[Characterization of Microplastic Surface Bacterial Community Structure and Prediction of Ecological Risk in Poyang Lake, China]

In recent years, the environmental pollution of microplastics in Poyang Lake has received increasing attention. Baisha Lake of Poyang Lake was selected as the study area, and samples of water and sediments of Baisha Lake and the microplastics therein were collected, and the polymer types of microplastics were identified as polyethylene (PE), polyester (PET), polypropylene (PP), and polystyrene (PS) using Fourier infrared spectroscopy. We also analyzed the structural composition of bacterial communities in water, in sediments, and on microplastic surfaces using 16S high-throughput sequencing. The species richness and diversity of bacteria on the microplastic surfaces were lower than those in the surrounding water and sediments. The results of NMDS analysis showed that the bacterial community structures on the microplastic surfaces differed greatly from those in the surrounding sediments and water. The bacterial community composition in water and sediment differed from that on the microplastic surfaces, and the dominant bacterial phyla on the microplastic surfaces were Proteobacteria and Bacteroidota, and their relative abundance on the microplastic surfaces was higher than that in sediment. The relative abundance of Proteobacteria was higher than that in water. The relative abundances of Bacteroidota and Actinobacteriota were significantly lower than that of water. Massilia and Pseudomonas were the dominant genera on the microplastic surfaces, and their relative abundances were significantly higher than those in the surrounding water and sediments. BugBase phenotype prediction revealed that the relative abundance of contains mobile elements, biofilm formation, potential pathogenicity, and stress tolerance phenotypes of microplastic bacterial communities were significantly higher than those of the surrounding water and sediments. The results revealed that microplastics may have contributed to the spread of harmful bacteria, including pathogenic bacteria, and increased the potential pathogenicity of bacterial communities. Additionally, microplastic surface bacterial communities had higher phenotypes of mobile gene element content. Revealing the potential harm of microplastic pollution to wetland ecology at the micro level may provide a scientific reference for maintaining the ecological stability of wetlands.

Prediction of chlorophyll a and risk assessment of water blooms in Poyang Lake based on a machine learning method

Four different methods were used to identify the important factors influencing chlorophyll-a (Chl-a) content: correlation analysis (CC-NMI), principal component analysis (PCA), decision tree (DT), and random forest recursive feature elimination (RF-RFE). Considering the relationship between Chl-a and its active and passive factors, we established machine learning combination models based on multiple linear regression (MLR), multi-layer perceptron (MLP), and support vector regression (SVR) to predict Chl-a content for Poyang Lake, China. Then, the predictive effects of different combination models were compared and evaluated from multiple perspectives. Considering the actual needs for eutrophication prevention and control, the concept of risk probability was then introduced to assess the risk degree of risk associated with water blooms in Poyang Lake. The results indicated that the mean R2 for the Chl-a predictions using the MLR, MLP, and SVR models was 0.21, 0.61, and 0.75, respectively. Consequently, the SVR model demonstrated higher precision and more accurate predictions. Compared to other methods, integrating the SVR model with the RF-RFE method significantly improved the prediction accuracy, with the R2 increasing to 0.94. For Poyang Lake, 8.8% of random samples indicated a low risk level with a water bloom probability of 21.1%-36.5%; one sample indicated a medium risk level with a risk probability of 45.5%. The research results offer valuable insights for predicting eutrophication and conducting risk assessments for Poyang Lake. They also provide reliable scientific support for making decisions about eutrophication in lakes and reservoirs. Therefore, the results hold significant theoretical importance, practical value, and potential for widespread application.

Response of the microbial community structure to the environmental factors during the extreme flood season in Poyang Lake, the largest freshwater lake in China

Background

Poyang Lake is the largest freshwater lake in China, and there are several studies on the composition and diversity of bacteria in Poyang Lake, while few quantitative studies were carried out on the response of the bacterial community to environmental factors during the extreme flood season in Poyang Lake.

Methods

The connected-lake heterogeneity of bacterial community composition (BCC) was investigated in Poyang Lake during the flood season in 2020. Illumina high-throughput sequencing technology was used in this study.

Results

The bacterial community structure in the water was different from that in the sediment of Poyang Lake during extreme flood seasons. The bacterial diversity in water was much lower than that in sediment. In the water column, the dominant phyla were Actinobacteriota, while the composition of bacteria in sediment was more complex than that in water, and the dominant phyla in sediment were Proteobacteria, Chloroflexi, Acidobacteriota, and Actinobacteriota. The bacterial diversity in the water of Poyang Lake showed seasonal dynamics, while no seasonal variation of bacterial communities in sediment was observed. The bacterial community structure in the sediment from the two bays and channel areas of Poyang Lake can be distinguished from each other. The microbial diversity in sediment gradually increased from the Sancha Bay to the Zhouxi Bay and then to the channel, but the total nitrogen (TN) concentration in sediment (STN) and the total phosphorus (TP) concentration in sediment (STP) showed opposite trends. This might be due to the anthropogenic disturbances from the extreme flood. The bacterial community structure in, water column was significantly correlated with WT, NH4-N, STP, SOM, Chl a, DO, TP, and Eh, while the bacterial community structure in sediment was significantly correlated with SOM and STP.

Conclusion

The bacterial community structure in water was greatly different from that in sediment in Poyang Lake during extreme flood seasons. The bacterial community structure in the water column was not only sensitive to the geochemical characteristics of the water but also affected by some nutrient concentrations in the sediment. During the wet seasons, bacterial diversity was only affected by SOM and STP.

Per- and polyfluoroalkyl substances in waterbird feathers around Poyang Lake, China: Compound and species-specific bioaccumulation

As a nondestructive means of environmental monitoring, bird feathers have been used to analyze levels of per- and polyfluoroalkyl substances (PFASs) in specific environments. In this study, feather samples from 10 waterbird species around Poyang Lake were collected, and a pretreatment method for PFASs in feathers was optimized. The results showed that a combined cleaning method using ultrapure water and n-hexane effectively removed external PFASs. Twenty-three legacy and emerging PFASs were identified in the feathers of waterbirds, of which hexafluoropropylene oxides (HFPOs), chlorinated polyfluoroalkyl ether sulfonates (Cl-PFESAs), and sodium p-perfluorinated noneoxybenzene sulfonate (OBS) were reported for the first time, with their concentrations ranging from 0.060-2.4 ng·g-1 dw, 0.046-30 ng·g-1 dw, and lower than the method detection limit to 30 ng·g-1 dw, respectively. Compound- and species-specific bioaccumulation of PFASs was observed in the feathers of different waterbird species, suggesting that different PFAS types can be monitored through the selection of different species. Moreover, the concentrations of most PFCAs (except perfluorobutyric acid), perfluorooctane sulfonate (PFOS), and perfluorooctane sulfonamide (FOSA) were significantly positively correlated with δ15N (p < 0.05), while the concentrations of HFPOs, Cl-PFESAs, and OBS had significant positive correlations with δ13C. This indicates that the bioaccumulation of legacy and emerging PFASs in waterbird feathers is affected by their trophic level, feeding habits, and foraging area.

[Spatial-temporal Distribution and Source Analysis of Polycyclic Aromatic Hydrocarbons in the Sediments of Poyang Lake]

The concentrations, spatial-temporal distribution, and influencing factors of 16 polycyclic aromatic hydrocarbons (PAHs) in the sediments of Poyang Lake were studied, and a quantitative source analysis of PAHs in different areas of the lake was conducted. PAHs were widespread within the sediments. The concentrations of ∑16PAHs in the surface sediments of all sites ranged from 203 to 2 318 μg·kg-1. The concentrations of PAHs in the surface sediments of the lake body were higher than those in the surface sediments of the inlet rivers. The ratio of PAHs in Poyang Lake was 4 rings > 5 rings > 6 rings > 3 rings > 2 rings; the composition of 4-ring PAHs was dominant, and its content accounted for 86.11% of ∑16PAHs. The 2- and 3-ring and some 4-ring PAHs, including Flua and Pyr, were more susceptible to SOM, and the 4 through 6-ring PAHs were more susceptible to ORP and heavy metals and other environmental factors. Spatially, the higher concentration of ∑16PAHs occurred in the area of the lake adjacent to Duchang County and Poyang County, where the terrain was relatively closed, and the water exchange with the surrounding area was less than that in other sections, which was not conducive to the migration, transformation, and degradation of pollutants. In the temporal distribution, the changes in PAHs concentration level and the development of GDP in Jiangxi Province showed high consistency, and the influence of economic development and human activities might have been the main reason for the increasing PAHs concentration level. The main sources of PAHs in surface sediments of Poyang Lake included petroleum pollution and oil and coal and biomass combustion sources, and there were some spatial differences in PAHs sources in different regions. This study can provide a reference for PAHs pollution in surface sediments of Poyang Lake, which is important for the ecological environmental protection and management of Poyang Lake.

The Multi-Kingdom Microbiome of Wintering Migratory Birds in Poyang Lake, China

Wild birds are a natural reservoir for zoonotic viruses. To clarify the role of migratory birds in viruses spread in Poyang Lake, we investigated the microbiome of 250 wild bird samples from 19 species in seven orders. The bacterial and viral content abundance and diversity were preliminarily evaluated by Kraken2 and Bracken. After de novo assembly by Megahit and Vamb, viral contigs were identified by CheckV. The reads remapped to viral contigs were quantified using Bowtie2. The bacterial microbiome composition of the samples covers 1526 genera belonging to 175 bacterial orders, while the composition of viruses covers 214 species belonging to 22 viral families. Several taxonomic biomarkers associated with avian carnivory, oral sampling, and raptor migration were identified. Additionally, 17 complete viral genomes belonging to Astroviridae, Caliciviridae, Dicistroviridae, Picornaviridae, and Tombusviridae were characterized, and their phylogenetic relationships were analyzed. This pioneering metagenomic study of migratory birds in Poyang Lake, China illuminates the diverse microbial landscape within these birds. It identifies potential pathogens, and uncovers taxonomic biomarkers relevant to varied bird habitats, feeding habits, ecological classifications, and sample types, underscoring the public health risks associated with wintering migratory birds.

Hydrological alteration drives chemistry of dissolved organic matter in the largest freshwater lake of China (Poyang Lake)

As the largest reactive organic carbon pool, dissolved organic matter (DOM) plays an important role in various biogeochemical processes in lake ecosystems. Recently, climate change-induced extreme events (e.g., floods and droughts) have significantly modified the hydrological patterns of lakes worldwide, and regulated the quality and quantity of DOM. However, the responses of DOM chemistry to hydrological alteration in lakes remain poorly understood. Here we investigated the influences of hydrological alteration on sources, composition, and characteristics of DOM in Poyang Lake, the largest freshwater lake in China, using a combination of bulk chemical, optical and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) techniques. Results show various sources of DOM (autochthonous, allochthonous, and anthropogenic inputs) and significant variations in DOM chemistry across four hydrological periods (the retreating, dry, rising, and flooding periods) in Poyang Lake. During the retreating, rising, and flooding periods, DOM was characterized by higher aromaticity, humification degree, and recalcitrance, and exhibited pronounced allochthonous signatures. In contrast, DOM contained more S-containing molecules and aliphatic compounds during the dry period, displaying relatively stronger autochthonous features. Terrestrial inputs and the lignin-CHOS formation process are likely the primary underlying mechanisms shaping the differences in DOM chemistry in Poyang Lake. Our research demonstrates the significant impacts of hydrological alteration on DOM dynamics, and provides an improved understanding of DOM biogeochemical cycles and carbon cycling in large aquatic systems under global climate change.

Response of Siberian Cranes (Grus leucogeranus) to Hydrological Changes and the Availability of Foraging Habitat at Various Water Levels in Poyang Lake

To assess the Siberian crane (Grus leucogeranus)'s response to changing water levels and habitat quality at Poyang Lake, we analyzed the lake's hydrological trends over the past two decades with the Mann-Kendall and Sen slope methods. Additionally, we explored the link between the crane population size and hydrological conditions at the lake from 2011 to 2019. Meanwhile, five environmental factors, including habitat type, distance from shallow lakes, human footprint index, elevation and normalized vegetation index were selected, and the distribution patterns of suitable habitats for the Siberian crane under 10 water level gradients with intervals of about 1 m (5.3-14.2 m) were simulated by using an improved habitat suitability index model that determines the weights of evaluating factors based on the MaxEnt model. The results showed that the overall trend of the inundated area in Poyang Lake was shrinking in the last 20 years, with a significant increase in the area of exposed floodland during the early wintering period (Z = -2.26). The prolonged drought resulting from this will force vegetation succession, thereby diminishing the food resources for cranes in their natural habitat. The mean inundated area in June demonstrated a significant negative correlation with the population of Siberian cranes in natural habitats (r = -0.75, p = 0.02). Shortage of the Siberian crane-preferred Vallisneria tuber due to June flooding was the primary driver of the crane's altered foraging strategy and habitat shift. In years with relatively normal June inundation, indicating abundant Vallisneria resources, the relationship between the inundated area during the dry season and the crane population fit well, with a quadratic curve (R2 = 0.92, p = 0.02). The dry season's inundated area primarily affected the crane population and distribution pattern by influencing the availability of food resources, and both excessive and insufficient inundation areas were unfavorable for crane survival. The modeling results for habitat suitability indicated that as the water level decreased, the trend of the area of good habitat for the Siberian crane showed an inverted bell shape, peaking at a water level of 8.8 m, with optimal conditions occurring between 8 and 10 m. The combined effects of climate and human activities have made the shortage of food resources in Poyang Lake the new normal. The degradation of natural habitats has led to a decline in the quality of Siberian crane habitats, and artificial habitats can only be used as refuges to a certain extent. Thus, formulating strategies to restore natural habitats and enhance the management of artificial habitats is crucial for the conservation efforts of Siberian cranes.

Bayesian model averaging by combining deep learning models to improve lake water level prediction

Water level (WL) is an essential indicator of lakes and sensitive to climate change. Fluctuations of lake WL may significantly affect water supply security and ecosystem stability. Accurate prediction of lake WL is, therefore, crucial for water resource management and eco-environmental protection. In this study, three deep learning (DL) models, including long short-term memory (LSTM), the gated recurrent unit (GRU), and the temporal convolutional network (TCN), were used to predict WLs at five stations of Poyang Lake for different forecast periods (1-day ahead, 3-day ahead, and 7-day ahead). The forecast results of the three DL models were synthesized through Bayesian model averaging (BMA) to improve prediction accuracy, and Monte Carlo sampling method was used to calculated the 90 % confidence intervals to analyze the model uncertainty. All the three DL models achieved satisfactory prediction accuracy. GRU performed best in most forecast scenarios, followed by TCN and LSTM. None of the models, however, consistently provided the optimal results in all forecast scenarios. Lake WL prediction accuracy of BMA had a further improvement in metrics of NSE and R2 in 80 % of the forecast scenarios and ranked at least top two in all forecast scenarios. The uncertainty analysis showed that the containing ration (CR) values were above 84 % while the relative bandwidth (RB) maintained reliable performance over the 7-day ahead prediction. The proposed framework in the present study can realize satisfactory WL forecast accuracy while avoiding complex comparison and selection of DL models, and it can also be easily applied to the prediction of other hydrological variables.

Spatiotemporal heterogeneity of inundation pattern of floodplain lake wetlands and impact on wetland vegetation

The inundation pattern is an important ecohydrological indicator for studying floodplain lake wetlands, as it is the key factor affecting the wetland vegetation distribution patterns. Poyang Lake, the largest freshwater lake in China, is a typical floodplain lake wetland. This study presents a hydrodynamic model and vegetation survey of Poyang Lake, analyzed the spatiotemporal heterogeneity of the inundation pattern (inundation duration and depth), assessed the response patterns of wetland vegetation concerning the inundation pattern, and examined the impact of the proposed Poyang Lake Water Conservancy Hub (PLWCH) on the inundation pattern and wetland vegetation. The results revealed that the inundation pattern of Poyang Lake had significant spatial heterogeneity. Inundation pattern was found to have a significant impact on the vegetation succession. The response relationship between the distribution areas of different wetland vegetation types and inundation pattern was in accordance with the Gaussian curve, and the ecological threshold range of the Carex spp. community was the greatest. Owing to factors such as climate change and anthropogenic activities, the inundation pattern of Poyang Lake varied significantly since 2003, with the average inundation duration and average inundation depth decreasing by 15 d and 0.32 m, respectively. Consequently, the spatial distribution of wetland vegetation changed significantly, whereby the Carex spp., Polygonum criopolitanum, and Phalaris arundinacea communities extended down to the lower elevation zone. In the future, the PLWCH may result in increases in the inundation duration and depth, restrain the downward vegetation extension trend, and promote the vegetation to move to higher elevations similar to the status prior to 2003. These findings provide a detailed description of the spatiotemporal heterogeneity of the inundation pattern and the drivers of wetland vegetation distribution patterns in floodplain lake wetlands, serving as a scientific basis for conservation and restoration of these ecosystems.

Nonstationary frequency analysis and uncertainty quantification for extreme low lake levels in a large river-lake-catchment system

Extreme hydrological events have become increasingly frequent on a global scale. The middle Yangtze River also faces a substantial challenge in dealing with extreme flooding and drought. However, the long-term characteristics of the extreme hydrological regime have not yet been adequately recognized. Moreover, there is uncertainty in the extreme value estimation, and this uncertainty needs to be distinguished and quantified. In this study, we investigated the nonstationary frequency characteristics of extreme low lake levels (ELLLs), taking the Poyang Lake as an example. Daily lake levels from 1960 to 2022 were utilized to estimate the return level using the generalized Pareto distribution (GPD). The uncertainty from three sources, i.e., the parameter estimator, threshold selection, and covariate, was quantified via variance decomposition. The results indicate that (1) the parameter estimator is the predominant source of uncertainty, with a contribution rate of approximately 87 %. The total uncertainty of the covariate, threshold, and interaction term is only 13 %. (2) Two indexes, namely the annual minimum water level (WLmin) and the days with peak over the 90 % threshold per year (DPOT90), decreased (0.01-0.03 m/year) and increased (0.17-1.39 days/year), respectively, indicating a progressively severe drought trend for Poyang Lake. (3) The return level with return period of 5 to 100 years significantly decreased after the early 21st century. A large spatial heterogeneity was identified for the variation in the return level, and the change rate of the return level with a 100-year return period ranged from 5 % to 40 % for the whole lake. (4) The ELLLs had a stronger correlation with the catchment discharge than with the Yangtze River discharge and the large-scale atmospheric circulation indices. This study provides a methodology with reduced uncertainty for nonstationary frequency analysis (NFA) of ELLLs exemplified in large river-lake systems.

The influence of wet-to-dry season shifts on the microbial community stability and nitrogen cycle in the Poyang Lake sediment

In lake environments, seasonal changes can cause exposure of the lake sediment, leading to soil formation. Although previous studies have explored how environmental changes influence microbial functioning in the water-level-fluctuating zone, few studies have investigated how wholescale habitat changes affect microbial composition, community stability and ecological functions in lake environments. To address this issue, our study investigated the effects of sediment-to-soil conversion on microbial composition, community stability and subsequent ecological functioning in Poyang Lake, China. Our results revealed that, during sediment-to-soil conversion, the number of total and unique operational taxonomic units (OTUs) decreased by 40 % and 55 %, respectively. Moreover, sediment-to-soil conversion decreased the microbial community connectivity and complexity while significantly increasing its stability, as evidenced by increased absolute values of negative/positive cohesion. In sediment and soil, the abundance of dominant bacteria, and bacterial diversity strongly affected microbial community stability, although this phenomenon was not true in water. Furthermore, the specific microbial phyla and genes involved in the nitrogen cycle changed significantly following sediment-to-soil conversion, with the major nitrogen cycling processes altering from denitrification and dissimilatory nitrate reduction to ammonium to nitrification and assimilatory nitrate reduction to ammonia. Moreover, a compensation mechanism was observed in the functional genes related to the nitrogen cycle, such that all the processes in the nitrogen cycle were maintained following sediment-to-soil conversion. The oxidation-reduction potential strongly affected network complexity, microbial stability, and nitrogen cycling in the sediment and soil. These results aid in the understanding of responses of microorganisms to climate change and extreme drought. Our findings have considerable implications for predicting the ecological consequences of habitat conversion and for ecosystem management.

Assessing habitat quality at Poyang Lake based on InVEST and Geodetector modeling

Poyang Lake is an essential natural wetland in the Yangtze River basin and plays a vital role in maintaining the ecosystem function and ecological security in the middle and lower reaches of the Yangtze River. However, the relative importance and spatial heterogeneity of the impacts of human activities and land use changes on ecological security needs to be further explored. Here, we analyzed the habitat quality level around Poyang Lake in 2022 and explored the factors of habitat quality change from a geographical perspective. The land use structure changes around the Poyang Lake basin from 2000 to 2022 were quantitatively analyzed, and then the relative importance and spatial heterogeneity of each factor on ecological security changes were investigated using geographic probes. The results show that (1) The worst quality habitat (0-0.1) consists mainly of construction land (1624.9 km2) with an area of 1634.64 km2; (2) Construction land continues to increase with the most significant change, and the dynamic land use attitude is 0.47. Grassland and mudflats have the greatest decrease. The increase in cultivated land in different periods is mainly due to the shift of water surface and forest land; (3) The drivers of habitat quality in Poyang Lake were significantly influenced by the interaction of socioeconomic factors. The explanatory power of population density interacting with the total year-end population and population density interacting with administrative area exceeded 0.84. These values were higher than the explanatory power of each individual factor, indicating that habitat quality was primarily associated with population density, total year-end population, and administrative area. These results suggest that human activities contribute to the degradation of wetlands around Poyang Lake. This study has significant reference value for coordinating human-land relationships in Poyang Lake, optimizing land management policy, and improving the sustainable development of cities.

Impact of land use on water quality in buffer zones at different scales in the Poyang Lake, middle reaches of the Yangtze River basin

The water quality of Poyang Lake (PYL) is significantly influenced by land use which is a crucial factor that can exhibit complex changes in the environment and can serve as an indicator of the intensity of human activity. Therefore, this study analyzed the spatial and temporal distribution characteristics of nutrients and investigated the effects of land-use factors on water quality in the PYL during 2016-2019. The main conclusions are as follows: (1) Although there was some variation in the accuracy of the water quality inversion models (random forest (RF), support vector machine (SVM), and multiple statistical regression models), they were homogeneous. In particular, ammonia nitrogen (NH3-N) concentration from band (B) 2 and B2-B10 regression model was more consistent with each other. In contrast, the overall concentration levels from the combined B9/(B2-B4) triple-band regression model were relatively low, with approximately 0.03 mg/L in most areas of PYL. (2) The optimal inversion method varied for different water quality parameters. For instance, RF obtained better inversion of total phosphorus (TP) and total nitrogen (TN), with the fitting coefficient (r2) of 0.78 and 0.81, respectively; SVM had higher accuracy in the inversion of permanganate index (CODMn), with r2 of approximately 0.61; the accuracy of multi-band combined regression model in the inversion of each water quality parameter was at a higher level. (3) The influence of land use on water quality at different scales of buffer zone was different. In general, the correlation between water quality parameters and land use was higher at large spatial scales (1000-5000 m) than at small spatial scales (100 m, 500 m). A common feature of all hydrological stations was the significant negative correlation between crops, buildings, and water quality at all buffer scales. This study is of great practical significance for promoting water environment management and water quality health in the PYL.

Anthropogenic activity, hydrological regime, and light level jointly influence temporal patterns in biosonar activity of the Yangtze finless porpoise at the junction of the Yangtze River and Poyang Lake, China

Under increasing anthropogenic pressure, species with a previously contiguous distribution across their ranges have been reduced to small fragmented populations. The critically endangered Yangtze finless porpoise ( Neophocaena asiaeorientalis asiaeorientalis), once commonly observed in the Yangtze River-Poyang Lake junction, is now rarely seen in the river-lake corridor. In this study, static passive acoustic monitoring techniques were used to detect the biosonar activities of the Yangtze finless porpoise in this unique corridor. Generalized linear models were used to examine the correlation between these activities and anthropogenic impacts from the COVID-19 pandemic lockdown and boat navigation, as well as environmental variables, including hydrological conditions and light levels. Over approximately three consecutive years of monitoring (2020-2022), porpoise biosonar was detected during 93% of logged days, indicating the key role of the corridor for finless porpoise conservation. In addition, porpoise clicks were recorded in 3.80% of minutes, while feeding correlated buzzes were detected in 1.23% of minutes, suggesting the potential existence of localized, small-scale migration. Furthermore, both anthropogenic and environmental variables were significantly correlated with the diel, lunar, monthly, seasonal, and annual variations in porpoise biosonar activities. During the pandemic lockdown period, porpoise sonar detection showed a significant increase. Furthermore, a significant negative correlation was identified between the detection of porpoise click trains and buzzes and boat traffic intensity. In addition to water level and flux, daylight and moonlight exhibited significant correlations with porpoise biosonar activities, with markedly higher detections at night and quarter moon periods. Ensuring the spatiotemporal reduction of anthropogenic activities, implementing vessel speed restrictions (e.g., during porpoise migration and feeding), and maintaining local natural hydrological regimes are critical factors for sustaining porpoise population viability.

[Analysis on the Current Situation of Phytoplankton in the Typical River-Lake Ecotone of Lake Poyang]

The typical river-lake ecotone (tail end area) of Poyang Lake, which is a sensitive area and prone to outbreaks of cyanobacteria bloom, is vulnerable to frequent human activities. To explore the diversity of phytoplankton community structure and the relevant driving mechanism in the typical river lake junction area of Poyang Lake, the water quality and phytoplankton at seven sampling points in the typical river lake junction area of Poyang Lake, at six sampling points in the middle section of Poyang Lake River, and at one sampling point in the main lake area were investigated in the field from 2019 to 2020 (dry season), April (flood season), July (wet season), and October (recession period). The results showed that there were seven phyla and 64 genera of phytoplankton in the typical river-lake ecotone of Poyang Lake, and the biomass and relative abundance of phytoplankton were dominated by diatoms and cyanobacteria. The biomass and abundance in the east of the typical river-lake ecotone of Poyang Lake were generally higher than those in the west, and the biomass and abundance in the river-lake ecotone were higher than those in the middle of the river. The dominant degree of cyanobacteria in the lake area and the river-lake ecotone was large, and the dominant degree of diatoms in the middle section of the river was large. The Monte Carlo test results showed that total nitrogen (TN), total phosphorus (TP), orthophosphate phosphorus (PO43--P), water depth (WD), water temperature (WT), and transparency (SD) were significantly related environmental factors affecting the distribution of the phytoplankton community. Redundancy analysis results showed that the typical river-lake ecotone in the west of Poyang Lake was highly affected by the hydration factors (TN, TP, and PO43--P), and the hydrological factors (WT, WD, and SD) in the typical river-lake ecotone in the east were highly significant. The impact factors of phytoplankton in the typical river-lake ecotone of Poyang Lake were seasonal, being greatly affected by hydration factors in winter and hydrological factors in summer.

Non-steady state fluctuations in water levels exacerbate long-term and seasonal degradation of water quality in river-connected lakes

The hydrological regimes and environmental changes in large riverine lakes are known for their complexity and high level of uncertainty. Scientifically uncovering the response mechanisms of water environments under complex hydrological conditions has become a challenging research objective, in the interdisciplinary of environmental science and hydrology. This study delved into the unstable response process between water level and quality of Poyang Lake, the largest freshwater lake as well as one of the most intense hydrological variability water bodies in China. We developed a non-steady state identification approach incorporates Seasonal and Trend decomposition using Loess (STL) and Wavelet Correlation (WTC) methods. The results showed that there were remarkable alterations in the hydrological regime and water quality at both seasonal and long-term scale of Poyang Lake over the past nine years. These alterations were accompanied by significant non-steady state characteristics, reflecting the changes in the response between water level and quality. The employment of the STL-WTC method revealed a significant nonlinear response between the long-term trends of water level and quality, in both the 4-month and 12-month frequency bands. In particular, our findings showed an intriguing shift towards in-phase behavior between water level and quality in the 12-month frequency band, rather than the anti-phase pattern observed previously. This correlation changed more significantly in seasons where the fluctuation pattern of water level varied sharply, such as summer and winter in Poyang Lake. Our study underscored the hydrological conditions and water quality of large lakes connected to rivers do not exhibit a long-term stable unidirectional response state, alterations in hydrological rhythms may induce a transition in the relationship from negative correlation towards nonlinear positive correlation between water level and water quality. Finally, this non-steady state fluctuation of water conditions can further exacerbate long-term and seasonal degradation of water quality.

Bioaccumulation of pharmaceuticals and personal care products (PPCPs) in freshwater pearl mussels Hyriopsis cumingii in Poyang Lake

Thirty-five PPCPs were measured in representative freshwater pearl mussels (Hyriopsis cumingii) in Poyang Lake, the largest lake of China, as well as their responses to sedimentary PPCPs. We observed 32 PPCPs in soft tissues of mussels at a total concentration of 2721.5 ± 929.3 ng·g-1 dry weight (dw), much higher than those in sediments (21 PPCPs, 273.2 ± 89.4 ng·g-1 dw). Anti-inflammatories were the primary contaminants detected in both sediments and mussels. PPCP concentrations in mussels exhibited significant organ-specific characteristics, and gonads were identified as a hotspot for these contaminants. Correlation analysis showed that gonads were more likely to assimilate triclosan from sediments. Biochemical analysis revealed a higher physiological sensitivity of glutathione synthesis in gonads to sedimentary PPCPs, suggesting the long-term oxidative damage. Our findings highlight the concern on the potential effects of sedimentary PPCPs to propagation of mussels, and emphasize the necessity to formulate strategies for sedimentary PPCPs control targeting a healthy lake.

Metagenomic Analysis of Environmental Samples from Wildlife Rescue Station at Poyang Lake, China

Objective

To improve the understanding of the virome and bacterial microbiome in the wildlife rescue station of Poyang Lake, China.

Methods

Ten smear samples were collected in March 2019. Metagenomic sequencing was performed to delineate bacterial and viral diversity. Taxonomic analysis was performed using the Kraken2 and Bracken methods. A maximum-likelihood tree was constructed based on the RNA-dependent RNA polymerase (RdRp) region of picornavirus.

Results

We identified 363 bacterial and 6 viral families. A significant difference in microbial and viral abundance was found between samples S01-S09 and S10. In S01-S09, members of Flavobacteriia and Gammaproteobacteria were the most prevalent, while in S10, the most prevalent bacteria class was Actinomycetia. Among S01-S09, members of Myoviridae and Herelleviridae were the most prevalent, while the dominant virus family of S10 was Picornaviridae. The full genome of the pigeon mesivirus-like virus (NC-BM-233) was recovered from S10 and contained an open reading frame of 8,124 nt. It showed the best hit to the pigeon mesivirus 2 polyprotein, with 84.10% amino acid identity. Phylogenetic analysis showed that RdRp clustered into Megrivirus B.

Conclusion

This study provides an initial assessment of the bacteria and viruses in the cage-smeared samples, broadens our knowledge of viral and bacterial diversity, and is a way to discover potential pathogens in wild birds.

Bacterial community structure of water, sediment and microplastics in Poyang Lake wetland

As a new type of pollutant, microplastics accumulate continuously in the environment. The environmental problems caused by microplastics have attracted wide attention. In this study, we collected water, sediment and four types of microplastics (film, foam, fiber and fragment) from wetland in East Lake area of Poyang Lake. We used high-throughput sequencing technology to analyze the bacterial diversity and community structure of water, sediment, and microplastics surface. The results showed that the bacterial richness and diversity of water and sediment were significantly higher than that on microplastics, and the bacterial richness of foaming microplastics was significantly lower than that of the other three types of microplastics. There were significant differences of bacterial communities between water, sediment, and microplastics. There were significant differences cross different types of microplastics. Proteobacteria, Bacteroidetes, and Actinobacteria were the main bacterial communities of water, sediment, and microplastics. The relative abundance of Bacteroidetes and Actinobacteria in water was higher than that in sediments and microplastics, while the relative abundance of Bacteroidetes and Actinobacteria in foaming microplastics was higher than that in other three types. At the genus level, the dominant ones included Massilia, Flavobacteria, and Pseudomonas. The relative abundance of Massilia and Pseudomonas in water and sediments was lower than that on microplastics, and the relative abundance of Flavobacteria was not different among water, sediment and microplastics. The relative abundance of Massilia in microplastics followed an order of fragment>fiber>film>foam, and that of Pseudomonas was film>fiber>foam>fragment. The results of metabolic pathway prediction analysis showed that except for foaming microplastics, the bacterial metabolic pathways on the surface of the other three types of microplastics were significantly different from those in water and sediment. The cellular processes, organismal systems, environmental information processing, and human diseases in bacterial metabolic pathways on microplastics surface were significantly higher than those in water and sediment. Our results suggested that microbial community structure on the surface of microplastics was significantly different from that in water and sediment, and that the morphology type of microplastics affected microbial community structure on the surface.

Exploring the optical properties and molecular characteristics of dissolved organic matter in a large river-connected lake (Poyang Lake, China) using optical spectroscopy and FT-ICR MS analysis

River-connected lakes are complicated and dynamic ecosystems due to their distinctive hydrological pattern, which could significantly impact the generation, degradation, and transformation processes of dissolved organic matter (DOM) and further regulate DOM chemistry in lakes. However, the molecular compositions and characteristics of DOM in river-connected lakes are still poorly understood. Thus, here the spatial variations of optical properties and molecular characteristics of DOM in a large river-connected lake (Poyang Lake) were explored via spectroscopic techniques and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The results showed high degree of spatial heterogeneity of DOM chemistry (variations in DOC concentrations, optical parameters, and molecular compounds) in Poyang Lake, and the diversity at the molecular level was primarily caused by the heteroatom compounds (N- and S- containing). Compared with classic lakes and rivers, DOM compositions of the river-connected lake had distinctive characteristics (differences in the AI_mod and DBE values, and CHOS proportions). And the composition characteristics of DOM between the southern and northern parts of Poyang Lake were different (such as the lability and molecular compounds), suggesting the changes of hydrologic conditions may affect the DOM chemistry. In addition, various sources of DOM (autochthonous, allochthonous, and anthropogenic inputs) were identified agreeably based on optical properties and molecular compounds. Overall, this study first characterizes the DOM chemistry and reveals its spatial variations in Poyang Lake at the molecular level, which could improve our understanding of DOM in large river-connected lake systems. Further studies are encouraged to investigate the seasonal variations of DOM chemistry under different hydrologic conditions in Poyang Lake to enrich the knowledge of carbon cycling in river-connected lake systems.

A strong short-duration convection near Poyang Lake in daytime of warm season

Poyang Lake (PL), the biggest freshwater lake in China, is situated in the East Asian Monsoon region, and has an important impact on local convection. In general, PL can result in convection in local region when it is a heat source in nighttime of warm season. However, at around noon on 4 May 2020 (PL is a cold source), a convection was triggered about 20 km west of PL, and rapidly enhanced and resulted in lightning when approaching PL, and then quickly weakened and disappeared after entering the main body of PL. In order to explore the convection formation, several observational data and the Weather Research and Forecasting model were applied in this study. Results show that when the convection approaches PL, its rapid enhancement is induced by PL, and after entering the main body of PL, its quick weakening is also resulted from PL. However, the initiation of the convection is mainly induced by the local topography west of PL under a favorable large-scale background. Mechanism analysis indicates that the strong low-level convergence near the west shore of PL associated with lake-land breeze is responsible for the rapid enhancement of the convection, and the low-level divergence over the main body of PL associated with the lake-land breeze and the increase of the low-level stability induced by cooling of PL jointly result in the quick weakening of the convection. The prevailing southerly wind in low level passes through the local topography (Meling Mountain) west of PL, and is divided into southwesterly wind (flow around Meiling) and southerly wind (flow over Meiling), and they converge in the north of Meling, triggering the convection. This study is not only important to deepen the understanding of PL affecting regional weather, but also helpful for improving the refined forecasting of convection near PL.

Human health ambient water quality criteria and risk assessment of pentachlorophenol in Poyang Lake Basin, China

Pentachlorophenol (PCP) has been widely used as an insecticide for killing oncomelania (the intermediate host of schistosome) in China and leads to severe environmental contamination. Poyang Lake, as the largest freshwater lake and bird habitat in China, was once a schistosomiasis epidemic area. In this study, the concentrations of PCP in water and aquatic products from Poyang Lake were determined and analyzed, and then the human health ambient water quality criteria (AWQC) was derived based on native parameters of Poyang Lake basin. Finally, a comprehensive analysis of the health risks of drinking water and different types of aquatic products consumption was carried out. The results showed that PCP concentrations were ranged from 0.01 to 0.43 μg/L in surface water and 3.90 to 85.95 μg/kg in aquatic products. Due to the carcinogenicity of PCP, the human health AWQC for PCP are 0.02 μg/L for consumption of water and organisms and 0.03 μg/L for consumption of organisms only. Deterministic and probabilistic risk analysis indicated that the non-carcinogenic risk of PCP were acceptable in Poyang Lake, while the carcinogenic risk cannot be ignored. The health risks of PCP caused by aquatic products consumption were higher than that by drinking water. The percentages of acceptable risk for the population in Poyang Lake Basin were 99.95% at acceptable level of 10^-4. Based on the sensitivity analysis, the impact of PCP concentrations on health risk values ranged from 53 to 82%. The study provided valuable information for regional water quality criteria development and water quality assessment.

A New Method for Spatial Estimation of Water Quality Using an Optimal Virtual Sensor Network and In Situ Observations: A Case Study of Chemical Oxygen Demand

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.

Habitat selection of wintering cranes in typical wetlands in the middle and lower reaches of the Yangtze River over the past 20 years, China

The wetlands in the middle and lower reaches of the Yangtze River are the main overwintering and perching places for cranes. To examine the habitat selection mechanism of cranes in this area, two natural wetland reserves, Shengjin Lake and Poyang Lake, which are the main habitats of typical cranes, were selected as the study area. Using 20 years of Landsat satellite image data (between 1999 and 2019), the vegetation cover index was calculated from a pixel dichotomy model, and the landscape pattern index was obtained through Fragstats. The entropy method was adopted to determine the weight of the landscape index, and then, the habitat suitability index was calculated. Combined with the number of typical crane populations in the reserve, the selection mechanism of overwintering habitat of cranes was revealed. On the change of land-use type, the crane habitat of Shengjin Lake transferred more to non-crane habitat, and other land types increased, resulting in the decrease of crane habitat area. However, the change of crane habitat in Poyang Lake Reserve was small, so it can accommodate more cranes to overwintering here. In terms of vegetation coverage, most of the vegetation cover areas of Shengjin Lake were woodland near or far from the lake, but the woodland was not the habitat of cranes. Most of the vegetation-covered areas of Poyang Lake are grassland near the lake, which provide rest and foraging places for cranes. In the landscape pattern, the number of landscape patches in Shengjin Lake was large, the degree of landscape fragmentation was higher than that in Poyang Lake, the landscape complexity was higher, and the landscape diversity was simpler. This is not conducive to the maintenance of crane habitat, but also reduces the attractiveness of overwintering cranes, while the landscape suitability of crane habitat in Poyang Lake was higher than that in Shengjin Lake, and cranes were more likely to choose Poyang Lake as their overwintering habitat.

Multi-methods to investigate spatiotemporal variations of nitrogen-nitrate and its risks to human health in China's largest fresh water lake (Poyang Lake)

Nitrogen-nitrate contamination has been recognized as the main threaten to the large lake surrounding with the intensive agriculture activities. However, there are still insufficient studies on the interannual evolution of nitrogen-nitrate, source and its impact on the environment and human health in the large fresh water lake. In this study, 248 samplings were collected in Poyang Lake from 2013 to 2018, multi-methods (mathematical statistics method, grey correlation analysis, person correlation analysis and human health risk assessment) to investigate the spatiotemporal variations, impact factors and potential health risks of NO₂^--N, NO₃^--N and NH₄⁺-N. The results showed that the middle region had the highest NO₂^- concentration (mean 0.04μg/l), the northern region had the highest NO₃^- concentration (mean 1.12 mg/l), and the southern region had the highest NH₄⁺ concentration (mean 0.48 mg/l). For NO₃^- and NH₄⁺, the concentration was higher than in the wet season. While the concentration of NO₂^- had the reverse trend. Grey correlation analysis and person correlation analysis results indicate that nitrogen fertilizer, waste water, pH, CODMn and temperature were main factors affecting the nitrogen concentration in Poyang Lake. Health risk assessment results revealed that potential hazards in the study area were acceptable (HR < 1). NO₃^- provided the highest health risks, and oral ingestion is the major source of local nitrogen health risk. Those results can provide the reference for developing the treatment methods of the international large freshwater lake.

[Enrichments, Migrations, and Conversions of Heavy Metal in the Soil/Sediment-Plant System Towards the Lake in Typical Poyang Lake Wetland]

A large area of periodic water-level-fluctuating zone (WLFZ) in the Poyang Lake, regulated by a special hydrologic rhythm, was deposited with significant amounts of nutrients and pollutants. In this study, the WLFZ located in a typical estuarine wetland was chosen and sampling transects were arranged according to different vegetation types towards the lake. Soil/sediment and dominant plant (different tissues) samples were collected, and contents and enrichment levels of heavy metals (Cr, Ni, Cu, Zn, As, Cd, Sb, and Pb) in these samples were analyzed. The migrations and conversions of heavy metal in the soil/sediment-plant system were evaluated, and driving environmental factors were explored. The results indicated that the contents of heavy metal in the soil/sediment presented an obvious single-peak distribution towards the lake, that is, the seasonally flooded zone was identified as the main deposited zone of heavy metals. There was a high enrichment level of Cu, Pb, and Sb in the soil/sediment from the WLFZ, and significant Cu and Sb pollution was identified (EF>5). The results from the potential ecological risk evaluation (RI) indicated that the ecological risk of the seasonally flooded zone was significantly higher than that in the flooded and unflooded zones, being at a low ecological risk (70 ≤ RI<140). There was no obvious spatial distribution of heavy metal contents in the dominant plant towards the lake, whereas significant seasonal differences were detected. The levels of heavy metals in plants at the growth phase (April) were higher compared to those at the other sampling times. The tissue distributions of heavy metal content basically followed the sequence of soil/sediment>root ≥ above-ground part, except for in Cd and Sb. The Cd content in the roots was significantly higher than that in the sediment/soil, and the Sb concentration was not significantly different among the three tissues. The bio-enrichment coefficient (BAF) and transfer factor (TF) of heavy metal in the dominant plant towards the lake did not show an obvious spatial pattern, and BAF and TF of heavy metals in the Artemisia capillaris Thunb. was higher than those in other dominant plants. The RDA revealed that pH, organic matter, plant height, and Fe-Mn oxides were the key environmental factors driving the migrations of heavy metals in the soil/sediment-plant system. These results will provide scientific basis and theoretical support for the biodiversity conservation and heavy metal pollution prevention and management in wetlands of the Poyang Lake.

Changes in the water environment and its major driving factors in Poyang Lake from 2016 to 2019, China

The hydrological exchange process between Poyang Lake (PYL), the largest freshwater lake in China, and the Yangtze River leads to drastic changes in water area (WA) and water level (WL), as well as apparent fluctuations in lake nutrients, algal organisms, and trophic level index. This study investigated the current status of the PYL water environment and the influence of hydrological changes on the nutrient status of the floodplain of the lake. Based on monthly measured data from six hydrological stations from 2016 to 2019, it was hypothesized that WA and WL were the key regulators of the spatial and temporal distribution patterns of lake water quality and algal growth, including water temperature, water clarity (Secchi depth [SD]), and nutrient levels. The results revealed that (1) the spatial and temporal distribution characteristics of major nutrients in PYL were influenced by dynamic changes in hydrological characteristics (SD, total nitrogen [TN], and total phosphorus [TP]); (2) the eutrophication level in PYL has been in a steady state in recent years, while the central area has been more prone to the risk of eutrophication (e.g., the peak eutrophication index during Period 1 [January to April] in the water near the Duchang station reached 70); and (3) there were significant correlations among environmental variables, nutrients, and algal organisms, with different spatial and temporal distribution characteristics (p < 0.05), while the changes in WA and WL considerably influenced the water environment in the PYL.

Determining Critical Thresholds of Environmental Flow Restoration Based on Planktonic Index of Biotic Integrity (P-IBI): A Case Study in the Typical Tributaries of Poyang Lake

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.

Identification and Genomic Characterization of Escherichia albertii in Migratory Birds from Poyang Lake, China

Escherichia albertii is an emerging zoonotic foodborne enteropathogen leading to human gastroenteritis outbreaks. Although E. albertii has been isolated from birds which have been considered as the potential reservoirs of this bacterium, its prevalence in migratory birds has rarely been described. In this study, E. albertii in migratory birds from Poyang Lake was investigated and characterized using whole genome sequencing. Eighty-one fecal samples from nine species of migratory birds were collected and 24/81 (29.6%) tested PCR-positive for E. albertii-specific genes. A total of 47 isolates was recovered from 18 out of 24 PCR-positive samples. All isolates carried eae and cdtB genes. These isolates were classified into eight E. albertii O-genotypes (EAOgs) (including three novel EAOgs) and three E. albertii H-genotypes (EAHgs). Whole genome phylogeny separated migratory bird-derived isolates into different lineages, some isolates in this study were phylogenetically closely grouped with poultry-derived or patient-derived strains. Our findings showed that migratory birds may serve as an important reservoir for heterogeneous E. albertii, thereby acting as potential transmission vehicles of E. albertii to humans.

Hydrological isolation affected the chemo-diversity of dissolved organic matter in a large river-connected lake (Poyang Lake, China)

The transportation processes during aquatic systems regulate the ultimate chemistry of dissolved organic matter (DOM), and in recent years, climate changes and human activities have altered the hydrological patterns of many rivers and lakes, which generated some severe issues, such as hydrological isolation. However, how hydrological isolation affects variations of DOM chemistry in large lake systems is still poorly understood. Here, optical properties and molecular compositions of DOM samples derived from a large river-connected lake (Poyang Lake, China) and its nearby seasonal sub-lakes (formed by hydrological isolation) were characterized using Fourier transform ion cyclotron resonance mass spectrometry (FT ICR MS) and ultraviolet-visible (UV-Vis) spectroscopy. The results revealed more abundance of organic matter in sub-lakes than that in the main lake according to high dissolved organic carbon (DOC) concentrations and absorption coefficients (a₂₅₄ and a₂₈₀). Large proportions of CHOS formulas were identified by FT ICR MS in sub-lakes DOM, which were produced through Kraft reactions (sulfide/bisulfide + lignin CHO → CHOS) in the interface of sediment/water, and greatly contributed to aliphatic compounds. In addition, obvious variations of compounds (such as polyphenols, highly unsaturated and aliphatic compounds) and lability of DOM were observed between sub-lakes and main lakes, which were mainly caused by the different degradation pathways of DOM (photodegradation in sub-lakes while biodegradation in the main lake). Our results demonstrated that hydrological isolation has significant impacts on DOM chemistry, and provides an improved understanding of the DOM biogeochemistry process in Poyang Lake and supports the management of the large lake systems.

The Ecological Differentiation of Particle-Attached and Free-Living Bacterial Communities in a Seasonal Flooding Lake-the Poyang Lake

Particle-attached (PA) and free-living (FL) bacterial communities play essential roles in the biogeochemical cycling of essential nutrients in aquatic environments. However, little is known about the factors that drive the differentiation of bacterial lifestyles, especially in flooding lake systems. Here we assessed the compositional and functional similarities between the FL and PA bacterial fractions in a typical flooding lake-the Poyang Lake (PYL) of China. The results revealed that PA communities had significantly different compositions and functions from FL communities in every hydrological period, and the diversity of both PA and FL communities was affected mainly by the water regime rather than bacterial lifestyles. PA communities were more diverse and enriched with Proteobacteria and Bacteroidetes, while FL communities had more Actinobacteria. There was a higher abundance of photosynthetic and nitrogen-cycling bacterial groups in PA communities, but a higher abundance of members involved in hydrocarbon degradation, aromatic hydrocarbon degradation, and methylotrophy in FL communities. Water properties (e.g., temperature, pH, total phosphorus) significantly regulated the lifestyle variations of PA and FL bacteria in PYL. Collectively, our results have demonstrated a clear ecological differentiation of PA and FL bacterial communities in flooding lakes, suggesting that the connectivity between FL and PA bacterial fractions is water property-related rather than water regime-related.

[Spatiotemporal distribution and multi-source characteristics of microplastics in the soil and water environment of Poyang Lake Wetland, China]

The increasing microplastics (MPs) pollution in freshwater wetlands has received global concerns. To investigate the spatiotemporal dynamics of MPs in the wetlands of Poyang Lake, surface water and sediment samples were collected from five rivers entering the lake as well as the confluence of Poyang Lake into the Yangtze River, in both dry and wet seasons. The MPs in water and sediment were extracted by the digestion-filtration method and flotation-separation-digestion-filtration method, respectively. Light microscope, Fourier transform infrared spectroscopy, and scanning electron microscope were used for microplastic characterization. The results showed that the abundance of MPs ranged from 32.1 to 127.3 n·L^-1 in water samples, and from 533.3 to 1286.6 n·kg^-1 in sediment samples during the wet season. In the dry season, the abundance of MPs ranged from 87.1 to 295.5 n·L^-1 in water and from 460.0 to 1368.0 n·kg^-1 in sediment. Compared with other freshwater wetlands, Poyang Lake had higher abundance of MPs. There were temporal and spatial differences among regions. The main forms of MPs included beads, fragment, film and fiber, and the corresponding polymer components were mainly polystyrene, polypropy-lene and polyethylene. Beads (35.7% in wet season and 52.0% in dry season) were the main form of MPs in water, while fragment (45.8% in wet season and 69.7% in dry season) was the main form of MPs in sediment. Small size (&lt;0.1 mm) MPs were dominant (&gt;50%) in water and sediment in both seasons. The abundance of MPs with different sizes decreased with the increases of size. The potential main sources of MPs in the wetlands of Poyang Lake included the discharge of industrial wastewater, discharge from urban and rural domestic sewage treatment plants, agricultural and fishing activities, and improper disposal of domestic wastes.

Tracing the organic matter source of cage culture sediments based on stable carbon and nitrogen isotopes in Poyang Lake, China

Collected sediment samples from the cage fish farm were measured to determine carbon and nitrogen stable isotope compositions and to understand the influence of the aquaculture waste on the sediment. The average δ¹³C of the sediment organic matter was -27.2 ‰ and -26.5 ‰, and the average δ¹⁵N value was 5.6 ‰ and 6.2 ‰ in October 2017 and November 2018, respectively. A linear mixing model was used to calculate the contribution ratios of the aquaculture waste in sediment organic matter. The contribution ratio of fish feces was 53.9 % and 25.5 %, and the contribution ratio of waste feed was 18.4 % and 52.6 % in October 2017 and November 2018, respectively. The sediment in the "cage fish area" was characterized by high waste feed ratio in sediment organic matter. The sediment organic matter was affected by the aquaculture waste even at sites 1500 m away from the cage fish farm.

Assessing the inundation dynamics and its impacts on habitat suitability in Poyang Lake based on integrating Landsat and MODIS observations

Poyang Lake, the largest freshwater lake in China, serves critical ecosystem function for water regulation and biodiversity conservation. However, it experienced dramatic changes in lake inundation due to recent climate change and human activities, causing ecological and economic problems. Here, we applied a multiple-index water detection rule to integrated Landsat and MODIS products to reconstruct surface water series at 30-m and 8-day resolutions and quantified the spatio-temporal inundation dynamics in Poyang Lake over the past 20 years (2000-2019). Furthermore, their influences on habitat suitability for herbivorous birds were also assessed from the perspectives of hydroperiod and vegetation growth threshold. The significant declining trend (-26.66 km² yr^-1, p < 0.001) for the annual minimum water areas throughout the 20 years implied that Poyang Lake was undergoing a continuous shrinkage in the low-water season. On the monthly scale, inundation frequency (IF) decreases were more significant in September-January, most of which occurred in the alluvial delta zones near the lake center. The altered water regime after the Three Gorges Dam (TGD) might be the dominant contributor responsible for the continuous lake shrinkage during the recent low-water period. The sub-lakes suffered from spring drought rather than winter drought, triggering vegetation successions regarding the reversed trend of the well-documented xerophilization in Poyang Lake. The recent earlier and prolonged dry seasons caused an increase of suitable habitat for herbivorous birds (13.92 km² year^-1, p < 0.1), but triggered a potential risk of food quality degradation when the migratory waterbirds peaked in December. These results provide a clear reference for optimizing the hydrologic management and biodiversity conservation of Poyang Lake.

The improved entropy weighting model in water quality evaluation based on the compound function

Entropy weight model (EWM) is widely used in water quality evaluation. In the conventional EWM, the weight is a monotone increasing function of the dispersion degree. However, this weighting principle often neglects the heavily polluted indicators. To solve this problem, an improved EWM is designed, in which the weight of the indicator is a compound function of its dispersion degree and pollution degree. In the clean domain, the weight increases with the dispersion degree, while in the polluted domain, the weight decreases with the dispersion degree. And for the same dispersion degree, the larger the pollution degree is, the higher the weight is, and vice versa. Subsequently, the improved EWM is applied to the water quality evaluation of Wucheng Wetland in Poyang Lake, China. Results are as follows: (i) For TP, COD_Mn, and NH₃-N, their dispersion degrees are 0.001, 0.158, and 0.084; and their pollution degrees are 0.971, 0.277, and 0.281, respectively. (ii) According to the improved EWM, the weights of TP, COD_Mn, and NH₃-N are 0.613, 0.197, and 0.190, respectively. (iii) The comprehensive water quality indices of estuary region, wetland region, and the central lake area are 32.5, 30.9, and 35.6, respectively, all of which belong to a "bad" grade. The water environment of Wucheng Wetland suffered serious damage of phosphorus, and the ecosystem faced a high threat. (iv) Compared with the conventional EWM, the improved EWM highlights the importance of polluted indicators, which makes the comprehensive evaluation results more rigorous and reasonable.

Seasonal flooding wetland expansion would strongly affect soil and sediment organic carbon storage and carbon-nutrient stoichiometry

In the past few decades, many non-flooding uplands (NF) and permanent flooding waters (PF) have been turned into seasonal flooding wetlands (SF) at the global scale. This trend could severely threaten global climate system by changing carbon cycling in terrestrial and aquatic ecosystems. However, the effects of SF expansion on soil and sediment organic carbon (SOC) storage and carbon-nutrient stoichiometry are far from clearly understood. Therefore, we explored SOC storage and carbon-nutrient stoichiometry among adjacent NF, SF and PF using 817 samples at 0-100 cm depth increment at Poyang Lake and Shengjin Lake in the middle-lower Yangtze River floodplain, China. The SFs of the two lakes were both Carex lakeshore wetlands. The NF of Shengjin Lake was a near-natural forest, while the NF of Poyang Lake was a disturbed grassland. The results showed that SOC storage at SFs of Poyang Lake and Shengjin Lake was 75.61 and 98.01 Mg C/ha at 0-100 cm depth increment. The difference in SOC storage among nearby NF, SF and PF depended on depth and disturbance. SOC storage at SF was equivalent to that at near-natural NF, but was much higher than that at disturbed NF. SOC storage at SF was 12.62%-24.50% higher than that at PF at 0-30 cm depth increment, but was 15.16%-25.87% lower than that at PF at 0-100 cm depth increment. Edaphic carbon and nutrients followed allometric relationships at most sites and C increased faster than N and P along the depth gradients. Carbon-nutrient stoichiometric relationships at SF and PF were similar, and were more coupled than those at near-natural NF. This research illustrates the strong effects of seasonal flooding on SOC sequestration in terrestrial and aquatic ecosystems, and expands our understanding of carbon cycling in these two ecosystems.

Water quality forecasting based on data decomposition, fuzzy clustering and deep learning neural network

Water quality forecasting can provide useful information for public health protection and support water resources management. In order to forecast water quality more accurately, this paper proposes a novel hybrid model by combining data decomposition, fuzzy C-means clustering and bidirectional gated recurrent unit. Firstly, the original water quality data is decomposed into several subseries by empirical wavelet transform, and then, the decomposed subseries are recombined by fuzzy C-means clustering. Next, for each clustered series, bidirectional gated recurrent unit is applied to develop prediction model. Finally, the forecast result is obtained by the summation of the predictions for the subseries. The proposed forecast model is evaluated by the water quality data of Poyang Lake, China. Results show that the proposed forecast model provides highly accurate forecast result for all of the six water quality data: the average of MAPE of the forecast results for the six water quality datasets is 4.59% for 7 day ahead prediction. Furthermore, our model shows better forecast performance than the other models. Particularly, compared with the single BiGRU model, MAPE decreased by 32.86% in average. Results demonstrate that the proposed forecast model can be used effectively for water quality forecasting.

Spatial distribution, receptor modelling and risk assessment of organophosphate esters in surface water from the largest freshwater lake in China

The occurrence and risk of organophosphate esters (OPEs) has become a global concern in recent years. This study investigated the occurrence, spatial distribution, and potential sources of thirteen OPEs and their associated ecological and human health risks in water samples from the largest freshwater lake, Poyang Lake, together with its five major inflow rivers and the water channel to Yangtze River. The total OPEs concentrations ranged from 38.44 ng/L to 428.94 ng/L, and the largest tributary Ganjiang River was much more polluted than other rivers. Chlorinated OPEs, such as tris (1-chloro‑2-propyl) phosphate and tri (2-chloroethyl) phosphate occupied the dominant composition of OPEs in the research area. Principal component analysis with multiple linear regression, positive matrix factorization, and correlation analysis were used to apportion the potential sources of OPEs in surface water. The combined contribution of polyvinyl chloride, polyester resins, and polyurethane foam (68.64%), antifoam agent and hydraulic fluids (21.50%), and the release of decorative materials and electric equipment from indoor (9.86%) were identified as the OPEs sources in the study region. The risk quotients (RQs) showed the ecological risk was negligible, but 2-ethylhexyl diphenyl phosphate exposures posed medium ecological risk to aquatic organisms. The carcinogenic and non-carcinogenic risks of the target OPEs were below the theoretical risk threshold values, however, toddlers were much more sensitive to the OPEs exposure in surface water than teenagers and adults. Oral ingestion was the principal exposure pathway, and the health risk via oral ingestion was 1-2 orders of magnitude higher than dermal contact exposure route.

The Effects of Water Level Fluctuation on Zooplankton Communities in Shahu Lake Based on DNA Metabarcoding and Morphological Methods

Background: The water level of Poyang Lake (China) fluctuates seasonally. Shahu Lake, a smaller body of water connected to Poyang Lake during the wet season, is separated in the dry season. Due to a special fishing method termed ‘lake enclosed in autumn’, the water level is lowered and reaches its lowest point in January, which is <0.5 m deep in the middle of the lake. Our research investigated the effect of water level changes on the zooplankton community composition in Shahu Lake. Methods: We used both DNA metabarcoding method (MBC) (18S rRNA gene V4 region) and morphological method (MOI) to track the zooplankton community structure over four seasons in Shahu Lake (China). Results: Totals of 90 and 98 species of zooplankton were detected by MOI and MBC, respectively, with rotifers being the main zooplankton component. The α-diversity index of both methods increased from spring to summer and decreased from summer to autumn, reaching the lowest value in winter. NMDS and a cluster analysis showed that all zooplankton communities detected by MOI and MBC were significantly separated by season. The zooplankton community in winter was separated from that of the other three seasons, but the summer and autumn communities were more similar. Conclusions: Changes in the water level had significant effects on the zooplankton community composition. We found that MBC was more able to detect the differences in the zooplankton composition than MOI. MBC also had more advantages in copepod recognition. In our study, 37 species of copepods were detected by MBC, but only 11 species were detected by MOI. We concluded that MBC should be used to research the seasonal variations of zooplankton.

[Microbial Community Structure on Microplastic Surface in the Grus leucogeranus Reserve of Poyang Lake]

As a new type of pollutant, microplastics have attracted increasing attention. Microplastics in aquatic ecosystems are accumulating at an unprecedented scale, causing significant environmental and economic impacts. In this study, sediments and different types of microplastic samples were collected from the Grus leucogeranus Reserve of Wuxing Reclamation Farm of Poyang Lake, which is the largest freshwater lake in China. The main types of microplastics were film (PE), debris (PP1), fiber (PP2), and foam (PS), and the polymers were identified as polyethylene, polypropylene, and polystyrene in the study area. The structures of microbial communities (fungi and bacteria) were identified using 16S high-throughput sequencing. The results showed that there was no significant difference in the Ace and Chao of bacteria between the surface of PE and PP1 and that of the surrounding sediments (P>0.05), whereas PP2 and PS were significantly lower than those in surrounding sediments (P<0.05). Ace and Chao of fungi showed that PE and PS had no significant differences with the sediment (P>0.05), and PP1 and PP2 were significantly lower than those in surrounding sediments (P<0.05). The species diversity Shannon and Simpson index of bacteria and fungi on different types of microplastic surfaces were lower than that of sediment. The bacterial communities on the sediment and microplastic surface mainly included Proteobacteria and Bacteroidetes. In the fungal community, Basidiomycota, Ascomycota, and Chytridiomycota were the dominant bacteria. Through KEGG functional prediction, it was found that most of the metabolic pathways with a significant difference between bacteria and sediments on the surface of microplastics and with an abundance ratio higher than 1% were related to metabolism. Compared with that of sediment, the metabolic pathways of PE and PP2 on microplastic surfaces were down-regulated mainly in cell motility, signal transduction, and carbohydrate metabolism, whereas the energy metabolism, general and global metabolism pathways, and cofactor metabolism were up-regulated. Compared with that of sediment, the bacterial metabolic pathways of PS and PP1 on microplastic surfaces were down-regulated, mainly including general and global metabolic pathways, translation, and exogenous biodegradation, and cell motility and signal transduction were up-regulated. However, the abundance of other functional genes in sediments and microplastic samples showed little difference. The results indicated that microplastics can change the structure of microbial communities, and the microbial community on the surface of microplastics could catalyze metabolic reactions and promote the decomposition of microplastics. The study of microplastic surface microbial structure in Poyang Lake can support management decisions to protect the ecological integrity of the lake.

In situ monitoring of phthalate esters (PAEs) pollution and environmental risk assessment in Poyang Lake Basin by DGT Technology using cyclodextrin polymer as binding phase

Poyang Lake is the first freshwater lake in China, which is an important drinking water source. In recent years, industrial pollution has led to the increased phthalate acid esters (PAEs) in Poyang Lake. PAEs are a class of typical endocrine disruptors that can accumulate in organisms and interfere with their secretion systems. Thus, the accurate determination of PAEs in Poyang Lake is important for health risk prediction and the development of corresponding control means. Monitoring organic pollutants in water using the diffusive gradient in thin films technique (DGT) has attracted much attention due to more accuracy and convenience than the traditional methods. This study used an inexpensive amphiphilic cyclodextrin polymer (PBCD) as the sorbent for the binding gel. This new binding gel has an ultra-high specific surface area and excellent adsorption performance. Diffusion coefficients of the five PAEs were determined, and the performance of DGT such as adsorption capacity and deployment time (1-4 days) was tested using five PAEs as models. The assembled PBCD-DGT was used to examine the performance in a complex simulated water environment. The sampling capability of PBCD-DGT was verified in Yangshan Lake, and a large-scale field application was conducted in Poyang Lake basin. The results of 11 sampling points showed that the concentration ranges of dimethyl phthalate, diethyl phthalate, diallyl phthalate, dipropyl phthalate, and dibutyl phthalate were 434-2594 ng/L, 40-314 ng/L, 80-527 ng/L, 45-308 ng/L, and ND-182 ng/L, respectively. The health risk index (HI) and ecological risk quotient (RQ) values of PAEs in the Poyang Lake watershed were far below 1, indictating a lower health and ecological risk. Considering that PAEs are bioaccumulative and persistent, it is very necessary to continue to pay attention to its pollution status and health and ecological risk changes in Poyang Lake Basin in the future.

[Spectral Characteristics of Dissolved Organic Matter in Sediments from Poyang Lake]

At present, there are few studies on the spectral characteristics of dissolved organic matter (DOM) in the sediments of the Poyang Lake basin. Therefore, excitation-emission matrix spectroscopy (EEMs) technology and ultraviolet-visible spectra combined with the parallel factor analysis (PARAFAC) were applied to investigate the fluorescent components and sources of DOM in sediments from Poyang Lake. The results showed that the DOM in sediments originated from both terrestrial and autochthonous sources with a high humification. Compared with the sub-lakes, the DOM from the main lake was characterized with a higher concentration of colored DOM, larger particle size, and higher aromaticity and humification degree. In addition, four fluorescence components of DOM in sediments were identified by the PARAFAC model, including three humic-like components (C1, C2, and C4) and one protein-like component (C3). The fluorescence intensity of the humic substances in the sub-lakes was higher than those in the main lake. Furthermore, the percentage of fluorescence abundance of C1 was the highest both in the sub-lakes (42%) and main lake (46%). The spatial distribution of the fluorescence intensity of the four components gradually increased from west to east, and the peak values were observed in the Duchang and Nanji Wetland. This may be related to the death of a large number of plants due to the rise in the water level during the wet season and human activities. Principal component analysis showed that although there were no significant differences in the four fluorescent components between the sub-lakes and the main lake, the humification degree of DOM in the sub-lakes was slightly higher than that in the main lake.

How does Three Gorges Dam regulate heavy metal footprints in the largest freshwater lake of China

Herein, a two-dimensional (2-D) vertically-averaged hydrodynamic model was applied to study the heavy metal particle footprints pre- and post-Three Gorges Dam (TGD) in Poyang Lake. Two defined indexes-Reserve Impact Index (σ_RII) and Species Impact Index (η_SII) were applied to assess the potential impact of the copper footprint on nature reserves and sensitive species quantitatively. The results demonstrated that the movement speed, distribution, and trajectory of copper particle footprints differed enormously pre- and post-TGD. By contrast, the post-TGD footprints were more complex because of the dam-induced variations in hydrology and meteorology. TGD had both pros and cons for the copper footprint on the reserves based on the results of σ_RII. It had changed the way for the transport of heavy metals and altered the patterns of exposure risk in the reserves. Sustainable management of Poyang Lake could be achieved by optimizing daily monitoring works. The η_SII for Finless Porpoises do not differ significantly between scenarios, but the η_SII for Siberian White Cranes increased by 0.92 and 0.83 for the two periods pre- and post-TGD, respectively. Heavy metals in food sources and the excreta of Siberian White Cranes could be of great concern in future studies. This study provides a theoretical basis for the in-depth study of the TGD-induced impact on Poyang Lake and provides a reference for the long-term treatment of Poyang Lake and the protection of key species.

Characterization of Subtype H6 Avian Influenza A Viruses Isolated From Wild Birds in Poyang Lake, China

Subtype H6 avian influenza A viruses (IAVs) are enzootic and genetically diverse in both domestic poultry and wild waterfowl and may cause spillovers in both pigs and humans. Thus, it is important to understand the genetic diversity of H6 IAVs in birds and their zoonotic potential. Compared with that in domestic poultry, the genetic diversity of H6 viruses in wild birds in China has not been well-understood. In this study, five H6 viruses were isolated from wild birds in Poyang Lake, China, and genetic analyses showed that these isolates are clustered into four genotypes associated with reassortments among avian IAVs from domestic poultry and wild birds in China and those from Eurasia and North America and that these viruses exhibited distinct phenotypes in growth kinetics analyses with avian and mammalian cells lines and in mouse challenge experiments. Of interest is that two H6 isolates from the Eurasian teal replicated effectively in the mouse lung without prior adaptation, whereas the other three did not. Our study suggested that there are variations in the mammalian viral replication efficiency phenotypic among genetically diverse H6 IAVs in wild birds and that both intra- and inter-continental movements of IAVs through wild bird migration may facilitate the emergence of novel H6 IAV reassortants with the potential for replicating in mammals, including humans. Continued surveillance to monitor the diversity of H6 IAVs in wild birds is necessary to increase our understanding of the natural history of IAVs.

Nanchangia anserum gen. nov., sp. nov., isolated from feces of greater white-fronted geese (Anser albifrons)

Two rod-shaped and Gram-stain-positive bacteria (strains C64^T and C62) were isolated in 2020 from faeces of greater white-fronted geese (Anser albifrons) from Poyang Lake, PR China. Their optimal growth conditions were at 37 °C, pH 7.0 and with 0.5 % (w/v) NaCl. The two isolates showed a highest 16S rRNA gene sequence similarity to Bowdeniella nasicola DSM 19116^T (92.1 %). Phylogenetic/phylogenomic analyses indicated that strains C64^T and C62 clustered independently in the vicinity of the genera Varibaculum, Winkia and Mobiluncus within the family Actinomycetaceae, but could not be classified clearly as members of any of these known genera. The average amino acid identity values between our isolates and available genomes of members of the family Actinomycetaceae were around the genus threshold value (45-65 %). The major cellular fatty acids of the strains were C_18 : 1ω9c and C_16 : 0. The predominant polar lipids were phosphatidylinositol, phosphatidylglycerol, phosphatidylcholine, diacylglycerol, triacylglycerol and cardiolipin. The amino acid composition of peptidoglycan contained alanine, glutamic acid and glycine. The major respiratory menaquinones were MK-8(H₄) and MK-9(H₄). The whole cell sugars included galactose, arabinose and glucose. On the basis of the results of the 16S rRNA gene sequences comparison, whole-genome phylogenomic analysis, phenotypic and chemotaxonomic characteristics, we propose that strains C64^T and C62 represent a novel species belonging to a novel genus within the family Actinomycetaceae, for which the name Nanchangia anserum gen. nov., sp. nov. is proposed. The type strain is Nanchangia anserum C64^T (=CGMCC 1.18410^T=GDMCC 1.1969^T=KCTC 49511^T=KACC 22143^T).

Sediment carbon short-term response to water carbon content change in a large floodplain-lake system

After carbon (C) enters a lake through surface runoff and atmospheric deposition, most of it, being influenced by the environmental conditions of the basin, is deposited into lake sediment, thus, becoming one of the most important C pools in the world. Therefore, it is critical to understand sediment response characteristics under the context of increasing C concentrations in lake water. Based on the changes of sediment C concentration at different depths in Poyang Lake, belonging to China's large floodplain-lake system, we revealed the sediment C short-term response characteristics to changes in lake water C concentrations as well as their associated impacting factors. We found that dissolved total carbon (DTC) concentrations increased by 25.78% in winter compared to spring, while total carbon (TC) sediment concentrations increased by only 4.37% during the corresponding period. Specifically, we found that there was a hysteresis effect in the response of sediment C to the increase of water C concentration in the short term. When DTC concentrations in water were below a threshold value (12.50 mg/L), sediment TC concentrations were generally maintained at approximately 5.79 mg/kg. We also believed that biological and environmental factors and sediment stratification characteristics collectively resulted in this sediment C hysteresis effect. Among these factors and characteristics, phytoplankton can affect sediment C response by changing C absorption and utilization in water or cause a synergistic effect along with environmental factors, which is the key link that causes this C sediment hysteresis effect to occur. Furthermore, we found that the combined effect of sediment C from different depths also resulted in a hysteresis effect in C deposition.

A comparison of metric scoring and health status classification methods to evaluate benthic macroinvertebrate-based index of biotic integrity performance in Poyang Lake wetland

Methods for metric scoring and health status classification in development of index of biotic integrity (IBI) vary considerably across published studies. The difference between ecosystem health assessment results from these alternative methods for scoring and classification has rarely been studied systematically. Poyang Lake in China has experienced severe degradation over recent decades. Here, we aimed to develop a benthic macroinvertebrate-based index of biotic integrity (B-IBI) to assess the wetland health of Poyang Lake, and to evaluate the difference in assessment results using different methods of scoring and classification. Data on benthic macroinvertebrate assemblages, water quality and human-induced disturbances were collected at 30 sampling sites. Forty-nine attributes of macroinvertebrate assemblages were tested, and only the attributes that were significantly correlated with disturbance gradients or showed strong discriminatory power between reference and impaired sites were selected as the B-IBI metrics. Two scoring, two thresholding and three classification methods were applied for metric scoring and health status classification. Five assemblage attributes, i.e. the number of taxa, Shannon-Wiener diversity index, % Diptera, ASPT index and the number of predator taxa, were selected as the B-IBI metrics. Health status assessments varied considerably among the various metric scoring and classification methods, suggesting the importance of standardizing the methods for scoring and classification to be able to compare assessment results across different areas and time periods. The wetland health of Poyang Lake was rated as fair, which indicates that the wetland has experienced anthropogenic pressure and substantial changes in macroinvertebrate assemblage structure. Further, sample sites adjacent to tributary river mouths were in poor or very poor condition, suggesting that pollutant input by rivers has strong negative impacts on wetland health. Effective management of the entire lake basin and its watershed is therefore important for the wetland conservation.

Corynebacterium anserum sp. nov., isolated from the faeces of greater white-fronted geese (Anser albifrons) at Poyang Lake, PR China

Two Gram-stain-positive, facultatively aerobic, non-motile and rod- to coccoid-shaped bacterial strains, 23H37-10^T and 4HC-13, were isolated from the faeces of greater white-fronted geese (Anser albifrons) at Poyang Lake, Jiangxi Province, PR China. Optimal growth was observed at 35-37 °C, pH 7.0-8.0 and with 0.5-1.5 % (w/v) NaCl. The 16S rRNA gene sequences of strains 23H37-10^T and 4HC-13 were identical. Phylogenetic and phylogenomic analyses indicated that strains 23H37-10^T and 4HC-13 formed an independent cluster within the genus Corynebacterium and showed 98.8, 97.4, 97.4 and 97.2 % 16S rRNA gene sequence similarity to Corynebacterium urogenitale LMM 1652^T, Corynebacterium urealyticum DSM 7109^T, Corynebacterium falsenii DSM 44353^T and Corynebacterium jeikeium NCTC 11913^T, respectively. Cells contained C_18 :1 ω9c, C_18 : 0 and C_16 : 0 as the major cellular fatty acids and MK-9 (H₂) as the predominant respiratory quinone. The polar lipids comprised diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol, phosphatidyl inositol mannosides, two unidentified phospholipids, four unidentified glycolipids and one unidentified lipid. Strain 23H37-10^T contained mycolic acids, with meso-diaminopimelic acid and arabinose as the major whole-cell hydrolysates. The genome G+C content of strains 23H37-10^T and 4HC-13 was 55.2 mol%. The digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) values between strains 23H37-10^T and 4HC-13 were 94.4 and 99.6 %, respectively. Strains 23H37-10^T and 4HC-13 had dDDH and ANI values of less than 70 and 96 % with all available genomes of the genus Corynebacterium, respectively. The differential genotypic inferences, together with phenotypic and biochemical characteristics, suggested that strains 23H37-10^T and 4HC-13 represent a novel species within the genus Corynebacterium, for which the name Corynebacterium anserum sp. nov. is proposed. The type strain is 23H37-10^T (=GDMCC 1.1737^T=KACC 21672^T).

Flooding variations affect soil bacterial communities at the spatial and inter-annual scales

Hydrological variations have substantial effects on the diversity and composition of soil bacterial communities in wetlands. At the spatial scale, the responses of soil bacterial diversity and composition to hydrological variations in wetlands have been extensively investigated. However, at the temporal scale, especially at the inter-annual scale, the corresponding bacterial responses are rarely reported. Therefore, we explored the effects of flooding variations on the diversity and composition of soil bacterial communities at a lakeshore wetland in two hydrological contrasting years. Three flooding variables, i.e. flooding duration (FD), total duration of the growing season (TGD), and exposure duration of the growing season (EGD), were used to characterize flooding regime. Soil bacterial communities were determined using 16S rRNA gene sequencing method. We found a very high soil bacterial diversity at the lakeshore wetland. The Shannon's indexes of soil bacterial communities varied from 5.61 to 7.11 in two years. Soil bacterial α-diversity followed a unimodal curve along the elevation gradient, and was significantly lower in the flooding year than in the drought year. Principal coordinate analysis demonstrated that the compositions of soil bacterial communities were separated in order of elevation and year along the first and second axes, respectively. The apparent habitat preferences of soil bacterial families were closely connected with their respiratory traits, and this trend was stronger at the inter-annual scale than at the spatial scale. Soil bacterial compositions were predominantly determined by the direct (by changing respiratory traits) and indirect (by changing soil pH) effects of TGD at the spatial scale, while they were simultaneously regulated by the direct effects of three flooding variables at the inter-annual scale. Our results enhance the understanding of soil microbial communities in wetlands and have large implications for developing general theories to predicting soil microbial functions.