (Ammonia Nitrogen) were 29,096.7 and 2587.3 tons, respectively. The model can provide support for integrated water resources regulation in other basins or regions through a simulation of the natural–social water resources systems, and help stakeholders and decision-makers establish and implement advantageous strategies for regional efficient utilization of water resources.

Water stress due to poor water quality has been becoming severe in many places across the world. Comprehensive water utility and water scarcity assessments require information integrating both water quantity and quality. While massive attentions have been paid to water quantity scarcity evaluations, little effort has been made to assess inter-annual variations of regional water scarcity resulting from both water quantity and quality. The study, taking water-abundant while stressed Jiangsu province (JSP) in eastern China as the study area, investigated (i) the development in green, blue and grey water footprint (WFs) for crop production, over 1986–2016, (ii) the inter-annual evolutions in blue and grey WFs for industry and households over 2010–2016 and (iii) the associated inter- and intra-annual variations in water scarcities resulting from water quantity and quality. Results showed that the annual total WF of crop production in JSP increased by 18% between 1986 and 2016. Grey WF accounted for 77% of the total WF at an annual average level. Crop production occupied 61% and household accounted for 34% in the total grey WF related to N. The monthly blue water scarcity levels in JSP increased by 4 (October 2016) – 62 (February 2012) folders when water quality effects were taken into account. The wetter the year, the lower the blue water scarcity of water quality and quantity. As a sensitive and crucial region with both severe water pollution scarcity and the role of water source region in the huge South-to-North water transfer project, it is of great necessity to enhance the water pollution management and increase information transparency among water authorities and consumers.

Geospatial technologies now allow routine observation of lakes and wetlands across large areas, but turning those observations into timely, actionable insight still requires scalable computing. Google Earth Engine (GEE) provides a web-based platform that brings multi-sensor Remote Sensing (RS) archives and parallel processing together in one environment. This review synthesizes how artificial intelligence (AI), machine learning (ML) and deep learning (DL) have been paired with GEE to map and monitor surface water quantity and quality. We summarize recent methods, compare model families commonly used on GEE, and discuss frequent processing pitfalls. To ground the review, we include a case study of three Nebraska lakes (2022–2023) that demonstrates month-to-month tracking of water extent and indicators of water quality. The results demonstrated the effectiveness of GEE in providing timely and accurate insights for surface water monitoring and assessment while also revealing current limitations and opportunities for improvement. Overall, we find that coupling AI methods with GEE can strengthen operational surface water assessment and inform decision-making under increasing environmental pressures.HighlightsUnlike previous reviews, this study systematically compares the accuracy of AI-GEE combinations across different water quality indicators and highlights common processing pitfalls.We review how machine and deep learning models are used in Google Earth Engine to make surface-water quality and quantity assessments more accurate and scalable.Showcase a three-lake case study from Nebraska that demonstrates, in practice, how GEE effectively monitors both water quality and water quantity over time.

Studying the change mechanism of water quantity and quality is the basis for joint optimization of water resources systems, which is a significant means for modern regional water resources management. A water quantity and quality joint optimization model is built based on multiple control objectives, which include water demand, observed flow rate, and observed pollutant concentration. A coupled water quantity and water quality model was developed for Nanning, China. The natural water cycle and social water cycle in Nanning City and the associated pollutant transport transformation process are simulated. The results indicate that simulation error of water resources allocation is below 5%, the Nash–Sutcliffe efficiency coefficients of the three hydrological stations are 0.85, 0.88, and 0.85 respectively, and the relative errors of the simulated results of three water quality monitoring stations are all within 1.83%, all of which indicates that the model performs well and the simulation results can reproduce the water use process and pollutant transport transformation process of Nanning in time and space. This study can provide effective support for water resources management in Nanning City.

With the development of industrial and agricultural production and the social economy, the demand for water resources has gradually increased. In this paper, based on the principles of system dynamics, a sustainable water resources utilization model with coupled water quality and quantity is established using STELLA software to assess the sustainable use of water resources. The model includes two modules: a water supply module and a water quality module. The water supply module includes four sub-systems: economy, population, water supply, and water demand. The water quality module consists of an environmental sub-system. The model is suitable for Tianjin, where water resources are scarce. Calibration is performed using data from 2013–2016, and verification is performed using data from 2017. The simulation results are good. In order to compare the sustainable use of water resources in different development scenarios in Tianjin for 2025, a sensitivity analysis is performed for each variable, and four decision variables are selected to establish four water resources use scenarios (Scenarios 1–4). The results show that, compared with scenario 1, water shortages in scenarios 2 and 3 are delayed. Scenario 4, with stable economic growth and environmental consideration, can effectively resolve the contradiction between water supply and demand in the future, and is more conducive to the improvement of water quality. Finally, based on the above research, measures to solve water resources problems are proposed, in order to provide a reference for the sustainable use of water resources and optimization of water resources allocation in Tianjin.

Maintaining good water quality in the Lijiang River is a scientific and practical requirement for protecting and restoring the environmental and ecological value of the river. Understanding the influence of non-point source pollution on the water quality of the Lijiang River is important for water quality maintenance. In this study, the pollutant flux in the upper reaches of the Lijiang River was calculated based on water quality monitoring, non-point source pollution, and point source pollution statistics. The Z–Q relation curve method, hydrologic analogy method, and contour map method were used to estimate the flow of the Lijiang River. We then constructed a water quantity–water quality balance model of the upper reaches of the Lijiang River based on an equilibrium equation of water quantity and a modified one-dimensional steady-state model of the river. Water quality changes in the upper reaches were simulated for a wet, normal, and dry season. The simulation errors were all within −30% to 30%, which was in line with the pollution simulation requirements of the Standard for hydrological information and hydrological forecasting (GB/T 22482-2008). The simulated reliability of each water quality indicator is at a high level, based on the calculated Nash–Sutcliffe efficiency coefficient. The overall model simulation results were good. The simulation results show that the impact of non-point source pollution on the water quality of the upper reaches of the Lijiang River was greater than that of point source pollution. The effect of different types of non-point source pollution on the water quality of the Lijiang River was as follows: rural domestic pollution > urban household pollution without centralized treatment > pollution from agricultural cultivation. This study provides technical support for the long-term hydrology and water quality monitoring of the Lijiang River and provides a basis for the reduction in non-point source pollution and the continuous improvement of the water quality in the Lijiang River Basin.