Lake Poyang,the largest freshwater lake in China,is critical to regional water security and wetland ecosystem integrity.Seasonal isolated lakes(SILs),key components of the Lake Poyang wetland system,experience dynamic changes in water level and volume that directly influence the lake's water balance and biodiversity conservation.However,due to sparse in situ observa-tions,complex surface conditions,and frequent wet-dry transitions,existing water volume estimation methods remain limited in ac-curacy and applicability.Here,we develop a novel framework for estimating SIL water volume by integrating multi-source remote sensing data,hydrological connectivity analysis,digital elevation models(DEMs),and limited hydrological measurements.For the first time,high-resolution time-series(8-day,30-m)data on water surface area,water level,and water volume were reconstructed for 102 SILs from 2000 to 2024.The results indicate that:(1)the timing of isolation varies spatially,with average Xingzi Station water levels of 13.85 m and 14.28 m marking the start and end of isolation in the Ganjiang North tributary;(2)the 102 SILs had an average area of 305.20 km2,accounting for 17.98％of Lake Poyang's surface water area,with the largest isolated area recorded in 2023(134.03 km2,8.29％of the lake's area that year);(3)during the rising,falling,and dry stages,the water volume of SILs represented 1.91％,4.13％,and 6％of the total lake volume,respectively.From 2000 to 2024,water volume in northern SILs showed a declining trend,while lakes in central and southern regions exhibited increasing trends,contributing positively to drought mitigation in the basin.Overall,this study provides a robust approach for hydrological monitoring and management of Lake Poyang and other small,shallow seasonal lakes,offering a scientific basis for sustainable water resource use and ecological conser-vation.
Stream ecosystems possess significant ecological value due to their rich aquatic biodiversity and unique characteristics,yet they are highly vulnerable and require urgent attention and protection.Zooplankton,as an important component of the aquatic food web,is often overlooked in terms of its functional role in stream ecosystems.To better understand the ecological function of zo-oplankton in these environments,this study focused on the headwaters of the Chishui River,a minimally disturbed basin,and com-pared the taxonomic and functional group characteristics of zooplankton under two distinct hydrological conditions:the dry season(December)and the wet season(May).Relationships between these characteristics and water environmental factors were also ana-lyzed.A total of 29 zooplankton species were identified,with species richness in the dry season(24 species)being twice that in the wet season(12 species).Compared to other aquatic systems,stream zooplankton density was extremely low,ranging from 0.02 to 4.90 ind./L.Based on functional traits such as habitat preference,body size,and feeding habit,taxonomic groups were classi-fied into 11 functional groups.Dominant functional groups included the occasional planktonic benthic scraper,the small to medi-um-sized swimming predator,and the small filter-feeder,all reflecting adaptive strategies to turbulent lotic habitats.Notably,the proportion of the benthic scraper group increased sharply from 17.7％in the dry season to 68.4％in the wet season,demonstrating high sensitivity to hydrological shifts.Mantel tests further revealed that functional group composition was significantly correlated with multiple environmental factors,including phytoplankton cell density,water temperature,pH,oxidation-reduction potential,total phosphorus,and ammonium nitrogen,indicating that functional groups serve as more sensitive environmental indicators than taxonomic groups.This study demonstrates that functional group classification can integrate species with similar ecological niches,effectively compensating for the limitations of taxonomic approaches in assessing stream zooplankton standing stock,thereby offering a new theoretical perspective for constructing diagnostic indicator systems for stream ecological health.
The interactive stress relationship between ecological security and urbanization within lake basins fundamentally mani-fests the interactive dynamics between humans and the environment.Against the backdrop of accelerating urbanization and mount-ing pressure on natural resource and environmental carrying capacity,lake basins face growing challenges in providing stable mate-rial support and ecological guarantees for regional sustainable development.Within the theoretical framework of the human-land re-lationship in regional systems,this study quantitatively analyzes ecological security and urbanization levels across various lake ba-sins and explores the spatial heterogeneity of their interactive stress relationship.The results indicate that:(1)Under the combined influence of ecological governance and regional development,ecological security and urbanization levels in different lake basins have improved to varying degrees,with their spatiotemporal evolution exhibiting significant spatial heterogeneity.(2)The stress ex-perienced in the interaction between ecological environment and urbanization varies across basins,showing distinct patterns of cou-pling and coordinated evolution.Developed basins tend to achieve a higher level of coordination,whereas basins with a strong eco-logical foundation often experience lagging urbanization.The differing degrees of stress exerted and endured in the ecological secur-ity-urbanization interaction across basins reflect regional disparities shaped by the combined effects of natural conditions and devel-opmental stages.(3)A complex interactive stress relationship exists between ecological security and urbanization,influenced by factors such as natural endowments and developmental stages.Ecological constraints in developed basins have progressively weak-ened;in ecologically sound but underdeveloped basins,ecological factors strongly constrain urbanization;in ecologically fragile and underdeveloped basins,a bidirectional stress pattern is observed.Promoting ecological governance and urbanization processes in a context-sensitive manner and exploring development pathways characterized by high adaptability and synergy are key to achie-ving high-quality development in lake basins.This study aims to systematically delineate the interactive stress relationship and evo-lutionary characteristics between ecological security and urbanization,thereby providing scientific reference and practical insights for sustainable urbanization and ecological civilization construction in lake basins.
Strategic critical minerals such as lithium,boron,and potassium play an irreplaceable role in global energy transition and high-technology sectors.However,systematic research on the multi-element synergistic enrichment mechanisms and their dy-namic driving factors in deep-water salt lakes remains insufficient.The Longmu Co salt lake in Tibet,a typical high-altitude deep-water salt lake characterized by brines enriched in lithium(Li),boron(B),potassium(K),rubidium(Rb),and cesium(Cs),serves as an ideal object for investigating these processes.This study employed a 2 km×2 km grid sampling strategy combined with a hydrological-climatic analysis model to systematically analyze the spatial distribution and vertical differentiation patterns of LiCl,B2O3,KCl,Rb2O,and Cs2O in the surface brines of Longmu Co salt lake in 2024,and to explore the driving factors behind the dynamic evolution of LiCl,B2O3,and KCl concentrations during 2009-2024.The results indicate that the average concentrations of LiCl,B2O3,and KCl in the Longmu Co salt lake brines in 2024 were 620.07 mg/L,441.44 mg/L,and 5.12 g/L,respective-ly.Vertical differentiation was pronounced,with LiCl concentrations in deep layers(＞30 m)increasing by 7.50％relative to sur-face layers(0-10 m),accompanied by synchronous enrichment of Rb2O and Cs2O.The thermocline barrier and bottom anoxic en-vironment represent the primary factors contributing to this vertical differentiation.Horizontally,high-value zones of LiCl and KCl formed in the eastern part of the salt lake due to evaporation-concentration effects,whereas concentrations decreased in the north-western region influenced by spring-water recharge dilution(mean annual discharge:3.41 m3/s).The differentiation of Rb2O and Cs2O was primarily controlled by clay mineral adsorption and hydrothermal input.The distribution of resource elements in Longmu Co salt lake is driven by the triple coupling of high-altitude extreme climate,plate tectonics,and hydrothermal activity;vertical differentiation is predominantly governed by physical water-body barriers,while horizontal differentiation is controlled by hydrologi-cal conditions and topographic variations.During 2009-2024,LiCl,KCl,and B2O3 concentrations declined by 21.87％,24.81％,and 28.83％,respectively.Glacier melting,spring runoff,and atmospheric precipitation recharge constitute the princi-pal factors influencing these concentration changes.The multi-element synergistic enrichment mechanism of this salt lake provides a scientific basis for the efficient exploitation and utilization of salt lake resources in Tibet,and holds significant strategic impor-tance for reducing China's external dependence on lithium resources.
The sustainable development of a river basin relies on the supply of ecosystem services from its aquatic ecosystems,mak-ing the health of riverine water ecosystems a critical safeguard.Taking the Weihe River Basin as the study area,this paper employs bibliometric analysis to review relevant domestic and international data and research findings from 2004 to 2024,and conducts an in-depth exploration of the water quality,habitat quality,biodiversity,and aquatic ecological health status in the basin.It summa-rizes the selection of indicators for aquatic ecological health assessment in the Weihe River Basin and clarifies the strengths,limita-tions,and applicable scopes of different assessment methods.On this basis,the study synthesizes the evolutionary trends of aquatic ecological health in the Weihe River Basin from 2004 to 2024.Overall,water quality in the Weihe River has improved.The diver-sity of plankton and periphytic algae declined during a certain period but has shown signs of recovery in recent years.Water pollu-tion and habitat degradation remain the primary factors threatening the aquatic ecological health of the basin,with the middle and lower reaches still facing severe pollution issues.Furthermore,by integrating ecological protection policies and regulations of the Weihe River Basin,this study evaluates the importance of aquatic ecological environment management for maintaining ecological health.Finally,in light of the"Hanjiang-to-Weihe Water Transfer Project",the potential impacts of increased water resources on the aquatic ecological health of the Weihe River Basin are discussed.
The occurrence of metalimnetic hypoxia in deep lakes poses a significant threat to the structural and functional integrity of lake ecosystems.As a reservoir of nearly 50％of China's Class Ⅰ freshwater resources,Lake Fuxian plays a critical role in nation-al water security.However,the spatiotemporal evolution and key drivers of metalimnetic hypoxia in Lake Fuxian under ongoing cli-mate warming remain inadequately understood.Based on high-frequency monitoring data from 2021 to 2024 and a process-based hydrodynamic-ecological model(GOTM-WET),this study reconstructed the evolution of metalimnetic hypoxia in Lake Fuxian spanning the period from 1945 to 2024.Scenario simulations were further conducted to elucidate the regulatory roles of key biogeo-chemical oxygen-consuming processes.Results reveal that metalimnetic hypoxia has occurred frequently during the stratified season since the 1980s.Relative to 1980,dissolved oxygen(DO)concentration in the hypoxic zone declined at a rate of(0.20±0.03)mg/(L·10 a),while its depth shoaled by(0.45±0.21)m/10 a and its thickness increased by(1.07±0.17)m/10 a.The volu-metric proportion of the hypoxic zone relative to the metalimnion rose by(6.44±0.98)％/10 a,and its annual duration extended by(31.20±5.08)days/10 a.These trends were significantly correlated with warming-induced intensification of thermal stratifica-tion,including increases in Schmidt stability,metalimnion thickness,and stratification duration.Model simulations indicated that phytoplankton respiration and dissolved organic matter(DOM)mineralization were the dominant oxygen-consuming processes,ac-counting for 34.6％and 27.5％of total oxygen consumption,respectively,followed by particulate organic matter(POM)minerali-zation(19.7％)and nitrification(16.7％),with sediment oxygen demand(SOD)contributing minimally(1.5％).Scenario ana-lyses further identified DOM mineralization and phytoplankton respiration as the primary drivers of hypoxia initiation,whereas POM mineralization,nitrification,and SOD played important roles in regulating the concentration,persistence,and vertical distribution of metalimnetic hypoxia.In summary,this study demonstrates that metalimnetic hypoxia in Lake Fuxian under climate warming is synergistically controlled by physical(thermal stratification)and biogeochemical(oxygen consumption)processes,offering scientif-ic support for understanding deep-lake ecosystem responses to climate change and informing management strategies.
Surface water resources in the Lake Dongting Basin play a vital role in sustaining ecosystems,protecting biodiversity,and regulating climate,yet they remain highly vulnerable to climate change and human activities.Although numerous studies have examined surface water area dynamics in the basin,most lack long-term,basin-wide analyses,rely largely on qualitative descrip-tions of driving mechanisms,and confine spatial assessments to the main lake area.To address these gaps,this study systematically investigates the spatiotemporal evolution of surface water area across the entire Lake Dongting Basin and its sub-basins,quantifies the contributions of climatic factors and human activities to surface water dynamics,and analyzes migration patterns of the surface water distribution centroid in sub-basins.Using multi-source remote sensing data and the JRC Global Surface Water Dataset,and applying the Mann-Kendall test,Pettitt test,Pearson correlation analysis,and centroid analysis models,this study delineates the spatiotemporal variation patterns and primary drivers of surface water area in the Lake Dongting Basin from 1990 to 2021.The re-sults indicate that:① over the past 30 years,the surface water area of the basin has exhibited an overall increasing trend,most no-tably in the Yuanjiang River system,where it expanded by 420.07％,with marked spatial heterogeneity and a three-stage temporal pattern characterized by"rapid expansion-fluctuating reduction-recovery growth";(2)the centroid of surface water distribution across the basin has shifted south westward,with the predominant fluctuation occurring along the east-west direction,amounting to a displacement of 19.56 km;centroid migration in sub-basins closely correlates with the spatial distribution of water conservancy projects and ecological restoration measures,reflecting the reshaping influence of human activities on surface water spatial patterns;(3)precipitation is the principal climatic factor driving the increase in surface water area,while human engineering interventions and ecological restoration measures—such as water conservancy construction and"returning farmland to lakes"—have substantially altered the spatial distribution pattern of surface water in the basin;(4)climate change accounts for approximately 40％-55％of the variation in surface water area,whereas human engineering regulation and ecological restoration measures contribute 45％-60％,representing the dominant driver and significantly modifying the spatial configuration of surface water.This study enhances the un-derstanding of long-term surface water resource variations in the Lake Dongting Basin and provides a scientific basis for formulating effective ecosystem protection and restoration strategies.
The aim of this study was to determine whether significant differences in vegetation characteristics exist across different elevations and land use types in the water-level fluctuation zone(WLFZ)of Danjiangkou Reservoir.From July to September 2024,samples were collected from 45 sites along three WLFZ elevation gradients:155-160 m,160-165 m,and 165-170 m.Results showed that a total of 170 species of large vascular plants,belonging to 140 genera and 55 families,were recorded in the WLFZ.The Asteraceae family had the highest species richness,followed by Poaceae,Fabaceae,and Euphorbiaceae.The vegetation was dominated by herbaceous plants,with annual herbs accounting for 46.47％,perennial herbs for 32.35％,and woody plants(in-cluding shrubs,lianas,and trees)for 21.18％.Dominant species varied significantly among elevation zones:Cynodon dactylon was dominant at 155-160 m,Digitaria sanguinalis at 160-165 m,and Artemisia annua at 165-170 m.Average vegetation bio-mass was(822.4±709.4)g/m2,and the mean Shannon-Wiener diversity index was 1.67±0.45.No significant differences were observed in vegetation cover,height,biomass,or diversity across elevation zones,although vegetation height tended to increase with elevation.In contrast,vegetation cover,biomass,and diversity differed significantly among land use types.Cover in grassland was significantly higher than in forestland(understory herb layer)and water conservancy facility land,while biomass in grassland and cropland was significantly higher than in forestland and water conservancy land.The vegetation diversity index was significantly higher in grassland,forestland,and water conservancy land than in cropland.Plant reproductive strategies and seed dispersal abili-ty were identified as intrinsic factors influencing vegetation distribution patterns,while human activities such as reservoir operation and land use were key external drivers.
Wetlands are among the most important carbon reservoirs in terrestrial ecosystems.They can act as both carbon sources and carbon sinks,with complex carbon cycling processes.However,the diurnal variation patterns of CO2 fluxes in wetlands remain poorly understood,introducing uncertainty into accurate assessments of wetland carbon sequestration capacity.This study was con-ducted in the seasonally flooded Lake Poyang.Based on eddy covariance observations in 2021(a normal flow year),we analyzed the diurnal differences in CO2 fluxes in the floodplain wetland of Lake Poyang,and identified the dominant controlling factors of daytime and nighttime CO2 fluxes using partial correlation and multiple regression analyses.The results showed that:(1)At the di-urnal scale,CO2 fluxes during the exposed period(January 1-May 14 and October 21-December 31)exhibited a typical"U"-shaped pattern,acting as a carbon sink during the daytime and a carbon source at night.In contrast,CO2 fluxes during the inun-dation period(May 15-October 20)remained relatively stable near 0 μmol/(m2·s),but the fluctuation amplitude of CO2 fluxes during day-night transitions increased significantly in the late inundation stage(August-October).(2)At the monthly scale,diur-nal differences in CO2 fluxes were pronounced during the exposed period but diminished during the inundation period,and this dy-namic was closely related to the shift between carbon source and sink functions of the wetland.(3)At the annual scale,CO2 fluxes in the floodplain wetland showed significant diurnal variability,with the annual mean nighttime flux being 25.50％higher than the daytime flux.Diurnal differences were most prominent during the exposed period,with an average flux difference of 10.22μmol/(m2·s).(4)The dominant controls on diurnal differences in CO2 fluxes varied substantially between periods.During the exposed period,daytime CO2 fluxes were mainly regulated by incident shortwave radiation and soil moisture,whereas nighttime fluxes were dominated by soil temperature.During the inundation period,daytime fluxes were primarily influenced by precipita-tion and soil moisture,while nighttime fluxes were jointly controlled by soil moisture,lake water level,and soil temperature.(5)The fundamental mechanisms driving diurnal differences differed between periods.During the exposed period,diurnal vari-ations in CO2 fluxes were driven by contrasting diurnal patterns of photosynthesis and respiration:photosynthesis dominated dur-ing the daytime,resulting in a CO2 sink,while respiration dominated at night,resulting in a CO2 source.During the inundation period,water cover suppressed plant and microbial activities,leading to muted diurnal differences in CO2 fluxes.This study re-veals the diurnal variation mechanisms and dominant controlling factors of CO2 fluxes in floodplain wetlands,providing an im-portant scientific basis for the management of wetland carbon and water resources and ecological protection.
Residence time is a key hydrodynamic indicator of water renewal and exchange capacity in lakes,directly influencing pollutant transport and migration processes and thus closely linked to a lake's water quality.In recent years,significant changes in the hydrological regime of Lake Poyang have exerted notable impacts on its aquatic environment.This study employs the MIKE21 hydrodynamic model coupled with a tracer module to quantitatively analyze the spatiotemporal distribution and interannual trends of residence time during the receding period(1980-2020)in Lake Poyang,and further elucidates its quantitative response to hydro-logical variations.Results indicate that residence time during the receding period exhibits strong spatiotemporal heterogeneity.The whole-lake average residence time is 36 d,with sub-regional averages ranked as follows:eastern lake bays(93 d)＞southern lake area(53 d)＞northern outflow channels(38 d)＞main lake area(26 d)＞Wucheng seasonal disconnected-lake group(17 d).Intera-nnually,the whole-lake average residence time shows a slight shortening trend over the past four decades.After the Three Gorges Dam began operation(2003-2020),the average residence time decreased by approximately 4 d relative to the pre-dam period(1980-2002).The northern outflow channels experienced the largest reduction(9 d),followed by the main lake area(5 d),while changes in other regions were minimal.Residence time was significantly longer in wet years than in dry years.During the re-ceding period,residence rate was positively correlated with water level.The decline in water level and the accelerated recession rate are identified as the primary drivers of the shortened residence time.These findings provide a scientific basis for water environ-ment management and ecological restoration in Lake Poyang.
Lake Dianchi,a representative plateau freshwater lake in China,has experienced escalating eutrophication in recent decades,largely driven by intensified anthropogenic activities and sustained nutrient inputs.To elucidate the composition and sources of sterols in surface sediments,we conducted systematic multi-site sampling and analyzed the spatial distribution of sterol biomarkers,total organic carbon(TOC),total nitrogen(TN),and C/N ratios in relation to watershed land use.Results revealed pronounced spatial heterogeneity in organic matter content and C/N ratios.The Caohai region,influenced by substantial urban run-off and multiple inflowing rivers,showed higher organic matter content and elevated C/N ratios relative to Waihai,following a dis-tinct southwest-to-northeast decreasing gradient.Within Waihai,deeper central zones exhibited greater organic matter and higher C/N ratios than peripheral shallow areas,forming a center-high,margin-low spatial pattern.Coprostanol and its epimer(C27)were concentrated in Caohai and the northeastern and southern parts of Waihai,indicating substantial sewage and anthropogenic inputs.Cholesterol and cholestanol(C27)were enriched in northern Caohai,central Waihai,and southern Waihai,reflecting autochtho-nous organic matter derived from plankton.Campesterol(C28),stigmasterol,and β-sitosterol(C29)were relatively enriched in central and southern Waihai—areas with intensive agriculture and high cropland coverage—suggesting strong agricultural influence.Dinosterol(C30)was notably concentrated in southern Waihai,consistent with high dinoflagellate biomass in this region.Hydrody-namic conditions also played a critical role:in the semi-enclosed,low-energy Caohai region,all organic indicators showed high values,whereas the Haikou-Shitoucun fault zone,characterized by large water-depth variations and strong hydrodynamic disturb-ance,exhibited low concentrations of organic matter and sterols.This study systematically characterizes multiple organic matter sources in Lake Dianchi sediments using sterol biomarkers,clearly differentiating autochthonous and allochthonous contributions.The results advance methodological approaches for organic matter source apportionment and provide a theoretical basis for under-standing eutrophication mechanisms and tracing pollution sources in complex aquatic systems.
Accurate and efficient monitoring of aquatic vegetation is essential for the protection and management of lake ecosys-tems.This study developed a novel classification approach to distinguish floating-leaved and emergent plants in the Nanji Wetland National Nature Reserve and Lake Poyang National Nature Reserve.The method first employed the normalized difference vegetation index to identify water bodies,then applied a self-constructed normalized difference mud index(NDMI)to minimize interference from mudflats.Subsequently,floating-leaved and emergent plants were differentiated based on variations in their radar backscatter-ing coefficients.The proposed method was compared against existing classification techniques.The results demonstrated that:(1)The backscattering coefficient-based approach significantly improved classification performance,achieving an overall accuracy of 89.72％and a Kappa coefficient of 0.8413.(2)The method maintained consistent performance across different imaging peri-ods,with overall accuracy consistently exceeding 80％,indicating high stability and reliability.(3)The incorporation of NDMI ef-fectively suppressed mudflat interference,preventing misclassification of exposed substrates after water recession,and proving par-ticularly suitable for floodplain wetlands with pronounced hydrological fluctuations.In summary,this study provides a robust tech-nical framework for discriminating aquatic vegetation types and offers valuable insights for monitoring wetland ecosystems with dy-namic water-level regimes.
Phosphorus is a key nutrient in lake ecosystems and a primary limiting factor for primary productivity,with its speciation and concentration significantly influencing phytoplankton community structure.To investigate the characteristics of phosphorus frac-tions and their effects on phytoplankton assemblages in Lake Changhu,a typical shallow lake in the middle and lower reaches of the Yangtze River,and to provide a scientific basis for its ecological restoration and precision management,we conducted seasonal sampling in March,May,September,and December 2024 at 10 sites,analyzing phosphorus forms,environmental variables,and phytoplankton community composition.Results showed that the annual average total phosphorus(TP)concentration was 0.117 mg/L,with levels ordered as September＞March＞May＞December and a decreasing gradient from west to east.Dissolved total phosphorus(DTP;mean of 0.060 mg/L)contributed slightly more to TP than particulate phosphorus(PP;mean of 0.056 mg/L).Seasonal variation in phosphorus forms was observed:PP dominated in March;PP slightly exceeded DTP in May;DTP prevailed in September and December,with dissolved organic phosphorus(DOP)predominant in September and dissolved inorganic phos-phorus(DIP)in December.DOP in September was significantly higher than in other months.Phytoplankton were dominated by Cyanophyta,Chlorophyta,Bacillariophyta,and Cryptophyta.Non-metric multidimensional scaling and permutational multivariate analysis of variance revealed significant temporal variation in community structure,showing a clear seasonal succession:from Bacil-lariophyta+Cryptophyta+Chlorophyta in March to Cyanophyta+Chlorophyta in May,then Cyanophyta in September,and finally Cryptophyta+Bacillariophyta+Cyanophyta+Chlorophyta in December.Dominant species included Cyclotella sp.(Bacillariophy-ta)in March,Merismopedia minima(Cyanophyta)in May,Komma caudata(Cryptophyta)in December,and Microcystis spp.(Cyanophyta)—a bloom-forming genus—in September,which was also dominant in May.Redundancy analysis and partial least squares path modeling identified DOP,water temperature,DTP,and suspended solids as the most influential factors on phyto-plankton community structure,with phosphorus fractions exerting significant direct effects.DOP showed the strongest effect,par-ticularly promoting Microcystis spp.abundance.These results demonstrate that phosphorus speciation significantly shapes phyto-plankton community structure in Lake Changhu and highlight the importance of quantitative assessment of different phosphorus forms—especially DOP—for evaluating ecological risks in eutrophic shallow lakes.
Lake Poyang,a critical wintering habitat for water birds along the East Asian-Australasian Flyway,supports Carex spp.as the dominant wetland plant and primary food source for overwintering geese,with its growth directly influencing foraging efficien-cy and energy intake.Recent alterations to the hydrological regime of Lake Poyang due to hydraulic engineering and extreme cli-matic events have disrupted Carex growth dynamics,resulting in a phenological mismatch with the migration schedule of wintering geese.Mowing,a common grassland management practice,can promote plant regrowth and modulate growth rhythms,thereby par-tially mitigating food resource mismatch and improving foraging conditions for geese.This study conducted a field experiment on ex-posed Carex in Lake Poyang floodplains during autumn and winter,applying different mowing frequencies across gradients of soil moisture under long-term management and monitoring.Results demonstrated that increased soil moisture significantly enhanced plant height and aboveground biomass,while belowground biomass peaked only under low soil moisture conditions 15 days after mowing.Repeated mowing significantly suppressed plant height and aboveground biomass and attenuated the promotive effect of soil moisture,leading to convergence of growth indicators across moisture gradients.Both soil moisture gradient and mowing frequency significantly influenced plant height,aboveground biomass,and belowground biomass of Carex,with optimal growth observed un-der high soil moisture(≥ 33.79％)and low mowing intensity(≤4 times).These findings offer quantifiable parameters for water regulation and mowing frequency to support the management of wintering waterbird habitats in Lake Poyang wetlands.
Lake Poyang represents a typical floodplain lake-wetland system in the middle reaches of the Yangtze River.Its high-amplitude water-level fluctuations significantly alter heat flux processes,profoundly affecting surface eco-hydrological processes and local climate.To investigate the response mechanisms of heat fluxes in Lake Poyang to flooding processes,this study applied an im-proved Variable Infiltration Capacity(VIC)land surface model incorporating a lake module to quantitatively simulate hydrological and energy processes in the Lake Poyang floodplain wetland.We examined the seasonal variations in water-heat fluxes and analyzed the driving mechanisms of flooding on the spatiotemporal distribution of heat fluxes.The results demonstrated that:(1)The model performed robustly in simulating flood dynamics and heat fluxes.For hydrological simulation,monthly averaged water levels agreed well with observations,exhibiting high correlation coefficients(R＞0.9)and Nash-Sutcliffe Efficiency coefficients(NSE＞0.8).For thermal fluxes,the simulated Bowen ratio closely matched reference values,with a correlation coefficient of 0.81 and NSE excee-ding 0.7,indicating the framework reliably captures hydrological rhythms and inundation heterogeneity,providing an effective tool for studying lake-wetland eco-hydrological processes under climate change;(2)Floodplain dynamics significantly regulate seasonal energy partitioning.During inundation(wet seasons),the water-dominated surface allocated 68％of net radiation to latent heat flux,reducing the Bowen ratio from 0.38(non-inundated)to 0.09,establishing a"high latent heat-low sensible heat"regime.In dry seasons with exposed mudflats,the latent heat proportion decreased to 56％;(3)Marked contrasts in energy partitioning exis-ted between the lake and surrounding land:latent heat flux over the lake was 29％higher than adjacent land,while sensible heat flux was 59％lower.Persistent high latent heat flux centers(annual mean:89 W/m2)formed in the frequently inundated north-eastern zone due to low-lying topography,exceeding values in the southwestern zone by 80％,creating a northeast-high to south-west-low spatial pattern;(4)Energy partitioning exhibited a three-stage coupling with soil moisture/water level:when volumetric soil water content was below 17％,the evaporative fraction increased slowly with moisture;above 17％,it showed a linear positive correlation;beyond 32％under inundation,the evaporative fraction decoupled from soil moisture,indicating distinct phased regu-latory effects.By coupling the VIC model with underwater terrain inundation analysis,this study reveals the regulatory mechanism of Lake Poyang's floodplain processes on regional energy balance,offering a novel approach to understanding water-heat exchange mechanisms in floodplain wetlands and providing important scientific insights into their eco-hydrological processes under climate change.
In 2022,frequent cyanobacterial blooms occurred in Lake Hulun,covering nearly the entire lake surface,degrading a-quatic landscapes,and posing serious threats to ecosystem health.To investigate the drivers of these large-scale blooms,water sam-ples were collected from surface,middle,and bottom layers at 13 sampling sites during spring,summer,and autumn of 2022.Cy-anobacterial species composition,abundance,biomass,and key water quality indicators were analyzed.A total of 22 cyanobacteri-al species were identified,with 10 dominant groups observed over the study period.Microcystis spp.remained the dominant genus across all seasons.The abundance and biomass of cyanobacteria varied significantly in different periods and depths.The abundance(2.58×109 cells/L)and biomass(3.30×102 mg/L)of cyanobacteria in summer were 1-2 orders of magnitude higher than those in spring and autumn.In spring,the abundance and biomass of cyanobacteria were the highest in the bottom layer of the lake,and the highest in the surface layer of the lake in summer and autumn.Correlation and redundancy analyses revealed seasonal differ-ences in influencing factors,identifying water temperature,nitrogen and phosphorus concentrations,dissolved oxygen,and pH as key environmental drivers of bloom dynamics.For management,we recommend moderate nutrient control with a dual nitrogen-phosphorus reduction strategy,along with enhanced bloom prediction,early warning,and emergency response capabilities.These measures are essential for mitigating bloom risks in eutrophic lakes such as Lake Hulun and may inform future cyanobacterial bloom control strategies in similar ecosystems.
Batrachospermaceae is a family of freshwater red algae characterized by filamentous fronds,many species of which are endangered due to the scarcity of their populations.This study applied a suite of analytical methods—including one-way ANOVA,principal component analysis,random forest modeling,and multiple linear regression—to examine the environmental preferences of Batrachospermaceae and compare them with those of two other common filamentous freshwater algal families,Zygnemataceae and Cladophoraceae(green algae),with the aim of elucidating the mechanisms underlying the endangerment of Batrachospermaceae.The results demonstrated that:(1)The distribution ranges of water temperature,pH,dissolved oxygen,specific conductivity,total dissolved solids,salinity,ammonia nitrogen,total phosphorus,and chemical oxygen demand in habitats where Batrachospermaceae occurred were narrower than those of Zygnemataceae and Cladophoraceae,indicating that Batrachospermaceae has lower environ-mental adaptability and stricter habitat requirements.(2)Water temperature,total phosphorus,total nitrogen,and chemical oxy-gen demand were identified as important environmental factors influencing the distribution of Batrachospermaceae.Compared with Zygnemataceae and Cladophoraceae,Batrachospermaceae was influenced by a greater number of key environmental factors,sugges-ting that its growth is subject to more constraints,which contributes to its endangered status.These findings provide a scientific ba-sis for the conservation and restoration of Batrachospermaceae.
Mesotrophic lakes and reservoirs,as critical sources of drinking water,exhibit unclear mechanisms governing the occur-rence of occasional algal blooms and the dynamics of nutrient limitation.This study investigated Duihekou Reservoir in Zhejiang Province through four years of in situ monitoring to elucidate fluctuations in algal growth rates and their dynamic coupling with intra-cellular nutrient quotas.Results indicated that during the diatom-dominated phase(December-April,DIA),the in situ algal growth rate varied markedly from-1.10 d-1 to 2.76 d-1,whereas during the cyanobacteria-dominated phase(July-August,CYA),it ranged from-0.43 d-1 to 0.81 d-1—higher than values typically observed in eutrophic systems—suggesting a high po-tential for rapid algal proliferation in mesotrophic waters.Growth rates in the DIA phase were primarily governed by nitrogen cell quotas,which may be attributed to the suppression of chlorophyll synthesis and nitrogen assimilation efficiency under light and tem-perature limitations.Therefore,a springtime rise in temperature and light intensity,coupled with elevated cellular nitrogen con-tent,could trigger diatom blooms.In contrast,growth rates in the CYA phase were co-regulated by phosphorus cell quotas and en-vironmental phosphorus quotas.Maintaining total phosphorus below 22 μg/L(95％CI:15-32 μg/L)could effectively suppress cyanobacterial blooms(chlorophyll-a＞10 μg/L).This study innovatively incorporates dynamic intracellular nutrient quotas to ana-lyze algal growth mechanisms,overcoming the traditional reliance on ambient nutrient concentrations,algal biomass,or N∶P ratios to determine nutrient limitation.The approach offers a new theoretical basis for water quality management and bloom forecasting in mesotrophic lakes and reservoirs.
In the context of global climate change,extreme heat events(heatwaves)have increased in both frequency and intensi-ty,posing growing threats to the stability of lake ecosystems.To evaluate these impacts,this study simulated short-term heatwaves using a mesocosm system and employed integrated metagenomic and metatranscriptomic sequencing to systematically analyze struc-tural and functional responses of aquatic microbial communities.Results demonstrated that while microbial community composition remained largely stable under short-term high-temperature stress,functional diversity increased significantly,with 467 unique func-tions identified relative to the pre-heatwave.Gene expression levels also changed considerably,particularly in metabolic and photo-synthetic pathways.Bray-Curtis dissimilarity analysis revealed increases of 0.12 in community composition distance and 0.16 in functional distance after heatwave exposure.These findings suggest that heatwaves mainly influence aquatic ecological processes by altering functional diversity rather than community structure.Overall,lake microbial communities show a capacity for rapid accli-mation to environmental fluctuations through functional adjustments,whereas structural changes occur over longer timescales.
Under the combined pressures of climate change and anthropogenic activities,lake ecosystems across the Lake Poyang Basin have undergone varying degrees of degradation.A comprehensive understanding of the long-term environmental evolution of the lake basin is therefore crucial for its ecological restoration and conservation.Based on 210 Pb dating,this study applied a multi-proxy analysis—including total organic carbon(TOC),total nitrogen(TN),C/N ratio,organic carbon accumulation rate(OCAR),total nitrogen accumulation rate(TNAR),and stable carbon isotope of organic matter(δ13Corg)—to sediment cores from Lake Junshan and Lake Qinglan in the southern Lake Poyang Basin.This approach was used to identify the main sources of sedi-mentary organic matter and elucidate the mechanisms driving changes in primary productivity and eutrophication over the past cen-tury.Results show that C/N ratios and δ13Corg values ranged from 7.7-10.5 and-23.9‰ to-22.0‰ in Lake Junshan,and from 8.7 to 11.3 and-26.3‰ to-21.7‰ in Lake Qinglan,indicating that sedimentary organic matter in both lakes was primarily de-rived from macrophytes and phytoplankton.After 1905 in Lake Junshan and after 1980 in Lake Qinglan,TOC and TN concentra-tions increased,reflecting a general trend of rising primary productivity.Differences in the response of δ13Corg to productivity chan-ges highlighted variations in aquatic plant community composition between the two lakes.Specifically,Lake Junshan—mainly in-fluenced by climate warming and aquaculture—underwent a successional shift over the past two centuries:from macrophyte domi-nance,through a transitional phase of macrophyte-algae co-dominance,to the current algal-dominated state.In contrast,Lake Qinglan experienced a decline in submerged vegetation after river diversion in 1958,largely due to increased sediment input.After 1980,additional pressures from domestic sewage and agricultural non-point source pollution associated with urbanization further ac-celerated this trend,leading to phytoplankton becoming the dominant source of sedimentary organic matter.By comparing ecologi-cal evolution across different sub-regions of Lake Poyang,this study provides a scientific basis for clarifying the mechanisms of eco-logical degradation driven by the interplay of multiple stressors.
