Multi-angle indicators system of non-point pollution source assessment in rural areas: a case study near Taihu Lake

An improved minimum cumulative resistance model for risk assessment of agricultural non-point source pollution in the coastal zone

Agricultural non-point source pollution (AGNPSP) is an important risk factor affecting the water environment. Among the areas where cropland NPSP occurs, the coastal zone should be of greater concern. Typhoons, heavy precipitation, and abundant rivers and ponds accelerate the transport process of AGNPSP to the offshore waters. It is urgent to construct a simple and accurate model to assess the risk of AGNPSP in the coastal zones. Thus, this study takes the nitrogen pollution from agricultural cultivation in the coastal zone of the Yellow River Delta as an example. A new minimum cumulative resistance (MCR) to agricultural non-point source pollution (AGNPSP-MCR) model is first proposed to simulate the transport process of cropland NPSP into the sea based on the "source-sink" theory in landscape ecology. Finally, the risk is assessed for AGNPSP transport into the sea. The results show the following. (1) The environmental factors of vegetation cover, rainfall erosivity, and soil erodibility are the three most important factors in pollution transportation, weighted 0.3433, 0.2608, and 0.2219, respectively, while the least influential factor is slope, with a weight of only 0.0053. (2) The minimum cumulative resistance of AGNPSP transportation shows a significant positive correlation with the distance to the river and sea, and is higher on the west sides away from the ocean, and smaller in the eastern coastal area near the sea. (3) Similarly, the regions facing serious AGNPSP risk are concentrated in the eastern coastal area, and the cropland area above medium risk was 252.72 km², accounting for 47.57% of the total cultivated land area. (4) Compared with the traditional MCR model, the AGNPSP-MCR model takes into account the quantitative differences of the transport process characteristics of AGNPSP, and it is constrained by the topographical parameter, so the results of AGNPSP risk are more reliable. This study provides a new reference for risk assessments of AGNPSP in the coastal zones.

Research on the Relationship between Urban Agricultural Nonpoint Source Pollution and Rural Residents’ Income Growth

Researching the relationship between urban agricultural nonpoint source pollution (UANSP) and increases in rural residents' income levels has significant practical implications for effectively controlling UANSP and improving the quality of life of urban residents, and it is conducive to achieving a win-win situation between economic and environmental benefits. This study chooses agricultural statistical data from Shanghai from 1998 to 2019, implements the EKC and the VAR model to dynamically analyze internal interaction between them, and thoroughly examines impact effect and explanatory contribution degree of each variable. The results show the following: (1) There was an inverted “N” curve between plastic film application intensity and rural residents' per capita disposable income; there was a linear decreasing relationship between the intensity of fertilizer and pesticide application and rural residents' per capita disposable income. (2) Nonpoint source pollution emissions will decrease as rural residents' income levels rise. Reduction of nonpoint source pollution can promote the short-term improvement of rural residents' income levels, but it has a negative effect on the long-term improvement of rural residents' income levels. (3) Fertilizer and pesticide application intensity had a low driving effect on rural residents' income growth, whereas plastic film application intensity had a strong driving effect. Therefore, the ANSP of Shanghai should be treated from both long-term and short-term perspectives on the basis of decreasing stage. In the long term, the government should increase farmers' sense of ownership in agricultural nonpoint source pollution control, prioritize the development of ecological circular agriculture, and gradually improve nonpoint source remote sensing monitoring and service management capabilities. In the short term, the government should reduce farmers' nonpoint source pollution through subsidies and technical assistance. To keep costs down, the government established an administrative reward and punishment system to control ANSP at the source.

Optimisation of Garbage Bin Layout in Rural Infrastructure for Promoting the Renovation of Rural Human Settlements: Case Study of Yuding Village in China

Optimising the layout of garbage bins is a requirement for improving the utilisation efficiency of rural infrastructure and continuously promoting the renovation of rural human settlements in China. This study selects Yuding Village in Chongqing, China, as the study area. The present distribution of garbage bins and the existing problems are analysed on the basis of interview materials and the point on interest data of garbage bins obtained from an on-the-spot investigation. Actor network theory (ANT) is suitable for small-scale micro research, and thus, this study uses ANT to construct a research framework for garbage bin layout optimisation. Then, it designs an optimisation path for the layout of garbage bins in Yuding Village by identifying different actors and their common interests, classifying the transformation of roles amongst various actors and building a stable heterogeneous network that can be used as a guide for determining the optimal spatial layout of garbage bins. This study combines a sociological theory with geospatial phenomena, providing a new idea for studying the optimal layout of infrastructure.

Coupling ITO3dE model and GIS for spatiotemporal evolution analysis of agricultural non-point source pollution risks in Chongqing in China

To determine the risk state distribution, risk level, and risk evolution situation of agricultural non-point source pollution (AGNPS), we built an ‘Input-Translate-Output’ three-dimensional evaluation (ITO3dE) model that involved 12 factors under the support of GIS and analyzed the spatiotemporal evolution characteristics of AGNPS risks from 2005 to 2015 in Chongqing by using GIS space matrix, kernel density analysis, and Getis-Ord Gi* analysis. Land use changes during the 10 years had a certain influence on the AGNPS risk. The risk values in 2005, 2010, and 2015 were in the ranges of 0.40–2.28, 0.41–2.57, and 0.41–2.28, respectively, with the main distribution regions being the western regions of Chongqing (Dazu, Jiangjin, etc.) and other counties such as Dianjiang, Liangping, Kaizhou, Wanzhou, and Zhongxian. The spatiotemporal transition matrix could well exhibit the risk transition situation, and the risks generally showed no changes over time. The proportions of ‘no-risk no-change’, ‘low-risk no-change’, and ‘medium-risk no-change’ were 10.86%, 33.42%, and 17.25%, respectively, accounting for 61.53% of the coverage area of Chongqing. The proportions of risk increase, risk decline, and risk fluctuation were 13.45%, 17.66%, and 7.36%, respectively. Kernel density analysis was suitable to explore high-risk gathering areas. The peak values of kernel density in the three periods were around 1110, suggesting that the maximum gathering degree of medium-risk pattern spots basically showed no changes, but the spatial positions of high-risk gathering areas somehow changed. Getis-Ord Gi* analysis was suitable to explore the relationships between hot and cold spots. Counties with high pollution risks were Yongchuan, Shapingba, Dianjiang, Liangping, northwestern Fengdu, and Zhongxian, while counties with low risks were Chengkou, Wuxi, Wushan, Pengshui, and Rongchang. High-value hot spot zones gradually dominated in the northeast of Chongqing, while low-value cold spot zones gradually dominated in the Midwest. Our results provide a scientific base for the development of strategies to prevent and control AGNPS in Chongqing.

Identification of Critical Source Areas of Nitrogen Load in the Miyun Reservoir Watershed under Different Hydrological Conditions

The spatiotemporal distribution of critical source areas (CSAs) will change with hydrological conditions. In this study, the CSAs of nitrogen load under different hydrological conditions in the Chaohe River watershed were identified using the cumulative pollution load curve method determined from the nitrogen pollution simulated using the Soil and Water Assessment Tool (SWAT) model. The results showed that: (1) The order of factors impacting nitrogen load intensity is as follows: fertilization intensity, rainfall, runoff, land use type, slope type, and soil type. (2) The primary and secondary CSAs are concentrated in the upper and lower areas of the watershed, where cultivated land (8.36%) and grassland (52.55%) are more abundant. The potential pollution source areas are concentrated in the upper and middle areas of the watershed, where cultivated land (6.99%), grassland (42.37%), and forest land (48.18%) are evenly distributed. The low-risk source areas are concentrated in the middle and left bank of the watershed, where forest land (67.65%) is dominant and the vegetation coverage is highest. The research results have significance for improving the accuracy of the implementation of best management practices, and can provide a reference for the formulation of drinking water protection policies for Beijing.

Impacts of Land Use and Land Cover on Water Quality at Multiple Buffer-Zone Scales in a Lakeside City

Understanding the effect of land use/land cover (LULC) on water quality is essential for environmental improvement, especially in urban areas. This study examined the relationship between LULC at buffer-zone scales and water quality in a lakeside city near Poyang Lake, which is the largest freshwater lake in China. Representative indicators were selected by factor analysis to characterize the water quality in the study area, and then the association between LULC and water quality over space and time was quantified by redundancy analysis. The results indicated that the influence of LULC on water quality is scale-dependent. In general, the LULC could explain from 56.9% to 31.6% of the variation in water quality at six buffer zones (from 500 m to 1800 m). Forest land had a positive effect on water quality among most buffer zones, while construction land and bare land affected the representative water quality indicators negatively within the 1200 m and 1500 m buffer zones, respectively. There was also a seasonal variation in the relationship between LULC and water quality. The closest connection between them appeared at the 1000 m buffer zone in the dry season, whereas there was no significant difference among the buffer zones in the wet season. The results suggest the importance of considering buffer-zone scales in assessing the impacts of LULC on water quality in urban lakeshore areas.

Enhanced removal of organic matter and typical disinfection byproduct precursors in combined iron-carbon micro electrolysis-UBAF process for drinking water pre-treatment

The organic matter and two types of disinfection byproduct (DBP) precursors in micro-polluted source water were removed using an iron-carbon micro-electrolysis (ICME) combined with up-flow biological aerated filter (UBAF) process. Two pilot-scale experiments (ICME-UBAF and UBAF alone) were used to investigate the effect of the ICME system on the removal of organic matter and DBP precursors. The results showed that ICME pretreatment removed 15.6% of dissolved organic matter (DOM) and significantly improved the removal rate in the subsequent UBAF process. The ICME system removed 31% of trichloromethane (TCM) precursors and 20% of dichloroacetonitrile (DCAN) precursors. The results of measurements of the molecular weight distribution and hydrophilic fractions of DOM and DBP precursors showed that ICME pretreatment played a key role in breaking large-molecular-weight organic matter into low-molecular-weight components, and the hydrophobic fraction into hydrophilic compounds, which was favorable for subsequent biodegradation by UBAF. Three-dimensional fluorescence spectroscopy (3D-EEM) further indicated that the ICME system improved the removal of TCM and DCAN precursors. The biomass analysis indicated the presence of a larger and more diverse microbial community in the ICME-UBAF system than for the UBAF alone. The high-throughput sequencing results revealed that domination of the genera Sphingomonas, Brevundimonas and Sphingorhabdus contributed to the better removal of organic matter and two types of DBP precursors. Also, Nitrosomonas and Pseudomonas were beneficial for ammonia removal.

Future Impacts of Climate Change and Land Use on Multiple Ecosystem Services in a Rapidly Urbanizing Agricultural Basin, China

Ecosystem services (ESs) in rapidly urbanizing agricultural basins are vulnerable to environmental changes. Adequately understanding the driving forces and the dynamics of ESs related to water quantity and quality can provide a basis for making sound management decisions on the development of basins. Here, we explored the impacts of future land use and climate changes on four ESs: nitrogen and phosphorous purification, water supply, and soil retention services in the Taihu Basin region of eastern China. Spatially explicit methods, a cellular automata-Markov (CA-Markov) model and the delta downscaling method were used to quantify the ESs, simulate land use changes, and project future climate changes, respectively. We built a business-as-usual land use scenario, representative concentration pathways (RCPs) scenarios for climate change, as well as a combined land use and climate change scenario to analyze the changes in the drivers and the responses of ESs. The results showed the following: (1) future land use changes would significantly enhance the nitrogen purification service while reducing the phosphorus purification service compared to other services; (2) climate change would have substantial effects on water supply and soil retention, but these impacts would vary with different RCPs scenarios during three future periods; and (3) the combined scenarios of both drivers would obviously influence all ESs and lead to a nitrogen purification service that was different from the other three services. Moreover, the policy implications of the results were discussed. The findings can help guide the creation of policies for land structure and patterns, climate change adaptation, and ecosystem-based management to promote the sustainable development of watersheds at the regional scale.

An Integrated Approach to Identify Critical Source Areas of Agricultural Nonpoint-Source Pollution at the Watershed Scale

Nonpoint sources are difficult to control because their nutrient contribution from different parts of a watershed can vary substantially. Identifying critical source areas of nutrient loss is an important step in watershed pollution mitigation programs. This study sought to use an integrated index model to differentiate between subbasins that serve as critical source areas of N and P nonpoint sources of pollution in China's Tiaoxi watershed. In contrast with previous N and P indices, multiple sources of pollution (i.e., agronomic activity, domestic wastewater, livestock farming, and aquaculture) were considered. Nitrogen and P source factors (i.e., N and P annual export loads) and transport factors were multiplied to determine the overall risk of nutrient loss in the integrated index model. Critical source areas were identified by a higher nutrient loss index. Of the 92 subbasins within the Tiaoxi watershed, 13 were determined to be critical sources for N, 10 for P, and seven for both N and P. Critical source area identification corresponds well with water quality data from the subbasins. The results show the potential use of the integrated index model for prioritizing and targeting watershed pollution mitigation activities at the subbasin level.

Analysis of Surface Water Pollution Accidents in China: Characteristics and Lessons for Risk Management

Understanding historical accidents is important for accident prevention and risk mitigation; however, there are no public databases of pollution accidents in China, and no detailed information regarding such incidents is readily available. Thus, 653 representative cases of surface water pollution accidents in China were identified and described as a function of time, location, materials involved, origin, and causes. The severity and other features of the accidents, frequency and quantities of chemicals involved, frequency and number of people poisoned, frequency and number of people affected, frequency and time for which pollution lasted, and frequency and length of pollution zone were effectively used to value and estimate the accumulated probabilities. The probabilities of occurrences of various types based on origin and causes were also summarized based on these observations. The following conclusions can be drawn from these analyses: (1) There was a high proportion of accidents involving multi-district boundary regions and drinking water crises, indicating that more attention should be paid to environmental risk prevention and the mitigation of such incidents. (2) A high proportion of accidents originated from small-sized chemical plants, indicating that these types of enterprises should be considered during policy making. (3) The most common cause (49.8% of the total) was intentional acts (illegal discharge); accordingly, efforts to increase environmental consciousness in China should be enhanced.

Identification of Major Risk Sources for Surface Water Pollution by Risk Indexes (RI) in the Multi-Provincial Boundary Region of the Taihu Basin, China

Environmental safety in multi-district boundary regions has been one of the focuses in China and is mentioned many times in the Environmental Protection Act of 2014. Five types were categorized concerning the risk sources for surface water pollution in the multi-provincial boundary region of the Taihu basin: production enterprises, waste disposal sites, chemical storage sites, agricultural non-point sources and waterway transportations. Considering the hazard of risk sources, the purification property of environmental medium and the vulnerability of risk receptors, 52 specific attributes on the risk levels of each type of risk source were screened out. Continuous piecewise linear function model, expert consultation method and fuzzy integral model were used to calculate the integrated risk indexes (RI) to characterize the risk levels of pollution sources. In the studied area, 2716 pollution sources were characterized by RI values. There were 56 high-risk sources screened out as major risk sources, accounting for about 2% of the total. The numbers of sources with high-moderate, moderate, moderate-low and low pollution risk were 376, 1059, 101 and 1124, respectively, accounting for 14%, 38%, 5% and 41% of the total. The procedure proposed could be included in the integrated risk management systems of the multi-district boundary region of the Taihu basin. It could help decision makers to identify major risk sources in the risk prevention and reduction of surface water pollution.

Inferring land use and land cover impact on stream water quality using a Bayesian hierarchical modeling approach in the Xitiaoxi River Watershed, China

Lake eutrophication has become a very serious environmental problem in China. If water pollution is to be controlled and ultimately eliminated, it is essential to understand how human activities affect surface water quality. A recently developed technique using the Bayesian hierarchical linear regression model revealed the effects of land use and land cover (LULC) on stream water quality at a watershed scale. Six LULC categories combined with watershed characteristics, including size, slope, and permeability were the variables that were studied. The pollutants of concern were nutrient concentrations of total nitrogen (TN) and total phosphorus (TP), common pollutants found in eutrophication. The monthly monitoring data at 41 sites in the Xitiaoxi Watershed, China during 2009-2010 were used for model demonstration. The results showed that the relationships between LULC and stream water quality are so complicated that the effects are varied over large areas. The models suggested that urban and agricultural land are important sources of TN and TP concentrations, while rural residential land is one of the major sources of TN. Certain agricultural practices (excessive fertilizer application) result in greater concentrations of nutrients in paddy fields, artificial grasslands, and artificial woodlands. This study suggests that Bayesian hierarchical modeling is a powerful tool for examining the complicated relationships between land use and water quality on different scales, and for developing land use and water management policies.