Journal of Hydroecology

Methane Diffusion and Ebullition in Reservoirs of the Yellow River Mainstream and Huangshui River Basin

Reservoirs are an important source of methane(CH₄) emissions. In this study, we explored the spatial and temporal characteristics of methane(CH₄) diffusion and ebullition in reservoirs of the northeastern Qinghai-Tibet Plateau and factors influencing the fluxes. In May and August 2023, air and water samples were collected at 57 sampling sites of 17 reservoirs in the mainstream of the Yellow River and Huangshui River basins. The headspace equilibrium method, thin boundary layer(TBL) model,and static chamber-gas-chromatography method were used to determine the dissolved CH₄ concentration, diffusion flux, and ebullition flux. Additionally, water environmental parameters were measured simultaneously to examine the influence of the physicochemical parameters on the CH₄ fluxes. Results show:(1) the seventeen reservoirs all acted as sources of CH₄ in both May and August, and ebullition was the most important emission pathway. Overall, the CH₄ diffusion and ebullition fluxes in August[0.09-82.83 mg/(m²·h), 0.01-3.34 mg/(m²·h)] were greater than those in May [0.02-25.82 mg/(m²·h),0.01-15.11 mg/(m²·h)], and spatially, CH₄ diffusion flux and ebullition fluxes of the Huangshui River basin [(0.44±0.81 mg/(m²·h),(1.41±3.02) mg/(m²·h)] were greater than those in the mainstream of the Yellow River [0.08±0.07 mg/(m²·h), 0.35±0.54 mg/(m²·h]. The contribution rate of ebullition was 73.83% for reservoirs in the mainstream of the Yellow River and 62.23% for those in the Huangshui River basin.(2) Reservoir age was a key influencing factor for CH₄ emission. There was a negative correlation between reservoir age and CH₄ fluxes in the mainstream of the Yellow River, while there was a positive correlation with CH₄ fluxes in the Huangshui River basin. CH₄ fluxes were also affected by water temperature, salinity, pH, total nitrogen, and total organic carbon. Redundancy analysis reveals that these key factors explained 79.5% of the flux variation in the mainstream of the Yellow River and 43.4% in the Huangshui River basin.(3) Compared with other regions, CH₄ emissions from reservoirs in the Huangshui River basin were moderately high, higher than those from most reservoirs in temperate/boreal zones but lower than those in tropical regions with higher biomass. The CH₄ emissions from small reservoirs on the Qinghai-Tibet Plateau should be paid particular attention. These results provide comprehensive data support for further study of CH₄ emissions from reservoirs on the Qinghai-Tibet Plateau and other regions.

Latitudinal and Vertical Variations of Temperature Sensitivity for Soil CH₄ and N_2O Emissions in Riparian Wetlands

Methane(CH₄) and nitrous oxide(N_2O) are the two most important greenhouse gases(GHGs)after carbon dioxide(CO₂), and their global warming potentials are 28 and 265 times higher than for CO₂.Thus, accurately determining the temperature sensitivity(Q₁₀) for CH₄ and N_2O emission rates is key for assessing and predicting the feedback relationships between GHG emissions and climate change. The Q₁₀of CO₂ emission has been extensively examined in previous studies, but the Q₁₀values for CH₄ and N_2O emissions and their spatial variation remain unclear. Riparian wetlands, located in a transition zone between aquatic and terrestrial ecosystems, are often hot spots of biogeochemical cycling and serve as important sources and sinks of greenhouse gases. In this study, 30 representative rivers in the tropicalsubtropical and temperate zones in a latitude range of 21.76°-45.08° N across eastern China were selected for research, and we investigated the latitudinal and vertical variations of Q₁₀for CH₄ and N_2O emissions from riparian soils, and the driving mechanisms. Soil samples were collected from both shallow(0-20 cm)and deep(40-60 cm) layers of riparian wetlands, and a 56-day soil microcosm incubation experiment was used to determine the emission rates of CH₄ and N_2O at 15 ℃ and 25 ℃. The Q₁₀value of CH₄ emission(CH₄-Q₁₀) increased with increasing latitude and soil depth, but the N_2O-Q₁₀did not change significantly with either latitude or soil depth. Correlation analysis and structural equation modeling(SEM) revealed that environmental factors such as geographic location, climate and soil properties jointly regulated the spatial variability of CH₄-Q₁₀. In temperate zone soils, CH₄-Q₁₀was negatively correlated with soil bulk density and positively correlated with total carbon(TC) and the carbon to nitrogen ratio(C/N). In tropicalsubtropical soils, CH₄-Q₁₀was positively correlated with pH and negatively correlated with nitrate nitrogen(NO₃~--N). The CH₄-Q₁₀in topsoil was weakly influenced by environmental factors, but CH₄-Q₁₀in deep soil was primarily regulated by climatic factors, such as mean annual precipitation. Further, N_2O-Q₁₀was weakly associated with environmental factors. The study confirms that N_2O emissions were more sensitive to warming, and the CH₄-Q₁₀in temperate subsoil was the highest, making them a potential key source of CH₄ emissions under future climate warming. The findings of this study will improve estimation of greenhouse gas emission potential in the riparian wetlands of China and better predict the potential impacts of global warming on GHG emissions.

Seasonal Variation and Factors Influencing the Partial Pressure of Carbon Dioxide in Karst Reservoirs

The partial pressure of carbon dioxide p(CO₂) in the water of karst reservoirs differs greatly from that in non-karst reservoirs due to the limestone(CaCO₃) geology, but recent studies of p(CO₂) in karst reservoirs are rare. In this study, Dongqing reservoir, a typical karst reservoir in southwest China,was selected for research and we explored the spatiotemporal distribution of p(CO₂) and the CO₂ exchange flux at the air-water interface and analyzed the relationship of p(CO₂) with physicochemical parameters and nutrient concentrations of the reservoir water. The aims of the study were to explore the role of karst reservoirs in aquatic carbon cycling and provide data support for understanding the source-sink characteristics of water bodies under different geological conditions. In July(wet season), December(dry season), and April 2023(normal season), a seasonal investigation was conducted with seven sampling point in the mainstream of Beipan River and Dabang River estuary to measure the physicochemical parameters of reservoir water and calculate the p(CO₂) and CO₂ exchange flux. During the wet, dry, and normal seasons, the respective mean values of p(CO₂) in the reservoir water were(83.72 ± 8.13),(109.47 ± 8.24),(97.60 ± 5.31) Pa and the mean water-air CO₂ fluxes were(13.71 ± 3.34),(47.30 ± 5.06), and(20.99 ±2.18) mmol/(m² · d), indicating that Dongqing reservoir is a net source of CO₂ to the atmosphere. The mean p(CO₂) values and the water-air CO₂ fluxes both followed the order: dry period > normal period >wet period and significant differences were observed among points. Correlation and regression analysis showed a significantly positive correlation between p(CO₂) and alkalinity(ALK)(P<0.01) during both the wet and dry seasons, primarily influenced by carbonate equilibria. During the normal season, p(CO₂)showed an extremely significant correlation(P<0.01) with total nitrogen(TN) and the carbon-to-nitrogen ratio(TOC:TN), with the dominant factor being CO₂ production by microbial decomposition of organic matter. The CO₂ exchang flux in Dongqing reservoir was lower than in either tropical or subtropical nonkarstic reservoirs, slightly lower than in temperate non-karst reservoirs, but not significantly different from other subtropical karst reservoirs.

Spatial and Temporal Patterns of Greenhouse Gas Emissions and Driving Factors in Miyun Reservoir and Surrounding Waters

Reservoirs,rivers,ponds and groundwater are important sources of greenhouse gases,but the spatial and temporal distribution and driving factors of greenhouse gas emission in water bodies needs further study.In this investigation,Miyun reservoir,its tributaries and the surrounding groundwater were selected for research,and we explored the distribution,saturation,and emission flux of dissolved N_2O,CO₂ and CH₄ and their relationship with physical and chemical indices of the water.During the dry and wet seasons of 2023 (May and August/September),water samples were collected at Miyun reservoir,4 tributaries(Qingshui,Chaohe,Baimaguan,and Baihe Rivers) and 14 surrounding groundwater sites for determination of greenhouse gases and physicochemical parameters.The dissolved concentrations of the three greenhouse gases in Miyun reservoir,its tributaries and surrounding groundwaters were all higher than their respective equilibrium concentrations (i.e.,supersaturated).The average N_2O,CO₂ and CH₄ emission fluxes of Miyun reservoir were,respectively,(0.008 833±0.001 560) mmol/(m²·d),(283.08±32.86) mmol/(m²·d),(0.026 76±0.004 353) mmol/(m²·d) during the dry season,and (0.005 130±0.002 369) mmol/(m²·d),(91.45±19.19) mmol/(m²·d) and (0.025 85±0.009 330) mmol/(m²·d) in the wet season.There were no significant differences in the emission fluxes of N_2O and CO₂ at different locations in Miyun reservoir during the same period,but significant seasonal variations were observed.In contrast,the seasonal variation in CH₄ emission fluxes was not significant.During the dry season,N_2O emission fluxes were high in Chaohe River and Baimaguan River,with an average value of (28.96±1.59) nmol/L,while the CO₂ and CH₄ emission fluxes were high in Qingshui River,with values of 515.49 mmol/(m²·d)and 0.209 9 mmol/(m²·d),respectively.However,there was little difference in the emission fluxes of the three greenhouse gases among rivers in the wet season,and their values were lower than in the dry season.In groundwater,the concentrations of dissolved N_2O and CO₂ in dry season were higher than in wet season,with mean values of (71.20±48.68) nmol/L and (806.27±282.08)μmol/L,respectively,but no significant difference in CH₄ concentration.Nutrient and water environmental indicators such as TN,NO₃-N,TOC,temperature,DO and electrical conductivity (EC) in Miyun reservoir and its surrounding water bodies,along with biological processes such as respiration,mineralization,and nitrification-denitrification contributed to increasing greenhouse gas concentration in water,thereby promoting emission fluxes of greenhouse gases from the reservoirs and rivers.During the two periods,the tributaries and groundwater exhibited similar trends in greenhouse gas concentrations and emission fluxes as those observed in Miyun reservoir,indicating a close hydraulic connection between the reservoir and surrounding waters.This study will provide scientific support for regulating greenhouse gas emissions from reservoirs and reducing nutrient loads in tributaries and groundwater.

Diurnal Variation of ■ in Autumn and Winter at Lingjiao Lake Based on NDIR CO₂ Sensor Measurements

Lingjiao Lake in Wuhan City, a typical urban lake, was selected for study and we investigated diurnal variation of the partial pressure of carbon dioxide( ■ : disselved CO₂ concentration) in the lake and its relationship with environmental variables. Our aim was to provide a deeper understanding of carbon dioxide exchange at the urban lake/air interface and support the formulation of emission reduction measures. In October 2023(autumn) and January 2024(winter), ■ was monitored continuously from 8:00 until 18:00 at three sampling sites using a non-dispersive infrared(NDIR) sensor according to the following schedule: Site 1(S1), October 21 and January 5; Site 2(S2), October 28 and January 3; Site 3(S3), October 29 and January 4. The water environmental parameters influencing ■ were determined hourly during the time that ■ was being monitored. Results show that the mean values of ■ in Lingjiao Lake varied with season and the average ■ in autumn [(19.72±24.18) μ mol/L] was double that in winter [(9.51±6.31) μ mol/L]. The ■ had a significant negative correlation with DO and pH, and a significant positive correlation with nutrients, including phosphate(PO₄^3--P), nitrite nitrogen(NO₂~--N),and nitrate nitrogen(NO₃~--N). Generally, the ■ from 10:00 to 12:30 accurately reflected daytime CO₂ content in Lingjiao Lake. However, the optimal sampling time changed with nutrient content. The significant differences between seasons and in diurnal patterns of ■ in Lingjiao Lake were primarily driven by nutrients, DO, and pH. Except for S3 in autumn, the daily average value of ■ at other sites can be replaced by values measured from 10: 00 to 12: 30. The optimal time for measuring ■ in Lingjiao Lake varied slightly, depending on water body characteristics and degree of eutrophication.

Research Progress on the Toxicological Effects of Four Typical Environmental Estrogens on Fish

Environmental estrogens， as a class of emerging contaminants， are widely detected in aquatic environments. They can disrupt the endocrine function of fish at extremely low concentrations (e.g.， 0.05 ng/L). To clarify the differential toxicity and mechanisms of action of these four estrogens in fish， this review synthesizes their effects on fish behavior， growth and development， immunotoxicity， and underlying molecular mechanisms. The key findings are as follows:(1) Behavioral effects: Environmental estrogens interfere with the neuroendocrine system and neurotransmitter balance， leading to reduced swimming performance， diminished aggression， and increased anxiety-like behaviors.(2) Growth and developmental effects: Environmental estrogens increase embryo mortality， induce developmental deformities in larvae (e.g.， craniofacial abnormalities， spinal curvature)， inhibit growth， and significantly disrupt sex differentiation and reproductive function. Moreover， this impairment of reproductive function demonstrates transgenerational inheritance characteristics.(3) Immunotoxicity: Environmental estrogens damage core immune organs， suppress the normal function of immune cells， and mediate sexually dimorphic immune responses. (4) Molecular mechanisms: The toxic effects are primarily mediated by estrogen receptors. Specifically， E2 and EE2 effectively bind to both nuclear receptors (ER) and membrane receptors (GPER)， activating both genomic and non-genomic pathways. Critically， current PNEC values may underestimate the sublethal effects of environmental estrogens on fish. This study provides crucial molecular insights for the ecological risk assessment of environmental estrogens and points to the imperative for future research to address the combined pollution effects of environmental estrogens and other contaminants on fish and to develop efficient and cost-effective estrogen degradation technologies.

Influence of Daily Stratification-Mixing Dynamics on the Vertical Distribution of Phytoplankton in Xiangxi Bay

Elucidating the mechanisms by which diurnal stratification–mixing processes influence the vertical distribution of phytoplankton in deep-water reservoirs， and thereby coupling algal vertical dynamics with the water-column stratification–mixing regime， can enhance our understanding of the initiation and termination of algal blooms in lakes and reservoirs. This study conducted a continuous 48-hour， multi-parameter synchronous observation in the Xiangxi Bay， a typical tributary of the Three Gorges Reservoir， during a summer algal bloom period. The results indicate that: 1) The physical structure of the water body exhibited a regular diel alternation. Strong daytime surface stratification inhibited vertical mixing (active mixing layer <0.5 m)， while nocturnal wind stirring and cooling convection jointly deepened the mixed layer to approximately 4 m. 2) The phytoplankton community was overwhelmingly dominated by Microcystis (86.70%). Its biomass (indicated by Chl-a) and vertical distribution showed a significant "downward during the day and upward at night" rhythm. Algae sank and were distributed more uniformly during the day (mean aggregation depth ～6 m)， whereas they migrated upward and formed dense surface aggregations at night. The mean cell density at night was (39.27±7.86)×10⁶ cells/L， which was significantly higher than the daytime mean of (27.95±5.27)×10⁶ cells/L (P<0.05). 3) This phenomenon is attributable to the coupling of active physiological regulation of phytoplankton with external physical forcing. During the day， stable stratification facilitated active sinking; the close temporal coincidence between the evening increase in wind speed and the onset of upward migration indicates that wind?induced turbulence was the dominant physical driver. Over the observed wind?speed range (up to 7.5?m?s?1)， wind?generated waves mainly enhanced surface aggregation of algae. At night， reduced stratification and intensified mixing jointly shaped the eventual pattern of upward accumulation. Meanwhile， the concurrent diel variations in dissolved oxygen (DO)， pH， and nutrients (DTN and DTP) imply that algal migration also represents an integrated response to the spatiotemporal heterogeneity of light and nutrient availability.

The influence of cascade development of the Jinsha River on the nitrogen and phosphorus ecological thresholds of phytoplankton

Cascade reservoir construction significantly alters river hydrological regimes and nutrient transport processes. However， the quantitative responses of phytoplankton communities to nitrogen (N) and phosphorus (P) under such development remain poorly understood. To investigate the impact mechanisms， this study conducted six field sampling campaigns from 2021 to 2023 in the upper reaches of the Yangtze River mainstem， from Zhimenda to Zhutuo. Using Threshold Indicator Taxa Analysis (TITAN)， the response thresholds of phytoplankton communities to total nitrogen (TN) and total phosphorus (TP) were compared， and indicator taxa were identified across three distinct river sections: an upper natural reach， a middle cascade reservoir reach， and a lower flowing reach. The results showed significant differences in community structure among the sections， with TN and TP identified as key driving factors. The upper natural reach exhibited the lowest TN (0.659–0.737 mg/L) and TP (0.011–0.017 mg/L) ecological thresholds， with indicator taxa dominated by clean-water diatoms (e.g.， Ceratoneis， Diatoma)， indicating high sensitivity to nutrient inputs. The middle cascade reservoir reach displayed the narrowest threshold ranges (TN: 0.702–0.709 mg/L; TP: 0.018–0.019 mg/L)， suggesting a highly concentrated community response. Indicator taxa here were differentiated， including positive responders like Coelastrum and negative responders like Asterionella， indicating a critical transitional state of the community. The lower flowing reach showed a divergence in nitrogen thresholds (negative: 1.165 mg/L; positive: 1.385 mg/L) with phosphorus thresholds similar to the middle reach (TP: 0.019–0.020 mg/L). Eutrophic taxa such as Pseudanabaena and Cryptomonas erosa emerged as positive indicators. Mechanistic analysis suggests that cascade development restructures habitat heterogeneity by altering hydrodynamics (slowed flow velocity， increased water residence time) and nutrient cycling (retention effects， internal nutrient loading). This not only screens for different species compositions but also drives shifts in species adaptive strategies， as evidenced by the reversed response direction of certain taxa like Nitzschia across reaches. This study provides a quantitative basis and mechanistic insights for nutrient management and ecological risk assessment in rivers under cascade development.

Research on the Evolution and Driving Mechanisms of Water Ecosystem Service Value in Typical Cities of the Henan Section of the Yellow River Basin

this study focuses on ten typical cities in the Henan section of the Yellow River basin. Oriented to the characteristics of "river–reservoir–wetland" aquatic ecosystems， a "provisioning–regulating–cultural" water ecosystem service value (WESV) accounting framework was constructed to reveal the spatiotemporal evolution characteristics and driving mechanisms of WESV from 2001 to 2023. Furthermore， using urbanization rate and energy consumption as common variables， and incorporating agricultural land productivity， forest area， or wastewater discharge as type-specific key variables according to city functional types， a VAR model was constructed. Granger causality tests， impulse response analysis， and variance decomposition were comprehensively applied to quantify the dynamic effects of different factors on WESV. The results show that WESV exhibited a two-phase evolution pattern of "sustained growth–high-level fluctuation" during the study period， with an average annual growth rate of approximately 3.58% from 2001 to 2015， followed by a high-level fluctuating plateau after 2016. Spatially， a relatively stable pattern of higher values in the east and lower values in the west was observed. By 2023， the total WESV of six high-value cities (Luoyang， Kaifeng， Xinxiang， Anyang， Zhengzhou， and Sanmenxia) accounted for 81.8% of the study area， with Luoyang having the highest value at 78.922 billion CNY. Regarding driving mechanisms， significant differences exist among cities with different functional types: among agriculture-dominated cities， agricultural land productivity contributed relatively highly in Zhengzhou (26.24%)；resource-constrained cities were mainly affected by urbanization rate (24.49%) and wastewater discharge (13.10%)；ecologically friendly cities exhibited pronounced internal heterogeneity， with Jiaozuo showing weak external driving forces， while Jiyuan was notably affected by energy consumption and urbanization. Meanwhile， WESV in all cities displayed strong historical inertia， with self-contribution rates exceeding 55%. The findings can provide a scientific basis for aquatic ecological protection， zoning and classification governance， and differentiated ecological management in the Henan section of the Yellow River basin.

Distribution of Arsenic in Subcellular Fractions of Acorus calamus L.

The subcellular distribution of heavy metals is an important aspect of metal tolerance in plants. In this study, Acorus calamus L. an emergent macrophyte, was selected for hydroponic testing and we investigated the effects of different concentrations(0, 200, 500 and 1000 μg/L) of arsenate [As(Ⅴ)]and arsenite [As(Ⅲ)] on the arsenic contents of subcellular fractions of roots, stems and leaves of A. calamus. The mechanism of arsenic tolerance was explored based on its subcellular distribution. We aimed to provide a theoretical foundation for phytoremediation of arsenic-contaminated water bodies using emergent macrophytes. The arsenic content in each subcellular fraction of root was significantly higher than that in stems or leaves under all concentrations of As(Ⅴ) and As(Ⅲ). At the same concentration, arsenic content in the water-soluble fraction(including vacuoles) of root cells was significantly higher than in the other three subcellular fractions, peaking at 25.03 mg/kg in the As(Ⅴ) treatment and 13.28 mg/kg for the As(Ⅲ) treatment. Under the highest concentration of As(Ⅴ) or As(Ⅲ), the distribution of arsenic in each subcellular fraction of stems and leaves was different from that in roots, with the highest arsenic content in the mitochondrial fraction [(3.52 mg/kg for As(Ⅴ) and 1.61 mg/kg for As(Ⅲ)], followed by water-soluble fraction. In the roots of A. calamus, the subcellular content of As(Ⅴ) was in the order of water-soluble > mitochondria > cell walls > nuclei/chloroplasts, while the subcellular distribution of As(Ⅲ) showed a trend of water-soluble > cell walls > mitochondrial > nuclei/chloroplasts. The proportions of As(Ⅴ) and As(Ⅲ) in the water-soluble fraction were 37.7%-40.5% and 31.0%-52.9%, respectively. As(Ⅴ) and As(Ⅲ) in the subcellular fractions of stems and leaves were predominantly concentrated in the water-soluble and mitochondrial fractions. Our results indicate that the soluble fraction of root cells is the primary location of As(Ⅴ) and As(Ⅲ) accumulation in A. calamus, and that the root, stem and leaf cells reduce the toxicity of inorganic arsenic primarily through vascular sequestration.

Progress of River Restoration Research at Home and Abroad

Research Progress of River Restoration Research at Home and Abroad

Plant Function and Selection for Constructed Wetlands

Fish Swimming Performance Related to Fishway Design

With the habitat destruction and fishery resources dwindling,fishway and other facilities have become important measures to mitigate the disadvantages of water conservancy construction.While early worldwide fishway construction mostly became decorations without consideration of fish.The re-rise of fishway construction in China need more reliable biological informations.The fish swimming performance is related to fishway design and determines its success or failure.Aiming at the fishway design,paper reviewed the decades of research achievements of fish swimming performance at home and abroad.Fish swimming performance has been classified into three distinct categories:sustained speed,prolonged speed and burst speed,among which the latter two are closely related to fishway design.Fish swimming speeds are affected by biological and physical constraints,including tail beat,length,time to exhaustion,temperature and oxygen consumption etc.Finally,the article describes the application of fish swimming performance in fishway design.Fish swimming performance research has been seldom reported in China,so that summary of research method and experience abroad can provide biological basis for our fish facilities construction and promote its development.

A Summary of Hydrology and Hydrodynamics Conditions of Four Chinese Carps' Spawning

Four Chinese Carps(FCC)are very important economy fishes in China,and the Yangtze River is their nature germplasm library.The scale of FCC's natural reproduction is of great significance to the protection of their resources.The spawning of FCC has closely relations with the hydrology and hydrodynamics conditions in rivers.In this paper,a comprehensive represent of the relations between the FCC's spawning and the water temperature and swelling is given,and a brief description of the distribution of FCC's spawning grounds and their hydrodynamics characters is also given.This work can provide some technical support for reservoir operation to the FC's spawning and also for the restoration of FCC's spawning grounds,which is very important to the protections of FCC's germplasm resources and aquatic ecosystems。

Progress of River Restoration Research at Home and Abroad

Research Progress of River Restoration Research at Home and Abroad

Plant Function and Selection for Constructed Wetlands

Research Progress on Ecological Restoration Technology Based on River Ecosystem Health

With the large-scale exploitation of river, river ecosystem is suffering serious damage. So river ecological restoration has become a big concern for public and the work has made considerable progress in recent years. In this paper, at first we analyzed the characteristics of river ecological system and the stresses it is facing at present, introduced the concept of river health and its evaluation methods, and reviewed the related research development of river ecological restoration home and abroad. Then, the technologies and typical practice cases of river ecological restoration were summed up in relation to water flow, connectivity, water quality and aquatic organisms. Finally, we put forward three suggestions on the further research of river ecological restoration: combining different restoration technologies; decision making from the aspect of river basin; monitoring and effect evaluation after ecological restoration. The study will provide reference and guidance for the restoration practice in future.