Journal of Hydroecology

Satellite-based Estimation of Spatiotemporal Variation of Dissolved Inorganic Nitrogen in the Coastal Waters of China

Dissolved inorganic nitrogen(DIN) is a crucial nutrient source for marine primary production and plays a significant role in regulating biological geochemical processes in marine ecosystems. However, driven by climate change and anthropogenic activities such as rapid urbanization and industrialization,DIN concentrations in coastal waters of China have exhibited pronounced changes in spatiotemporal distribution. Therefore, systematically identifying the spatiotemporal variation and influencing factors of DIN is crucial for health assessment and scientific management of coastal ecosystems. In this study, a DIN concentration inversion model suitable for China's coastal waters was developed by integrating satellite remote sensing imagery with machine learning algorithms. The parameters of the random forest(RF)model were optimized using Recursive Feature Elimination(RFE) and Grid Search with Cross-Validation(GridSearchCV) to improve model performance. Based on the optimized model, we estimated DIN concentrations in typical coastal areas within 50 nautical miles of the shorelines of the Bohai Sea, Yellow Sea,East China Sea, and South China Sea using MODIS image data during the period 2003-2021. Additionally, the Spearman rank correlation coefficient was used to assess the correlation between DIN concentration and human activities. On the test set, the coefficient of determination(R²) of the model was as high as0.836, with a mean absolute error(M_AE) of 0.047 mg/L. From 2003 to 2021, DIN in the coastal waters of China presented significant spatial heterogeneity, with higher concentrations observed nearshore and in semi-enclosed bays. During this period, the average annual DIN concentration in the coastal water of Bohai Sea was highest(0.315±0.045) mg/L, and with greater annual fluctuations than the East China Sea(0.200±0.006) mg/L and Yellow Sea(0.193±0.007) mg/L. The annual average DIN concentration in the South China Sea was the lowest and most stable(0.118±0.017) mg/L. DIN concentrations presented pronounced seasonal variations, with the highest levels observed in winter(0.221±0.007) mg/L and the lowest in summer(0.155±0.005) mg/L, and followed a unimodal annual pattern, initially decreasing and then increasing. The impacts of human activities on DIN concentration varied across regions: DIN concentrations were positively correlated with wastewater discharge and GDP in East China; In South China, DIN concentrations were influenced by agricultural expansion and urban pollution; In North China, DIN concentrations exhibited a negative correlation with GDP and marine aquaculture; while in Northeast China,no significant correlation was observed between DIN concentrations and human activities. This study provides an effective technical path for remotely sensing DIN concentration in China's coastal seas, and a scientific basis for evaluating and managing coastal water quality.

Mechanism of Sea Use Compatibility Based on Ecosystem Management

In this study, we examined compatible sea use based on ecosystem management. Our aim was to provide scientific support for addressing multi-use conflicts and challenges in marine spatial planning(MSP), and promote intensive economic development of marine space while achieving high-quality protection of marine resources. Firstly, we summarized practical compatible sea uses developed at home and abroad, and identified existing problems with the current mechanism. A framework for a compatible sea use mechanism was then constructed, based on a four-dimensional space-time model with three compatibility modes: functional, spatial, and temporal. On this basis, the compatibility of various sea use activities was analyzed, and an implementation path for a compatible sea use mechanism was proposed that combined the basic principles of ecological protection and sea use efficiency. Establishing a compatible sea use mechanism is an important approach for supplementing and improving marine spatial planning and promoting ecosystem-based marine spatial management. This compatible sea use mechanism could leverage the entire chain of ecosystem-based marine spatial management, including marine spatial planning,planning technical review, sea use approval, and sea use supervision. Specific paths included constructing a coordinated and hierarchical compatible sea use mechanism between the national and local levels, clarifying the spatial access requirements for ecological control zones and reserved zones, selecting typical ecosystems for pilot exploration, and accelerating the research on compatible sea use rules and standards.In the future, it will be necessary to further clarify the types of compatible sea use, design compatibility matrices, establish technical standard of monitoring and evaluation systems for compatible sea use, and continuously improve the mechanism to facilitate the transition from the current marine spatial management system to an ecosystem-based management system.

Ecological Vulnerability Assessment and Influencing Factor Analysis for an Island City Based on the PVOR Model

Accurate assessment of ecological vulnerability for island cities facing a combination of natural and anthropogenic stresses is crucial for maintaining insular ecosystem integrity and guiding sustainable resource utilization. In this study, the Pingtan comprehensive experimental zone of Fujian Province was selected for case study and we explored the spatiotemporal distribution of ecological vulnerability in the zone based on the Pressure-Vigor-Organization-Resilience(PVOR) conceptual model, developed as part of this project. Meanwhile, we analyzed key influencing factors of ecological vulnerability using geodetector. The construction of the PVOR model was based on data from remote sensing images, statistical surveys, and geospatial information in the study area at five-year intervals from 2000 to 2020. The weighting of each indicator was established using game theory combination weighting. Applying this framework, we conducted long-term spatiotemporal evolution monitoring of ecological vulnerability in the study area from 2000 to 2020 and analyzed key influencing factors. Results show:(1) The comprehensive ecological vulnerability index was 0.52, 0.53, 0.58, 0.59 and 0.64, respectively, in 2000, 2005, 2010, 2015and 2020, a consistent increase. The ecological vulnerability in Pingtan was generally classified as mild to moderate, accounting for approximately 70% of the total study area. However, the high-vulnerability area expanded by 21.3%, and environmental degradation was evident. The areas of rising ecological vulnerability were primarily concentrated in urban construction and development zones, land reclamation areas, and regions surrounding artificial coastlines.(2) Ecological vulnerability exhibited strong spatial clustering and significant spatial autocorrelation characteristics, with the global Moran's I value increasing from0.929 to 0.958(P<0.05). High-high clustering areas(regions with high vulnerability surrounded by highvulnerability areas) were primarily concentrated in the urban center of the Haitan subdistrict and were expanding, while low-low clustering areas were mainly distributed in the Junshan area in the north.(3) Geographical detector analysis revealed that ecological quality(q=0.59), habitat quality(q=0.63), island development intensity(q=0.53), and landscape fragmentation(q=0.31) were the key factors influencing ecological vulnerability. Further, the interactive effects between factors exceeded the individual contributions of any single factor and the interactive effects were non-linear. Our study will provide a scientific basis for ecological restoration and spatial planning in island cities.

Ecological Health Assessment of Beibu Gulf Based on the Multi-Trophic Index of Biological Integrity

A scientific assessment of the ecological health of Beibu Gulf will support development of strategies to protect water quality and manage the environment. In this study, we evaluated the ecological health of Beibu Gulf based on a multi-trophic index of biological integrity(M-IBI) developed for this study. In October 2022(wet season) and January 2023(dry season), water samples were collected at 69sampling stations to monitor multi-trophic aquatic organisms using environmental DNA(eDNA) metabarcoding technology. The aquatic organisms detected included fish, macroinvertebrates, small invertebrates,algae, protists, and prokaryotes. Then, based on taxa richness, dominance abundance, network density,phylogenetic mean pairwise distance, and ecological risk taxa, a multi-trophic index of biological integrity(M-IBI) was constructed, with five classifications(excellent, good, fair, bad, very bad) according to the index values. Results show that a total of 214 fish species, 163 macroinvertebrate species, 32 small invertebrate species, 188 protist species, 422 algal species, and 318 prokaryotic taxa were identified. Dominant groups were Clupeiformes(fish), Arthropoda(macroinvertebrates), Calanoida(small invertebrates), Spirotrichea(protists), Mamiellophyceae(algae), and Proteobacteria(prokaryotes), and the dominant group structure of different taxa was the same in both wet and dry seasons. Seven invasive fish species, 36 harmful algal species, and 10 pathogenic functional groups were detected. Macroinvertebrates exhibited the highest network density(0.221), while prokaryotes showed the greatest phylogenetic distance(0.991).The ecological health assessment results show that the M-IBI value during the wet season was in the range of 0.664 to 0.871, with the mean M-IBI value of 0.762?±?0.049, categorized as good(corresponding threshold: 0.724-0.768). The M-IBI value during the dry season was lower, ranging from 0.588 to 0.813,with a mean value of 0.699?±?0.051, categorized as fair(corresponding threshold: 0.679-0.723). In conclusion, the combination of eDNA metabarcoding with a multi-trophic index of biological integrity enables effective assessment of marine ecosystem health and offers a scientific basis for ecological protection and early warning of risk in the Beibu Gulf.

Water Resources Evaluation and Influencing Factors Based on Water Footprint in Gansu Province from 2010 to 2023

To calculate the water footprint of Gansu Province， analyze the spatio-temporal evolution patterns， and systematically assess the regional water resource carrying capacity， providing a theoretical basis for the optimal allocation of water resources in Gansu Province. Taking the water footprint of Gansu Province from 2010 to 2023 as the object， a logical framework of "spatio-temporal distribution - driving mechanism - carrying capacity" was constructed. Combined with the bottom-up calculation method of water footprint， the geographical detector model and water resource evaluation indicators， the spatio-temporal evolution characteristics， driving mechanisms and water resource carrying capacity were systematically analyzed. The results show that: (1) The total water footprint of Gansu Province from 2010 to 2023 was 299×10⁸ to 528×10⁸m³. From the perspective of water footprint composition， the agricultural water footprint was the highest， accounting for 91.91%， and the water footprint of export products was the lowest， accounting for 0.46%; (2) The water footprint of Gansu Province showed obvious spatial differentiation characteristics. The high-value areas were mainly distributed in Qingyang， Pingliang and Wuwei， the medium-value areas were mainly distributed in Lanzhou， and the low-value areas were mainly distributed in Jiayuguan and Jinchang; (3) In the exploration of the driving factors of water footprint changes， the pure application amount of chemical fertilizer had the strongest impact on water footprint changes， and the total value of imported goods had the weakest impact. The interaction of two factors was greater than that of a single factor， and the interaction between urbanization rate and temperature had the strongest impact on water footprint changes.

Chitosan-modified natural mineral material flocculation of cyanobacteria for synergistic phosphorus control research

This paper reviews the research on chitosan-modified natural mineral materials in flocculating cyanobacteria and synergistically controlling phosphorus， aiming to provide theoretical references and technical ideas for synchronously inhibiting abnormal algal proliferation and controlling endogenous phosphorus release in the management of eutrophic water bodies. Such materials can not only flocculate cyanobacteria and make them settle on the sediment surface to inhibit their resurgence， but also adsorb phosphorus during the sedimentation process and form a barrier layer to block endogenous phosphorus release， with good ecological safety. It elaborates on the synergistic performance and safety of the materials in algal flocculation and phosphorus control， analyzes the action mechanisms in the application process (such as electrostatic neutralization， enmeshment and bridging， adsorption， physical barrier， etc.)， discusses application strategies including dosing time (middle and lower layers in winter and spring， surface layer in summer)， location and methods， and reviews their applications in the fields of water environment management， ecological restoration and plant growth promotion. Finally， research suggestions are put forward， such as constructing an evaluation system， strengthening the synergistic function of algal flocculation and phosphorus control， and promoting application development.

Community Structure and Biodiversity Dynamics of Macrobenthos in the Environmental Dredging Area， Lake Chaohu

Environmental dredging is an effective way to control the internal nutrient release from sediment in lakes. However， it has not been widely applied in lake restoration because it may remove macrobenthos while removing the surficial contaminated sediments. To examine the influence of environmental dredging on macrobenthos， the community structure of macrobenthos was monitored in the dredging and the surrounding control areas before， during， and after the environmental dredging project at the estuary of Nanfei River of Lake Chaohu. Then， the dynamics in macrobenthos community similarity， dominant species， density， biomass， and biodiversity were evaluated systematically. It was found that the density and biomass of the benthic community decreased temporarily at some sites after dredging， but the density and biomass increased by 51.7% and 31.1%， respectively， compared with the control area within one year after dredging. Two more macrobenthos species were examined in the dredged area than that of the control area. The Jaccard and S?rensen similarity indices of macrobenthos community structure in the dredged area and the control area were at a very similar level. The key dominant species， Limnodrilus hoffmeisteri and Microchironomus sp.， maintained their dominant position during and after dredging. There was also no significant change in the Shannon-Wiener index and Pielou index of macrobenthos after dredging.

Characteristics of Bacterial Community Structure in Mapam Yumco Water Body and Influencing Factors

The study of differences in bacterial community composition and structure at different sampling points and regions in plateau water bodies， as well as the exploration of their correlations with environmental factors， can provide a theoretical foundation for understanding bacterial species diversity and community structure in plateau water bodies. This paper focuses on Lake Mapam Yumco in Ngari，Xizangt， as the research subject. Using high-throughput sequencing technology， bacterial genes in the water were analyzed via 16S rRNA Illumina sequencing. A total of 2，466，720 bacterial raw sequences were obtained， classified into 7，283 operational taxonomic units (OTUs)， and annotated into 51 phyla， 121 classes， 269 orders， 389 families， and 674 genera. The dominant phyla were Proteobacteria (36.96%)， Bacteroidota (28.31%)， Actinobacteria (18.90%)， and Verrucomicrobiota (8.01%)， while the dominant genera were Flavobacterium (18.90%) and hgcI＿clade (14.56%). Correlation analysis revealed that Chemical Oxygen Demand (COD)， Ammonium Nitrogen (NH??-N)， pH， Total Nitrogen (TN)， and Total Phosphorus (TP) were significant factors influencing bacterial community diversity in Lake Mapam Yumco. The results indicate that Lake Mapam Yumco has high microbial community richness and diversity， with a complex and stable community structure， reflecting a healthy ecosystem. These findings provide foundational data and theoretical support for the protection of Lake Mapam Yumco and other plateau freshwater lakes， contributing to the ecological barrier construction of the Qinghai-Tibet Plateau

Impacts of landscape patterns on water-holding services in the Weihe River Basin

Revealing the interrelationship between landscape patterns and ecosystem water conservation services in the Weihe River basin holds significant implications for advancing water resource conservation and ecosystem restoration within the watershed. Utilising elevation， land use， soil， and meteorological data from the Weihe River Basin spanning 2000—2020， the InVEST model was employed to calculate the basin's water conservation capacity. Fragstats 4.2 software analysed the landscape pattern characteristics of the basin， while Pearson's correlation coefficient and the bivariate local Moran's I function were applied to investigate the relationship between water conservation capacity and landscape pattern. The results indicate: (1) The water conservation capacity of the Weihe River Basin exhibited a fluctuating upward trend from 2000 to 2020. Spatially， it generally distributed higher in the south and lower in the north， though low-value areas showed a northward shift; (2) Landscape fragmentation increased while diversity rose within the basin. Among landscape types， the proportion of cultivated land patches decreased， whereas grassland and built-up areas expanded; (3) Water conservation capacity showed significant positive correlations with PD， LSI， DIVISION， and SHDI， while exhibiting negative correlations with LPI and CONTAG. Increased landscape diversity and fragmentation enhanced water conservation， whereas greater patch connectivity and expansion weakened it; (4) Higher water conservation capacity correlates with greater connectivity， larger area， and larger maximum size of forest and grassland patches. Conversely， lower water conservation capacity is associated with greater connectivity， larger area， and larger maximum size of agricultural and built-up patches.

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.

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.