Journal of Hydroecology

Spatial Heterogeneity and Influencing Factors of Microplastics in the Freshwater Environment of China

In this study, we systematically reviewed the abundance, characteristics, and sources of microplastic pollution in the freshwater environment of China. The study was based on relevant literature using the keywords "China, " "microplastic, " "river, " "lake, " "reservoir, " and "estuary" in two major English search engines(Web of Science and ScienceDirect) and from the China National Knowledge Infrastructure(CNKI) database. A total of 191 articles met the screening criteria, encompassing four major freshwater environments: rivers, lakes, reservoirs and estuaries. Studies included both surface water and sediment and were primarily concentrated in the Yangtze, Pearl, and Yellow River basins. Results show that microplastic pollution is widespread in the freshwater environment of China and there is significant spatial heterogeneity in abundance. The maximum and minimum values of microplastic abundance in surface waters differed by 6 orders of magnitude and by 3 orders in sediments. Overall, the distribution was characterized by high levels in the eastern coastal areas and low levels in the central regions, and the microplastic content in rivers and estuaries was usually higher than that in lakes and reservoirs. The characteristics of microplastics in different river basins were relatively consistent: the primary polymer types were polypropylene(PP) and polyethylene(PE); the primary shapes were fibers and fragments; the colors were transparent, white, black and other; and there are certain differences by region. The presence of microplastics is closely related to human activities and surface water type, and there is significant seasonal variation.Further, inconsistencies in sample collection, experimental methods, and classification methods make it difficult to compare different assessments of microplastic pollution. In the future, it will be necessary to expand the scope of microplastic pollution surveys, strengthen long-term longitudinal monitoring, study the sources, movement and sinks of microplastics, enhance detection capabilities, and develop standardized methods for collecting and classifying microplastics.

Water Quality Benchmarks and Ecological Risk Assessment of Chlortetracycline in the Fresh Waters of China

Chlortetracycline(CTC) is an emergent pollutant in the surface freshwaters of China and assessing the pollution extent and the ecological risk is crucial for establishing water quality benchmarks for CTC. In this study, we investigated water quality benchmarks for CTC in China's aquatic ecosystems. To begin, the toxicity of CTC to dominant freshwater organisms was retrieved from the ecotoxicological database. Water quality benchmarks for CTC were then established using species sensitivity distributions(SSDs), toxicity percentile ranking, and benchmark requirements from the literature. On this basis, an ecological risk assessment was developed for selected freshwater regions in China. Results show:(1) SSDs best reflect the impact of CTC on surface water ecosystems. The derived short-term and long-term water quality benchmarks for CTC are 196.20 µg/L and 28.09 µg/L, respectively. We recommend adopting the longterm benchmark as the reference value for aquatic organisms in freshwater basins across China.(2) An ecological risk assessment of CTC pollution across six major freshwater basins, including the Yangtze River and Huaihe River, was conducted using the risk quotient(RQ) method, and the results revealed that CTC poses a minimal risk to aquatic life at most monitoring sites. However, CTC concentrations exceeding the safety threshold were identified in the Ziya River(Shijiazhuang), certain areas of the lower Yangtze River, and the Nanming River in Guiyang.(3) Overall, the ecological risk remains relatively low at the basin scale, but CTC concentrations in waters adjacent to aquaculture and livestock farm discharge outlets are expected to be significantly higher than the basin-wide average. Therefore, we recommend strengthening monitoring and risk assessment of surface waters in regions with concentrated animal husbandry and aquaculture.

Biotoxicity of Two Typical Microplastics and Microcystin on Adult Zebrafish

Microplastics(MPs) and cyanotoxins are prevalent toxic pollutants in freshwater fishery environments. It is important to understand the toxic response produced by their combined action in freshwater fisheries, and assess their potential threats and ecological risks. In this study, the microplastics polystyrene(PS) and polylactic acid(PLA) and the cyanotoxin microcystin-LR(MC-LR) were selected as representative toxic substances, and adult zebrafish(Danio rerio) were selected as the test organism. Single and combined exposures to PS, PLA, and MC-LR were carried out and the toxic responses selected included oxidative stress, energy metabolism, neurotransmitter capacity, gonadal cell apoptosis, and liver detoxification ability, based on 96 h acute toxicity tests and 50 d long-term exposure tests. The integrated biomarker response index(I_IBR) was used to comprehensively evaluate the toxic effects of the pollutant exposures on zebrafish, aiming to provide a scientific basis for understanding the biological impacts of combined pollution from MPs and MC-LR. With 96 h acute toxicity testing, single and combined exposures to PLA induced a more significant response than PS in terms of increased malondialdehyde(MDA) content,increased dehydrogenase(LDH) and acetylcholinesterase(AChE) enzyme activity, and decreased catalase(CAT) and superoxide dismutase(SOD) activities. However, with 50 d long-term toxicity testing, singular and combined PS exposure induced a larger increase than PLA in the activity of Caspase-3, a key enzyme in gonadal apoptosis in zebrafish. I_IBRanalysis suggests that zebrafish exhibit a higher sensitivity to PLA during acute exposure tests, but a higher sensitivity to PS during long-term exposure tests. Further, during both acute and long-term exposures, the inclusion of MC-LR consistently demonstrated synergistic toxic effects. To conclude:(1) Both the non-biodegradable PS and the biodegradable PLA produce a significant toxic response in fish.(2) When MC-LR co-exists with PS and PLA in freshwater systems, the toxic response of fish is more severe.

Effect of Suspended Particulate Matter on the Aging and Leaching of Plastics in Lakes

Microplastics are a relatively new pollutant, and their environmental behavior in the aquatic environment has become a research hotspot in recent years. After biodegradation, weathering processes(such as photooxidation and mechanical wear), will alter the surface morphology and physiochemical properties of microplastics discharged into water, accompanied by the release of substances leached from the plastic. Mechanical degradation is important to the aging and deterioration of plastics and plays a crucial role in the migration and transformation of plastics. In this study, we explored the effects of different concentrations of suspended particulate matter on the aging and leaching of plastics, aiming to provide a scientific basis for assessing the ecological risk and regulating plastic pollution. Cellophane(CP), the most abundant type of plastic in the water of Taihu Lake, was selected for research, and a 28-day aging experiment of CP was conducted with five suspended particulate matter treatments(0, 50, 100, 250, 500 mg/L). The conclusions are as follows:(1) CP was mechanically degraded layer by layer, with surface roughening, peeling and hole formation during the aging process. The high concentration of suspended particles(500 mg/L) significantly inhibited the photooxidative degradation of CP, resulting in obviously weaker aging characteristics compared with the low concentration groups.(2) The aging process altered the molecular structure of CP, decreasing the oxygen to carbon ratio.(3) The variation trends of DOC concentration in the CP leachate differed under the influence of varying concentrations of suspended particulate matter.(4) Tryptophan and tyrosine were released from CP during aging, and the CP fluorescence index decreased with time when exposed to sunlight.

Effects of Nanoscale Fluorescent Polystyrene Microsphere on the Stress Level and Immune Function of Bullfrog(Lithobates catesbeiana) Tadpoles

Microplastics are a potential risk factor in the decline of amphibian populations. However, it is still unclear whether the variations of morphological phenotypes induced by microplastics intakes are associated with consequential physiological cost. In this study, we explored the physiological mechanisms of bullfrogs(Lithobates catesbeiana) tadpoles responding to microplastic exposure, aiming to provide new experimental evidence for a deeper understanding of the relationship between nanoplastics and the health status of amphibians. Bullfrog tadpoles at Gosner stage 33 were exposed to 50 nm fluorescent polystyrene microsphere solutions(12.48 mg/mL) with a clean water group as control. Differences in tadpole body size, stress level, and immune function were measured on day 1, 4, 7 and 10. Results show:(1) The ratio of body weight to total body mass in the experimental group was significantly lower than that of the control group only on day 4(P<0.05).(2) The response of tadpoles to phytohemagglutinin(PHA-P)peaked at 3 h after injection in both control group and experimental group and the response did not vary with exposure duration, with no significant differences between the control group and experimental group(P>0.05).(3) Except for the percentage of basophils, the percentages of other subtypes of leukocytes and the ratio of neutrophils to lymphocytes(N/L) fluctuated with the duration of exposure in the control group, while except for the percentage of neutrophils and N/L, the percentages of other subtypes of leukocytes fluctuated with the exposure durations in the experimental group. Both the percentages of neutrophils and N/L on day 1 and 10, and the percentage of monocytes on day 1, 4, and 10 in the experimental group were significantly lower than those in the control group(P<0.05), while the percentage of lymphocytes on day 1 and 4, and percentages of basophils and eosinophils on day 10 were significantly higher than those in the control group(P<0.05). In conclusion, the exposure duration of fluorescent polystyrene microspheres can temporarily affect the growth of bullfrog tadpoles, with no inhibitory effect on the PHAP response, and the bullfrog tadpoles are able to stay healthy by regulating the percentage of leukocytes and N/L.

Study on the Influence of Island Structure Evolution on Hydraulic Characteristics of Island-type Fishway

River connectivity is a core characteristic of aquatic ecosystem health. The extensive construction of river-blocking structures has caused the disruption of longitudinal river connectivity， severely hindering habitat exchange and population reproduction of migratory fish. Fishway is a key engineering measure to restore fish connectivity in rivers. To optimize the hydraulic characteristics of island-type fishway and provide technical reference for river connectivity restoration， a new type of island-type fishway was taken as the research object. The combination of physical model test (with a geometric scale of 1:20 and following the gravity similarity criterion) and CFD numerical simulation was adopted to investigate the effects of island structure evolution (island shape and island spacing) on hydraulic characteristics such as flow velocity， turbulent kinetic energy and longitudinal water surface profile in the pool. The optimal structural parameters matching the hydraulic requirements of fish upstream migration were screened， and the accuracy of the numerical simulation model was verified with quantitative indicators such as RMSE， MRE and R. Meanwhile， the ecological adaptability between hydraulic characteristics and fish upstream migration was analyzed combined with the biological kinematic characteristics of juvenile grass carp， the target fish species for small hydropower station fishway engineering in southeast China. The results showed that the rectangular island type (NI model) had a better effect on controlling the flow velocity in the pool than the improved curved island types， and the island spacing D=3b could effectively inhibit the proportion of high-velocity zone (S4) at the front of the petal structure and reduce the flow velocity stress of fish upstream migration. The maximum turbulent kinetic energy in the pool was always below 0.01 m/s， meeting the requirements of low turbulent kinetic energy environment for fish migration. Although the curved island types enriched the distribution of turbulent kinetic energy， the overall intensity of turbulent kinetic energy was significantly higher than that of the rectangular island type (P<0.05)， which was easy to increase the swimming energy consumption of juvenile grass carp. The water levels on both sides of the pool of the island-type fishway showed stepwise alternating changes， and the water level at the center line rose gently. The NI model had a more significant water level lifting effect， with a smaller standard deviation of water level change (0.8 mm)， which was more in line with the hydraulic requirements of fish step-by-step upstream migration and could provide resting space. The structural optimization basis of the island-type fishway established based on the research results could effectively improve the hydraulic environment in the pool， making the hydraulic conditions of the pool closer to the upstream migration requirements of juvenile grass carp， and providing technical support for the engineering design and optimization of fishway in river connectivity restoration， as well as ecological reference for the protection of freshwater fish habitat and the stability of aquatic biological community structure.

Assessment of River Health in the Upper Reaches of the Xiangjiang River Based on the Benthic Index of Biotic Integrity

Rivers are an important component of ecosystems. In recent years， with the continuous deepening of industrialization， human activities have increasingly intensified disturbances to river ecosystems. To systematically assess the ecological health status of the upper reaches of the Xiangjiang River， 19 sampling sites (including 5 reference sites and 14 impaired sites) were established in the upper reaches of the Xiangjiang River in 2024 to conduct a survey of benthic macroinvertebrates. A Benthic Index of Biotic Integrity (B-IBI) was developed to evaluate the health status of the upper Xiangjiang River. The results showed that a total of 89 macroinvertebrate taxa were recorded， belonging to 3 phyla， 6 classes， 17 orders， and 55 families. Dominant species included Bellamya sp.， Semisulcospira sp.， Parafossarulus eximius， Radix sp.， Corbicula fluminea， and eight other taxa. Through distribution range testing， discriminative ability analysis， and Pearson correlation analysis of 25 candidate parameters， the total number of taxonomic units， Margalef index， and Shannon-Wiener index were ultimately selected as core metrics. These metrics were standardized using the ratio method to construct the B-IBI index system for the upper Xiangjiang River. A grading evaluation standard was established based on the 25th percentile of the reference sites. The evaluation results indicated that the overall health status of the upper Xiangjiang River was "fair，" with 4 sites classified as healthy， 3 as sub-healthy， 8 as fair， 3 as poor， and 1 as very poor. Overall， the health status of the headwater rivers in the high-altitude mountainous areas of the south and west was significantly better than that of the low-altitude mainstream and first-order tributaries， indicating significant disruption of river ecological health by human activities. The B-IBI system developed in this study can provide a scientific basis and fundamental data support for ecological health monitoring and adaptive restoration of the upper Xiangjiang River.

Fish community structure characteristics and key environmental factors in the Pengxi River Basin during the initial phase of the Yangtze River decade–long fishing ban

The Pengxi River， a first-order tributary on the left bank of the Yangtze River's Three Gorges Reservoir， plays a vital ecological role in water conservation， maintaining water quality for the reservoir， serving as a drinking water source for millions， supporting agricultural irrigation， preserving biodiversity， and providing ecological products. This study conducted seasonal fish surveys at 40 sampling sites in the Pengxi River basin during December 2021 (winter)， April 2022 (spring)， and July 2022 (summer). Using biodiversity indices， abundance-biomass comparison (ABC) curves， and redundancy analysis (RDA)， the research systematically analyzed the characteristics of fish community structure and the environmental influencing mechanisms. A total of 80 fish species (5 orders， 17 families， 57 genera) were recorded， with carnivorous species dominating (45%). The dominant species were Coilia brachygnathus， Pseudobrama simoni， and Hypophthalmichthys molitrix. Research indicates that， apart from the Margalef richness index (D) which showed a significant difference between sub-basins 1 and 3(P < 0.05)， neither the Shannon-Weiner index (H') nor the Pielou evenness index (J') exhibited significant differences across temporal and spatial dimensions. However， the ABC curve revealed a trend toward miniaturization of individuals in the community (W-value: 0.0013 in December， 0.0019 in April， and 0.0012 in July). RDA revealed that key environmental factors influencing fish community composition varied temporally， with turbidity， Zn， and pH being the primary drivers. This study represents the first comprehensive survey of fish resources across the entire Pengxi River basin， including its two major tributaries， the Nan River and Puli River， providing baseline data on fish community structure during the initial stage of the fishing ban in the Pengxi River basin. Recommendations include strengthening monitoring of invasive species and controlling non-point source pollution and algal blooms.

Nitrogen and phosphorus migration during the decomposition of three types of aquatic macrophytes and their effects on water quality

To investigate the decomposition characteristics of aquatic macrophytes with different life forms and their effects on the aquatic environment， this study selected three representative species: the emergent plant Typha orientalis， the floating-leaved plant Nymphaea tetragona， and the submerged plant Ceratophyllum demersum. A 68-day decomposition simulation experiment was conducted under an initial biomass of 2 g/L. The results showed that: (1) The decomposition rate exhibited distinct stage-wise dynamics. For all three species， the rate peaked on day 3 and then gradually declined， except for N. tetragona， which showed a secondary increase during days 19–26. The final mass loss rate followed the order: N. tetragona (51.5%) > C. demersum (35.3%) > T. orientalis (18.8%). (2) The decomposition process significantly affected water quality. Parameters such as dissolved oxygen (DO) first decreased and then increased， whereas chemical oxygen demand (COD_Mn)， total organic carbon (TOC)， total nitrogen (TN)， and total phosphorus (TP) concentrations increased initially and then decreased. These variations were significantly greater than those in the control group (P < 0.05). Among the species， N. tetragona had the most pronounced influence on water quality， indicating that floating-leaved plants decompose rapidly and release substances intensively. (3) Decomposition drove the migration and redistribution of nitrogen and phosphorus within the “water–plant–sediment” system. By the end of the experiment， TN and TP concentrations in the water had declined from their peaks， while N and P contents in the sediment were markedly enriched. In the N. tetragona treatment， sediment N increased by 560.4% and P by 1694% relative to initial values， suggesting that decomposition serves as a key pathway for nutrient accumulation in sediments， establishing a long-term legacy of internal nutrient loading. This study reveals that aquatic plant decomposition can enhance sediment nutrient loads through nutrient redistribution， with floating-leaved species contributing the most. The findings provide a scientific basis for ecological restoration and internal nutrient pollution control in lakes and wetlands.

Assessing Fish Diversity and Distribution of the Key Indicator Species Hucho bleekeri in the Upper Dadu River Using eDNA Technology and Traditional Fishing Gear Methods

The upper reaches of the Dadu River， serving as a crucial strategic water source in China， harboring a unique cold-adapted fish germplasm resource. To investigate fish diversity and characterize community structure in this region， this study employed environmental DNA (eDNA) technology integrated with traditional fishing gear surveys. This combined approach facilitated a comparative analysis aimed at evaluating the advantages and limitations of each method in fish monitoring applications. A comprehensive total of 32 fish species were documented throughout the study area. eDNA metabarcoding proved highly effective in detecting fish biodiversity， successfully identifying 29 species. In contrast， conventional fishing gear methods captured only 12 species. Nine species were identified by both approaches. Of significant ecological note was the detection of Hucho bleekeri. While this species was not captured during traditional fishing surveys， its presence was confirmed via eDNA analysis， specifically through the identification of its genetic sequences at sampling sites designated BWX2 and SEZ4. Regarding the composition of the fish community， results derived from both eDNA and capture-based surveys consistently indicated Cypriniformes as the dominant taxonomic order and Cyprinidae as the dominant family. Furthermore， both approaches concurred that three species (Schizopygopsis chengi， Triplophysa stenura and Schizothorax davidi) exhibited high dominance indices within the assessed assemblages. Diversity analysisrevealed a pronounced and statistically significant difference between different methods: the Shannon’s diversity index， the Simpson’s diversity index， and the Margalef’s richness index were all significantly higher when calculated based on eDNA detection data compared to those derived from the traditional fishing gear surveys. This study demonstrates that eDNA technology， with its superior sensitivity， effectively compensates for the limitations of traditional gear-based surveys.The integration of these methods enhances the accuracy and comprehensiveness of fish diversity assessments in the upper Dadu River， providing critical baseline data and technical support for the conservation of fish resources in this region.

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.