Accurate water quality estimation is important for water environment monitoring and water resource management and has emerged as a pivotal aspect of ecological rehabilitation and sustainable development. However, due to the strong spatial heterogeneity of water quality parameters, it is still challenging to obtain highly accurate spatial patterns of them. Taking chemical oxygen demand as an example, this study proposes a novel estimation method for generating highly accurate chemical oxygen demand fields in Poyang Lake. Specifically, based on the different water levels and monitoring sites in Poyang Lake, an optimal virtual sensor network was first established. A Taylor expansion-based method with integration of spatial correlation and spatial heterogeneity was developed by considering environmental factors, the optimal virtual sensor network, and existing monitoring stations. The proposed approach was evaluated and compared with other approaches using a leave-one cross-validation process. Results show that the proposed method exhibits good performance in estimating chemical oxygen demand fields in Poyang Lake, with mean absolute error improved by 8% and 33%, respectively, on average, when compared with classical interpolators and remote sensing methods. In addition, the applications of virtual sensors improve the performance of the proposed method, with mean absolute error and root mean squared error values reduced by 20% to 60% over 12 months. The proposed method provides an effective tool for estimating highly accurate spatial fields of chemical oxygen demand concentrations and could be applied to other water quality parameters.

Hydropower construction and climate change have aggravated river hydrological changes, which have reduced the water flow regime in the Ruhe River Basin. The reduced flow of the river seriously affected the water supply of nearby residents and the operation of the river ecosystem. Therefore, in order to alleviate the contradiction between water use for hydropower facilities and environmental water use, the urgent need is to explore the ecological flow-threshold of rivers. This study took the Fuhe River Basin as the research object, and summarized the monitoring data of eight hydrological stations from recent decades. Based on this, we explored the response law of P-IBI and flow, a tool to quickly measure the health of the ecosystem. Through the response relationship between alterations in environmental factors of the river and phytoplankton index of biotic integrity (P-IBI), it was determined that environmental flow was the dominant influencing factor of P-IBI. According to P-IBI, the threshold of environmental discharge in the Fuhe River was limited to 273~826.8 m3/s. This study established a regulatory framework for the river flow of large rivers by constructing P-IBI and determining the critical thresholds of environmental flow by constraining the constitution. These results provide a theoretical basis for better planning and improvement of river ecosystem restoration and river utilization.

Microplastics (MPs) are widely detected in wetlands as emerging pollutants of global concern. Co-occurrence of MPs and trace metals in wetlands is common and the vector effects of MPs on other environmental pollutants have been increasingly reported. However, the interaction of different MPs and trace metals under environmentally realistic conditions is not well understood. Here, we investigated the adsorption capacity of MPs for metals under simulated conditions of Poyang Lake wetlands in Jiang Xi, China, a Ramsar site of international importance for conservation and sustainable use. ICP-MS was used to quantify the amount of adsorbed metals onto different types of MPs. SEM-EDS and micro-FTIR were used to examine the morphological and chemical characteristics of MPs before and after metal adsorption. The influence of internal (polymer types and particle sizes of MPs) and external factors (water pH values, organic matters, ion strength, and sediment) on metal adsorption was systematically investigated. Metal adsorption equilibrium was most achieved at 72 h. The adsorption capacity of MP types to metal ions tended to decrease as PP > PE > PS, and the amount of adsorbed metals decreased as Cu > Pb > Cd. The amount of adsorbed metals generally decreased with the increase of particle size of MPs. With the increase of water pH and K+ strength, the adsorption of metals by MPs showed an increasing and then decreasing trend; the adsorption capacity of MPs increased with the increase of fulvic acid. Under the simulated sedimentary conditions, the adsorption of different metals by MPs also tended to be Cu > Pb > Cd, which was mainly determined by metal concentrations in the sediments collected in situ. The results of this study improve our understanding of metal-MP interaction under simulated environmental conditions, shedding new light on the environmental behavior of MPs and metals in wetlands.

BACKGROUND: Oncomelania hupensis is the only intermediate host of Schistosoma japonicum and plays a decisive role in its transmission. The variation of water level greatly affects the reproduction and growth of snails. Therefore, in this paper, we analyze the variations of water level in the Poyang Lake region from 1993 to 2016 combined with satellite imagery to elucidate the evolution of the snail breeding environment.
METHODS: By employing remote sensing data from 1993 to 2016 (April-June and September-November), the vegetation area of Poyang Lake and the vegetation area at different elevations were extracted and calculated. Moreover, the average daily water level data from the four hydrological stations (Hukou station, Xingzi station, Tangyin station and Kangshan station) which represent the typical state of Poyang Lake were collected from 1993 to 2016. The variance of the monthly mean water level, inundation time and the average area were analyzed by variance to find a significance level of α = 0.05.
RESULTS: According to hydrological data before and after 2003, the average water level after 2003 is significantly lower than that before 2003 in Poyang Lake. After 2003, the time of inundateing the snail breeding period was later in April to June than that before 2003, while the time of wate-falling stage in September to November moved forward after 2003 than before 2003. Of them, the lowest water level affecting the breeding and growing period of O. hupensis in the northern part of Poyang Lake decreased from 11 m to 9 m. After 2003, the expansion of meadow area in the north part of Poyang Lake was mainly concentrated in the elevation of 9-11 m, and the newly increased infested-meadow in the lake area was mainly concentrated in the north part of Poyang Lake.
CONCLUSIONS: By comparing the change of water level characteristics in different parts of the Poyang Lake area as well as changes in meadow area before and after 2003, it is found that the water level changes mainly affect the snail breeding area in the northern part of Poyang Lake. The results are helpful for improving scientific measures for snail control in Jiangxi Province. This approach could also be applicible to Dongting Lake area and other lake areas affected by water level changes and can bring significant guidance for snail control in lake areas.

The relationships between inflow and outflow water quality data for Poyang Lake from 1996 to 2016 are discussed and the main influencing factors are identified. TN and TP were the main factors causing a decline in water quality in Poyang Lake during the study period. The water quality of both the inflow and outflow rivers was generally good between 1996 and 2003; however, water quality declined over the study period, which is attributed to an increase in nutrients loads in the watershed. From 2004 to 2011, the water quality of the \"Five Rivers\" decreased significantly, which caused the water quality of Poyang Lake to decline. Due to the high purification capacity of Poyang Lake, the water quality of the outflow during this period was relatively good. A decline in water quality after this point was affected by pollution loads and hydrological conditions. Specifically, from 2012 to 2016, water quality in Poyang Lake and of the inflow water declined further. This was combined with a decrease in the water-purification capacity of the lake due to changes in the hydrological conditions, resulting in lower water quality at the outflow. Overall, the water quality of the inflow river has been closely related to the water quality in Poyang Lake. The concentrations of TN were significantly higher in the southern and eastern areas of Poyang Lake compared to the western areas. Higher nutrient loading from the Ganjiang River and the Xinjiang River has been an important driver. The concentrations of TP in the southern area of the lake have been significantly higher than in the eastern and western areas. This is attributed to comparatively high TP loads in the Ganjiang River and the Fuhe River. Compared to the changes in hydrological conditions, variations in nutrient loading have had a greater effect on water quality in the lake.

OBJECTIVE: To grasp the distribution status of Oncomelania hupensis snails in Poyang Lake area, so as to provide the evidence for formulating and adjusting the schistosomiasis prevention and control strategy in lake areas.
METHODS: The vector grid was created and sampled randomly by 200 m × 200 m in the spatial database of grassland, and the distribution of snails was investigated in the selected grid by using the method of mechanical sampling by 50 m × 50 m. At the same time, the elevation of investigation points was extracted based on the topographic map of Poyang Lake.
RESULTS: Totally 949 and 210 investigation points were collected from the south and north of Poyang Lake areas, accounting for 3.04% and 3.21% of all the investigation points in the respective region. The number of investigation points, the appearance rate of snail frame, and the average density of alive snails were 15 231, 8.15%, and 0.463/0.1 m2, respectively. The elevation of snail distribution area of the south and north Poyang Lake areas were 11-16 m and 9-16 m respectively. The elevation of concentrated snail belts of the south Poyang Lake area were 12-13 m and 15-16 m, and the elevation of concentrated snail belts of the north Poyang Lake area was 12-14 m.
CONCLUSIONS: The distribution of snails is in the range of 9-16 m. The suitable habitats of snail breeding are moving from the south Poyang Lake area to the north Poyang Lake area, and from high elevation to low elevation. In the future, the schistosomiasis prevention and control measures could be formulated based on the geographical characteristics of current snail distribution in order to consolidate the achievements of schistosomiasis control.
[摘要]目的 掌握鄱阳湖区草洲钉螺分布现状, 为制订和调整湖区血吸虫病防治对策提供依据。 方法 对鄱阳湖区 草洲空间数据库按200 m × 200 m创造矢量网格, 对网格进行随机抽样, 并对抽取的网格以50 m × 50 m开展系统抽样法 调查螺情; 同时以2009年鄱阳湖区湖底地形图为基础提取所有调查螺点的高程数据, 分析有螺点的平均高程和极值, 明 确钉螺在草洲分布高程范围。 结果 鄱阳湖区南湖和北湖分别选取网格样本949个和210个, 占各自区域总样本的 3.04%和3.21%; 共调查螺点15 231框 (每框面积为0.1 m2), 有螺框出现率8.15%, 活螺平均密度为0.463只/0.1 m2; 鄱阳湖 区南湖和北湖有螺区域高程分布分别为11～16 m和9～16 m, 南湖密螺带分布高程为12～13 m和15～16 m, 北湖密螺 带分布高程为12～14 m。 结论 鄱阳湖区草洲钉螺分布在9～16 m的高程范围内, 湖区适宜钉螺孳生, 繁殖生境已向鄱 阳湖北部及下高程区移动。在今后的血吸虫病防治工作中, 可依据现行钉螺孳生的地理特点, 制定出更为科学的防治措 施, 进一步巩固血吸虫病防治成果。.

Comprehensively evaluating water quality with a single method alone is challenging because water quality evaluation involves complex, uncertain, and fuzzy processes. Moreover, water quality evaluation is limited by finite water quality monitoring that can only represent water quality conditions at certain time points. Thus, the present study proposed a dynamic fuzzy matter-element model (D-FME) to comprehensively and continuously evaluate water quality status. D-FME was first constructed by introducing functional data analysis (FDA) theory into a fuzzy matter-element model and then validated using monthly water quality data for the Poyang Lake outlet (Hukou) from 2011 to 2012. Results showed that the finite water quality indicators were represented as dynamic functional curves despite missing values and irregular sampling time. The water quality rank feature curve was integrated by the D-FME model and revealed comprehensive and continuous variations in water quality. The water quality in Hukou showed remarkable seasonal variations, with the best water quality in summer and worst water quality in winter. These trends were significantly correlated with water level fluctuations (R = -0.71, p < 0.01). Moreover, the extension weight curves of key indicators indicated that total nitrogen and total phosphorus were the most important pollutants that influence the water quality of the Poyang Lake outlet. The proposed D-FME model can obtain scientific and intuitive results. Moreover, the D-FME model is not restricted to water quality evaluation and can be readily applied to other areas with similar problems.