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25 May 2026, Volume 2026 Issue 3 Previous Issue   

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Carbon Cycling Processes and Organic Matter Characteristics

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Spatiotemporal characteristics of carbon dioxide and methane in cascade reservoirs in the Nanpanjiang-Hongshui River Basin Rongrong YANG, Ziyan CHEN, Yi WU, Lijun HOU, Xia LIANG 2026, 2026 (3):  1-16.  doi: 10.3969/j.issn.1000-5641.2026.03.001 Abstract ( 30 )   HTML ( 0 )   PDF (2671KB) ( 18 )   Save In order to understand the spatiotemporal characteristics and key regulatory factors of greenhouse gas emissions from karst cascade reservoirs, four dammed reservoirs with different hydrological regulation characteristics in the Nanpanjiang-Hongshui River Basin were studied. The results show significant regional characteristics of the carbon dioxide (CO2) and methane (CH4) concentrations and emission fluxes from the reservoirs. The diffusive fluxes of CO2 and CH4 in the watershed were 4.98~260.11 mmol·m−2·d−1 and 0.01~0.27 mmol·m−2·d−1, respectively, of which the CO2 fluxes were higher than the average level of reservoirs in China. Estimation of the greenhouse gas emissions from the reservoirs indicated that the total greenhouse gas emissions of the basin system have clear spatial differences. Hydraulic load is the key factor regulating the greenhouse gas emission of karst dammed rivers in the Nanpanjiang-Hongshui River Basin. The CO2 emission flux of reservoirs was found to decrease first and then increase with the increase of hydraulic load, and there is a correlation between hydraulic load and methane concentration in the reservoirs. This study is of great significance for a comprehensive understanding of the greenhouse gas emission law and control mechanism of karst dammed rivers and can provide theoretical support and data reference for carbon emission assessment as well as carbon reduction in the karst reservoirs. Figures and Tables | References | Related Articles | Metrics

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Long-term variations and driving factors of dissolved organic carbon transport in the Yangtze River using machine learning Xingyu LU, Ying WU, Junning FAN, Yuping YE, Jia WANG 2026, 2026 (3):  17-29, 43.  doi: 10.3969/j.issn.1000-5641.2026.03.002 Abstract ( 17 )   HTML ( 2 )   PDF (2067KB) ( 17 )   Save Analyzing variations in riverine dissolved organic carbon (DOC) concentration and flux is essential for understanding global carbon cycle processes and refining carbon budget estimations. Machine learning and big data analysis have become invaluable in this field. However, research on Chinese rivers is limited due to lack of long-term continuous observational data and non-uniform temporal distribution of key influencing factors. Consequently, mechanisms driving seasonal and long-term variations in riverine DOC and their influencing factors remain unclear. This study compared various machine learning methods using long-term, monthly DOC concentration data from the Yangtze River’s Xuliujing Station, as well as watershed characteristic data. Using the optimal model, we simulated monthly DOC concentration changes at Xuliujing Station from 2001 to 2020 and employed the SHAP (SHapley Additive exPlanations) method to analyze the impact of watershed characteristics on DOC concentration and flux. The findings demonstrated that the Random Forest algorithm yielded the highest accuracy, achieving an R² of 0.72 and an RMSE of 0.09 mg·L−1. Over the study period, DOC concentrations ranged from 1.24 to 2.27 mg·L−1, with a mean of 1.67 mg·L−1. Annual DOC flux varied between 0.93 and 2.41 Tg·a−1, averaging 1.46 Tg·a−1. Notably, the seasonal pattern of DOC concentration shifted from low during the flood season and high during the dry season to high levels in both seasons. This shift was primarily due to anthropogenic water regulation activities and changes in watershed ecosystem patterns. Over the long term, both DOC concentration and flux at Xuliujing Station have significantly increased, at rates of 0.026 mg·L−1·a−1 and 0.0025 Tg·a−1, respectively (both p<0.05). Human activities were the predominant driving factor, accounting for 54.1% of the changes in DOC concentration. This study provides valuable insights into the evolving patterns of DOC concentration and flux in the Yangtze River over recent decades and the mechanisms by which driving factors influence these changes. It also provides a novel perspective for the big data analysis of riverine carbon cycling. Figures and Tables | References | Related Articles | Metrics

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Distribution and modulators of dissolved organic matter in the East China Sea during spring Hongsheng CAO, Qi WU, Fang CAO 2026, 2026 (3):  30-43.  doi: 10.3969/j.issn.1000-5641.2026.03.003 Abstract ( 19 )   HTML ( 1 )   PDF (4466KB) ( 28 )   Save Dissolved organic matter (DOM) plays an essential role in marine carbon cycling by modulating carbon sequestration and ecosystem dynamics through its degradation and transformation. As the largest marginal sea in China, the East China Sea (ECS) is a critical pathway for export of terrestrially derived DOM to the Pacific Ocean. This dynamic system is influenced by multiple environmental factors, including Yangtze River inputs, Kuroshio intrusion, and anthropogenic activities, which collectively contribute to the complex sources and transformations of DOM. However, the distribution of DOM and its underlying driving factors remain understudied in the ECS. Here, measurements of dissolved organic carbon (DOC) and its optical properties (absorbance of chromophoric DOM, CDOM; excitation-emission matrices on the fluorescent DOM, EEMs on the FDOM) were made in ECS water during a cruise in spring 2023 to provide insights into the mechanisms modulating DOM variability. The results showed strong variations in both quantity and quality of DOM, with the highest DOC concentration and absorption coefficient of CDOM (aCDOM(355)) close to the coast and decreasing offshore. DOC decreased from the surface to the bottom layer, whereas aCDOM(355) values showed an increasing trend. Four fluorescent DOM components were resolved by parallel factor analysis: two autochthonous protein-like components, C1 and C2; one terrestrial humic-like component, C3, and one marine humic-like component, C4. The fluorescence intensity of each component decreased as distance offshore increased. Elevated fluorescence intensities of C1 and C2 were observed in the surface and bottom layers, whereas minimum values were observed in the middle layer. The fluorescence intensities of C3 and C4 decreased as water depth increased. Principal component analysis (PCA) enabled differentiation of water samples following hydrodynamic gradient. The penetrating front in the ECS resulted in enhanced cross-shelf transport of terrestrially derived DOM, while phytoplankton blooms significantly altered the amount and compositions of DOM. Overall, the DOM in the ECS in spring 2023 was primarily of terrestrial origin, while autochthonous production, microbial transformation, and bottom resuspension were collectively responsible for its variability. This study provides a fundamental framework for characterizing DOM distribution patterns in the ECS during spring. Figures and Tables | References | Related Articles | Metrics

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Characteristics and associated sources of fluorescent dissolved organic matter in the Yellow River Estuary, the Changjiang River Estuary and their adjacent seas Qiuxun LIN, Boshuang WU, Guangyue DU, Yuxuan FU, Yifan PAN, Mengting QI, Zhenyang SONG, Yongqiang ZHOU, Xiaofei LI 2026, 2026 (3):  44-55.  doi: 10.3969/j.issn.1000-5641.2026.03.004 Abstract ( 25 )   HTML ( 0 )   PDF (2815KB) ( 13 )   Save Fluorescent dissolved organic matter (FDOM) indices, sources, and their relationships with nutrients in the Yellow River Estuary, the Changjiang River Estuary and their adjacent seas in July 2024 were investigated through field sampling and laboratory analysis. The fluorescence index ranged from 2.71 to 4.45 in the Yellow River Estuary and its adjacent sea and from 3.22 to 5.69 in the Changjiang River Estuary and its adjacent sea. The biological index values were 1.75~3.48 and 1.49~4.81, respectively, indicating that autochthonous sources contributed most to the organic matter. The humification index of the Yellow River Estuary, the Changjiang River Estuary and their adjacent seas ranged from 0.22 to 0.85 and 0.10 to 1.14, respectively, suggesting weak humification and strong autogenic processes. Spatially, the fluorescence index and biological index increased while the humification index decreased toward the sea, indicating that organic matter is primarily driven by autochthonous production with minimal humification. The FDOM and fluorescence index were significantly higher in the Changjiang River Estuary than in the Yellow River Estuary, suggesting greater concentrations of organic matter and more substantial autochthonous sources in the Changjiang River Estuary and its adjacent sea. The fluorescence index and biological index were significantly negatively correlated with nutrient concentrations, while the humification index was positively correlated with nutrients. These results indicate that nutrient inputs significantly influence FDOM, further altering the organic matter composition and water quality in estuaries. Figures and Tables | References | Related Articles | Metrics

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Driving mechanisms of carbon fluxes by functional traits in Phragmites australis and Spartina alterniflora dominated salt marshes of the Yangtze River Estuary Ming GE, Linjing REN, Ying HUANG, Xiuzhen LI 2026, 2026 (3):  56-68.  doi: 10.3969/j.issn.1000-5641.2026.03.005 Abstract ( 19 )   HTML ( 0 )   PDF (2189KB) ( 7 )   Save Coastal wetlands, recognized as vital blue carbon ecosystems, exhibit carbon sequestration functions that are strongly associated with plant functional traits. This study investigated the regulatory mechanisms of functional traits on carbon sequestration in the Yangtze River Estuary using two dominant salt marsh species: Phragmites australis and Spartina alterniflora. We quantified key functional traits, including morphological traits, photosynthetic parameters, and chlorophyll concentration, while simultaneously measuring ecosystem carbon fluxes (CO2 and CH4 emissions). Results demonstrate significant interspecific differences in functional traits: S. alterniflora exhibited superior leaf area index (LAI), chlorophyll concentration, photosynthetic efficiency, and CO2 assimilation capacity compared with P. australis. The photosynthetic capacity of P. australis was predominantly regulated by LAI, whereas that of S. alterniflora was mainly regulated by chlorophyll concentration. The CO2 fluxes showed a strong positive correlation with leaf traits and photosynthetic parameters. In contrast, CH4 emissions showed no association with leaf traits; however, they were influenced by morphological traits, such as aboveground biomass, plant height and plant density. These findings highlight that plant functional traits differentially mediate carbon sequestration pathways and greenhouse gas dynamics in coastal wetlands, providing critical insights for vegetation-based blue carbon management strategies. Figures and Tables | References | Related Articles | Metrics

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Effects of Phragmites australis and Spartina alterniflora litter decomposition on soil organic carbon at different tidal flat elevations Xinhan DONG, Zhongzheng YAN 2026, 2026 (3):  69-87.  doi: 10.3969/j.issn.1000-5641.2026.03.006 Abstract ( 24 )   HTML ( 0 )   PDF (1233KB) ( 8 )   Save In this study, we examined the synergistic effects of tidal inundation and vegetation type on litter decomposition and soil carbon dynamics in coastal wetlands, quantifying their influence on organic carbon (OC) fractions and providing a scientific foundation for enhancing wetland carbon sequestration. Specifically, we assessed how the co-effects of hydrological conditions and plant, species contribute to promoting the cycling of carbon. The study was conducted in the Chongming Dongtan wetland area of the Yangtze Estuary, in which we performed a 1-year in situ litter decomposition experiment, using Phragmites australis and Spartina alterniflora, to compare two tidal flood environments, namely, high (HM) and low (LM) elevational marshland areas. The rates of plant decomposition were determined based on the litter bag method, and soil samples were analyzed for the contents of soil organic carbon (SOC), particulate organic carbon (POC), mineral-associated organic carbon (MAOC), microbial biomass carbon (MBC), and dissolved organic carbon (DOC), using density fractionation and fumigation extraction techniques. The results revealed higher rates of decomposition in HM than in LM, with S. alterniflora and P. australis being characterized by rates of 0.0032 d–1 and 0.0021 d–1 in HM, respectively, which were 16% and 15% higher than those in LM at 360 days. Whereas initially, the decomposition of P. australis was more rapid in LM (p<0.01), the rates in HM were more pronounced during the latter stages of measurement. In HM, we detected significant elevations in the stocks of soil POC, MAOC, and SOC, associated with the efficient conversion of POC and MBC to MAOC, whereas in LM, we observed a lower DOC-to-MBC conversion and limited accumulation of POC. In addition, the type of vegetation was found to have an influence on carbon dynamics, with the levels of P. australis SOC peaking earlier in HM due to efficient conversion, whereas during the latter stages of the experiment, the levels of S. alterniflora SOC surpassed those of P. australis. Comparatively, in LM, the type of plant had a minimal influence on the dynamics of carbon fractions. Collectively, our findings provide evidence that by shaping the soil environment, tidal inundation can have a pronounced regulatory effect on the rates of plant decomposition and soil carbon stocks, with the species of plant modulating the conversion of carbon fractions in response to differing hydrological conditions. Compared with the marshland at lower elevations, that at higher elevations was established to have a greater carbon sequestration potential. On the basis of these observations, we recommend that wetland management should integrate hydrological and vegetation factors to optimize carbon storage, and further research should focus on the microbial mechanisms underlying these processes. Figures and Tables | References | Related Articles | Metrics

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Assessment of carbon stock by reef-building oysters in the Dashentang Area, Tianjin Meiling ZHENG, Ying CUI, Sen LIU, Dan YU, Yuyan MA, Hongyou JIANG, Huan SUN, Fuxin NIU 2026, 2026 (3):  88-97.  doi: 10.3969/j.issn.1000-5641.2026.03.007 Abstract ( 20 )   HTML ( 0 )   PDF (1809KB) ( 4 )   Save This study aimed to quantify the carbon stock contributed by reef-building oysters in the Dashentang oyster reef ecosystem, Tianjin. For the first time, the carbon stock of Crassostrea gigas (C. gigas) was evaluated using an inventory-based approach. Stepwise regression analysis was applied to examine the relationship between oyster carbon density and water quality parameters, thereby identifying the environmental factors that influence carbon density. In addition, a regression model was developed to predict the shell dry weight from shell height. Results revealed that in June and October 2024, the average total carbon density of C. gigas in the Dashentang Area of Tianjin was 34.37 t C/hm2 and 25.81 t C/hm2, respectively, corresponding to total carbon stocks of (6945.40±422.88) t C and (5214.01±458.33) t C, indicating higher carbon stock in June than in October. Water temperature and turbidity accounted for 77.6% of the total carbon density variability, thereby indicating that water temperature and turbidity influenced the carbon density in the study area. Furthermore, the goodness of fit of the power function ($ \ln y= $$ \ln0.002+2.126\ \ln x $) regression model for the shell dry weight and shell height demonstrated excellent fit (R2=0.958), confirming that shell dry weight can be reliably estimated from shell height for practical applications. Figures and Tables | References | Related Articles | Metrics

Biodiversity and Ecological Responses

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Aquaculture and natural habitats: Comparison of diversity and community structure of benthic ciliates in China’s intertidal zones Xu LI, Yuan XU 2026, 2026 (3):  98-109.  doi: 10.3969/j.issn.1000-5641.2026.03.008 Abstract ( 18 )   HTML ( 0 )   PDF (2538KB) ( 7 )   Save In recent years, continuous coastal development has led to large-scale conversion of natural mudflats to aquaculture mudflats in intertidal zones, resulting in the loss of benthic biodiversity and alterations in community structure. However, systematic understanding of the differences in benthic biodiversity and community structure between aquaculture and natural mudflats, as well as their driving mechanisms—particularly large-scale spatial drivers—remains limited. This study focused on benthic ciliate communities in China’s intertidal aquaculture and natural mudflats. Using one-way analysis of variance (ANOVA), linear regression (LR), distance-based redundancy analysis (dbRDA), and variation partitioning analysis (VPA), we examined the differences in three dimensions of α-diversity (taxonomic, functional, and phylogenetic diversity) and community structure (species composition and functional composition) of benthic ciliates between the two types of mudflat, along with their driving factors. The results revealed that: ① no significant differences exist in local environmental variables between the two regions, indicating that aquaculture activities did not significantly modify habitat physicochemical conditions; ② significant differences existed in α-diversity, species composition, and functional composition of benthic ciliates between aquaculture and natural mudflats; ③ mean annual temperature (MAT) emerged as the primary driver of the observed differences in ciliate α-diversity and community structure. The results of this study demonstrate that large-scale climatic variables, rather than aquaculture impacts, are the key drivers of divergent patterns in benthic ciliate diversity and community structure between the two mudflat types. These findings provide critical insights for balancing intertidal mudflat aquaculture development with biodiversity conservation. Figures and Tables | References | Related Articles | Metrics

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Effects of the ecological restoration project in the coastal wetlands of the Yangtze River Estuary on benthic ciliate communities Pengquan ZHONG, Wei WANG, Jiawei ZHANG, Xu LI, Ziqing ZHOU, Miaoxun WANG, Yuan XU 2026, 2026 (3):  110-123.  doi: 10.3969/j.issn.1000-5641.2026.03.009 Abstract ( 23 )   HTML ( 0 )   PDF (2195KB) ( 6 )   Save To evaluate the effects of the ecological restoration project involving Bolboschoenus maritimus in the Chongming Dongtan salt marsh wetland of the Yangtze River Estuary on the benthic community, this study employed principal coordinates analysis (PCoA), similarity percentage (SIMPER), and other methods to compare the community structure and diversity of benthic ciliates in the restoration area and the adjacent natural Bolboschoenus maritimus area over four consecutive seasons. The results are as follows: ① After restoration, the sediment median grain size, organic matter content, and ammonium levels in the restored area increased significantly; ② Significant differences were observed in the species composition of benthic ciliate communities between the restored and natural areas of Bolboschoenus maritimus. Salinity, phosphate, pH, oxidation-reduction potential, and meiofaunal biomass were the primary driving factors; ③ The α diversity of the benthic ciliate community in the natural area was significantly higher than that in the restored area. Silicate, salinity, ammonium, organic matter content, and sediment median grain size were the main factors influencing the diversity. In summary, the restored area exhibited a distinct benthic ciliate community composition and lower diversity compared to the natural area, suggesting that a longer recovery period may be needed for the sedimentary environment and benthic ciliate community in the restored area to reach the natural state. Figures and Tables | References | Related Articles | Metrics

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Characteristics of Microcystis in brackish water and its effects on Metazoan Zooplankton Xinran JIANG, Xuechu CHEN, Yingying HUANG, Wenhui YOU, Xinlu LI 2026, 2026 (3):  124-133, 184.  doi: 10.3969/j.issn.1000-5641.2026.03.010 Abstract ( 17 )   HTML ( 0 )   PDF (987KB) ( 7 )   Save The migration of freshwater harmful cyanobacteria into estuarine brackish waters poses a significant threat to local ecosystems. The different forms in which these cyanobacteria produce algal toxins, such as microcystins (MCs), can exert varying impacts on zooplankton communities. This study aimed to investigate the predominant forms of MCs produced by Microcystis in brackish waters and their subsequent effects on the survival and community composition of metazoan zooplankton. An in situ mesocosm experiment was conducted in a nearshore brackish wetland. Rectangular mesocosms (1.5 m depth, 150 L volume) were established in the open water area, filled with ambient wetland water filtered through a No. 25 plankton net, and inoculated with Microcystis colonies collected from Dianshan Lake to achieve an initial chlorophyll a concentration of 60 μg/L. The experiment included three replicate mesocosms and ran for 14 days. Data were processed using Microsoft Excel and statistically analyzed with SPSS 23.0. One-way analysis of variance (ANOVA) and t-tests were used to determine statistical significance. The survival of Microcystis and changes in microcystin forms (particulate vs. dissolved) were analyzed, alongside the effects of these toxin fractions on zooplankton abundance and community structure. The results demonstrated that Microcystis survived at a salinity of 4‰, with MCs predominantly existing in the intracellular (particulate) form. Within the mesocosms, intracellular microcystin concentrations initially increased and subsequently decreased, while the proportion of extracellular (dissolved) microcystins remained low (3%~8%) and presented a decreasing trend. Low salinity (≤7‰) appeared to promote intracellular microcystin synthesis. Conversely, both algal growth and intracellular microcystin synthesis were significantly inhibited when salinity was increased to 10‰, accompanied by a significant increase in microcystin release. Differential sensitivity and tolerance to MCs were observed among metazoan zooplankton groups. Particulate MCs were associated with slower-acting but longer-lasting toxicity, resulting in final zooplankton abundance significantly lower than initial levels, with copepods becoming proportionally more dominant in the community structure. In contrast, conditions favoring dissolved MCs led to substantial acute mortality, followed by a recovery phase where final abundance significantly exceeded initial levels, and rotifers emerged as the dominant group. These findings indicate that the partitioning of Microcystis toxins in brackish environments directly influences zooplankton abundance and community composition, thereby impacting the aquatic ecosystem. This research provides a crucial scientific basis for assessing the ecological risks of Microcystis toxins in brackish waters and for informing the development of effective water management strategies. Figures and Tables | References | Related Articles | Metrics

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Evolution of biodiversity in the Doulonggang estuary coastal wetland, Yancheng, China Haixia WEN, Qing HU, Zhanghua WANG, Xiaolin MA 2026, 2026 (3):  134-147.  doi: 10.3969/j.issn.1000-5641.2026.03.011 Abstract ( 19 )   HTML ( 0 )   PDF (2613KB) ( 6 )   Save Coastal wetlands play an important role in the ecosystem. However, human activities such as pond aquaculture can alter their landscape patterns and biodiversity in the ecosystems. Environmental DNA (eDNA) technology can effectively reconstruct past biological communities and evaluate changes in biodiversity. In the present study, a sediment core was obtained from a wetland at the Doulonggang estuary in Yancheng, Jiangsu Province. By analyzing eDNA in the sediments and historical remote sensing images, in addition to performing 210Pb dating, the present study comprehensively explored how land use change affected biodiversity in the 2008–2023 period. 210Pb dating and historical remote sensing data showed that the sedimentary records included three phases of land use, including natural wetland (2008–2015), aquaculture ponds (2015–2019), and wetland restoration (2019–2023). eDNA in the sediments indicated that in the natural wetland phase, terrestrial herbaceous plants (26.69%~37.90%) and a brackish water community prevailed. In the aquaculture pond phase, the proportions of aquatic arthropods (such as Calanoida) and algae surged sharply, reflecting the ecological simplification caused by the artificial aquaculture system. In the wetland restoration phase, the proportion of diatoms (Bacillariophyta) increased to 89.04%, and the terrestrial herbs recovered gradually, indicating ecosystem restoration. The α-diversity index further confirmed that species diversity and evenness were the lowest when the area became an aquaculture pond in 2015 and then recovered gradually. The Bray-Curtis similarity index showed that there were significant differences in the biological composition among the three phases, with the main difference attributed to the proportion of diatoms. Therefore, this study shows that the ecological restoration project has enabled the wetland biological composition at the Doulonggang estuary to recover toward a natural wetland state. However, restoration of the ecosystem lags behind the landscape change, and long-term monitoring is necessary to promote the complete ecological restoration of the wetland. This study contributes to a deeper understanding of the dynamic change process of coastal wetland ecosystems under the interference of human activities and provides a scientific basis for ecological restoration and management of tidal flat wetlands. Figures and Tables | References | Related Articles | Metrics

Environmental Quality and Ecological Remediation

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Heavy metal contamination and microbial response in groundwater of the Yangtze River Estuary sea-land interaction zone Jinlin YAN, Jiawei ZHANG, Wenxiao LIU, Yue LI, Jiahui FAN, Jinlong WANG, Hongpo DONG 2026, 2026 (3):  148-160.  doi: 10.3969/j.issn.1000-5641.2026.03.012 Abstract ( 19 )   HTML ( 0 )   PDF (3551KB) ( 12 )   Save In the sea-land interaction zone, groundwater is influenced by multiple environmental factors, posing a high risk of heavy metal pollution. This study assesses the environmental conditions of the sea-land interaction zone in the Yangtze River Estuary by analyzing the concentrations of eight heavy metals (Cr, Ni, Cu, Zn, Cd, Pb, As, and Hg) and examining the composition of microorganisms and heavy metal resistance genes (MRGs) in groundwater. The results indicate that the average concentrations of heavy metals in well water stations are below the Class Ⅲ limits of the National Groundwater Quality Standard (GB/T 14848-2017). At interstitial water stations, all heavy metals except Pb also remain below these limits. Pearson correlation analysis reveals significant positive correlations between As and Hg (r=0.661, p<0.01), As and Zn (r=0.915, p<0.05), and Cd and Hg (r=0.918, p<0.05), suggesting common pollution sources. Most stations have a single-factor pollution index below 1, indicating safe levels. However, a small number of interstitial water stations record Pb index values between 1 and 3, indicating mild to moderate pollution. The multi-factor comprehensive pollution index is 0.27 for well water stations (safe), and 1.73 for interstitial water stations (mild pollution). Metagenomic analysis of groundwater samples identifies 21 MRGs and 39 classified bacterial phyla that potentially harbor these genes. This study provides insights into the distribution, potential sources, and microbial involvement in heavy metal contamination in groundwater of the sea-land interaction zone of the Yangtze River Estuary. Figures and Tables | References | Related Articles | Metrics

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Effects of planting density and area of floating-bed plants on nitrogen and phosphorus removal from water Shufan JIANG, Chunfu TONG, Tao WANG, Shengnan ZHANG, Wei OUYANG 2026, 2026 (3):  161-173.  doi: 10.3969/j.issn.1000-5641.2026.03.013 Abstract ( 17 )   HTML ( 0 )   PDF (5406KB) ( 13 )   Save The study investigated the effects of planting density and area of floating-bed plants on the removal of nitrogen and phosphorus from water using the floating-bed of Iris pseudacorus L. as the experimental subject. Five planting densities (4, 8, 12, 16, and 20 plants/m2) and one control group were set via a water tank control experiment. Additionally, three planting areas were established, namely S (representing the experimental floating-bed area of 80 cm×80 cm), 50%S, and 25%S. The results showed that the floating-bed of I. pseudacorus significantly reduced the total nitrogen content in the water (p<0.05), but not the total phosphorus content (p>0.05). Moreover, planting density significantly affected the nitrogen and phosphorus concentrations in water (p<0.05). The total nitrogen and phosphorus removal rate was the highest at 16 and 8 plants/m2, respectively. In contrast, both nitrogen and phosphorus removal rates were the lowest at 12 plants/m2. The variation of planting density significantly affected the contribution rates of nitrogen and phosphorus removal by stems, leaves, and roots (p<0.05). The contribution rates in 12 and 16 plants/m2 were higher than those in other low- and high-density groups. The variation of floating-bed planting area also significantly affected the total phosphorus removal rate from water (p<0.05), but not the total nitrogen removal rate from water (p>0.05). An increased planting area was beneficial for enhancing the phosphorus removal, while variations in the planting area significantly affected the contribution rate of roots to nitrogen and phosphorus removal (p<0.05), with the highest values for 50%S. Variations in planting density or area can alter the planting distance and living space of plants, affecting the plant biomass and nutrient distribution, such as nitrogen and phosphorus distributions to varying degrees, and influencing the different growth characteristics of plant stems, leaves, and roots. The ability of plants to absorb and remove nitrogen and phosphorus from water depends not only on the total plant biomass and nutrient reserves, but also the synergy of the absorption through stems, leaves, and roots. Therefore, in the practical application of floating-bed, the proper planting density and area should be selected according to the characteristics of water quality. Figures and Tables | References | Related Articles | Metrics

Estuarine Dynamic Processes and Material Transport

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Cross-sectional distribution and transport of water and suspended sediment during the dry season in the upper North Branch of the Yangtze Estuary Haofei REN, Erfeng ZHANG, Yaping WANG, Ming TANG, Zhishang LI, Heqin CHENG 2026, 2026 (3):  174-184.  doi: 10.3969/j.issn.1000-5641.2026.03.014 Abstract ( 18 )   HTML ( 0 )   PDF (1440KB) ( 7 )   Save Water and suspended sediment transport is a key process related to the erosion-deposition evolution of an estuary. The previous studies were mostly based on single fixed-point observations in flood season. However, understanding of the situations in the dry season and the distribution along the cross section is insufficient. Based on navigational observations along a cross section during spring and neap tides in January 2021, this study investigated the cross-sectional distributions of current velocity, suspended sediment concentration (SSC), water and sediment fluxes, as well as the characteristics of water and sediment transports during the dry season in the upper reach of the North Branch of the Yangtze Estuary. Results indicate that there are differences in start/end times of flood and ebb tides between different locations in the cross section: earliest at shallow waters on the south side, next at deep trough on the north side, and latest near the deep trough in the northern section, inducing differences in cross-sectional distribution of current velocity at different times. The average current velocities during flood and ebb tides both obviously decrease from deep waters on the north side to shallow waters on the south side. The cross-sectional distribution of average SSC during flood and ebb tides is related to the magnitude of SSC: higher at shallow waters on the middle and south sides than at deep waters on the north side when SSC is low; however, with minor difference in the cross section when SSC is high during spring tides. The water and unit-width sediment fluxes indicate a decreasing trend from deep waters on the north side to shallow waters on the south side during both spring and neap tides, consistent with the cross-sectional distribution of current velocity and water depth. The net sediment transport in a tidal cycle reveals a pattern of moving seaward at deep waters on the north side, and landward at shallow waters on the middle and south sides during neap tides. During spring tides, the extent of landward sediment transport in the cross section is larger, and the volume of landward transport is significantly larger than seaward transport, as well as landward transport during neap tides. This study facilitates a deeper understanding of water and sediment transport characteristics in the upper reach of the North Branch and provides a foundation for further exploration of the control factors of geomorphological erosion and deposition. Figures and Tables | References | Related Articles | Metrics

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Impact of strong northerly winds on saltwater intrusion in the Changjiang Estuary under different tidal patterns Qianqiang ZHOU, Jianrong ZHU, Rui MA 2026, 2026 (3):  185-202.  doi: 10.3969/j.issn.1000-5641.2026.03.015 Abstract ( 16 )   HTML ( 0 )   PDF (9453KB) ( 16 )   Save Previously measured data indicate differences in salinity variation at the water intake of reservoirs in the Changjiang Estuary during strong northerly winds and different tidal patterns. In this study, a three-dimensional numerical model of saltwater intrusion in the Changjiang Estuary was used to simulate the impacts of climatic winds and strong northerly winds at a speed of 10 m/s for 5 days during four tidal patterns (neap tide, middle tide after neap tide, spring tide, and middle tide after spring tide) on saltwater intrusion and the unsuitable water intake time of the reservoirs. Numerical experimental results showed that the maximum unsuitable water intake time at the water intake of the Qingcaosha Reservoir reached 15.87 days, an increase of 11.63 days compared to that under the climatic wind condition in the experiment of strong northerly wind in the neap tide. The maximum unsuitable water intake time in Dongfengxisha and Chenhang Reservoirs reached 20.12 and 7.95 days, with increases of 5.36 and 4.48 days in the experiments of strong northerly winds during the middle tide after spring tide and neap tide, respectively. Strong northerly winds amplified the landward net water and salt fluxes in the North Branch, with the effect being most pronounced during the spring tide experiment; the practical salinity units (psu) increased significantly in the upper reaches, with a maximum value of 6 in the neap tide experiment. In the South Branch, the seaward net salt flux increased and peaked at 20 t/s in the spring tide experiment. Furthermore, the water diversion ratio increased significantly under northerly winds, with an increase of 4.79% compared with that under the climatic wind condition. In the North Channel, the net water fluxes decreased the most, and a large amount of salt was transported landward in the neap tide experiment. Furthermore, the isohaline of 0.45 (the salinity standard for drinking water) crossed the water intake of the Qingcaosha Reservoir, and the impact of saltwater intrusion was the most serious in the middle tide after neap tide experiment. Additionally, the salinity in the middle-lower reaches increased significantly by up to 8 under the influence of the strong northerly wind in the neap tide experiment. The seaward net water and salt fluxes increased under strong northerly winds in the South Channel, with the maximum net water fluxes in the neap tide experiment and net salt fluxes in the middle tide after spring tide. In contrast, salinity in the middle-lower reaches decreased, particularly in the South Passage, due to the increased water diversion ratio. The net water and salt fluxes increased during different tidal patterns under strong northerly winds in the North Passage, with the most notable increase in the neap tide experiment. Moreover, salinity in the lower reaches increased in the neap tide experiment and middle tide after neap tide experiment. The seaward net water and salt fluxes increased in the neap tide experiment in the South Passage, and salinity decreased slightly in all experiments, with the most remarkable decrease observed in the neap tide experiment. Figures and Tables | References | Related Articles | Metrics