Journal of Hydroecology

Research Progress on Geochemical Cycling of Organic Phosphorus and Its Ecological Effects on the River-Lake Continuum

At present, systematic research on the geochemical characteristics of phosphorus, especially organic phosphorus(OP), in the river-lake continuum is insufficient. In response, we systematically reviewed the phosphorus geochemical cycle and its ecological effects on the river-lake continuum and riverlake interface through bibliometrics analysis. Our focus was the impacts of hydrodynamic, hydrochemical(water temperature, pH, organic matter, ion composition), and biochemical factors on organic phosphorus cycling along the river-lake continuum, including potential ecological and environmental effects. We aimed to provide a robust theoretical framework for advancing our understanding of phosphorus chemodynamics in watersheds, and for supporting more precise and effective control of external phosphorus loading. Based on data collection and comparative analysis, it is evident that significant differences exist in the specific chemical speciation and concentrations of organic phosphorus between inflow rivers and lake water bodies within the same watershed, especially in transitional zones and interfaces. Under natural conditions, particulate phosphorus(PP) can account for up to 80% of total phosphorus(TP) in rivers, where dissolved phosphorus(DP) is predominantly present as dissolved inorganic phosphorus(DIP), along with substantial amounts of degraded low-molecular-weight(1-10 kDa) colloidal organic phosphorus(COP).In contrast, in some lakes, dissolved phosphorus can constitute up to 70% of total phosphorus, with dissolved organic phosphorus(DOP) being the dominant form, and colloidal organic phosphorus primarily existing as high-molecular-weight(10 k Da-0.7 µm) fractions. Dramatic changes in hydrological, hydrodynamic, hydrochemical, and biochemical factors in river-lake continuum profoundly affect the structure and components of organic phosphorus and its geochemical cycling in the basin. We recommend that future research strengthen the investigation of phosphorus geochemical cycling processes and input loading in key areas of the river-lake continuum, such as river-lake interfaces and estuaries, along with studies on self-purification capacity, influencing factors, and key parameters for simulating and accounting in the river-lake continuum. This will provide geochemical theory to support regional sediment phosphorus pollution risk assessment, estuarine ecological restoration and dredging, and the formulation of phosphorus management targets at river-lake junctions.

Nutritional Status of Chinese Lakes and Influencing Factors

Lake eutrophication is a key environmental issue that threatens the security of aquatic ecosystems and limits the sustainable development of river basins. In this study, we systematically assessed the eutrophication status of lakes of China and analyzed the primary controlling factors. A total of 45 typical lakes across the country were selected for research. Water quality data was collected at 7 monitoring sites on each lake during the wet season of 2024. We comprehensively evaluated the nutrient status of the lakes, analyzed the influence of physical and geographical factors such as topography and water depth on eutrophication, and explored the distributions of nitrogen and phosphorus concentrations and their relationships with eutrophication status. Approximately 39.2% of the lakes exhibited some degree of eutrophication, most of which were co-limited by nitrogen and phosphorus. Lakes in the Yunnan-Guizhou Plateau and the Eastern Plain regions were more eutrophic, while the eutrophication degree of lakes in the Inner Neimenggu-Xinjiang Plateau showed significant regional differences, reflecting the synergistic effects of natural landform and the intensity of human activity. In terms of spatial scale, shallow lakes were generally more prone to eutrophication than deep lakes. Further analysis revealed that eutrophication of shallow lakes was more pronounced in high-altitude areas, likely related decreased water mixing, lower biodegradation rate, and enhanced nutrient retention. The nutrient level of lakes in areas with high farmland coverage was significantly higher than in forested areas, reflecting the important effect of land use on nutrient inputs. Statistical analysis shows that the total phosphorus concentration in lakes was positively correlated with chlorophyll-a content, while the nitrogen-phosphorus ratio had a nonlinear negative correlation with chlorophyll-a concentration, indicating a higher risk of nitrogen-phosphorus imbalance during algal blooms. In conclusion, the management of lake eutrophication requires differentiated, site-specific strategies with strengthened synergistic control of nitrogen and phosphorus. To alleviate lake eutrophication in China, priority should be given to preventing and controlling eutrophication in shallow plateau lakes and lakes located in intensive agricultural regions.

Annual Variation and Driving Factors of Total Nitrogen and Total Phosphorus Concentrations in Gehu Lake, 1985-2021

Excessive nitrogen and phosphorus inputs are driving eutrophication and accelerated functional decline in lakes. In this study, we systematically analyzed the interannual variations of total nitrogen(TN) and total phosphorus(TP) in Gehu Lake based on the long-term observation data from 1985 to 2021,and interpreted the underlying causes from the perspectives of exogenous inputs(inflow rivers and netpen aquaculture), endogenous sources(degradation of macrophyte and algal growth), and ecological degradation. We aimed to provide fundamental support and a scientific basis for nutrient control and water environment management of Gehu Lake. The annual average concentrations of TN and TP in Gehu Lake were 0.67-4.22 mg/L and 0.015-0.193 mg/L during 1985-2021, respectively, and the interannual concentrations initial increased(1985-2005) and then decreased(2006-2021). Exogenous and endogenous pollution inputs and aquatic ecological degradation were the main causes for the elevation of nitrogen and phosphorus concentrations in Gehu Lake. From 1985 to 2005, the increase in exogenous input from inflow rivers, the expansion of pen net aquaculture in the lake, and the degradation of macrophytes were synchronous with the continuous rise in TN and TP concentrations in the lake. After 2006, the reduction of input from inflow rivers and the removal of enclosure net aquaculture were the main drivers for the declining TN and TP concentrations. In 2021, the average concentrations of TN and TP in Gehu Lake were equivalent to the levels in 1996 and the early 21 st century, respectively. Significant progress had been made in the treatment of nitrogen and phosphorus pollution in Gehu Lake, but water quality targets and ecological improvement requirements have not yet been met. Continuing efforts are needed in scientifically setting water quality targets for inflow rivers, controlling sediment pollution, and restoring macrophyte vegetation. These measures are essential for promoting sustained decreases in nitrogen and phosphorus concentrations and improving ecology in Gehu Lake.

Migration of Nitrogen and Phosphorus in Ice-Water and Eutrophication Assessment in Ulansuhai Lake(2016-2024)

Ulansuhai Lake was selected for research and we explored the migration of nitrogen and phosphorus in ice and water, and lake eutrophication, during the ice-on periods from 2016 to 2024. Our objectives were to clarify nutrient redistribution caused by lake surface water freezing and the spatiotemporal distribution of nitrogen and phosphorus in the ice and water of Ulansuhai Lake to provide a reference for managing and protecting the aquatic environment. Ice and water monitoring data at 12 sampling sites was collected in January during the ice-on periods from 2016 to 2024. The data was analyzed to obtain ice-water partitioning of nutrients, nutrient spatiotemporal distribution, nitrogen and phosphorus species composition, and the degree of lake eutrophication. Ice-water partition coefficients and the trophic level index(TLI) were calculated, and significant differences were identified using Pearson correlation analysis. Results show that the degree of nutrient exclusion during ice formation varied by nutrient type. The ice-water distribution coefficient of total phosphorus(TP) was 1-2 times larger than for total nitrogen(TN). The ice-water partition coefficients of TN and TP gradually increased from north to south, primarily influenced by under-ice water flow velocity. From 2016 to 2024, the average TN concentration trended upward in the ice and downward in the water, while the average TP concentration increased in the middle layer of ice and decreased in the other ice layers and water, primarily associated with aquatic plant biomass. Different forms of nitrogen exhibited a vertical distribution pattern of high-low-high from ice surface to bottom,whereas stratification of TP and dissolved total phosphorus(DTP) varied with habitat. The positive correlation between algal growth and TP concentration was significant(R=0.24, P=0.02). During the study period, eutrophication in Ulansuhai Lake improved from severe to mild because of freshwater replenishment and ecological restoration in the watershed. This study provides data support and a scientific basis for controlling pollution during the ice-on period and preventing algal blooms in Ulansuhai Lake.

Causal Analysis,and Prevention and control Measures of Cyanobacterial Blooms in Langhe River Bay of Danjiangkou Reservoir

Langhe River is a first-class tributary of Hanjiang River and an important water source for Danjiangkou reservoir. The river's water quality thus has a direct influence on the water quality of the reservoir and the stable operation of the South-to-North Water Diversion Project. Cyanobacterial blooms have occurred frequently in the lower Langhe River in recent years, seriously threatening water resource security. In this study, we analyzed the spatiotemporal patterns of nutrients, mechanisms driving eutrophication, and factors associated with algal blooms(causal analysis) in Langhe River bay of Danjiangkou reservoir. Our objective was to support ongoing efforts to control algal blooms in the reservoir. The study section of lower Langhe River stretched 16.8 km from Langhe bridge to the reservoir. During the high-incidence period of algal blooms in 2021(August-September), water quality and algal monitoring were carried out at 6 sites(X1-X6) in the study section on 14 occasions(7 times each during August and September). The data was then analyzed using a suite of methods including the single-factor pollution index, trophic state index and redundancy analysis. The primary formation mechanism of cyanobacterial blooms was elucidated and, finally, prevention and control measures were proposed. Overall water quality in the Langhe River study section was classified as mildly polluted. The single-factor pollution index showed significant spatial differences in pollution degree among sampling sites, with severe pollution observed at Langhe Middle School(X1) and Bowan bridge(X2), where total nitrogen, total phosphorus, and the permanganate index were the primary pollutants. The X2 site was characterized by “high temperature, high pH, high DO, high nutrients, and low transparency”, with a peak cyanobacterial density of 1.2×10⁸ cells/L and the comprehensive trophic state index indicating mild eutrophication. Redundancy analysis revealed that pH had the highest independent explanatory power for cyanobacteria distribution(69.6%), followed by COD_Mnand total nitrogen. Cyanobacterial blooms resulted from the synergistic effects of exogenous nutrient input and low flow conditions in the Langhe River backwaters [flow velocity of 0.05 m/s and HRT(hydraulic residence time) of approximately 18 hours]. The persistent “high pH-high DO” conditions during the day indicate high algal productivity because photosynthesis produces oxygen and consumes carbon dioxide(CO₂, a weak acid in water). Based on our causative analysis, an integrated “sourcetransport-converge” management strategy was proposed, including upgrading wastewater treatment plants, constructing a low weir system to enhance water flow, releasing filter-feeding fish, and establishing an online monitoring and early warning system. The findings of this study provide references to prevent eutrophication by better managing inflow rivers in the water source area of the Middle Route of the South-to-North Water Diversion Project.

Ecological health assessment of the Anning River based on fish index of biotic integrity

Serving as the largest tributary in the lower Yalong River basin， Anning River exhibits typical mountain river characteristics and holds significant ecological importance. Assessing the aquatic ecological health of the Anning River Basin provides essential scientific evidence for formulating fisheries management and conservation strategies. In this study， comprehensive fish assemblage surveys were conducted at 28 sites across the mainstem and tributaries of the Anning River basin in November 2020 and April 2021. A total of 60 fish species were identified， representing 39 genera， 13 families， and 5 orders. Using upstream tributary sites 19#， 20#， and 21# as reference sites， 24 preliminary candidate metrics across five categories were subjected to range testing， discriminatory power analysis， and redundancy evaluation. Based on this screening process， a fish-based Index of Biotic Integrity (F-IBI) system for the Anning River was established， comprising nine core metrics from five ecological categories: total number of species， Shannon–Wiener diversity index， proportion of Cyprinid species， number of non-native species， number of tolerant species， proportion of demersal-spawning species， proportion of carnivorous species， number of mid-upper water column species， and number of benthic species. Assessment results showed that the mainstem of the Anning River exhibited a “fair” level of ecological health， whereas the tributaries were rated as “good”， indicating better ecological conditions in tributary systems. The midstream section exhibited better ecological health than the upstream and downstream. The core metrics of the F-IBI were significantly associated with multiple environmental factors. Among these， conductivity exhibited the highest independent explanatory power (14.49%)， followed by urban area (12.06%) and meadow area (10.74%)， whereas river width contributed the least (4.78%). These results offer a scientific basis for the ecological assessment and zoned management of the Anning River and other mountain rivers.

Effects of Landscape Patterns on the Spatial Differentiation of Riverine Nitrogen and Phosphorus in China and the Modulating Role of Hydrological Periods

The effects of landscape patterns on the spatial differentiation of riverine nitrogen and phosphorus are a key prerequisite for basin-scale water environment management; however， most existing studies rely on a single statistical method and rarely compare landscape-level and class-level effects within a unified framework. In this study， 110 fourth-order sub-basins in China were used as basic units. Based on total nitrogen (TN) and total phosphorus (TP) monitoring data from 2021 and 30 m resolution land-use data， global and local Moran's I tests were applied to examine spatial autocorrelation during the wet and dry seasons. Correlation analysis， redundancy analysis (RDA)， elastic net penalized regression， bioenv analysis， and variation partitioning were integrated to identify key landscape factors and the contributions of “source–sink” landscapes at both the landscape and class levels. The results showed that TN and TP concentrations exhibited significant positive spatial autocorrelation in both hydrological periods. Landscape fragmentation and edge-effect indices (PD， ED， LSI) were positively associated with nutrient concentrations， whereas aggregation and connectivity indices (PLADJ， CONTAG， LPI) showed overall negative associations. Edge density (ED) consistently exhibited positive coefficients and high model-entry frequency across all four penalized regression models， making it the key landscape factor stable across hydrological periods. Source and sink landscapes showed significant coupling effects on spatial water quality differentiation， with the total explanatory rate being higher in the wet season (65.57%) than in the dry season (61.54%). This study demonstrates that edge expansion and landscape fragmentation are the key pattern characteristics driving elevated riverine nitrogen and phosphorus levels， and that the influence of source–sink landscape patterns on water quality is modulated by hydrological periods， providing quantitative indicators for the zoned and classified management of non-point source pollution and landscape pattern optimization across basins. Landscape patterns influence the spatial differentiation of riverine total nitrogen (TN) and total phosphorus (TP) by regulating pollutant generation， hillslope runoff， river-network connectivity， and nutrient retention and transformation. To address the limited understanding of multidimensional landscape metrics， multi-method validation， and source–sink contribution partitioning at the national sub-watershed scale， this study selected 110 HydroSHEDS Level-4 sub-watersheds in China as analytical units. River water-quality monitoring data from 2021 and 30 m land-use data were integrated， and dry and wet seasons were defined using the 25th and 75th percentiles of monthly precipitation in each sub-watershed. Spatial autocorrelation analysis， directional correlation analysis， redundancy analysis (RDA)， Elastic Net regression， bioenv analysis， and variation partitioning were used to quantify the effects of landscape patterns on the spatial differentiation of TN and TP and their hydrological-period differences. The results showed that TN and TP exhibited significant positive spatial autocorrelation in both seasons， indicating clear regional clustering. Fragmentation and edge-effect metrics， including patch density (PD)， edge density (ED)， and landscape shape index (LSI)， were generally positively associated with TN and TP， whereas aggregation and connectivity metrics， including percentage of like adjacencies (PLADJ)， contagion index (CONTAG)， and patch cohesion index (COHESION)， were generally negatively associated with nutrient concentrations. These results suggest that landscape fragmentation and edge complexity may increase nutrient export risk， while continuous sink landscapes can help reduce pollutant delivery to rivers. Landscape-level RDA explained 38.92% and 37.17% of nutrient variation in the dry and wet seasons， respectively. At the class level， cropland had a higher explanatory rate in the dry season (37.8%)， whereas built-up land showed a stronger role in the wet season (36.9%). The optimal bioenv indicator shifted from PD in the dry season (r = 0.299) to ED in the wet season (r = 0.308)， indicating the enhanced role of edge structure in characterizing nutrient spatial differences during the wet season. Variation partitioning showed that source–sink landscapes explained more variation in the wet season (65.6%) than in the dry season (61.5%)， and their shared contribution exceeded the independent contribution of either landscape group. These findings indicate that riverine nitrogen and phosphorus differentiation is characterized by hydrological-period dependence and source–sink coupling， providing support for identifying high-risk sub-watersheds， optimizing source–sink landscape patterns， and implementing season-specific nutrient management.

Analysis of Seasonal Variations in Phytoplankton Co-occurrence Network Characteristics and Influencing Factors in Rivers and Reservoirs

This study focuses on representative rivers (Binan River， Beibei River， Meijiang River)， lakes (Xiuhu Lake， Qinglonghu Lake)， and reservoirs (Jintang Reservoir， Tongxin Reservoir， Yanjinghe Reservoir) in the upper reaches of the Three Gorges Reservoir area， located in Bishan District， Chongqing. Through seasonal monitoring of water physicochemical parameters and phytoplankton community surveys conducted in 2024， combined with diversity analysis， co-occurrence network construction， Mantel tests， and redundancy analysis， we systematically investigate the differences in phytoplankton community structures across different water body types and their driving mechanisms. Key findings include:(1) A total of 210 phytoplankton species (84 genera， 8 phyla) were identified， dominated by Cyanobacteria， Chlorophyta， and Bacillariophyta. Species richness peaked in summer (134 species). Lake-reservoirs exhibited cyanobacteria-dominant assemblages， with the invasive species Raphidiopsis raciborskii exceeding bloom thresholds (>10⁷ cells/L) in summer.(2) Riverine phytoplankton showed significantly higher α-diversity (Shannon index) than lake-reservoirs in spring and summer (p<0.05). β-Diversity analysis indicated greater community heterogeneity in lake-reservoirs， significantly exceeding rivers in summer and autumn.(3) Co-occurrence networks revealed higher complexity (node/link numbers) in rivers than lake-reservoirs except winter. Conversely， lake-reservoirs demonstrated superior network stability， evidenced by higher average weighted degree， graph density， and robustness.(4) Environmental driving mechanisms exhibited significant variations: Phytoplankton communities in lakes and reservoirs were strongly influenced by environmental factors during summer and autumn (Mantel R = 0.624-0.515)， whereas the influence of environmental factors on riverine communities was weaker in winter (R = 0.461). This study reveals significant divergence in diversity， network stability， and environmental responses between phytoplankton communities in lotic (river) and lentic (lake/reservoir) ecosystems. These findings provide a theoretical basis for aquatic ecological monitoring and conservation efforts in the Three Gorges Reservoir area.

Changes and Evolution of the Waterway Ecosystem Following Regulation Engineering

Inland waterway projects， while fulfilling shipping functions， also exert persistent impacts on river ecosystems. Scientifically assessing the ecological effects of such engineering constructions and revealing the system recovery process are crucial for achieving sustainable shipping development. Taking the Sulian Waterway Regulation Project as an example， this study integrated the Ecopath model with Principal Component Analysis (PCA) to construct a "state-function" dual-dimension analytical framework. It systematically compared four sequential temporal nodes—pre-construction， construction， early recovery， and early recovery phase—to quantitatively analyze the dynamic response processes of ecosystem structure and function. The results showed that: (1) PCA clearly revealed the temporal trajectory of the ecosystem's external state， transitioning from a baseline stable state， through a strongly disturbed state and a recovery response state， to a structural adjustment state; (2) The Ecopath model identified that the system's functional core (key functional groups) exhibited dynamic succession and structural resilience， with culter species remaining keystone throughout all stages， and other benthic macroinvertebrates becoming key functional groups during and after the disturbance; (3) State evolution directed the direction of functional reorganization; however， the functional network demonstrated resistance characterized by "state-function decoupling" during the construction period， and exhibited "functional recovery preceding state recovery" as a leading feature during the recovery phase. The revealed asynchronous response mechanism of "state-driven change， functional resistance， and functional precedence" provides a theoretical basis and practical reference for system state diagnosis， key species protection， and adaptive management in the ecological restoration of waterway ecosystems.

Interspecific Differentiation and Identification of Two Pampus Species in Zhoushan Coastal Waters Based on Geometric Morphometrics and DNA Barcode

To establish a species identification system for Pampus argenteus and P. punctatissimus and to clarify their interspecific genetic differences， specimens of two Pampus species distributed in the coastal waters of Zhoushan， Zhejiang Province were employed as research materials. Key differential indices were detected based on truss-network morphometric parameters using one-way analysis of variance (one-way ANOVA) and principal component analysis (PCA). A classification model was established and discriminant functions were then derived via Fisher’s linear discriminant method. In addition， the mitochondrial COI gene sequences were determined and analyzed for base composition， genetic diversity parameters and interspecific genetic distances， and a phylogenetic tree was further constructed. The results revealed highly significant differences (P<0.01) in the anterior trunk region (X₁， X₂， X₄， X₅， X₆， X₇， X₉) and caudal region (X₁₄， X₁₇). Scatter plots of principal component analysis (PCA) also showed a clear distinguishability between the two Pampus species. The discriminant functions were constructed using 9 screened key variables， with a comprehensive accuracy of 95.8%， providing a reliable tool for rapid morphological identification. Analysis of the 660-bp mitochondrial COI gene sequences showed that the base composition exhibited a typical A+T bias in vertebrate mitochondrial DNA. Genetic diversity analysis indicated that P. argenteus had higher haplotype diversity， while P. punctatissimus possessed greater nucleotide diversity. The average interspecific genetic distance was calculated to be 0.124， which was much larger than the universal threshold for species delimitation and accompanied by a distinct barcode gap. Phylogenetic tree showed that the two Pampus species formed independent evolutionary clades. This study established morphological discriminant formulae and molecular identification standards for P. argenteus and P. punctatissimus in Zhoushan coastal waters by integrating morphological and molecular evidence. The results will provide a scientific basis for future resource monitoring， conservation management， and phylogenetic studies of these species.

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.