Threshold and resilience management of coupled urbanization and water environmental system in the rapidly changing coastal region

Fertilization intensities at the buffer zones of ponds regulate nitrogen and phosphorus pollution in an agricultural watershed

The sudden increase in water nutrients caused by environmental factors have always been a focus of attention for ecologists. Fertilizer inputs with spatio-temporal characteristics are the main contributors to water pollution in agricultural watersheds. However, there are few studies on the thresholds of nitrogen (N) and phosphorus (P) fertilization rates that affect the abrupt deterioration of water quality. This study aims to investigate 28 ponds in Central China in 2019 to reveal the relationships of basal and topdressing fertilization intensities in surrounding agricultural land with pond water N and P concentrations, including total N (TN), nitrate (NO3--N), ammonium (NH4+-N), total P (TP), and dissolved P (DP). Abrupt change analysis was used to determine the thresholds of fertilization intensities causing sharp increases in the pond water N and P concentrations. Generally, the observed pond water N and P concentrations during the high-runoff period were higher than those during the low-runoff period. The TN, NO3--N, TP, DP concentrations showed stronger positive correlations with topdressing intensities, while the NH4+-N concentrations exhibited a higher positive correlation with basal intensities. On the other hand, the NO3--N concentrations had a significant positive correlation with the topdressing N, basal N, and catchment slope interactions. Significant negative correlations were observed between all water quality parameters and pond area. Spatial scale analysis indicated that fertilization practices at the 50 m and 100 m buffer zone scales exhibited greater independent effects on the variations in the N and P concentrations than those at the catchment scale. The thresholds analysis results of fertilization intensities indicated that pond water N concentrations increased sharply when topdressing and basal N intensities exceeded 163 and 115 kg/ha at the 100 and 50 m buffer zone scales, respectively. Similarly, pond water P concentrations rose significantly when topdressing and basal P intensities exceeded 117 and 78 kg/ha at the 50 m buffer zone scale, respectively. These findings suggest that fertilization management should incorporate thresholds and spatio-temporal scales to effectively mitigate pond water pollution.

Effect of urbanization and urban forests on water quality improvement in the Yangtze River Delta: A case study in Hangzhou, China

In the context of rapid global urbanization, the sustainable development of ecosystems should be considered. Accordingly, the Planetary Boundaries theory posits that reducing the amount of nitrogen and phosphorus pollutants entering bodies of water is necessary as excess levels may harm the aquatic environment and reduce in water quality. Thus, based on the long-term monitoring data of representative urban rivers in the Yangtze River Delta region, we evaluated the nitrogen and phosphorus pollution of water bodies in different urbanization stages and further quantified the effect of urban forests on water quality improvement. The results showed that, with the continuous progression of urbanization, the proportion of impervious surface area increased, along with the levels of nitrogen and phosphorus pollution in water bodies. The critical period of water quality deterioration in urban rivers occurred during the medium urbanization level when the proportion of impervious surface area reached 55-65 %, and the probability of an abrupt increase in total nitrogen (TN) and total phosphorus (TP) concentration exceeded 95 %. However, increasing the area of urban forests during this period reduced TN pollution by 36.64 % and TP pollution by 49.03 %. The results of this study support the expansion of urban forests during the medium urbanization stage to improve water quality. Furthermore, our results provide a reference and theoretical basis for urban forest construction as a key aspect of the sustainable development of the urban ecosystem in the Yangtze River Delta and similar regions around world.

Spatial scale effects of integrated landscape indicators on river water quality in Chaohu Lake basin, China

Climate change and rapid urbanization have changed the characteristics of basin landscapes. Non-point-source (NPS) pollution affects river water quality. Exploring the impact of landscapes on river water quality is crucial for the control of water pollution in a basin. Current researchers focus on the impact of landscape pattern change on NPS pollution in the basin, but few consider climate, terrain, soil, and other geographical factors. In this study, we selected a subtropical agricultural basin in China named Chaohu Lake basin as the study area, added precipitation, soil erosion resistance, and slope to the original landscape pattern indicators. We quantified the spatial scale effect and seasonal dependence of integrated landscape indicators on water quality and comprehensively analyzed the optimal spatial scale and key landscape indicators. According to the nonlinear relationship between the key landscape indicators and river nutrients, we also determined the Type-1 threshold values of key landscape indicators for water quality protection in the basin. The results showed that the rivers in Chaohu Lake basin were mainly polluted by nitrogen and phosphorus. The strength of interpretation of the integrated landscape indicators of river water quality increased with riparian zone width. We determined the subbasin scale to be the optimal spatial scale. The key landscape indicators affecting water quality in the wet season at the optimal scale were precipitation and aggregation index of construction land (AIbul), whereas those in the dry season were AIbul and COHESION. The interpretation of the key landscape indicators in the wet season was slightly higher than that in the dry season. The above conclusions provide a scientific reference for NPS pollution control and water quality protection in subtropical agricultural basins.

Influences of landscape pattern on water quality at multiple scales in an agricultural basin of western China

Determining the associations between landscape pattern and river water quality and quantifying the abrupt change points of landscape metrics are vital to optimize landscape planning and improve basin water quality. This study took an agricultural basin in western China as a case study. River water quality of 61 sub-basin outlets were monitored during wet and dry seasons from 2020 to 2021. Landscape metrics were extracted at 100 m, 300 m, 500 m riparian buffer and sub-basin scales, respectively. Relationships between water quality and landscape pattern at multiple scales were explored by using redundancy analysis (RDA). Results showed that urban-related landscape metrics served as the primary contributor to degrade water quality during both seasons, followed by cropland-related metrics, which might be attributed to the increase of urban land and reduction of agricultural chemical fertilizer use. Landscape metrics could better explain the water quality variations during wet season than dry season. The explanatory abilities of landscape metrics to overall water quality appeared little difference among spatial scales during wet season, whereas landscape metrics within 100 m riparian buffer had much larger explanatory rate than other spatial scales during dry season. Results of abrupt change point analysis revealed that the abrupt change interval values (ACIVs) of percentage of urban land (PLAND_urban) and the largest patch index of urban land (LPI_urban) differed among COD, TN, and TP. The recommended threshold values of PLAND_urban and LPI_urban for COD, TN, and TP management were smaller than 11.0%, 2.5%, and 1.0%, respectively. When the PLAND_urban or LPI_urban exceeded 19.0%, the TN, TP, and COD pollution would all significantly accelerate. Therefore, a limit value of 19% of PLAND_urban and LPI_urban, respectively is put forward. From dry season to wet season, the ACIVs of PLAND_urban and LPI_urban for COD concentration increased, whereas they decreased for TN and TP concentrations. Our results can provide scientific insights into sustainable landscape planning and effective water quality protection in agricultural basins.

Study on the threshold relationship between landscape pattern and water quality considering spatial scale effect-a case study of Dianchi Lake Basin in China

It is of great significance to analyze the threshold relationship between landscape pattern and water quality for watershed water environment treatment. However, previous studies did not consider the influence of spatial scale on threshold. Therefore, this study proposed the idea of the relationship between landscape pattern and water quality threshold considering the spatial scale effect to solve the above problems. Firstly, the percentage of landscape composition area under 9 spatial scales (riparian buffer zone and sub-basin) of 20 rivers entering the lake in Dianchi Lake Basin was extracted to identify the optimal spatial scale of landscape pattern and water quality by redundant analysis (RDA). Then, a variety of nonlinear regression models such as power regression, exponential regression, quadratic regression, and segmented regression are used to quantitatively detect the thresholds of landscape pattern and water quality. The results show that (1) the spatial scale has a significant influence on the threshold relationship between landscape pattern and water quality, and the total interpretation rate of landscape pattern on water quality is the largest at the buffer scale of 1100 m riparian zone, which is an effective buffer for river governance. (2) Different spatial scales have different effects on the threshold relationship between landscape pattern and water quality. In the nonlinear regression model of landscape pattern and water quality in the buffer zone of 1100 m riparian zone, the significance and R² of the equation are better than those of the sub-basin. (3) From the nonlinear relationship between landscape pattern and water quality, it is found that the landscape threshold can be quantitatively identified when the water quality changes abruptly or reaches the I ~ V water quality standard. Among them, the type-1 landscape threshold at the water quality mutation point can be used as the long-term goal of water quality protection in Dianchi Lake Basin, and the type-2 landscape threshold can be used as the short-term goal of water quality adjustment. The research results can provide a scientific basis for the governance of water environment and the rational planning of landscape pattern in Dianchi Lake Basin, and have practical significance for guiding the sustainable development of cities.

Urban stormwater management for sustainable and resilient measures and practices: a review

Stormwater drainage in urban areas has become a challenge due to the rapid and random growth of urban areas, removal of vegetation, reduction in the effectiveness of drainage infrastructure, and climate change. Sustainable Urban Drainage Systems (SUDS), Low Impact Development (LID), Best Management Practices (BMP), Water Sensitive Urban Design (WSUD) and the Sponge City Programme (SCP) are various aspects for urban stormwater management in a few parts of the world. Urban hydrology plays a vital role in the urban stormwater management system. However, optimal results can only be possible when the combined effect of climate change, land use patterns, reuse, treatment, ecology, and societal aspects are considered. There is a need to provide sustainable and resilient urban drainage systems to manage stormwater more efficiently. The present review has thoroughly discussed various features related to urban stormwater management, highlighted key drivers, identified knowledge gaps in each of the measures and/or practices, recommended future research needs of urban stormwater management to become sustainable and resilient. Integrated modelling approaches considering various key drivers including reuse and real time governance enables stormwater management to be sustainable and resilient in urban environments.

A New Method for Continuous Monitoring of Black and Odorous Water Body Using Evaluation Parameters: A Case Study in Baoding

Water is an important factor in human survival and development. With the acceleration of urbanization, the problem of black and odorous water bodies has become increasingly prominent. It not only affects the living environment of residents in the city, but also threatens their diet and water quality. Therefore, the accurate monitoring and management of urban black and odorous water bodies is particularly important. At present, when researching water quality issues, the methods of fixed-point sampling and laboratory analysis are relatively mature, but the time and labor costs are relatively high. However, empirical models using spectral characteristics and different water quality parameters often lack universal applicability. In addition, a large number of studies on black and odorous water bodies are qualitative studies of water body types, and there are few spatially continuous quantitative analyses. Quantitative research on black and odorous waters is needed to identify the risk of health and environmental problems, as well as providing more accurate guidance on mitigation and treatment methods. In order to achieve this, a universal continuous black and odorous water index (CBOWI) is proposed that can classify waters based on evaluated parameters as well as quantitatively determine the degree of pollution and trends. The model of CBOWI is obtained by partial least squares machine learning through the parameters of the national black and odorous water classification standard. The fitting accuracy and monitoring accuracy of the model are 0.971 and 0.738, respectively. This method provides a new means to monitor black and odorous waters that can also help to improve decision-making and management.

Identifying and Mapping the Responses of Ecosystem Services to Land Use Change in Rapidly Urbanizing Regions: A Case Study in Foshan City, China

Rapid urbanization has degraded some important ecosystem services and threatens socioeconomic sustainability. Although many studies have focused on the effect of urbanization on ecosystem services, the effect and its threshold have not been well-identified spatially. In this study, we propose a research framework by integrating nighttime light data, the InVEST (Integrated Valuation of Environmental Service and Tradeoffs) model, and a spatial response index to characterize the response of ecosystem services to rapid urbanization. We considered Foshan City as a case study to explore the effect of rapid urbanization on ecosystem services during 2000–2018. Our results showed that rapid urbanization resulted in a 49.13% reduction in agricultural production and a 10.13% reduction in habitat quality. The spatial response index of agricultural production, habitat quality, soil retention, water yield, and carbon sequestration were 14.25%, 2.94%, 0.04%, 0.78%, and 0.07%, respectively. We found that developing urban areas had the highest spatial response index, indicating that this area was the crucial area for future land management. We consider that our research framework can help identify the key areas affected by rapid urbanization. Visualizing the spatial response index and extracting the threshold for different levels of urbanization will be conducive to sustainable urban management and planning.

Impact of rapid urbanization on the threshold effect in the relationship between impervious surfaces and water quality in shanghai, China

The threshold effect in the relationship between impervious surfaces and water quality has been a focus in past decades, but little attention has been paid to how the threshold effect changes during a rapid urbanization period. This study reveals the temporal variation of threshold effect in the relationship between the percentage of total impervious area (PTIA) and water quality indicators in a reticular river network area in Shanghai, China. The PTIA was surveyed and defined using the ISC method (impervious surface coefficients). A segmented regression model was used to disclose the non-linear relationship between PTIA and water quality. It is confirmed that the threshold effect was different in terms of water quality indicators, but the effect size became smaller as the threshold increased with urbanization level during the period of 1989-2010. Meteorological conditions make influence on the threshold effect, it can be found that the effect is more significant under higher air temperature conditions, while in the lower temperature situation, there is no significant threshold effect.

Community composition and antibiotic resistance of bacteria in bottlenose dolphins Tursiops truncatus - Potential impact of 2010 BP Oil Spill

Aquatic contamination, oil spills in particular, could lead to the accumulation of antibiotic resistance by promoting selection for and/or transfer of resistance genes. However, there have been few studies on antibiotic resistance in marine mammals in relation to environmental disturbances, specifically oil contaminations. Here we initiated a study on antibiotic resistance bacteria in bottlenose dolphins Tursiops truncatus in relation to oil contamination following the 2010 BP Oil Spill in the northern Gulf of Mexico. Bacterial communities and antibiotic resistance prevalence one year after the 2010 BP Oil Spill were compared between Barataria Bay (BB) and Sarasota Bay (SB) by applying the rarefaction curve method, and (generalized) linear mixed models. The results showed that the most common bacteria included Vibrio, Shewanella, Bacillus and Pseudomonas. The prevalence of antibiotic resistance was high in the bacterial isolates at both bays. Though bacterial diversity did not differ significantly among water or dolphin samples, and antibiotic resistance did not differ significantly among water samples between the two bays, antibiotic resistance and multi-drug resistance in dolphin samples was significantly higher in the BB than in the SB, mainly attributed to the resistance to E, CF, FEP and SXT. We also found sulfamethoxazole-trimethoprim-resistant Stenotrophomonas maltophilia the first time in the natural aquatic environment. The higher antibiotic resistance in the dolphins in BB is likely attributed to 2010 BP Oil Spill as we expected SB, a more urbanized bay area, would have had higher antibiotic resistance based on the previous studies. The antibiotic resistance data gathered in this research will fill in the important data gaps and contributes to the broader spatial-scale emerging studies on antibiotic resistance in aquatic environments.

Adaptation as an indicator of measuring low-impact-development effectiveness in urban flooding risk mitigation

Frequent and intensive urban flooding requires an extensive adoption of low-impact development (LID) to supplement traditional drainage infrastructures. Our study conceptualizes the resilient infrastructure framework with a particular reference to adaptation, an adjustment capacity in the social-ecological system to withstand various natural hazards and absorb negative impacts. We argue that adaption is an indicator for measuring LID effectiveness. A methodological framework is adopted using a time-dependent technique with a hydrodynamic inundation model to evaluate LID effectiveness. Results of a case study in Gongming, Shenzhen, China, show that LID projects can effectively reinforce adaptation capacity. However, spatial inequality and accumulation of different levels of adaptation are evident. This outcome is due to a relatively low absorption capacity because most areas will have a relatively high recovery capacity but retain a low absorption capacity with the construction of LID projects. A relatively mild increase in absorption capacity is due to the quality of man-made infrastructural development is conflicting across different areas of Gongming, for example some infrastructures are constructed by the government, whereas others by developers and villagers. In addition, the topographical factor makes some areas in Gongming lower-lying than others and is therefore increasingly vulnerable to urban flooding during rainstorms given the difficulty of discharging the surface runoff, thereby limiting the effectiveness of LID projects. Furthermore, the spatial inequality of adaptation improvement where LID projects cannot be evenly distributed within the research area leads to the unequal distribution of adaptation. These findings can confirm that the government can practically use adaptation as an indicator in evaluating LID effectiveness and identifying the problematic stages of drainage resilience in urban flooding risk mitigation.

Landscape patterns regulate non-point source nutrient pollution in an agricultural watershed

Landscape pattern critically affects hydrological cycling and the processes of non-point source nutrients pollution. However, little is known about the quantitative relationship between landscape characteristics and the river water quality, and very few studies have addressed the abrupt changes in river water quality with the gradient of landscape metrics. The present study was conducted in a typically intensive agriculture watershed of eastern China including 13 sub-watersheds with different landscape pattern metrics. We adopted redundancy analysis, nonparametric deviance reduction approach, bootstrap sampling and other statistical methods to reveal the quantitative relationship between landscape pattern metrics and water quality variables; then, the phenomenon of an abrupt change in river water quality was explored with different landscape pattern gradients. The results show that landscape pattern significantly affects river water quality, and this effect was quite different in dry and rainy seasons. In the studied watershed, landscape pattern metrics could respectively explain 71.1% and 55.3% of the total variance in the river water quality in dry and rainy seasons. The configuration metrics of landscape pattern had a stronger ability than their composition metrics to explain the variance in water quality. In the dry season, largest patch index of forestland (LPI_for), the most important landscape index, explained 37.9% of the total variance in water quality. While, in the rainy season, the most important landscape index was the largest patch index of farmland (LPI_far), and it could explain 32.4% of that variance. In the studied watershed, when the LPI_for was <35% or LPI_far was over than 50%, water quality would typically change abruptly, at which the probability of a change in river water would suddenly rise substantially.

Empirical Framework for a Relative Sustainability Evaluation of Urbanization on the Water⁻Energy⁻Food Nexus Using Simultaneous Equation Analysis

The water–energy–food (WEF) nexus attracts much attention due to the elevated public concern regarding environmental conservation and sustainability. As we head into a new era of civilization, population increase and modernized lifestyles have led to an increasing need for water, energy, and food. However, severe hydrological precipitation significantly impacts agricultural harvest, and such influence becomes more apparent under the influence of climate change. Meanwhile, the major method of electricity generation (i.e., fossil fuel burning) has a negative impact on the environment. These inevitable threats are crucial and have to be dealt with for a society on the road towards sustainability. In the present study, an integrated evaluation of the WEF nexus was conducted for two areas with different levels of urbanization using empirical multiple linear regression in a simultaneous equation model (SEM). By incorporating the collected data into the SEM, the weighting coefficient of each identified variable was obtained, and the nexus implication was assessed in model simulation at different scenarios considering the population growth, agro-technology advancement, energy structure improvement, and available water resources. In the simulated results, three observations were found: (1) the rural area is more sustainable than the urban one; (2) the sustainability for both the investigated areas is significantly subject to their water supply and demand; and (3) food production was found to have a less important effect on the sustainable development of the urban area. This study identified the key factors in the WEF nexus exploration, which are economically and environmentally important for resource allocation. An empirical model was developed to correlate sustainable achievement with WEF management, as well as strategic policies that should be implemented under the pressure of urbanization.

Simulation modeling for a resilience improvement plan for natural disasters in a coastal area

Floods are threats to ecosystems that are caused by natural disasters such as typhoons and heavy rain, and to respond to these threats, resilience needs to be improved. In this study, the response of the social-ecological system of Haeundae-gu (Busan, Republic of Korea) to disasters is analyzed by using a causal loop diagram, and a resilience improvement plan is presented by simulating the disaster resilience using green infrastructure through the System Resilience Dynamics Model. First, the resilience values are highest when green infrastructure is applied at the maximum applicable ratio (30%) compared with no application. Second, in the public and private areas of Haeundae-gu, resilience according to green roof scenario was higher until approximately 8 h after the beginning of rainfall, but then the resilience according to infiltration storage facility scenario was higher. In the transportation and industrial areas, the overall resilience according to infiltration storage facility scenario was higher than the resilience according to porous pavement scenario. This study demonstrates that a resilience improvement plan based on simulation can support decision making to respond to disasters such as typhoons.

Effects of a vegetable-eel-earthworm integrated planting and breeding system on bacterial community structure in vegetable fields

Agricultural production combined with planting and breeding, which can reduce chemical fertilizer and pesticide applications, reduce losses due to natural disasters, and improve the output and quality of agricultural products, is an important way to achieve green, circular and efficient production. To assess effects on soil bacterial community structure, a vegetable-eel-earthworm integrated planting and breeding platform (VEE-IPBP) combined with experiment planting was established at Chongming Island, Shanghai and compared to traditional planting. High-throughput sequencing to reveal soil bacterial community structure was performed on samples collected at 0, 3 and 6 years after implementation of the two models. Over time, the Shannon index first increased and then decreased in the VEE-IPBP system and was reduced by 3.2% compared to the traditional planting (In the same time and space scale, the single-degree planting method of dryland vegetables under mechanical cultivation is adopted) (p < 0.05). In contrast, Chao and Ace indices were increased by 2.4% and 3.2%. Thus, soil bacterial diversity was markedly different in the two planting models. The abundance of Proteus, Cyanophyta and Cyanophyta in soil increased after 6 years, and the proportion of Lysinibacillus increased significantly, contributing to improvement in soil disease resistance. Redundancy analysis (RDA) showed that the soil pH and water content were the main factors influencing the change in soil bacterial community structure in the two planting models, and the dominant species of soil bacteria were Lysobacter and Bacillus.

The Impacts of Spatiotemporal Landscape Changes on Water Quality in Shenzhen, China

The urban landscape in China has changed rapidly over the past four decades, which has led to various environmental consequences, such as water quality degradation at the regional scale. To improve water restoration strategies and policies, this study assessed the relationship between water quality and landscape change in Shenzhen, China, using panel regression analysis. The results show that decreases in natural and semi-natural landscape compositions have had significant negative effects on water quality. Landscape composition and configuration changes accounted for 39⁻58% of the variation in regional water quality degradation. Additionally, landscape fragmentation indices, such as patch density (PD) and the number of patches (NP), are important indicators of the drivers of water quality degradation. PD accounted for 2.03⁻5.44% of the variability in water quality, while NP accounted for -1.63% to -4.98% of the variability. These results indicate that reducing landscape fragmentation and enhancing natural landscape composition at the watershed scale are vital to improving regional water quality. The study findings suggest that urban landscape optimization is a promising strategy for mitigating urban water quality degradation, and the results can be used in policy making for the sustainable development of the hydrological environment in rapidly urbanizing areas.

Optimal fresh water blending: A methodological approach to improve the resilience of water supply systems

Climate change and socioeconomic factors have increased the complexity of urban water supply systems. Thus, fresh water sources are being gradually diversified to improve the reliability and resilience of the systems. However, as the number of source blending options grows, optimization tools are needed to design drinking water supply systems that comply with indicators of cost, resilience, and water quality. This paper proposes a pioneering methodological approach, based on an ant-colony-optimization (ACO) algorithm, to optimize the blending of drinking water from different sources to minimize operational costs of a given system originating from a number of impaired water sources while complying with water quality standards. To evidence the potential of the ACO algorithm to solve such a system, a virtual case study was designed that considers eight fresh water sources, including seawater desalination and potable reuse. Seven scenarios were developed with different weightings to service outage, water conveyance and treatment costs while complying with water quality goals in regard to total organic carbon, nitrates, and total dissolved solids. It was shown that the cost per volumetric unit of water can vary considerably depending on the weightings of the three cost items. This paper provides a rigorous scientific approach to propose a methodology supporting the decision-making process of selecting a mixture of different sources to achieve the overall lowest system cost. Hence, this work contributes to improving the resilience and sustainability of urban water supplies.