Abstract:Inland waters are an important natural source of methane to the atmosphere, a potent greenhouse gas. The potential of sediment methane production (PMP) under anaerobic conditions is a key indicator for the level of atmospheric emissions of methane. However, there is a lack of cross-system studies on the sediment PMP in inland waters， the underlying driving mechanisms are still unclear. In this study, we collected data on PMP in inland waters in China including reservoirs, lakes, rivers and wetlands. Combined with some unpublished data (a total of 210 data points), the temporal and spatial distribution of sediment PMP in several different systems was explored, and the drivers of the sediment PMP were identified. We found that PMP was seasonally variable, showing a trend of being significantly greater in the rainy season than in the dry season (about 3.5 times); damming caused a significant increase in PMP by more than ten times, and sediment PMP in reservoirs and lakes was significantly greater than that of rivers or wetlands. Correlation analysis showed that eutrophication caused by human activities had a significant driving effect on sediment PMP. Water temperature, water depth and sediment organic matter content had a significant positive stimulating effect on sediment PMP, while salinity had a significant inhibitory effect. In the context of global climate change, in order to make good future projections of carbon emissions from inland waters, human disturbances such as damming and eutrophication must be well incorporated, in addition to the natural process of global warming.

Abstract:With the intensification of anthropogenic disturbances, such as water resource development, water pollution, and overfishing, fish diversity and population abundance have significantly declined, posing a severe threat to aquatic ecosystems. Systematic monitoring of fish movement behavior and physiological responses to environmental changes, along with the scientific analysis of the relationship between behavioral responses and environmental factors, is critical for designing habitat conditions centered on the ecological needs of fish species. This is essential for advancing fish conservation research. The development of acoustic and electronic tagging systems has provided a robust scientific tool for fish conservation studies. These tags, with diverse functionalities, can be implanted in fish bodies or attached externally to enable systematic monitoring of fish movement behavior and habitat information. This paper provides a comprehensive review of the acoustic and electronic tags commonly used in fish conservation research, classifying them into four categories based on their functions: short-range coded identification and counting tags, spatial tracking and positioning tags, physiological state monitoring tags, and environmental data logging tags. First, the fundamental features and technical principles of these tags are introduced. Then, the applications and research progress of each tag type are discussed in detail, focusing on areas such as fish passage efficiency monitoring, fish movement tracking, physiological state assessment, and habitat information evaluation. Finally, the existing challenges and future development directions of acoustic and electronic tagging technologies in fish conservation are highlighted based on the current state of applications. This study aims to systematically summarize the application status and developmental trends of acoustic and electronic tagging technologies in fish conservation research, providing scientific and technical guidance for aquatic ecosystem protection.

Abstract:Dawangtan Reservoir is a typical large drinking water source reservoir in the south subtropical region. Cyanobacterial dominance and algal blooms caused by eutrophication pose major threats to its water supply security. Understanding the characteristics of the phytoplankton community and the driving factors behind cyanobacterial dominance is of great significance for algal bloom prevention and the management of reservoir water supply safety. A quarterly investigation of the aquatic environment and phytoplankton community in the Dawanqtan Reservoir was conducted in 2021 to explore the seasonal dynamics of the phytoplankton community and the driving factors behind the dominance of filamentous cyanobacteria. The results indicated that the phytoplankton in Dawangtan Reservoir comprised 127 species from 7 phyla, with Chlorophyta, Bacillariophyta, and Cyanophyta being the dominant groups in terms of species composition, belonging to 26 functional groups. The phytoplankton cell density ranged from 1.2×106 to 430×106 cells/L, exhibiting the order of autumn ＞ spring ＞ winter ＞ summer, while the biomass ranged from 0.14 to 51 mg/L, with the order of autumn ＞ winter and spring ＞ summer. The dominant genera wereLimnothrix andPseudanabaena, and the functional group S1 was the long-term dominant functional group. The comprehensive trophic level index (TLI) of the reservoir ranged between 36.02 and 49.57, indicating a mesotrophic state. Mantel tests and redundancy analysis (RDA) revealed that water temperature, transparency, and nitrogen concentration were significant explanatory variables influencing the dominance of filamentous cyanobacteria. The absolute dominance of filamentous cyanobacteria occurred in Autumn, characterized by lower transparency and nitrogen concentration but higher water temperature, representing a high-risk period for blooms ofLimnothrix andPseudanabaena. Combined with functional group analysis, the results indicate that the turbid environment of large reservoirs is an important factor promoting the dominance of filamentous cyanobacteria. In Autumn, water temperature and nutrient conditions fall within the optimal range for the growth ofLimnothrix andPseudanabaena, serving as key drivers for their massive proliferation. Given the threat posed by filamentous cyanobacteria such asLimnothrix andPseudanabaena, attention should be paid to the causes of increased turbidity and water color in reservoirs to improve water transparency and thereby limit the formation of filamentous cyanobacterial dominance.

Abstract:To quantitatively evaluate the concentration of algae-derived phosphorus in Lake Taihu and the influence of the algal community structure on it and to better understand the relationship between algal evolution and the internal phosphorus cycle of the lake, this study calculated the concentration of total algae-derived phosphorus in Lake Taihu and its proportion to total phosphorus in the lake based on the monitoring data and investigation data of algae and water quality of Lake Taihu from 2021 to 2023. The results showed that from 2021 to 2023, the total algal density of Lake Taihu decreased from 6.3 × 10⁷ cells/L to 4.4 × 10⁷ cells/L （annual average value）, the proportion ofMicrocystis decreased from 79.8% to 35.6%. On the other hand, the density and proportion of cryptophyta, chlorophyta and bacillariophyta increased significantly, and the whole lake's algal community changed significantly. During the same period, the total phosphorus concentration in the Lake Taihu fluctuated from 0.053 mg/L to 0.062 mg/L. The average proportion of particulate total phosphorus was 60.4%, of which the proportion of algae-derived phosphorus in particulate total phosphorus and total phosphorus was 49.4% and 29.6%, respectively, indicating that algae-derived phosphorus is an important component of particulate phosphorus. According to the further subdivision of the algal community structure, it is found that the algae-derived phosphorus in Lake Taihu is mainly contributed by three categories, including cyanophyta, bacillariophyta and chlorophyta. From 2021 to 2022, the contribution rates of cyanophyta to algae-derived phosphorus were 66.5% and 65.7%, respectively. With the rapid decrease in cyanophyta density in 2023, their contribution and proportion of algae-derived phosphorus also significantly decreased, while the contribution and proportion of algae-derived phosphorus from bacillariophyta increased from 23.9% to 56.1%. The total algae and cyanophyta density in 2023 had significantly decreased compared to 2021, but due to the increase in the proportion of bacillariophyta, chlorophyta and other categories, the increase in algae-derived phosphorus provided by them compensated for the decrease in cyanophyta algae-derived phosphorus, ultimately leading to an increase in the total algae-derived phosphorus in the entire lake instead of a decrease. Although the increase in algal density of bacillariophyta and other categories is not as significant as the decrease in cyanophyta density, they have larger cell volume and higher monomeric phosphorus content, thus exhibiting a more significant compensatory effect on algal-derived phosphorus.

Abstract:Methylphosphonate (MPn), a typical organophosphonate characterized by a C—P bond, profoundly influences phosphorus cycling and methane (CH₄) production mechanisms in aquatic ecosystems through its biosynthesis and degradation processes. However, there is limited research on the dynamics of MPn in water bodies and the MPn accumulation capacity of algae. This study employed liquid chromatography-tandem quadrupole time-of-flight mass spectrometry (LC-MS/MS) to quantify MPn in 21 water samples and 15 algal species. Combined with field monitoring, algal laboratory cultivation, and raw water incubation experiments (including MPn/Pi addition, BES treatment, algal filtration, and dark treatment), the relationship between MPn dynamics and CH₄ generation was investigated. The results revealed that MPn was detected in 52.4% (11/21) of water samples ((1.50±0.24)-(6.99±0.59) μg/L), and 93.3% (14/15) of algal strains accumulated intracellular MPn ((1.87±0.57)-(22.24±5.81) μg/L). Notably,Microcystis sp.FACHB-3602 exhibited dynamic MPn accumulation during 7 days of cultivation (peak value: （8.63±0.85） μg/L), indicating that algae are a significant biological source of MPn in aquatic ecosystems. In both water samples and algae, the contribution of MPn-P to dissolved organic phosphorus(0.70%-37.85%, 0.21%-0.90%) was significantly higher than that of MPn-C to dissolved organic carbon (0.00%-0.05%, 0.00%-0.01%), highlighting the dominant role of MPn in phosphorus cycling from an ecological stoichiometric perspective. Raw water incubation experiments demonstrated that MPn addition increased CH4 production by 157.43% compared to the control, while the simultaneous addition of inorganic phosphorus (Pi) suppressed CH₄ generation. Algal filtration reduced CH₄ roduction by 23.96%, whereas dark treatment promoted CH₄ accumulation. These findings suggest that algal-bacterial interactions regulate MPn turnover and aerobic CH₄ production, modulated by inorganic phosphorus availability. This study provides critical theoretical insights for further exploration of MPn's role in aquatic phosphorus cycling and aerobic CH₄ production mechanisms.

Abstract:The study of attached algae communities' assembly mechanisms is essential for understanding the restoration of river ecosystem structure and function. This study analyzed attached algae communities in three representative rivers flowing through Guangzhou—Chebei River (natural habitat), Liede River (highly canalized), and Shahe River (mixed habitat)—that are subject to a low water level operation strategy. The analysis covered four consecutive flood seasons from 2020 to 2023, focusing on the recovery and environmental drivers of these communities under near-natural restoration measures. The results showed that 193 algal species across 6 phyla, 53 families, and 90 genera were recorded, with Bacillariophyta being dominant (51.26%). No significant spatial differences in algal standing stocks were found, while significant annual differences occurred, indicating higher temporal than spatial heterogeneity. Chebei River had the highest total number of species (184), while Liede River showed the highest abundance (2.17×109 cells/m²), biomass (3.16×103 mg/m²), Shannon diversity index (3.14), and Evenness index (0.66). Annually, Liede River had the largest increases in species and Shannon diversity index (41.43% and 15.58%, respectively), and Shahe River had the highest abundance and biomass increase (92.62% and 96.53%, respectively), with Evenness index remaining stable at around 0.6. These findings highlighted the effectiveness of near-natural restoration for attached algae recovery. Niche breadth and overlap analysis indicated that the attached algal communities in the studied rivers maintained overall stable niche breadth, with niche overlap between most species being below the competition threshold (0.6). These results reflect high resource-use efficiency, low interspecific competition pressure, and a relatively stable state of the community. The standardized random rate analysis revealed that either deterministic or stochastic processes could dominate the restoration process, and their relative contributions were regulated by environmental heterogeneity. Redundancy analysis further identified that total nitrogen, total phosphorus, dissolved oxygen, water depth and flow velocity are key factors affecting the rivers attached algae communities. The findings provide empirical support and a scientific basis for the effective implementation of near-natural restoration in urban river channels.

Abstract:Chlorophyll-a is an important indicator of primary productivity in lake ecosystems, and its concentration changes reflect the nutritional status and ecological health of lakes. Based on water quality and environmental data from Lake Chagannaoer between 2011 and 2024, this study used correlation and redundancy analysis to reveal the interannual and seasonal variation characteristics of chlorophyll-a concentration and its key driving factors. The results showed that between 2011 and 2024, the interannual variation of chlorophyll-a concentration in Lake Chagannaoer was stable, mainly regulated by hydrological conditions, nutrient inputs, and human activities. Seasonally, chlorophyll-a concentration follows the pattern of summer＞winter＞autumn＞spring. In spring, water dilution led to a decrease in chlorophyll-a concentration, while in summer, the rise in temperature promoted phytoplankton proliferation. Autumn cooling inhibited reproduction, and winter freezing led to the migration of nutrients into the water, with photosynthesis under the ice maintaining relatively high chlorophyll-a concentrations. The study further found that in spring and autumn, chlorophyll-a concentration was positively correlated with total nitrogen and negatively correlated with total phosphorus; whereas in summer and winter, chlorophyll-a concentration was negatively correlated with total nitrogen and positively correlated with total phosphorus, reflecting the seasonal impact of nutrient changes on phytoplankton growth. Redundancy analysis further indicated that the seasonal variation of chlorophyll-a concentration was influenced not only by the current season's climate and environmental factors but also by the interactions between consecutive seasons, creating cross-seasonal chain effects. Future research should focus on inter-seasonal relationships and environmental effects to further uncover the complexity of lake ecosystems, providing scientific evidence for lake management and conservation.

Abstract:After the impoundment of the Three Gorges Reservoir for more than 20 years, over 50% of first-order tributaries have experienced harmful algal blooms (HABs), primarily dominated by cyanobacteria, green algae and dinoflagellates. Investigating the relationship between HABs and endogenous nutrient accumulation can help in early HAB warning and ecological predictions in the Three Gorges Reservoir. Sediment cores are invaluable for studying internal nutrient accumulation and its impact on HABs. This study focused on two first-order tributaries in Yunyang County of the Three Gorges Reservoir—the Pengxi River, frequently impacted by HABs, and the Modao River, with rare occurrences of HABs. Sediment cores were collected from the mid-reaches of both rivers to investigate the effects of HABs on sediment deposition under similar climatic and geographic conditions. Using 210Pb dating, sediment deposition depth after Three Gorges Reservoir impoundment was 45 cm for Pengxi River, with a sedimentation rate of 2.25 cm/a. In contrast, sediment deposition depth in Modao River was 30 cm, with a sedimentation rate of 1.50 cm/a—only 65% of the sedimentation rate in the Pengxi River during the same period. The sediment core data showed that before the impoundment, the sedimentation fluxes of organic matter(OM), total nitrogen(TN), total phosphorus(TP), available phosphorus(AP), available nitrogen(AN) in the sediment of Pengxi River were 13.35, 0.81, 0.61, 0.01 and 0.02 g/(m²·a), respectively, while in Modao River, they were 12.90, 0.79, 0.54, 0.01 and 0.01 g/(m2·a), respectively. As of 2023, after the impoundment, the sedimentation flux of OM in Pengxi River and Modao River were 25.95 and 14.32 g/(m²·a), respectively, with the latter being only 55.18% of the former. In Pengxi River, the sedimentation fluxes of OM, TN, TP, AP, and AN increased by 94.38%, 53.09%, 31.15%, 77.78%, and 55.56%, respectively, compared to pre-impoundment levels, while in Modao River, the increases were only 11.01%, 13.92%, 16.67%, 7.19%, and -2.17%, respectively. The 16S and 18S DNA high-throughput sequencing was performed on samples collected at 5 cm intervals from the top 20 cm of sediment cores from Pengxi River and Modao River. The results showed no significant difference in the prokaryotic community composition. However, in terms of eukaryotic communities, the sediment core from Pengxi River exhibited higher biodiversity and species richness compared to the sediment core from Modao River. Combining sediment core dating, nutrients, and sequencing data, the analysis revealed that from 2010 to 2023, the relative abundance of dinoflagellates and green algae in the 0-5 cm section of the Pengxi River sediment core increased by 208% and 9%, respectively, compared to the 15-20 cm section. In contrast, their relative abundances decreased respectively by 50% and 70% in Modao River. Correlation analysis showed that the relative abundance of dinoflagellate in the sediment core was significantly positively correlated with OM, while the relative abundance of green algae was significantly positively correlated with TP and AP. It suggests that dinoflagellate blooms are the primary cause of the differences in endogenous OM deposition between the two rivers after impoundment, while green algae blooms are related to the accumulation of endogenous phosphorus. Studies on sediments and HABs have demonstrated that Three Gorges Reservoir impoundment has enriched Pengxi River with nutrients, intensifying HABs frequency and scale while significantly influencing internal nutrient accumulation. Endogenous OM accumulation indicates an increasing risk of HABs, particularly dinoflagellate blooms, in primary tributaries of the Three Gorges Reservoir. OM and endogenous phosphorus in sediments can serve as key indicators for predicting HAB scales in Three Gorges Reservoir tributaries.

Abstract:Phytoplankton play a key role in maintaining ecosystem stability and function. However, research on the community structure of phytoplankton in lake ice during the ice-covered period and its relationship with environmental factors remains limited. To reveal the characteristics of phytoplankton communities in lake ice and their influencing factors, a sampling survey was conducted in February 2023 on the phytoplankton and physicochemical indicators in the ice of Lake Dongjuyanhai, Wuliangsuhai, Hasuhai, and Chagannaoer. The results showed: (1) A total of 132 species of phytoplankton were identified in the ice layers of Lake Wuliangsuhai, Lake Dongjuyanhai, Lake Chagannaoer, and Lake Hasuhai, with Cyanophyta dominating in abundance, accounting for 50.01%. In terms of species number, Chlorophyta and Bacillariophyta accounted for 34.85% and 33.33%, respectively. (2) In Lake Dongjuyanhai ice, 26 species of phytoplankton were identified, with Chlorella sp. as the dominant species; in Lake Wuliangsuhai ice, 80 species were identified, withLimnothrix sp. as the dominant species; in Lake Hasuhai ice, 54 species were identified, withMicrocystis sp. as the dominant species; and in Lake Chagannaoer ice, 34 species were identified, withUlothrix zonataas the dominant species. (3) The ecosystem in the ice of Lake Dongjuyanhai is relatively simple, with low phytoplankton diversity; the phytoplankton diversity in the ice of Lake Wuliangsuhai is higher; the phytoplankton diversity in the ice of Lake Hasuhai and Lake Chagannaoer is at a moderate level. The similarity of algae among different lakes varies significantly, with the highest similarity between Lake Wuliangsuhai and Lake Hasuhai, the largest difference between Lake Dongjuyanhai and Lake Wuliangsuhai, and Lake Chagannaoer exhibiting some uniqueness. (4) In the ice layers of different lakes, the survival of dominant phytoplankton species was influenced by a combination of environmental factors, including salinity, temperature, total nitrogen, and total phosphorus, with significant differences in the response of different species to these factors. Future studies should focus on the dynamic relationship between dominant phytoplankton species and environmental factors in ice layers to better guide lake ecological conservation.

Abstract:In the context of accelerated economic development, freshwater ecosystems are increasingly subject to the process of eutrophication, which has precipitated a series of ecological issues within aquatic environments, including water quality deterioration and a decline in biodiversity. The most critical step in the ecological restoration of eutrophic shallow lakes is to achieve the transition of primary producers from phytoplankton to submerged macrophytes. Current ecological restoration projects of lakes frequently emphasize water quality improvement, yet research on the impact on greenhouse gas fluxes is lacking. This study investigated the restored and unrestored areas of Lake Xuanwu (Nanjing) to compare the physicochemical parameters of the water and the carbon dioxide (CO2) and methane (CH4) fluxes at the water-atmosphere interface between the two areas. The results demonstrated that the concentration of chlorophyll-a (Chl.a) in the unrestored area was significantly higher than that in the restored area in all four seasons, reaching up to five times as much in the summer. The concentrations of total nitrogen (TN) and phosphorus (TP) in the unrestored area were found to be significantly higher than those in the restored area. The CO2 diffusion flux in the restored area was consistently lower than that observed in the unrestored area across all seasons. The CH4 diffusion flux at the water-atmosphere interface in the unrestored area was found to be higher than that in the restored area in all seasons. Within the unrestored area, the phytoplankton biomass demonstrated a strong positive correlation with TP, pH, and Chl.a, and a strong negative correlation with nitrate nitrogen, dissolved inorganic carbon, etc. In the area that had been restored, there was a strong positive correlation between the submerged plant biomass and salinity and conductivity, and a negative correlation with ammonia nitrogen, phosphate, CO2 and CH4 fluxes. It is evident that ecological restoration has a multifaceted impact on the environment, including the enhancement of water quality in eutrophic shallow lakes and the reduction of carbon-containing greenhouse gas emissions. The objective of the present study is to provide scientific references for the purpose of improving the carbon sequestration and sink function of lakes.

Abstract:Based on the data of six pollution indicators from monitoring sections of eight major rivers flowing into Lake Taihu during 2016-2023, this study deeply analyzed the temporal and spatial differentiation characteristics of pollution in these rivers. The positive definite matrix factor analysis model (PMF) was used to quantitatively analyze the pollution sources. The results showed that the concentrations of various pollution indicators in the inflowing rivers generally presented a downward trend year by year. Regarding temporal distribution, the concentrations of ammonia nitrogen and total nitrogen were relatively high in winter (January-February and December), while the concentrations of permanganate index, chemical oxygen demand and total phosphorus were higher in summer (June-September). The biochemical oxygen demand after 5 days concentration had two peaks in a year, occurring in March-May and August-September, respectively. Regarding spatial distribution, the Wangyu River, Xiaoxi Harbor in the northern Lake Taihu area, and the Dagang River in the southwestern mountainous area had relatively low concentrations of various pollution indicators. In contrast, the Wujin Port, Taige Canal, Taige South Canal, Dapu Port, and Wuxi Port in the western lake area had higher pollutant concentrations and made significant contributions to the nitrogen and phosphorus in Lake Taihu. Further research found that the main pollution sources of the rivers entering Lake Taihu mainly included four types: domestic sources, aquaculture sources, livestock and poultry breeding and farmland planting sources, and industrial sources, with contribution rates of 32.5%, 19.8%, 40.3%, and 7.4% respectively. Among them, the contribution ratios of pollution sources and the temporal change trends of five rivers with high pollution levels, such as Wujin Port and Taige Canal, were the same. During the flood season, they were mainly affected by agricultural non-point sources, while in winter, they were mainly influenced by domestic sources. In recent years, aquaculture sources had significantly contributed to pollutant loads in the Taige Canal and Taige South Canal during flood seasons, while livestock breeding and farmland cultivation sources exerted more pronounced impacts on water quality in Dapu Port and Wuxi Port. Domestic wastewater discharges emerged as a critical factor affecting water quality in Wujin Port. Therefore, it is crucial to reduce the amount of pollutants entering the river from livestock, poultry, aquaculture, and farmland drainage and continuously promote the construction of environmental infrastructure to achieve the full collection and treatment of sewage, so as to improve the water quality of Lake Taihu.

Abstract:Based on the monitoring data of water quality at 5 stations in Lake Baiyangdian in the past 30 years, this study comprehensively applied multivariate statistical analysis methods and literature research to systematically reveal the trends of water quality evolution, influencing factors, and control measures in Lake Baiyangdian. Results showed that: ①The years 2005 and 2015 were the periods of poor water quality in Lake Baiyangdian over the past 30 years. From 2022 to 2023, the water quality of the lake area remained stable at Class Ⅲ, and by 2023, the water quality was at its best level over 30 years. The main pollution indicators in recent years have been COD and TP. ② From 2009 to 2023, the COD, TN, and TP concentrations in the Dianqu area were in significant downward trends, with an annual decrease rate of 0.611 mg/(L·a) (α=0.05), 0.212 mg/(L·a) (α=0.01), and 0.013 mg/(L·a) (α=0.05), respectively. ③The water quality indicators across various monitoring stations in Lake Baiyangdian could be spatially categorized into three groups, with the Nanliuzhuang station in the western region showing the poorest water quality. Eutrophication indicators were further classified into two categories, with northern sites exhibiting a higher nitrogen-to-phosphorus ratio than the southern sites. Over recent years, Lake Baiyangdian has become predominantly phosphorus-limited despite being a nitrogen-polluted system overall. ④The inflow and water level were the key factors affecting the water quality of Lake Baiyangdian in recent years. From a regional perspective, targeted management strategies were necessary for different areas of the lake. In the western region, particularly at the Nanliuzhuang site, efforts should focus on controlling external nutrient inputs. In the northern sites, priority should be given to reducing total nitrogen concentrations, while in the southern sites, the main focus should be on controlling chemical oxygen demand and total phosphorus levels. In the next step, the multi-site and multi-factor observation data should be further combined with the application of a hydrodynamic-water quality coupling model for simulation and traceability analysis, which can guarantee the comprehensive decision-making of water quality in Lake Baiyangdian, and provide support for the ecological water replenishment and the control of endogenous pollution such as substrate and humus, as well as the synergistic pollution management in the watershed.

Abstract:To explore the impact of changes in agricultural cropping-breeding mode(ACBM) on river water quantity and quality, the Four Lakes Main Channel(FLMC) in the Jianghan Plain was taken as the research object. Based on observation data from 2010 to 2023, the trend of annual water quantity and quality changes was analyzed. Remote sensing images and statistical yearbook data were used to identify the interannual area change characteristics of different land use types and the trends of nitrogen and phosphorus point source load over nearly 10 years. Redundancy analysis (RDA) and correlation heat map were applied to explore the response of the main channels nitrogen and phosphorus concentration to the changes. The results indicated that: ① From 2010 to 2023, the concentration of total nitrogen and total phosphorus in FLMC exhibited an inter-annual pattern of “increase-decrease-stabilization”. The annual performance was lower in winter and spring, and higher in summer and autumn. Spatially, the concentrations were lower at the inlet and outlet and higher in the central reach. The annual displacement of the total trunk canal is mainly concentrated between April and September, accounting for 65.7% of the annual total. ② Over the past decade, the ACBM in the Sihu Basin has changed significantly. The dry land cultivation area decreased by about 15%, and paddy field area increased by about 19%. The freshwater aquaculture area increased by about 2% from 2010 to 2016, and decreased by more than 4% from 2016 to 2022. ③The variation characteristics of the total water quantity in the FLMC were not only affected by rainfall, but also related to the variation of rainfall-runoff of different land use types in the basin, among which paddy field and dry land were the main contributors, accounting for 366% and -236% of the total water quantity variation, respectively. ④ Over the recent 10 years, the concentration of total nitrogen and total phosphorus in the FLMC were positively correlated with the pollution loads (79.7% interpretation), and the main factors that caused the changes of N and P pollution loads in the basin were freshwater breeding and livestock breeding. In addition, the contribution of paddy cultivation to N and P loads increased from 6% to 26% in nearly 10 years, and the proportion of N and P loads gradually became prominent. This trend suggests that the risk of water environment pollution in the future cannot be ignored.

Abstract:The form of phosphorus in lake sediments is a key internal factor affecting its migration and transformation in aquatic ecosystems. This study collected surface and core sediment samples from 36 sites in Lake Hulun and systematically analyzed the distribution characteristics of phosphorus forms in the sediments and their correlations with particle size, pH, organic carbon, and simultaneously extracted iron, aluminum, calcium, and manganese. Significant positive correlations between P (phosphorus) contents and Al (Aluminum), Ca (Calcium), Fe (Iron) and Mn (Manganese) highlighted the potential effects of metallic oxides on surface adsorption and co-precipitation. Simultaneously, contributed by the larger specific surface area property, P and both mean grain size and pH exhibited significant negative correlations. Additionally, our results also highlighted the stability of Fe-P (Iron-bound phosphorus), Al-P (Aluminum-bound phosphorus), and Ca-P (Calcium-bound phosphorus) were strongly associated with pH. TOC (total organic carbon) contributed most significantly to P distributions, followed by grain size. This study provides fundamental data on the migration and transformation of phosphorus in northern lake sediments in China, offering new perspectives on understanding the geochemical characteristics of phosphorus in different lake areas and their responses to natural and anthropogenic processes nationally.

Abstract:Emergent plants can not only absorb nutrients from water and sediment as a sink during the growth period, but also release nutrients such as nitrogen and phosphorus into the water environment as a source during the decline period. When the biomass is high, this release may lead to secondary pollution of the water body. To explore the nutrient release rule of typical emergent plants in Lake Hengshui and the microbial mechanism affecting plant decomposition, two dominant species Phragmites australis and Typha angustifolia, were selected as research subjects. In-situ decomposition experiments were conducted using the decomposition-bag method in Lake Hengshui at the end of February 2023. The “vertical decomposition” of plants was simulated in the experimental group which was not in contact with the water surface, and the decomposition of emergent plants was simulated in the experimental group which was flooded under the water surface. The results showed that: (1) The decomposition rates ofP. australis andT. angustifolia were significantly different under flooded and non-flooded conditions. Flooded conditions enhanced the decomposition ofP. australis andT. angustifolia, but long-term flooding might lead to the accumulation of elements. (2) The decomposition rate ofT. angustifolia was faster than that ofP. australis, because the decomposition rate was positively correlated with the initial N and P contents and the relative abundance of nitrogen and phosphorus cycling genes, and negatively correlated with the initial cellulose, lignin and soluble sugar contents. (3) The abundance of nitrogen-fixing genes increased gradually with the degree of decomposition, and the increase of N content in the litter of both species was positively correlated with the nitrogen-fixing genes of nitrogen-fixing microorganisms.

Abstract:The treatment of organic micropollutants has become a globally concerned environmental issue. Integrating the watershed characteristics and establishing an effective screening method to identify high-risk contaminants is key to achieving effective control of organic micropollutants. In this study, we focused on the shallow lake area （Lake Taihu）, and utilizing the concentration and toxicological data of contaminants in water and sediment, we developed a screening method for preferential control of organic micropollutants based on exposure risk and hazard risk indicators. Using the 2/3 cumulative rank method, 123 aqueous phase contaminants were scored, and 33 contaminants, including fluvalinate, permethrin and triphenyl phosphate etc, were identified as priority contaminants. Among them, 31 substances were determined through aqueous phase data assessment, while ethynylestradiol and perfluorododecanoic acid were added as supplementary targets following the incorporation of sediment exposure risk assessment data, which shows that exposure data of contaminants in sediments serves as an essential supplement to the scoring system for priority control frameworks. Among the selected 33 priority contaminants, 17 substances appear in various control lists of different countries, but 16 substances have not received sufficient attention. The uncertainty in this paper mainly stems from the lack of toxicity data for some contaminants and the acquisition of related thresholds, as well as insufficient timeliness and synchronization of monitoring data. It is recommended that future work should focus on establishing monitoring standards for organic micropollutants and improving toxicity data. This study can provide support for the effective control of emerging contaminants in river and lake regions nationwide.

Abstract:To investigate the occurrence characteristics and transmission laws of organochlorine pesticides (OCPs) in Lake Luhu, a typical suburban lake in the middle reaches of the Yangtze River, water and sediment samples were collected from 40 sites in Lake Luhu, located in Jiangxia District, Wuhan, China. 24 kinds of OCPs were quantified by gas chromatography (GC-ECD) to analyze the pollution characteristics, sources and multi-medium transmission laws. The results showed that all 24 kinds of OCPs were detected in the study area, and the total amounts of OCPs from 0.64 to 6.97 ng/L in dissolved phase, 0.06 to 5.61 ng/L in suspended particulate matter, 0.47 to 14.16 ng/g(dw) in surface sediments, respectively. Compared with other lakes, the OCPs concentrations were relatively low. HCHs accounted for the largest proportion in dissolved phase, while HCHs, DDTs and Aldrin were the main pollutants in suspended particulate matter and sediment. The characteristic ratio traceability analysis showed that HCHs and DDTs were mainly historical residues in the study area. The main sources of HCHs in water and sediment were agrolindane application and mixed sources, respectively, and DDTs were mainly degraded in an anaerobic environment. The multi-medium transmission of OCPs was analyzed by the cosine theta similarity metric, partition coefficient and fugacity approach. The distribution coefficient (K_d) between dissolved phase and suspended particulate matter showed that OCPs in water were more easily adsorbed by suspended particulate matter with an increase in the octanol-water partition coefficient (K_OW). The fugacity fraction between water and sediment (ff_SW) decreased with an increase in K_OW, indicating that the sediments in the study area were sinks of OCPs with high K_OW, such as HCB and Aldrin.