Comparison of antimony and arsenic behaviour at the river-lake junction in the middle of the Yangtze River Basin

As typical metalloid toxic elements widely distributed in environmental media, the geochemical behaviour of antimony (Sb) and arsenic (As) affects environmental safety. We selected the surface waters and sediments at the river-lake junction of Dongting Lake as the research objects, analysed the concentration and chemical partitioning of Sb and As, assessed its contamination and ecological risk levels, and discussed its sources and potential influencing factors. The concentrations of dissolved Sb and As in surface waters were low (< 5.46 µg/L), and the concentrations of Sb and As in surface sediments were 2.49-22.65 mg/kg and 11.10-136.34 mg/kg, respectively. Antimony and As in sediments were mainly enriched in the fraction of residues, but the proportion of As in bioavailability was significantly higher than that of Sb. Although the contamination level of Sb was higher than that of As, the risk assessment code (RAC) showed that the ecological risk level of As was higher than that of Sb. Rainwater erosion and mining activities (in the midstream of Zijiang River) were the main contaminated sources of Sb, while As was affect mainly by rainwater erosion. The contamination and ecological risk of Sb in the inlet of the Zijiang River should receive considerable attention, while those of As in the inlet of the Xiangjiang River should also be seriously considered. This study highlights the need for multi-index-based assessments of contamination and ecological risk and the importance of further studies on the environmental behaviour of metalloids in specific hydrological conditions, such as river-lake junctions.

Geochemical processes of phosphorus‑iron on sediment-water interface during discharge of groundwater to freshwater lakes: Kinetic and mechanistic insights

Groundwater is widely recognized as a source of lake materials. When it discharges into lakes, phosphorus(P)‑iron(Fe) geochemical reactions occur due to environmental changes, affecting P discharge from groundwater. However, redox kinetics of Fe and associated P geochemical processes at the sediment-water interface are not fully understood. Taking Dongting Lake as an example, this study explored Fe and P geochemical processes at the sediment-water interface under groundwater discharge with high Fe and P concentrations. We incubated sediments from Dongting Lake under anoxic-oxic conditions with different initial aqueous P/Fe ratios and pH. Aqueous PO43--P and Fe2+, and solid P and Fe phases in sediments were analyzed, and experimental data were further simulated using numerical reactive models. At the beginning of the experiment, aqueous P and Fe were adsorbed rapidly on sediments. Under anoxic conditions, the Fe reduction rate decreased with decreasing content of poorly crystalline ferric (oxyhydr)oxides, and the addition of aqueous P and Fe at neutral pH enhanced the reduction rate. The increased aqueous P was dominated by desorption caused by sediment Fe reduction and then fixed by gibbsite adsorption and hydroxyapatite precipitation. Under oxic conditions, Fe(II) oxidation under was pH- and (P:Fe)ini-independent, with a sharp rate decline. Furthermore, the final sediment Fe(II) content was higher than the initial content, indicating the formation of a low-oxidizability Fe(II) phase. The P dynamics were dominated by adsorption on the produced Fe-oxides. The numerical models also suggested that heterogeneity in natural sediments promotes hydroxyapatite formation at low pH, but restricts it at high pH. The findings reveal that although aqueous P concentration decreased during groundwater discharge to lakes, PO43--P concentration remained much higher than that in natural lake water, increasing the risk of lake eutrophication. The paper provides references for further understanding of P loading from groundwater discharge into lakes.

[Driving Factors Analyze of Phytoplankton Community by Comparison of Population and Functional Groups and Water Quality Evaluation in Dongting Lake]

Phytoplankton is the most important component of water ecosystems, which could indicate the state of the water environment owing to its sensitivity to water environment variation. However, its response to the environment is influenced by classification methods. To understand the phytoplankton population(phyla and genera) and functional groups(FG) for driving response characteristics and applicability to the environment in Dongting Lake, a total of four samples were collected from the lake from March to December 2019, and the distribution characteristics of the phytoplankton population and functional groups and their responses to environmental factors were compared and analyzed. Meanwhile, the applicability of the TLI index, Shannon-Wiener index, and Q index was compared in Dongting Lake. The results showed that a total of 61 genera belonging to six phyla of phytoplankton were detected in Dongting Lake, which could be divided into 23 functional groups and nine dominant functional groups. The succession trend of functional groups was P/MP/D(March)→MP/P/J(June)→MP/H1(September)→Y/P/MP(December). The results of hierarchical segmentation showed that the population distribution and change in phytoplankton were driven by environmental factors more than the area in Dongting Lake. The main environmental factors affecting phytoplankton population and functional groups were water temperature(WT), permanganate index, dissolved oxygen(DO), conductivity(Cond), water level(WL), and total phosphorus(TP). RDA analysis showed that phytoplankton functional groups identified phytoplankton response to environmental factors better than phytoplankton population. It was shown that using the Q index to evaluate water quality had better applicability in Dongting Lake.

Effects of Summer and Autumn Drought on Eutrophication and the Phytoplankton Community in Dongting Lake in 2022

Since July 2022, the Yangtze River basin has experienced the most severe hydro-meteorological drought since record collection started in 1961, which has greatly affected the ecological environment of the Dongting Lake (DTL) basin. To investigate the effects of drought events on the eutrophication and phytoplankton community structure of DTL, the lake was sampled twice in August and September 2022 based on the water level fluctuations resulting in 47 samples. Furthermore, we combined the comprehensive trophic level index (TLI) and phytoplankton Shannon-Wiener diversity index (H) to characterize and evaluate the eutrophication status. The key influencing factors of the phytoplankton community were identified using redundancy analysis (RDA), hierarchical partitioning, and the Jaccard similarity index (J). Our results showed that the TLI of DTL changed from light-moderate eutrophication status (August) to mesotrophic status (September), whereas the H changed from light or no pollution to medium pollution. The phytoplankton abundance in August (122.06 × 104 cells/L) was less than that in September (351.18 × 104 cells/L) in DTL. A trend in phytoplankton community succession from Bacillariophyta to Chlorophyta and Cyanophyta was shown. The combination of physiochemical and ecological assessment more accurately characterized the true eutrophic status of the aquatic ecosystem. The RDA showed that the key influencing factors in the phytoplankton community were water temperature (WT), pH, nitrogen and phosphorus nutrients, and the permanganate index (CODMn) in August, while dissolved oxygen (DO) and redox potential (ORP) were the key factors in September. Hierarchical partitioning further indicated that temporal and spatial variations had a greater impact on the phytoplankton community. And the J of each region was slightly similar and very dissimilar, from August to September, which indicated a decreased hydrological connectivity of DTL during drought. These analyses indicated that the risk to the water ecology of DTL intensified during the summer-autumn drought in 2022. Safeguarding hydrological connectivity in the DTL region is a prerequisite for promoting energy flow, material cycle, and water ecosystem health.

[Characteristics and Source Analysis of Heavy Metals in Farmland Soil on the South of Dongting Lake]

Based on the grid distribution method, 1589 topsoil samples were collected from farmland on the south side of Dongting Lake from April to August 2020. The content, potential ecological risk, spatial distribution characteristics, and source analysis of heavy metals in the soil were studied. The concentrations and pH of As, Cd, Pb, Cu, Zn, Ni, Cr, and Hg in the soil were determined using ICP-MS, ICP-OES, HG-AFS, and ISE methods. The results showed that the average concentrations of Zn, Cr, Pb, Cu, Ni, As, Cd, and Hg were 118.18, 82.21, 52.1, 33.76, 32.81, 18.25, 0.42, and 0.13 mg·kg^-1, respectively. All heavy metals had medium or high variability. The soil was mainly weakly acidic with a pH between 3.96 and 7.90. Hg and Cd had high ecological risks. The spatial distribution of heavy metals showed a tendency of being high in the southwest and low in the northeast. The PMF and PCA methods were used to analyze the sources and calculate the contribution rates of the eight types of heavy metals. The PMF results showed that the contribution rates of soil heavy metals in the study area were as follows:agricultural activity sources (36.98%), natural sources (32.94%), water and soil exchange sources (17.05%), and atmospheric dry and wet deposition sources (13.03%). The PCA results showed that the soil heavy metals in the study area mainly came from agricultural activity sources (68.04%), natural sources (31.02%), and atmospheric deposition sources (0.94%). The conclusions of the two source analysis methods tended to be consistent, that is, agricultural activities were the main source of soil heavy metals in the study area. The vertical profile analysis showed that the contents of Cd, Hg, and Pb elements were high in the surface layer and low in the deep layer, and the phenomenon of anthropogenic input was obvious. These results can provide a scientific basis for the formulation of prevention and control countermeasures of farmland soil heavy metal pollution around Dongting Lake.

Characteristics and DGT Based Bioavailability of Cadmium in the Soil-Crop Systems from the East Edge of the Dongting Lake, China

Contamination of heavy metals (including the cadmium, Cd) in agricultural soils has become an increased issue, posing a threat to the crop safety and human health. In order to evaluate the contamination characteristics and bioavailability of Cd in the soil−crop systems from the East edge of the Dongting Lake, four kinds of agricultural products for typical crops (rice, peanut, sweet potato, and corn) and corresponding rhizosphere soils were collected and analyzed for the Cd concentrations. The technique of diffusive gradients in thin-films (DGT) was applied to evaluate the Cd bioavailability in the rhizosphere soils. Concentrations of Cd ranged from 0.04 to 2.95 mg/kg (average 0.24 mg/kg) with 73.9% sites above the background levels, especially for paddy soils. Cd concentrations in the agricultural products ranged from 0.01 to 2.19 mg/kg (average 0.18 mg/kg), with Cd enrichment observed in the peanut samples. No obvious correlations (R2 < 0.25) were observed between the Cd concentrations in the agricultural products and total Cd concentrations in the rhizosphere soils, this indicated that the total Cd concentrations in the soils cannot predict the concentrations in the agricultural products of crops. While the DGT measured Cd concentrations showed good correlations (R2 = 0.64−0.90) with the concentrations in the most agricultural products of crops, which may be used to evaluate the safety of the soil and further safety of the agricultural products of crops. Overall, DGT showed a good potential for prediction of heavy metal bioavailability in soil since the DGT technique can simulate the sustained supply of heavy metals from solid to liquid in the soils.

Ecosystem Service Values in the Dongting Lake Eco-Economic Zone and the Synergistic Impact of Its Driving Factors

Ecosystem service values (ESVs) are crucial to ecological conservation and restoration, urban and rural planning, and sustainable development of land. Therefore, it is important to study ESVs and their driving factors in the Dongting Lake Eco-Economic Zone (Dongting Lake). This paper quantifies the changes in ESVs in the Dongting Lake using land use data from 2000, 2005, 2010 and 2018. The eXtreme Gradient Boosting (XGBoost) model is used to study the effects of individual driving factors and the synergistic effects of these driving factors on ESVs. Our analysis suggests that: (1) From 2000 to 2018, the largest dynamic degree values in the Dongting Lake are in unused land types, followed by construction lands and wetlands. The ESVs of the Dongting Lake show an increasing trend, with those of forestlands being the highest, accounting for approximately 44.65% of the total value. Among the ESVs functions, water containment, waste treatment, soil formation and protection, biodiversity conservation and climate regulation contribute the most to ESVs, with a combined contribution of 76.64% to 76.99%; (2) The integrated intensity of anthropogenic disturbance shows a U-shaped spatial distribution, decreasing from U1 to U3. The driving factors in descending order of importance are the human impact index, total primary productivity (GPP), slope, elevation, population, temperature, gross domestic product, precipitation and PM2.5; (3) When the GPP is low (GPP < 900), the SHAP (SHapley Additive exPlanation) value of the high human impact index is greater than zero, indicating that an increase in GPP increases the ESVs in the Dongting Lake. This study can provide technical support and a theoretical basis for ecological environmental protection and ecosystem management in the Dongting Lake.

Inter-annual and intra-annual variations in water quality and its response to water-level fluctuations in a river-connected lake, Dongting Lake, China

The hydrological conditions of river-connected lakes are complex primarily owing to their considerable water-level fluctuations (WLFs). Water quality in such lakes varies with hydrodynamic variations; however, their relationship is not clear. To identify the unique relationship between water level and water quality in river-connected lakes, we used the comprehensive pollution index (CPI) and regression analysis to analyze the spatiotemporal variation in water quality in Dongting Lake from 2015 to 2018 and the effects of water level on water quality. Four water quality parameters were selected: total nitrogen (TN), total phosphorus (TP), permanganate index (CODMn), and chlorophyll a (Chl-a). The results showed significant spatial variation in the lake water quality, with relatively high concentrations of TN, TP, CODMn, and Chl-a in East Dongting Lake. TN and TP decreased by 12.15% and 37.61%, respectively, from 2015 to 2018, whereas CODMn increased from 1.781 to 2.009 mg/L. Seasonally, TN and TP concentrations were low in the summer and autumn, with high concentrations in the winter and spring. In contrast, CODMn and Chl-a concentrations exhibited opposite trends. The pollution level in Dongting Lake ranged between slightly and moderately polluted, with a CPI ranging from 0.76 to 1.32 across all sampling sites during 2015-2018. The water level in Dongting Lake initially increased and, then, decreased in a year, with marked WLFs owing to seasonal shifts in precipitation and human activities. The water level had significant negative relationships with TN and TP concentrations and a significant positive relationship with CODMn concentration (p < 0.05). Based on the results, strict control of excessive external nutrient loading should be actively implemented in Dongting Lake, in addition to hydrological regulation for effective lake water quality management.

[Distribution Characteristics and Risk Assessment of 209 Polychlorinated Biphenyls in Dongting Lake and the Inflow Rivers]

In order to fully understand the pollution of polychlorinated biphenyls (PCBs) in Dongting Lake, 209 PCB congeners were quantitatively detected and analyzed by isotope-dilution high-resolution mass spectrometry in 21 surface water sampling sites of Dongting Lake and the inflow rivers of the lake. The results showed that a total of 50 PCB congeners were detected in the study area. The ρ(ΣPCBs) ranged from 0.077 to 10 ng·L^-1, with an average concentration of 2.7 ng·L^-1 and a median concentration of 1.9 ng·L^-1. The order of contamination concentrations were as follows:the inflow rivers of the lake > lake region > outlet. Compared with the reports of domestic and foreign studies, PCB pollution in Dongting Lake is at a low level. The main pollutants in the surface water were dichlorobiphenyls and tri- and tetrachlorobiphenyls, with relative abundances of 67%, 14%, and 16%, respectively. PCB11, PCB17, PCB18, PCB20+33, PCB28, PCB47+75, PCB52, and PCB68 were the most widely distributed and detected in more than 80% of samples. Among them, ρ(PCB11) was the highest, with an average concentration of 1.6 ng·L^-1, accounting for 59% of ρ(ΣPCBs), from the domestic organic pigment production process of unintentional emissions. Atmospheric transport deposition and historical residue were the main sources of PCBs in water. According to the toxicity equivalent factor method, the ecological toxicity risk of the study area was evaluated, and the results showed that the TEQ in the water was far lower than the relevant standard limit, indicating that the pollution of PCBs in the surface water of Dongting Lake and the inflow rivers would not cause harm to exposed organisms.

Is water quality better in wet years or dry years in river-connected lakes? A case study from Dongting Lake, China

Water quality is essential for lake systems, which are not only influenced by climate change and human activities but are also controlled by high-frequency hydrological rhythms. However, the differences in water quality during different hydrological periods have not been addressed in detail. Here, a 15-year water quality dataset (2004-2018) was selected to explore the variation trends and their relationship with water level in different hydrological periods in Dongting Lake, a typical river-connected lake in China. The hydrological periods were classified into hydrological years and hydrological phases based on the characteristics of water level fluctuations. The results showed that annual variation in the water level in Dongting Lake fluctuated between 23.63 and 25.81 m from 2004 to 2018, and also displayed considerable water level differences ranging from 7.66 m (dry years) to 9.97 m (wet years) within a year. The water level of the lake phase showed significant differences among the different hydrological years. The concentration of TP, COD_Mn, and NH₃-N showed significant decreasing trends, whereas that of TN showed a significant increasing trend from 2004 to 2018. The TN concentration in wet years was significantly higher than that in dry years, which could be attributed to sewage discharge and hydrological conditions. The contributions of the lake phase to the total sewage discharge successively decreased from 64.54% in wet years to 59.47% in dry years, while the river phase showed the opposite trends, ranging from 35.46% to 40.53%, reflecting the strong relationship between water regimes and pollutant fluxes. A regression analysis indicated the different responses of water quality to water level fluctuations over hydrological years, and water quality in different hydrological phases clearly separated the lake and river phases, highlighting the influence of water level fluctuations on water quality within a year. To maintain the water quality of Dongting Lake, the control of external load should not be relaxed, and hydrological regulation should be actively carried out within each year.

Distribution and assessment of cadmium contamination in sediments from the Four River inlets to Dongting Lake, China

The total concentrations of Cd in bulk sediments and those of the BCR sequential extraction fractions of sediments from inlets of the Four Rivers that feed Dongting Lake were determined using ICP-MS techniques. The results suggested that Cd was heterogeneously distributed in the inlet sediments of the rivers, with the highest degree of enrichment in sediments from the Xiangjiang River. The Cd anomaly was defined as Cd enrichment in sediments with an EF (enrichment factor) > 10.0, and it was identified in the inlet sediments of the Xiangjiang River. Cd in the sediments was dominated by acid-soluble Cd at a proportion of 23.9-69.8 (%) compared to its total concentrations in the sediments. The inlet sediments of the Four Rivers were contaminated with Cd, with the highest degree of contamination in the inlet sediments of the Xiangjiang River. The Cd contamination as well as the Cd anomaly in the sediments were closely related to the industrial activities (e.g. smelting and refining for ore minerals) in the areas, and Cd contamination at high levels may represent an ecological risk for the lake watershed. Cd contamination of the inlet sediments may also impact the lake basin sediments and is harmful to the lake ecological system, particularly for sediments of the Xiangjiang River. Therefore, it is essential to control and treat Cd contamination in the inlet sediments for ecological environmental protection of lake watersheds.

Occurrence, spatial distribution, source, and ecological risk assessment of organochlorine pesticides in Dongting Lake, China

The occurrence, distribution, sources, and ecological risks of organochlorine pesticides in Dongting Lake of China were investigated. The average concentrations of organochlorine pesticides (OCPs) in 22 surface water samples and 14 sediment samples were 90.07 ng/L and 80.65 ng/g dw, respectively. Sixteen types of OCPs, dominated by HCHs, DDTs and heptachlor, were detected in the Dongting Lake. The relationships of OCP residues between Dongting Lake and its tributary rivers have been discussed and the hydraulic connections with the Yangtze River and the Three Gorges Dam (TGD) were also considered. Results showed that the shortage of runoff, earlier dry season, and reduction of sediment deposition extremely deteriorated the hydraulic conditions, magnified the water cycle, and restrained the self-purification of OCPs. The ∑OCPs in surface water were concentrated in the inlets of Yangtze River, Lishui River, Zishui River, Yuanshui River, and Xiangjiang River. Moreover, the ∑OCPs in the outlet of the Yangtze River also maintained a high level, indicating that OCPs posed adverse effects on the Yangtze River. Risk assessments of OCPs in the surface water of Dongting Lake were estimated according to available water quality guidelines and health risk assessment models. The results indicated that OCPs in the surface water of Dongting Lake were safe for aquatic organisms and human health. In addition, sediment quality guidelines (SQGs) were also applied to evaluate the potential ecotoxicological risks of OCPs in sediments. The results presented that contaminants of γ-HCH; o,p'-DDD; and dieldrin in sediment had adverse effects on benthic organisms, indicating that fundamental solutions should be proposed to control OCP contamination in Dongting Lake.

Contribution of groundwater discharge and associated contaminants input to Dongting Lake, Central China, using multiple tracers (222Rn, 18O, Cl-)

Lacustrine groundwater discharge (LGD) can play an important role in water and contaminant mass balance of lakes. Dongting Lake is the second largest fresh lake in China which is connected to Yangtze River and has quite prominent ecological status and function within Yangtze River basin. However, the effect of groundwater discharge on the balance of water and contaminant in Dongting Lake has long been overlooked. This study estimated the groundwater discharge and associated contaminants input into Dongting Lake during the dry season using multiple tracers (²²²Rn, ¹⁸O, Cl^-). After sensitivity analysis of different models, it is found that the result of ²²²Rn mass balance model is the most reliable. Based on the ²²²Rn mass balance model, the groundwater discharge rate is estimated to be 73.94 mm/d and the contribution of LGD to water balance is 10.94%. As the main nutrient components, NH₃-N, P and Si from groundwater input account for 23.65%, 5.12% and 30.15%  % of the total input, respectively. As the main heavy metal components, Fe, Mn and As from groundwater input all account for more than 50% of the total input. Although the LGD rate is relatively small, the contaminant input from LGD is significant enough, which may be a potential threat to the ecological stability of Dongting Lake. In this study, the mass balance models of multiple tracers were integrated to understand the role of groundwater in maintaining the water balance and pollution status of Dongting Lake, which has certain reference significance for the LGD study in plain lakes or reservoirs with complex water systems in humid regions.

Evaluation and variation trends analysis of water quality in response to water regime changes in a typical river-connected lake (Dongting Lake), China

Lake water pollution has caused many serious ecological issues globally. An emerging public concern over water quality deterioration in lakes has heightened the need to evaluate the water quality of lakes at long-term scales, particularly for those with high hydrological alterations. This study combines the Mann-Kendall (M-K) test and self-organising map (SOM) to characterise and evaluate water quality trends in Dongting Lake, China, from 1991 to 2018, before and after the inauguration of the Three Gorges Dam (TGD). Herein, six water quality parameters were selected, namely pH, permanganate index (COD_Mn), ammonia nitrogen (NH₃-N), total nitrogen (TN), total phosphorus (TP), and the five-day biochemical oxygen demand (BOD₅). Our results show that the concentrations of TN and BOD₅ increase significantly throughout the study period (|Z| ≥ 1.96). The number of abrupt change points for the six water quality parameters in the post-TGD period was greater than that in the pre-TGD period, which indicates an increased risk of water deterioration in the post-TGD period. The SOM results show that the pH values ranged from 7.64 to 7.85 among the four clusters; besides, the concentrations of the remaining water quality parameters from 1991 to 1997 and 2000 to 2003 were relatively lower, suggesting that the water quality in the pre-TGD period was better. The classification of TN and TP ranged from Level Ⅳ-Ⅴ among the clusters, which did not satisfy the level Ⅲ standard for potable water, thereby posing a higher ecological risk to the Dongting Lake. These results indicate the deterioration of the water quality in Dongting Lake during the post-TGD period under the influences of pollution load and hydrological regulation. Therefore, strict controls on the external nutrient loading and hydrological regulations should be considered for water quality management.

Occurrence, spatiotemporal distribution and potential ecological risks of antibiotics in Dongting Lake, China

We investigated the occurrence and distribution of 18 antibiotics in surface water from Dongting Lake, as well as in influents and effluents from a municipal wastewater treatment plant (WWTP) and a swine farm. The total concentrations of target antibiotics in surface water ranged from limit of quantification to 3107 and 5.32-107 ng L^-1 in the dry season and wet season, respectively. Among these studied antibiotics, ciprofloxacin (CIP) and lomefloxacin were as the main components in the dry season, while CIP, oxytetracycline, and chlortetracycline were the main components in the wet season. The concentrations of target compounds exhibited obvious temporal-spatial variation characteristic in the studied region, suggesting their different emission sources related to pig breeding, aquaculture, and human activities, as well as possible degradation in the aquatic system. We estimated that the daily total input and output masses of antibiotics in the influent and effluent from the swine farm were 12.1 mg d^-1 pig^-1 and 7.49 μg d^-1 pig^-1, while they were 103 μg d^-1 inhabitant^-1 and 22.9 μg d^-1 inhabitant^-1 in the WWTP. The risk assessment results indicated that CIP posed a moderate or high risk to algae in most locations in Dongting Lake.

Investigation on microplastic pollution of Dongting Lake and its affiliated rivers

At present, the occurrence and pollution of microplastics have caused widespread concern, but there are still few studies on inland lake and its affiliated rivers. In this study, we monitored the existence and characteristics of microplastics in Dongting Lake and its affiliated rivers. Our sampling site covers almost the entire lake district. A total of 15 surface water samples and 15 sediment samples were collected. The abundance of microplastics achieved 0.62-4.31 items/m² in plankton net samples, with 21-52 items/100 g dw in sediments. The microplastics were dominated by fiber, 0.9-0.333 mm of surface water and ˂0.1 mm of sediments in size. The color of transparent occupied the majority in all microplastics samples. There was no significant difference in the average concentration of microplastics between the four river mouths and the whole lake and the rivers may have important potential contribution to the microplastics pollution in the lake.

Assessment of the impact of the Poplar Ecological Retreat Project on water conservation in the Dongting Lake wetland region using the InVEST model

The Poplar Ecological Retreat (PER) project is a significant environmental protection initiative implemented to protect the Dongting Lake wetlands ecosystem in China, and the ecological impacts of this project have gradually become a hot topic. In this study, water conservation was selected as an indicator of ecosystem function to explore the impact of the project by using the water yield module of the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) model and geographic statistical methods. Water yield and land-use changes were quantitatively evaluated, and significant changes in the wetland landscape configuration occurred after the PER project because forest beach, moss marshland and mudflat areas were transformed into a poplar-retreat area. Thus, the proportion of the poplar-retreat area and average water yield increased. By using the principal component and cluster analysis methods, climate change and landscape patterns were shown to be the dominant driving factors affecting water conservation under stable meteorological conditions. Moreover, the landscape heterogeneity that resulted from the landscape patterns had a greater impact than climate change, which means that reducing human activities can enhance water conservation. Additionally, the correlation between landscape heterogeneity and water yield indicated that reducing landscape fragmentation and improving aggregation also benefit water conservation. Therefore, the PER project is successful at enhancing ecological functions and protecting wetland environments, and it represents a good example of maintaining ecological sustainability despite local economic performance restrictions. This project serves as an important reference for the establishment of sustainable wetland ecological policies by national governments, and the results can provide theoretical support for landscape ecology and eco-hydrology research.

[Response of Chromophoric Dissolved Organic Matter Dynamics to Different Hydrological Scenarios in the Two Largest Freshwater Lakes Connected to the Yangtze River]

Poyang Lake and Dongting Lake are the two largest freshwater lakes in China connected to the Yangtze River. Changes in the water quality of the two lakes are critical to the water security of the residents surrounding the lakes. Analyses of the optical properties, including chromophoric dissolved organic matter (CDOM) absorption and fluorescence spectroscopy coupled by parallel factor analysis (PARAFAC), were carried out to investigate the dynamics of CDOM in the two lakes in different hydrological scenarios. Our results indicated that different hydrological scenarios have more notable effects on the CDOM dynamics in Poyang Lake compared to those in Dongting Lake. In Poyang Lake, the mean CDOM absorption a(254) and dissolved organic carbon (DOC) were higher in the wet season than in the dry-to-wet transition season, and higher still than in the dry season (t-test, P<0.01), and the mean of the CDOM absorption spectral slope S_275-295 was higher in the dry season than in the dry-to-wet transition season and higher still than in the wet season (t-test, P<0.01). In Dongting Lake, the mean of a(254) was not significantly different between different hydrological periods, and SUVA₂₅₄ reached its maximum in the dry-to-wet transition season. Four fluorescent components were identified using parallel factor analysis. The contribution percentage of CDOM protein-like components in the two lakes was higher during the dry season, and the protein-like components and humic-like components contributed roughly the same amount in the dry-to-wet season, whereas the humic-like components accounted for the main proportion in both lakes during the wet season. From the perspective of spatial distribution, the fluorescence intensity of the four components of Poyang Lake was lower in the southern upstream than in the northern downstream lake regions during the dry season, whereas in the wet season a contrast pattern was found, i.e., with high values found in the upstream lake regions. The spatial difference of fluorescence intensity of the four components in the east of Dongting Lake during the dry season was greater than that in the wet season. We found that DOC increased with increasing water level (r²=0.99, P<0.01) in Poyang Lake and tryptophan-like C2 decreased with increasing water level (r²=0.99, P<0.05) in Dongting Lake. Therefore, the water quality of the two lakes should be managed in a targeted manner according to the response characteristics of CDOM in the two lakes under different hydrological scenarios.

Occurrence and ecological risk of pharmaceutical and personal care products in surface water of the Dongting Lake, China-during rainstorm period

The pharmaceutical and personal care product (PPCP) residues in freshwater lakes are being highlighted around the world. The occurrence and ecological risk of 34 PPCPs classified as antibiotics, non-steroidal anti-inflammatory drugs (NSAID), cardiovascular drugs, psychotropic drugs, anti-inflammatory drugs, psychostimulants, and pesticides during rainstorm period in surface water of the Dongting Lake, China, were studied. Twenty-six out of thirty-four PPCPs were detected, and the total concentrations of antibiotics ranged from 0.15 to 214.75 ng L^-1 in surface water. The highest average concentration was observed for diclofenac, followed by diethyltoluamide (DEET). The PPCP concentrations were much lower in Dongting Lake compared to other rivers and lakes due to the strong dilution effect of rainstorm, while the detection rate remains high. Caffeine and DEET were detected with 100% frequency in Dongting Lake, and the detection rates of diclofenac, mefenamic acid, and roxithromycin were above 90%. The pollution levels of antibiotics decreased in the order of East Dongting Lake > South Dongting Lake > West Dongting Lake, which may be related to the distribution of aquaculture plants, sewage treatment plants, and population density. The risk quotient (RQ) method was used to evaluate ecological environment risk under the worst case and the results suggested that clarithromycin, diclofenac, roxithromycin, and erythromycin might pose a significant risk to aquatic organisms in Dongting Lake, especially clarithromycin. This study can provide data support for further research on the dilutive effect and mechanism of rainwater runoff on PPCPs in lakes on a large scale.

Neonicotinoid insecticides in surface water from the central Yangtze River, China

Neonicotinoid insecticides (NNIs) are extensively used insecticides worldwide, yet the data on NNIs residues in the Yangtze River, China is scarce. Occurrence and distribution of six NNIs and a metabolite (desmethyl-acetamiprid) in surface water were investigated in the central Yangtze River, China at 20 sites from March to July and September 2015. Acetamiprid (ACE), imidacloprid (IMI) and thiamethoxam (THM) were the most frequently detected NNIs and IMI had a highest median concentration of 4.37 ng/L, followed by ACE (2.50 ng/L), THM (1.10 ng/L), nitenpyram (NTP; 0.34 ng/L), clothianidin (CLO; 0.10 ng/L), and thiacloprid (THCP; 0.02 ng/L). Significantly higher concentrations and detection frequencies of NNIs were observed in the summer than in the spring, which may be explained by the heavier precipitation in summer. Spatial variation with higher levels among the lower sites than the upper sites may be related with the agriculture land use. NNI contamination presented a low risk to aquatic life according to the risk quotient method, while IMI had potential risk to aquatic life according to the threshold of IMI (8.3 ng/L) in freshwater recommended in Netherland. Using the relative potency factors method for chronic cumulative risk assessment for NNIs, potential exposure to NNIs through water ingestion are three orders of magnitude lower than the recommended relative chronic reference dose. Ongoing environmental monitoring of NNIs is needed due to the increase use of NNIs in China.

[Distribution Characteristics and Influencing Factors of Phosphorus in the Dongting Lake at Different Water Periods]

To study the distribution characteristics and influencing factors of phosphorus in the Dongting Lake at different water periods, water samples were collected from 18 representative monitoring sections located in the Dongting Lake and its upper rivers from January to December 2016. Various forms of phosphorus concentration in the samples were analyzed. The results showed that, overall, the average concentrations (range) of total phosphorus (TP), total dissolved phosphorus (DTP), and phosphate (DPO) in the Dongting Lake were 0.085 mg·L^-1(0.030-0.176 mg·L^-1), 0.062 mg·L^-1(0.017-0.151 mg·L^-1), and 0.053 mg·L^-1(0.007-0.144 mg·L^-1), respectively. These forms of phosphorus concentrations were all characterized by the intermediate season (IS) > the dry season (DS) > the wet season (WS), with obvious seasonal variation characteristics. In the spatial distribution, the phosphorus concentration increased from west to east in DS and IS and decreased from the west to east in WS. In terms of time distribution, various forms of phosphorus were characterized by obvious seasonal distribution in the east, west, and outlet of the Dongting Lake. The phosphorus concentration in WS was higher than that in DS and IS in the West Dongting Lake. However, the concentration was higher during DS and IS than that in WS for the east and outlet of lake. Various forms of phosphorus concentrations in the west were highest in the Dongting Lake during WS, while those in the outlet and east were relatively highest in DS and IS. Therefore, the phosphorus pollution in the West Dongting Lake should receive more attention during WS, and the pollution in the east and outlet requires higher attention during DS and IS. In terms of form composition, according to the monthly data of the sections, the values of ρ(TPO)/ρ(TP) and ρ(DPO)/ρ(TPO) were mainly above 60% in the water body of the Dongting Lake and its upper rivers. DTP was the main form of TP, and DPO was the main form of DTP. It indicated that the phosphorus in the Dongting Lake and its upper rivers was mainly soluble, which is different from that before the impoundment of the Three Gorges Reservoir. The spatio-temporal distribution of suspended particles (SS) and phosphorus in the Dongting Lake had a certain synergistic effect. The concentration of SS and phosphorus in each water period showed a significant or extremely significant correlation. Therefore, SS was considered as an important factor affecting the seasonal variation of phosphorus in the Dongting Lake. In this study, it was concluded that the Nanzui section, the Daxiaoxihu section, and the East Dongting Lake area were clearly affected by surrounding human activities, respectively including domestic, agricultural, and sand mining sources of phosphorus pollution. The water in the West Dongting Lake has even been affected by mild and moderate eutrophication in 2016. These phenomena should be paid more attention.

Changes in chemical fractions and ecological risk prediction of heavy metals in estuarine sediments of Chunfeng Lake estuary, China

The changes of available forms of heavy metals would affect their corresponding ecological risks in sediments. The distribution of chemical fractions of heavy metals in sediment profiles from Chunfeng Lake estuary was investigated and then a prediction model for potential ecological risk index (PMRI) was proposed to forecast the changes of ecological risks caused by the aging process of metals in sediments. The results show that the estuarine sediments were polluted by As and Cd. The proportions of available metals were generally decreased with depth, while those of the residual forms showed an opposite trend. The aging rates of Cd and As were found to be 0.21 and 0.12%/year, respectively. The PMRI model showed that the total ecological risk of metals in sediments decreased from moderate to low risk level (<150) after 25 years, while cadmium would need 47 years in contrast to the 15 years for As.

Microplastics in Sediment and Surface Water of West Dongting Lake and South Dongting Lake: Abundance, Source and Composition

Microplastic pollution was investigated in sediment and surface water in West Dongting Lake and South Dongting Lake for the first time. The abundance of microplastics ranged from 616.67 to 2216.67 items/m³ and 716.67 to 2316.67 items/m³ in the lakeshore surface water of West Dongting Lake and South Dongting Lake, respectively. The highest levels of microplastic pollution were found in the lakes' outlets. In the lake center sites of the West Dongting Lake and South Dongting Lake, the abundance of microplastics ranged from 433.33 to 1500 items/m³ and 366.67 to 1566.67 items/m³, respectively. Meanwhile, the study found that in lakeshore sediment of West Dongting Lake and South Dongting Lake, microplastic concentrations ranged from 320 to 480 items/m³ and 200⁻1150 items/m³. Polystyrene (PS) and polyethylene terephthalate (PET) were most common in the surface water and sediment samples, respectively. In addition, we suggest that the effects of polymer types in microplastics should be taken into account when considering abundance. This study can provide valuable points of reference to better understanding microplastic pollution in inland freshwater areas.

Responses of macroinvertebrates and local environment to short-term commercial sand dredging practices in a flood-plain lake

In parts of the developing world, the expansion of industrial sand mining activities has led to serious environmental concerns. However, current understanding of the effects of this activity on an inland water ecosystem remains limited. Herein, we choose the "most affected" lake in China (Dongting Lake), to assess short-term (1year) effects of sand dredging on key environmental parameters and on the structure of the macroinvertebrate assemblage. Within the dredged area we observed increases in water depth (on average 2.17m), turbidity and changes in sediment composition (e.g., increase in % medium sand, and a decrease in % clay). In addition, dredging was associated with a 50 % reduction in taxa richness, Simpson and Shannon-Wiener indices, and a 72 and 99 % reduction in abundance and biomass, respectively. Indirect effects were also observed in the zone surrounding the extraction sites (ca. 500m), most likely as a result of the dredging processes (e.g., sediment screening and overspill) and water flow. No such effects were observed at a nearby reference site. The direct removal of sediment and indirect alteration of physical conditions (e.g., water depth, turbidity and sediment composition) appear to be the most likely cause of variations in the benthic community. Implications of our findings for the planning, management and monitoring of sand dredging in inland waters are discussed.

Monitoring monthly surface water dynamics of Dongting Lake using Sentinel-1 data at 10 m

High temporal resolution water distribution maps are essential for surface water monitoring because surface water exhibits significant inner-annual variation. Therefore, high-frequency remote sensing data are needed for surface water mapping. Dongting Lake, the second-largest freshwater lake in China, is famous for the seasonal fluctuations of its inundation extents in the middle reaches of the Yangtze River. It is also greatly affected by the Three Gorges Project. In this study, we used Sentinel-1 data to generate surface water maps of Dongting Lake at 10 m resolution. First, we generated the Sentinel-1 time series backscattering coefficient for VH and VV polarizations at 10 m resolution by using a monthly composition method. Second, we generated the thresholds for mapping surface water at 10 m resolution with monthly frequencies using Sentinel-1 data. Then, we derived the monthly surface water distribution product of Dongting Lake in 2016, and finally, we analyzed the inner-annual surface water dynamics. The results showed that: (1) The thresholds were −21.56 and −15.82 dB for the backscattering coefficients for VH and VV, respectively, and the overall accuracy and Kappa coefficients were above 95.50% and 0.90, respectively, for the VH backscattering coefficient, and above 94.50% and 0.88, respectively, for the VV backscattering coefficient. The VV backscattering coefficient achieved lower accuracy due to the effect of the wind causing roughness on the surface of the water. (2) The maximum and minimum areas of surface water were 2040.33 km² in July, and 738.89 km² in December. The surface water area of Dongting Lake varied most significantly in April and August. The permanent water acreage in 2016 was 556.35 km², accounting for 19.65% of the total area of Dongting Lake, and the acreage of seasonal water was 1525.21 km². This study proposed a method to automatically generate monthly surface water at 10 m resolution, which may contribute to monitoring surface water in a timely manner.

Remote observation of water clarity patterns in Three Gorges Reservoir and Dongting Lake of China and their probable linkage to the Three Gorges Dam based on Landsat 8 imagery

The Secchi disk depth (Z_SD) plays a critical role in describing water clarity. Several studies have shown linkages between Three Gorges Dam (TGD) and the downstream lacustrine ecosystem in the middle and lower Yangtze River basin. However, the potential influence on the Z_SD fluctuation in the entire anthropogenic reservoirs of Three Gorges (ER) and Dongting Lake (DTL) has not been reported, possibly due to technical obstacles in obtaining statistically significant spatial and temporal results. We addressed this challenge by using remote sensing technology: the Landsat 8 Operational Land Imager (OLI). We proposed a new, robust remote-sensing algorithm to estimate Z_SD from OLI imagery using red and green band-ratio, leading to MAPE of 21.68% and RMSE of 0.076m for Z_SD ranging from 0.1m to 1.05m. After satisfactory image-based validation, the algorithm was implemented on OLI data to derive Z_SD patterns over ER and DTL from 2013 to 2017. Several crucial findings can be drawn: 1) Spatial-temporal patterns of Z_SD exhibited notable fluctuations over both ER and DTL, and they also demonstrated a significant correlation with each other because of the opposite temporal cycle of Z_SD fluctuations between ER and DTL; 2) Temporally, monthly fluctuations of Z_SD between ER and DTL had opposite temporal cycles, which was mainly attributed to the surface runoff and sediment discharge driven by the outbound runoff variations of TGD. Spatially, the heterogeneity of the Z_SD pattern in ER might have resulted from the different geographical regions being divided by large anthropologic hydrological facilities, such as TGD; 3) The relationship between Z_SD and total suspended matter (TSM) showed a significant negative correlation, as did the relationship between Z_SD and K_d(490). These findings demonstrate that TSM often plays a principal role in light attenuation of extremely turbid inland waters; 4) An inversed phenomenon of water clarity was observed at the intersection of DTL and the Yangtze River around Chenglingji site (YRAC), which was due to the opposite temporal cycle of Z_SD fluctuations between DTL and ER after the impoundment of TGD; and 5) Owing to the analysis of noise-equivalent Z_SD, OLI data can be used to derive Z_SD, since the imagery uncertainty is 0.07m by means of our band-ratio algorithm, which demonstrates similar results to MODIS. The proposed Z_SD-derived algorithm in this study could be suitable for other turbid lakes or reservoirs to formulate related strategies of water quality management in the middle and lower Yangtze River basin, and the unveiled findings here improve our understanding of Z_SD spatiotemporal fluctuations in large river-connected lakes, such as Poyang Lake.

Responses to Sedimentation in Ramet Populations of the Clonal Plant Carex brevicuspis

In aquatic ecosystems, sedimentation is an important factor that affects plant growth, mainly due to sediment depth. Clonal morphological plasticity is an effective strategy in clonal plants for acclimatization to sediment burial. To date, few studies have examined growth responses to sedimentation on the clonal plants at the ramet population level. This study aimed to explore the interactive effects of population size and burial depth on growth and clonal morphology of Carex brevicuspis. Three population sizes (2, 8, and 32 ramets) and 3 burial depths (0 cm, 5 cm, and 10 cm) were used in this experiment. Under shallow (5 cm) and deep (10 cm) burial conditions, biomass accumulation and relative growth rate (RGR) were lower than in the no burial treatment (P < 0.05). RGR of the small and medium populations was especially high compared to the large populations (P < 0.05). Biomass allocation was higher to belowground parts than aboveground parts, except for the small populations in the 5 cm burial treatments. Both shallow burial and smaller populations led to more biomass being allocated to aboveground parts. Deep burial elongated the first order spacer more than shallow burial, and sedimentation had negative effects on the second order spacer length. The number of new ramets did not decrease in the 5 or 10 cm burial treatments compared to the unburial treatment, and larger populations usually had more ramets than smaller ones; the proportion of clumping ramets was higher than the proportion of spreading ramets, and deeper burial and smaller populations led to higher proportions of spreading ramets. These results indicated that the growth of C. brevicuspis was limited by sediment burial at the ramet population level. Smaller populations enable C. brevicuspis to adjust its escape response to burial stress, may allow this species to effectively survive and widely distribute in Dongting Lake wetland.

Occurrence, source, and ecological risk of antibiotics in Dongting Lake, China

The pollution characteristics and ecological risk of 12 classified as sulfonamide, trimethoprim, quinolone, and tetracycline antibiotics in Dongting Lake, China, were studied. The total concentrations of the antibiotics ranged from 1.06 to 135.40 ng L^-1 for all sampling sites. The highest average concentration was observed for sulfadiazine, followed by sulfamethoxazole. The detection frequencies (over 60%) of sulfonamides were higher than those of other antibiotics. The direct discharge of the aquaculture, livestock, and poultry wastewater might be the main pollution sources of antibiotics in the Dongting Lake. The pollution levels of antibiotics decreased in the order of East Dongting Lake > South Dongting Lake > West Dongting Lake, which may be related to the distribution and the scale of the aquaculture, livestock, and poultry sources. The seasonal changes of antibiotic concentration were relatively diversified, with the dry season generally having higher concentrations than the wet season. The results of the ecological risk assessment indicated that sulfamethoxazole, ciprofloxacin, and sarafloxacin might pose a significant risk to the aquatic organisms in Dongting Lake, especially in Potou and Nandu. This study enriches the research of emerging pollutants in freshwater lake. Graphical abstract.

Residues and health risk assessment of typical antibiotics in aquatic products from the Dongting Lake, China-"Did you eat "Antibiotics" today?"

The contamination level of 12 antibiotics in 8 species of fish and shrimp from the Dongting Lake, China, was firstly studied. In total, the concentrations of antibiotics in fish and shrimp were lower, which were far lower than the maximum residue limits. The most abundant compound was enrofloxacin followed by sulfadiazine, sulfamethoxazole, sarafloxacin, and sulfadimidine with the highest content from 0.37 to 1.06 ng g^-1. The concentrations in Silurus asotus, Cyprinus carpio, and Palinuridae were higher. Concentrations in fish and shrimp from different water layers showed spatial difference, with the order of benthos and middle-lower species > middle-upper species. In addition, the antibiotic content could be affected by the diet, which showed the concentration level of antibiotics decreased in the order of carnivorous > omnivorous > phytophagous species. Human health risk assessment based on potential fish consumption indicates that main antibiotic risk factors were enrofloxacin and sarafloxacin, and main risk species were Silurus asotus and Palinuridae. The daily risk quotient of these antibiotics to rural residents was lower than townsmen. This study is the first report of antibiotic content in fish and shrimp from the Dongting Lake, which could enrich the research of emerging pollutants in aquatic products.

[Research on living status of Oncomelania hupensis in autumn and winter and its correlates in Eastern Dongting Lake area]

OBJECTIVE

To explore the dynamic changes of Oncomelania hupensis snail densities in autumn and winter and the relationship between hydrological and meteorological factors and snail growth and decline.

METHODS

From Octobers to Decembers of 2007 to 2014, a bottomland close to eastern Dongting Lake was selected as the study field. The snails and elevation of the points were surveyed, and the hydrological and meteorological data were collected. The snail densities and death rates of every month were calculated. The meteorological and hydrological data were described, and the relationship between the snail densities and associated factors were fitted by the multiple regression model.

RESULTS

The snail density was highest in October 2012 (41.88 per 0.1 m²) and lowest in November 2008 (1.23 per 0.1 m²). The snail mortality was highest in November 2008 (73.72%) and lowest in October 2012 (1.09%). The multiple regression model found a linear relationship between hydrological and meteorological factors and snail densities. The correlation coefficient between the prediction of ln (snail density) and its measurements by using this model was 0.927 (P = 0.001).

CONCLUSIONS

The average minimum temperature in January and time of starting flood have an obvious influence on the snail densities in autumn and winter.

Effects of river-lake interactions in water and sediment on phosphorus in Dongting Lake, China

As a large river connected lake, Dongting Lake is influenced by anthropogenic activities and the discharge from its upstream tributaries in the lake basin and by the water recharge via a connection to the Yangtze River (YR) outside the basin. This makes the lake phosphorous cycle more complex than that in other disconnected lakes. Here, we calculated section fluxes and ran a hydrodynamic model to investigate the phosphorus (P) variations in response to the changing interactions in the water and sediment between the YR, four tributaries, and the lake. Results show that particulate P was the dominant form with a significant linear relationship with suspended sediment (r ² = 0.906). The sediment input reduction from the YR through three water inlets, which is closely related to the Three Gorges Reservoir operation since 2003, led to a decrease in the total P (TP) concentration in the western Dongting Lake. However, the impact and range of this decrease were fairly limited. Compared with the limited effect of the YR, the raised TP flux from the Yuanjiang tributary controlled the TP concentration at the outlet of the western Dongting Lake. Apart from the influence of the YR and the tributaries, anthropogenic activities (sand dredging) in the eastern Dongting Lake also contributed to a high TP concentration around the S10 area through sediment resuspension. We suggest that, compared with the reduction in TP flux and sediment load from the connected Yangtze River outside the basin, the elements within the basin (increased TP input from tributaries and sand dredging) have a greater effect on the variations of TP in Dongting Lake.

[Study on spatial - temporal characteristics of Schistosoma japonicum infections among human in Hunan Province, 2004-2011]

Objective To explore the spatial-temporal characteristics and changing regularities of Schistosoma japonicum infections among human from 2004 to 2011. Methods The township level spatial databases of schistosomiasis in Hunan Province from 2004 to 2011 were established, and the related spatial analysis was performed by SPSS 17.0, ArcGIS 10.1 and SaTScan 7.03. Results The schistosome infection rate among human in Hunan Province sharply decreased from 3.0% in 2004 to 0.8% in 2011. However, the rate among residents in parts of some townships in 2011 was still hovering at a higher level (P₉₀ = 2.12%), and the higher rate was distributed along the Oncomelania hupensis snail ridden areas outside embankment. The autocorrelation analysis showed that the global Moran's I for schistosome infection rate among human was 0.34 to 0.53 from 2004 to 2011, and was higher than the expected value (Z > 8.71, P < 0.05). The local G statistics indicated that the positive hotspot high-high clustering areas were mainly near the coast of Dongting Lake from 2004 to 2011, and the number of townships with schistosomiasis endemic in the clustering areas reached 30 to 70. The spatial scan analysis showed that the number of townships in the clustering areas ran up to 145 to 183 from 2004 to 2011. Conclusions The schistosome infection rate among human decreased significantly in Hunan Province from 2004 to 2011. However, the rate in parts of some townships still remains at a comparatively high level, and there are positive spatial correlation and spatial agglomerations in the schistosome infection rate among human, suggesting that the prevention and control work on schistosomiasis in these areas should be strengthened in the future.

Rodents, goats and dogs - their potential roles in the transmission of schistosomiasis in China

Schistosomiasis in China has been substantially reduced due to an effective control programme employing various measures including bovine and human chemotherapy, and the removal of bovines from endemic areas. To fulfil elimination targets, it will be necessary to identify other possible reservoir hosts for Schistosoma japonicum and include them in future control efforts. This study determined the infection prevalence of S. japonicum in rodents (0-9·21%), dogs (0-18·37%) and goats (6·9-46·4%) from the Dongting Lake area of Hunan province, using a combination of traditional coproparasitological techniques (miracidial hatching technique and Kato-Katz thick smear technique) and molecular methods [quantitative real-time PCR (qPCR) and droplet digital PCR (ddPCR)]. We found a much higher prevalence in goats than previously recorded in this setting. Cattle and water buffalo were also examined using the same procedures and all were found to be infected, emphasising the occurrence of active transmission. qPCR and ddPCR were much more sensitive than the coproparasitological procedures with both KK and MHT considerably underestimating the true prevalence in all animals surveyed. The high level of S. japonicum prevalence in goats indicates that they are likely important reservoirs in schistosomiasis transmission, necessitating their inclusion as targets of control, if the goal of elimination is to be achieved in China.

[Dynamic simulation analysis of effects of project of ditching for drain on Oncomelania hupensis snail control and flood prevention security in Dongting Lake region]

OBJECTIVE

To evaluate the effects of the project of ditching for drain on Oncomelania hupensis snail control and flood prevention security and explore the optimal engineering design plan in Dongting Lake region.

METHODS

A retrospective study was performed on the previous studies about the project of ditching for drain. The reference values of project indices were determined. The outside levee of Nanhu New Distinct of Yueyang City in Dongting Lake region was selected as the study area, and the cross section of marshland perpendicular to the center line of the levee was extracted to research. According to the situations of various water levels, a dynamic simulation was performed on the effect and security of the project of ditching for drain through the software FLAC^3D.

RESULTS

The retrospective study showed that the project would be effective when the relatively subsoil water level decreased by 0.35 m, and the soil water content decreased correspondingly. The dynamic simulation by FLAC^3D showed that the minimum safe distances between transverse ditch 1, vertical ditch and levee toe should be 25 m and 13 m respectively. The digging depth of transverse ditch and vertical ditch should be 1.2 m and 1.0 m respectively. If the width of marshland in drought period was less than 500 m, one transverse ditch was efficient. Otherwise, more transverse ditches should be set with the intervals of 300 m.

CONCLUSIONS

The project of ditching for drain is an effective ecological snail elimination method. Optimizing the digging depth of ditches and distances between transverse ditches, vertical ditch and levee toe will ensure the effects and security of the project.

Remote sensing of diffuse attenuation coefficient patterns from Landsat 8 OLI imagery of turbid inland waters: A case study of Dongting Lake

The diffuse attenuation coefficient, K_d(λ), is an important optical property. Environmental change and anthropogenic activities, however, have made it challenging to accurately assess K_d(λ) patterns in the extremely turbid inland waters. We addressed this challenge by using new Landsat 8 Operational Land Imager (OLI) imagery. For the bio-optical complexity of water, we proposed an empirical band-ratio algorithm for estimating K_d(490) using our in situ measurements. Based on the acceptable performance of an OLI image-based atmospheric correction and K_d(490) validation, the algorithm was then applied to OLI images to estimate K_d(490) patterns from April 2013 to April 2016, leading to several key findings: (1) Spatial-temporal patterns of K_d(490) varied significantly in Dongting Lake. The temporal heterogeneity of K_d(490) could be explained primarily by surface-runoff changes driven by regional precipitation. The spatial heterogeneity was due to sediment resuspension, resulting from sand dredging and shipping activities; (2) K_d(490) values that were inversed at the intersection of Dongting Lake and Yangtze River were observed for the first time near the Chengliji site and resulted from the opposing temporal cycle of K_d(490) variations between Dongting Lake and the Yangtze River; (3) There was a significant positive correlation between K_d(490) and total suspended matter (TSM). This confirms that TSM often plays a principal role in the attenuation of light in extremely turbid water bodies; (4) The empirical band-ratio algorithm worked well, not only for the broader Landsat archives, but also for the narrower Sentinel-2/3 for K_d(490) estimation, which demonstrates that the algorithm could be used to quantitatively monitor multi-decade records of Landsat observations and future applications of inland water quality in turbid inland waters, such as Dongting Lake and Poyang Lake.

Occurrence and controls on transport and transformation of nitrogen in riparian zones of Dongting Lake, China

Dongting Lake is the second largest freshwater lake in China. It is suffering from significant eutrophication as a result of excessive nutrients inputs, among which nitrogen (N) is becoming a major contributor. The objective of this study is to document the occurrence and controls on N transport and transformation in riparian zones of Dongting Lake wetland. Field experiments were conducted in the cultivated Li River (LR) and uncultivated Yuan River (YR) regions of the wetlands from June to November, 2014. Groundwater depth, redox potential (Eh), pH, and temperature were measured in situ. Groundwater and surface water samples were collected to determine concentrations of nitrate nitrogen (NO3 (-)-N), nitrite nitrogen (NO2 (-)-N), and ammonia nitrogen (NH4 (+)-N). The results showed that NH4 (+)-N was the dominant N pollutant with maximum average value of 2.7760 mg L(-1). All the groundwater samples were rated to Class V based on NH4 (+)-N content according to the groundwater quality standard, indicating the load of N in riparian zones had exceeded their capacity for assimilation and purification. Internal controls (including Eh and pH, temperature, and groundwater depth) and external controls (including surface water, land use, and rainfall) were analyzed in detail. The results suggested that Eh and pH were more significant in controlling N transport and transformation than temperature and groundwater depth; external controls influenced N fates through imposing an effect on internal controls. This study will provide important insights and a scientific basis for N pollution treatment and better protection of the Dongting Lake wetlands.

Relationship between Dongting Lake and surrounding rivers under the operation of the Three Gorges Reservoir, China

The natural flow properties of the Yangtze River have been changed completely following the construction of the Three Gorges Dam. The dam's operation has affected the resources and environment in the middle and lower reaches of the Yangtze River, changing the hydrological conditions and ecological environment of the Dongting Lake. During three different dispatching periods of the reservoir, we took triplicate samples of the river and lake water. All the samples were analysed for δ(2)H and δ(18)O to determine the relationship between the lake and the Yangtze River (and other rivers), and to evaluate objectively the influence of the dam's operation on the lake. During the period of water-supply dispatch, the Four Rivers and Miluo River are the main recharge sources of the lake. During the flood-storage dispatching period, the Dongting Lake is recharged largely by the Three Outlets and the Four Rivers, whereas during the period of water-storage dispatch, most of the lake's water originates from the Miluo, Xiang, Zi, and Yuan rivers. Although the Yangtze River only contributes significantly to the lake's recharge through the Three Outlets during the flood-storage dispatching period, the lake discharges large amounts of water into the Yangtze River during all three periods. Through the operation of the reservoir, it should be ensured that the water level of the Dongting Lake is not too low during the dry season, nor too high during the wet season, thus preventing the lake region from future flood and drought disasters.

Polychlorinated dibenzo-p-dioxins and dibenzofurans in water and six fish species from Dongting Lake, China

There have been few studies of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in environmental water because of the large volume of water required for PCDD/Fs analysis. Water quality directly affects aquatic organisms, and little is known about how PCDD/Fs are transported in aquatic environments. PCDD/Fs were analyzed in eight water samples from Dongting Lake, China, which was contaminated with PCDD/Fs because of sodium pentachlorophenate use between the 1960s and the 1980s. The total PCDD/F concentrations in the samples were 36-345 pg L(-1), and the mean was 191 pg L(-1). Octachlorodibenzo-p-dioxin was the most abundant PCDD/F congener in every sample, contributing 67-95% of the total 2,3,7,8-chlorinated PCDD/F concentrations. The toxic equivalent (WHO-TEQ) concentrations in the samples were 0.17-0.37 pg L(-1), and the mean was 0.28 pg L(-1), which is higher than the Canadian environmental quality guideline (0.038 pg L(-1) WHO-TEQ for freshwater) and the United States Environmental Protection Agency water quality criterion (0.014 pg L(-1) WHO-TEQ). PCDD/Fs were also determined in six fish species collected from Dongting Lake, to assess the concentrations, accumulation patterns, and potential for toxic effects. The total 2,3,7,8-chlorinated PCDD/F concentrations in the fish samples were 2.2-17.9 pg g(-1) (wet weight), and the dominant congeners were octachlorodibenzo-p-dioxin, 1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin, 1,2,3,4,7,8-hexachlorodibenzo-p-dioxin, and 2,3,4,7,8-pentachlorodibenzofuran. The PCDD/F WHO-TEQs were 0.10-0.92 ww (3.3-65.3l w) pg g(-1) in different species of fish. PCDD/F congener patterns in fish may be affected by food chain biomagnification and the lipid content of the species.

A multi-component integrated approach for the elimination of schistosomiasis in the People's Republic of China: design and baseline results of a 4-year cluster-randomised intervention trial

Despite major successes in its control over the past 50years, schistosomiasis japonica continues to be a public health problem in the People's Republic of China (P.R. China). Historically, the major endemic foci occur in the lakes and marshlands along the Yangtze River, areas where transmission interruption has proven difficult. The current endemic situation may alter due to the closure of the Three Gorges Dam. Considerable environmental and ecological changes are anticipated that may result in new habitats for the oncomelanid intermediate snail host of Schistosoma japonicum (Sj), thereby increasing the risk of transmission. The current national control program for P.R. China involves a multi-component integrated strategy but, despite targeting multiple transmission pathways, certain challenges remain. As the Chinese government pushes towards elimination, there is a requirement for additional tools, such as vaccination, for long-term prevention. Whereas the zoonotic nature of schistosomiasis japonica adds to the complexity of control, it provides a unique opportunity to develop a transmission blocking vaccine targeting bovines to assist in the prevention of human infection and disease. Mathematical modelling has shown that control options targeting the various transmission pathways of schistosomiasis japonica and incorporating bovine vaccination, mass human chemotherapy and mollusciciding could lead to its elimination from P.R. China. Here we present the study design and baseline results of a four-year cluster randomised intervention trial we are undertaking around the schistosomiasis-endemic Dongting Lake in Hunan Province aimed at determining the impact on schistosome transmission of the multi-component integrated control strategy, including bovine vaccination using a heterologous "prime-boost" delivery platform based on the previously tested SjCTPI vaccine.