Integrating Ecological Restoration of Agricultural Non-Point Source Pollution in Poyang Lake Basin in China

Phosphorus flow characteristics in the waste system of Poyang Lake Watershed over the past 70 years

With the intensification of human activities, the amount of phosphorus (P)-containing waste has increased. When such waste is not recycled, P is released into the environment, leading to environmental issues such as the eutrophication of water bodies. In this study, based on the material flow analysis method, a P Waste Flow analysis model (P-WFA) was developed to analyze the P flow in the waste system of Poyang Lake, the largest freshwater lake in China. To address the research gap in long-term P flow analysis at the watershed scale, this study quantified the P content in the waste system of the Poyang Lake Watershed from 1950 to 2020. The analysis revealed that from 1950 to 2020, the total P input into the waste system increased from 5.49 × 104 tons in 1950 to 2.28 × 105 tons in 2020. The breeding industry system was identified as the primary source, accounting for 25.19-41.59 % of the total waste system. Over the past 70 years, P loss to surface water from waste systems has been primarily facilitated by manure from the breeding industry, as well as drainage from crop farming systems (77.74 % in 2020). At the same time, the P recycling rate (PRR) of the waste system exhibited an initial increase followed by a decrease, increasing from 44.14 % to 47.75 % before dropping to 44.41 %. Population growth, urbanization, and changes in consumption levels in Jiangxi Province have led to changes in the dietary structure and fertilizer use, consequently affecting the P cycling pattern. This study presents a comprehensive P flow model for waste systems in the Poyang Lake Watershed. This model can be used as a reference to enhance P cycling and manage P loss in other large freshwater lakes.

Source-oriented health risk assessment of groundwater nitrate by using EMMTE coupled with HHRA model

Conventional concentration-oriented approaches for nitrate risk diagnosis only provide overall risk levels without identifying risk values of individual sources or sources accountable for potential health risks. Therefore, a hybrid model combining the end-member mixing model tool on Excel™ (EMMTE) with human health risk assessment (HHRA) was developed to assess the source-oriented health risks for groundwater nitrate, particularly in the Poyang Lake Plain (PLP) region. The results indicated that the EMMTE and the Bayesian stable isotope mixing model (MixSIAR) exhibited remarkable consistency in source apportionment of groundwater nitrate. The source contribution of groundwater nitrate in PLP was related to land use types, hydrogeological conditions, and soil properties. Notably, manure and sewage sources, contributing up to 53.4 %, represented the largest nitrate pollution sources, with a significant contribution of soil nitrogen and nitrogen fertilizers. The non-carcinogenic risk for four potential sources was below the acceptable threshold of 1. Given the factors including rainfall dilution and economic development, attention should be directed towards mitigating the health risks posed by manure and sewage. This study can verify the efficacy of EMMTE in source apportionment and offer valuable insights for decision-makers to regulate the largest sources of nitrate contamination and enhance groundwater management efficiency.

Output characteristics and driving factors of non-point source nitrogen (N) and phosphorus (P) in the Three Gorges reservoir area (TGRA) based on migration process: 1995-2020

Although physical models at present have made important achievements in the assessment of non-point source pollution (NPSP), the requirement for large volumes of data and their accuracy limit their application. Therefore, constructing a scientific evaluation model of NPS nitrogen (N) and phosphorus (P) output is of great significance for the identification of N and P sources as well as pollution prevention and control in the basin. We considered runoff, leaching and landscape interception conditions, and constructed an input-migration-output (IMO) model based on the classic export coefficient model (ECM), and identified the main driving factors of NPSP using geographical detector (GD) in Three Gorges Reservoir area (TGRA). The results showed that, compared with the traditional export coefficient model, the prediction accuracy of the improved model for total nitrogen (TN) and total phosphorus (TP) increased by 15.46 % and 20.17 % respectively, and the error rates with the measured data were 9.43 % and 10.62 %. It was found that the total input volume of TN in the TGRA had declined from 58.16 × 10⁴ t to 48.37 × 10⁴ t, while the TP input volume increased from 2.76 × 10⁴ t to 4.11 × 10⁴ t, and then decreased to 4.01 × 10⁴ t. In addition Pengxi River, Huangjin River and the northern part of Qi River were high value areas of NPSP input and output, but the range of high value areas of migration factors has narrowed. Pig breeding, rural population and dry land area were the main driving factors of N and P export. The IMO model can effectively improve prediction accuracy, and has significant implications for the prevention and control of NPSP.

Spatial optimization of ecological ditches for non-point source pollutants under urban growth scenarios

Non-point source (NPS) pollution is regarded as the major threat to water quality worldwide, and ecological ditches (EDs) are considered an important and widely used method to collect and move NPS pollutants from fields to downstream water bodies. However, few studies have been conducted to optimize the spatial locations of EDs, particularly when the watershed experiences urbanization and rapid land-use changes. As land-use patterns change the spatial distribution of NPS loads, this study used a cellular automata-Markov method to simulate future land-use changes in a typical agricultural watershed. Three scenarios are included as follows: historical trend, rapid urbanization, and ecological protection scenarios. The spatial distributions of particulate phosphorus loads were simulated using the revised universal soil loss equation and sediment transport distribution model. The results suggested that the total particulate phosphorus (TP) load in the Zhuxi watershed decreased by 10,555.2 kg from 2000 to 2020, primarily because the quality and quantity of forests in Zhuxi County improved over the last 20 years. The TP load in Zhuxi watershed would be 2588.49, 2639.15, and 2553.32 kg in 2040 in historical trend, rapid urbanization, and ecological protection scenarios, respectively, compared with 2308.1 kg in 2020. This indicated that urban expansion increases the TP load, and the faster the expansion rate, the more the TP load. Consequently, the optimal locations of EDs were determined based on the intercepted loads and the period during which they existed during land-use changes. The results suggested that rapid urbanization would consequently reduce the space available for building EDs and also increase the cost of building EDs to control the NPS pollution in the watershed.

Effect of Plant Buffer Zone–Antifouling Curtain Wall on Reducing Non-Point Source Pollution in Paddy Fields, China

In view of the nitrogen and phosphorus non-point source pollution caused by paddy field drainage in southern China, two paddy fields in Nanjing and Yuyao cities were selected to study the effect of plant buffer zone–antifouling curtain walls on reducing non-point source pollution. The results showed that the designed plant buffer zone–antifouling curtain wall systems could significantly reduce the concentration of total nitrogen (TN) and total phosphorus (TP) in drainage of the two paddy fields. Compared with paddy field drainage in Nanjing, the interception rate of TN in the plant buffer zone and antifouling curtain wall were 33.0% and 59.3%, respectively; the removal rates of TP were about 18.4% and 40.3%, respectively. In addition, the contents of ammoniacal nitrogen (NH3-N), nitrate nitrogen (NO3-N) and Chemical Oxygen Demand (COD) were also significantly reduced. For the Yuyao experimental area, compared to the paddy field without the soil plant buffer zone (the control), the concentration of each indicator in the discharge water of the paddy fields with the soil plant buffer system operation mode was significantly reduced, the rejection rate of the TP, TN, total dissolved phosphorus (TDP), NO3-N and NH3-N were 64.28%, 70.66%, 83.73%, 65.22% and 80.69%, respectively. In summary, the construction of a plant buffer zone–antifouling curtain wall (soil plant buffer zone) has an obvious effect on the reduction of non-point source pollution in paddy fields, which could improve yield and fertilizer utilization. The plant buffer zone–antifouling curtain wall could be popularized and applied in local areas and southern China.

Cleaner agricultural production in drinking-water source areas for the control of non-point source pollution in China

With continuous population growth and acceleration of urbanization in China, environmental problems in drinking-water source areas have become increasingly prominent. In some places, domestic wastewater and aquaculture sewage are directly discharged into water bodies without any treatment. Also, large amounts of domestic garbage and aquaculture waste are often randomly stacked, seriously polluting the surrounding groundwater and surface water and deteriorating the water quality. Notably, some agricultural production activities can also cause non-point source pollution, resulting from eutrophication of water bodies. In some instances, these activities can lead to nitrogen losses of 0.7%-83.9% and phosphorus losses of 0.6%-82.8%. In view of this situation, the implementation of cleaner agricultural production is of great significance for protecting the environment in drinking-water source areas and maintaining drinking-water safety. Specific practicable measures include formula fertilization through soil testing, integrated pest management, and water-saving irrigation technology. For the livestock- and poultry-breeding industry, it is necessary for large-scale farms to construct excreta discharge treatment facilities, carry out harmless treatment and resource utilization of organic wastes, establish rural biogas septic tanks, and make use of domestic-sewage and livestock-breeding wastewaters. Also, fixed garbage-dumping sites should be built in rural water-source areas, and a unified garbage-disposal station set up to reduce the pollution discharge of domestic garbage. Moreover, it is crucial to strictly control the development and utilization of hillsides in the middle and upper reaches of the drinking-water source area, as well as strengthen the restoration of vegetation and the construction of soil and water conservation forests in these areas.

Regional assessment of human-caused ecological risk in the Poyang Lake Eco-economic Zone using production-living-ecology analysis

In this study, based on the regional land-use risk space division (regional ecological risk source/receptor space identification) using production–living–ecology analysis, three spatial function indexes, i.e., production, living, and ecology function indexes, were proposed for regional ecological risk assessment (RERA) with respect to human disturbance. The first two indexes can be regarded as regional ecological risk source indexes, whereas the final index can be regarded as a regional ecological risk receptor index. Using an artificial assignment method based on the land-use types and Defense Meteorological Program Operational Line-Scan System (DMSP/OLS) nighttime light intensity data, these three spatial function indexes were effectively manifested. By incorporating these indexes with eco-environmental vulnerability proxies, an RERA framework was established and applied in the Poyang Lake Eco-economic Zone (PLEZ), which is an ecological-protection and economic-development coordination-oriented region in China. The results suggest that (1) the DMSP/OLS nighttime light intensity data correlated well with the spatial distribution of regional urban/town areas; consequently, it was reasonable to use this dataset for representing regional production-living function space (urban/town area). (2) Overall, the forestlands and winter waterbodies of Poyang Lake were in the high-risk grade, and so did the Nanchang City construction land area; in contrast, the final risk levels of winter wetlands and croplands were relatively low. (3) Owing to the highest human disturbance (including both production and consumption human activities) and eco-environmental vulnerability level, urban/town areas such as Nanchang City had the highest final risk grade. (4) The low, medium, high, and very high-risk grades accounted for 21.22%, 39.53%, 36.31%, and 2.94% of the region, respectively. I believe that the proposed land use function indexes will be helpful in conducting human-caused RERA research in the future. Furthermore, the assessment results can provide a scientific basis for regional ecological risk management within the PLEZ.

Assessment and analysis of agricultural non-point source pollution loads in China: 1978-2017

China's successful agriculture development has resulted in public concerned environmental problems. However, continuous and detailed data about Chinese agricultural non-point source pollution (ANPSP) loads are lacking. To assess and analyze Chinese ANPSP loads from 1978 to 2017, an inventory analysis was performed, and a socioeconomic and spatiotemporal analysis in the scale of provinces was conducted. The results showed that the pollution loads of chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP) increased by 91.0%, 196.2% and 244.1%, respectively, and their variation underwent a free development stage, reform promotion stage, market regulation stage and policy incentive stage. The results of the pollution source analysis showed that over the past 40 years, the total percent contribution to COD by livestock and poultry breeding (LPB) and rural household waste (RHW) accounted for 83.1%-96.6%, the total percent contribution to TN by mineral fertilizers (MF) and LPB accounted for 72.3%-80.8%, and the total percent contribution to TP by LPB, RHW and MF accounted for 69.1%-88.6%. In addition, Shandong, Guangdong, Sichuan, and Henan were the top producers of ANPSP loads, and their COD, TN, and TP loads accounted for approximately 32%, 30%, and 35% of the national totals, respectively. The discharge intensity of COD, TN and TP decreased by 79.2%, 67.8%, and 62.6%, respectively. The discharge intensity exhibited a phasic feature that aligned with the national economic plan in the temporal scale and was closely related to the agricultural conditions in the spatial scale.

A bi-level multiobjective stochastic approach for supporting environment-friendly agricultural planting strategy formulation

In this study, integration of analytic hierarchy process method and entropy method (AHP-EW) for quantifying the knowledge and experience accumulated by regional managers as well as the socioeconomic situation, the partial least squares regression (PLS) for reflecting the relationship between irrigation water use efficiency and agronomic inputs, and the ecosystem service value for measuring environmental impacts of changing crop planting area were considered in one framework simultaneously. With help of these efforts, a bi-level multiobjective stochastic approach to improve irrigation water use efficiency and decrease the pollution production of agronomic measures in the process of agricultural production. The proposed framework integrate bi-level multiobjective programming and stochastic expectation programming to not only make tradeoffs among multiple concerns from two-level decision makers, but also deal with the randomness of runoff. Then, the proposed approach was applied to a real-world case in the middle reaches of the Heihe River basin, northwest China. Results show that the developed approach can improve irrigation water use efficiency, reduce CO₂ emission, expand ecosystem service values, and provide more profitable and environment-friendly agricultural planting strategies to decision makers, which can further contribute to the sustainable development of agriculture. Furthermore, by comparing the bi-level multiobjective stochastic programming (BMSP) model with the other six models originated from developed model, it can be found that 1) the single objective model can obtain the best value of that objective, but cannot readily consider other important aspects; 2) the multiobjective models can make tradeoffs among multiple objectives; 3) the BMSP model can reflect the leader-follower relationship in the optimization process. The approach is applicable for arid and semiarid regions that face similar problems to determine agricultural planting strategies.

A Game Theory-Based Approach for Exploring Water Resource Exploitation Behavior in the Poyang Lake Basin, China

Exploring the relationship between competition and cooperation in water resource exploitation by applying a game model is crucial for achieving stable equilibrium in the presence of environmental externalities. To explore this, we used the Poyang Lake Basin, which is divided into three overly exploited sub-regions, as an example. This paper selected the different types of sub-regions of Poyang Lake Basin as the research subjects, and then proposed a game model to study evolutionarily stable equilibrium strategies. The results are as follows: (1) the behavior of the sub-regions of Poyang Lake Basin are affected by one another and cannot achieve equilibrium through independent games, which also need external forces to coordinate the three reaches; (2) the benefits improve gradually from the state of “non-cooperation” to “full cooperation” and reach an ideal equilibrium when all the sub-regions choose the strategy of cooperation; (3) the strategic choice of sub-reaches is difficult to maximize the overall benefits of the basin in the absence of external constraints. To ensure that the sub-regions choose the cooperative strategy, the central government should support the cooperative subsidies of local governments. In addition to improving the equilibrium state of the sub-reaches, this study proposes the following policy implications: constructing a basin plan and promoting fiscal transfer payments, inducing an industrial gradient transfer, and strengthening the payment for the use of water resources.

Effect of aquatic macrophyte growth on landscape water quality improvement

The water of urban landscape park is often confronted with microalgal blooms due to its stagnancy. Bioremediation using the combined emergent and submerged plants to control the microalgae growth was investigated in the present study. Two water bodies (Bei and Xin) of Yuyuantan Park in Beijing were selected for the field experiments, and the other lakes with different vegetation of macrophytes were selected as the comparison. The concentrations of chlorophyll a (chl a), chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP), and water temperature and transparency were monitored before and after bioremediation from 2015 to 2017. Results showed that the effects of microalgal inhibition were more significant 2 years after bioremediation. Specifically, the chl a of Dong Lake without any vegetation of macrophytes was up to 65.1 μg/L in summer of 2017, while the Bei and Xin Lakes was only 6.2 and 11.3 μg/L, respectively. In addition, the water quality and transparency also improved, with water bodies being crystal clear. Submerged plants played major roles in microalgal control and water quality improvement, compared to the lakes with only emergent plants. The intensity of humic acid-like substances in three-dimensional fluorescent spectra was stronger for the lakes with submerged plants.

Removal of non-point source pollutants from domestic sewage and agricultural runoff by vegetated drainage ditches (VDDs): Design, mechanism, management strategies, and future directions

Domestic wastewater and agricultural runoff are increasingly viewed as major threats to both aquatic and terrestrial ecosystems due to the introduction of non-point source inorganic (e.g., nitrogen, phosphorus and metals) and organic (e.g., pesticides and pharmaceutical residues) pollutants. With rapid economic growth and social change in rural regions, it is important to examine the treatment systems in rural and remote areas for high efficiency, low running costs, and minimal maintenance in order to minimize its influence on water bodies and biodiversity. Recently, the use of vegetated drainage ditches (VDDs) has been employed in treatment of domestic sewage and agricultural runoff, but information on the performance of VDDs for treating these pollutants with various new management practices is still not sufficiently summarized. This paper aims to outline and review current knowledge related to the use of VDDs in mitigating these pollutants from domestic sewage and agricultural runoff. Literature analysis has suggested that further research should be carried out to improve ditch characteristics and management strategies inside ditches in order to ensure their effectiveness. Firstly, the reported major ditch characteristics with the most effect on pollutant removal processes (e.g., plant species, weirs, biofilms, and substrates selection) were summarized. The second focus concerns the function of ditch characteristics in VDDs for pollutant removal and identification of possible removal mechanisms involved. Thirdly, we examined factors to consider for establishing appropriate management strategies within ditches and how these could influence the whole ditch design process. The current review promotes areas where future research is needed and highlights clear and sufficient evidence regarding performance and application of this overlooked ditch system to reduce pollutants.

Water Bacterial and Fungal Community Compositions Associated with Urban Lakes, Xi'an, China

Urban lakes play a vital role in the sustainable development of urbanized areas. In this freshwater ecosystem, massive microbial communities can drive the recycling of nutrients and regulate the water quality. However, water bacterial and fungal communities in the urban lakes are not well understood. In the present work, scanning electron microscopy (SEM) was combined with community level physiological profiles (CLPPs) and Illumina Miseq sequence techniques to determine the diversity and composition of the water bacterial and fungal community in three urban lakes, namely Xingqing lake (LX), Geming lake (LG) and Lianhu lake (LL), located in Xi’an City (Shaanxi Province, China). The results showed that these three lakes were eutrophic water bodies. The highest total nitrogen (TN) was observed in LL, with a value of 12.1 mg/L, which is 2 times higher than that of LG. The permanganate index (COD_Mn) concentrations were 21.6 mg/L, 35.4 mg/L and 28.8 mg/L in LG, LL and LX, respectively (p < 0.01). Based on the CLPPs test, the results demonstrated that water bacterial communities in the LL and LX urban lakes had higher carbon source utilization ability. A total of 62,742 and 55,346 high quality reads were grouped into 894 and 305 operational taxonomic units (OTUs) for bacterial and fungal communities, respectively. Water bacterial and fungal community was distributed across 14 and 6 phyla. The most common phyla were Proteobacteriaand Cyanobacteria. Cryptomycota was particularly dominant in LL, while Chytridiomycota and Entomophthormycota were the most abundant fungal phyla, accounting for 95% of the population in the LL and 56% in the LG. Heat map and redundancy analysis (RDA) highlighted the dramatic differences of water bacterial communities among three urban lakes. Meanwhile, the profiles of fungal communities were significantly correlated with the water quality parameters (e.g., COD_Mn and total nitrogen, TN). Several microbes (Legionella sp. and Streptococcus sp.) related to human diseases, such as infectious diseases, were also found. The results from this study provides useful information related to the water quality and microbial community compositions harbored in the aquatic ecosystems of urban lakes.