River Inlet Research Articles

An Integrated Approach to Riverbed Morphodynamic Modeling Using Remote Sensing Data

River inlets, deltas, and estuaries represent delicate ecosystems highly susceptible to climate change impacts. While significant progress has been made in understanding the morphodynamics of these environments in recent decades, the development of models still requires thorough testing and data integration. In this context, remote sensing emerges as a potent tool, providing crucial data and the ability to monitor temporal changes. In this paper, an integrated approach combining remote sensing and morphodynamic modeling is proposed to assess river systems comprehensively. By utilizing multispectral or RGB optical imagery from satellites or UAVs for river classification and remotely derived bathymetry, echo sounder data for ground truth, and photogrammetric modeling of emerged areas, we outline a procedure to create an integrated and continuous digital terrain model (DTM) of a riverbed, paying particular attention to the wet–dry interface. This method enables us to identify the river centerline, its width, and its slope variations. Additionally, by applying a linear morphodynamic model that considers the spatial variability of river morphology commonly found in estuarine environments, it is possible to predict the wavelength and migration rate of sediment bars. This approach has been successfully applied to recreate the DTM and monitor the morphodynamics of the seaward reach of the Roya River (Italy).

Analysis of Water Quality of Le'an River in Poyang Lake Basin Based on CCME-WQI Method

As the largest freshwater lake in China, Poyang Lake plays a key role in supporting the balance of aquatic ecosystems, and the water quality of its inlet rivers affects the lake's water quality. Le'an River, a typical inlet river of Poyang Lake, was selected as the research object. Based on the water quality data of six monitoring points in the upper, middle, and lower reaches of the mainstream of Le'an River from 2012 to 2020, the CCME-WQI method was used to evaluate the water quality of the river after systematically analyzing the spatiotemporal variation of the concentration of pollutants in the mainstream of the river. Finally, the main influencing factors of the water quality of the river were extracted and analyzed according to the PCA method. The results showed that： ① The water volume upstream and downstream of the river was more seriously polluted in the pre-study time period, which was due to the presence of Dexing Copper Mine in the upstream and small and medium-sized mines and farmland downstream. ② Before 2017, the water volume downstream of Le'an River had the worst water quality, with TP and NH4+-N exceeding the standard rate of 43.3% and 85.0%, respectively, and the lowest WQI mean value of 86.2. After 2017, due to the effective management of pollutant discharges in the watershed, the water volume downstream of the river improved significantly and continued to be in an excellent state, and the mean value of the WQI reached 100.0. ③ The factors influencing the water quality of the mainstem of the Le'an River could be divided into four categories： human activities, seasonal factors, atmospheric deposition of pollutants, and the physical and chemical properties of the water volume itself, with human activities being the dominant factor for water quality changes at Dawuhekou and Shizhenjie, whereas the seasonal factors had the greatest influence at the remaining locations. ④ Organic matter pollution was obvious in the upper and lower Le'an River water volume, and the water volume at Dawuhekou was mainly affected by nearby mining activities, whereas the water volume at Shizhenjie was mainly affected by agriculture. Le'an River had serious organic matter pollution downstream before 2017, and mining and agricultural activities in the watershed had a high degree of impact on water quality. The treatment of mineral processing wastewater should be upgraded, and the discharge of pollutants from agriculture in the downstream of the watershed should be regulated.

Advancing non-optical water quality monitoring in Lake Tana, Ethiopia: insights from machine learning and remote sensing techniques

Water quality is deteriorating in the world's freshwater bodies, and Lake Tana in Ethiopia is becoming unpleasant to biodiversity. The objective of this study is to retrieve non-optical water quality data, specifically total nitrogen (TN) and total phosphorus (TP) concentrations, in Lake Tana using Machine Learning (ML) techniques applied to Landsat 8 OLI imagery. The ML methods employed include Artificial Neural Networks (ANN), Support Vector Regression (SVR), Random Forest Regression (RF), XGBoost Regression (XGB), AdaBoost Regression (AB), and Gradient Boosting Regression (GB). The XGB algorithm provided the best result for TN retrieval, with determination coefficient (R2), mean absolute error (MARE), relative mean square error (RMSE) and Nash Sutcliff (NS) values of 0.80, 0.043, 0.52, and 0.81 mg/L, respectively. The RF algorithm was most effective for TP retrieval, with R2 of 0.73, MARE of 0.076, RMSE of 0.17 mg/L, and NS index of 0.74. These methods accurately predicted TN and TP spatial concentrations, identifying hotspots along river inlets and northeasters. The temporal patterns of TN, TP, and their ratios were also accurately represented by combining in-situ, RS and ML-based models. Our findings suggest that this approach can significantly improve the accuracy of water quality retrieval in large inland lakes and lead to the development of potential water quality digital services.

First record of the snapping shrimp Alpheus cf. lobidens (Decapoda, Caridea, Alpheidae) in the Gulf of Cadiz, an unexpected introduction to European waters from the Persian Gulf

Abstract In 2015, an unknown snapping shrimp of the genus Alpheus was collected in the San Pedro River inlet (Bay of Cadiz, SW Spain). Initially, its identification was not possible only based on DNA barcoding or morphology, considering the difficulties in the Alpheus taxonomy and the low percentage of DNA sequences of Alpheus spp. available in public databases. However, recent studies from Kuwait, Qatar and Iraq describing the morphology of Alpheus cf. lobidens allowed us to place the exotic Alpheus in this species complex. There are also recent sequences of 16S mtRNA and COI deposited in GenBank and BOLD that match >99% of similarity with the sequences of the specimens from the Bay of Cadiz. These sequences have the same origin in the Persian Gulf, but they have been attributed to different Alpheus species. Here we discuss these mismatches, and data about the distribution in the Gulf of Cadiz as well as the habitat of Alpheus cf. lobidens. Additionally, DNA barcodes, and a detailed morphological description and illustrations are provided. Some hypotheses about possible ways of introduction are discussed, and the most plausible route seems to be a natural expansion to the west after entering the Mediterranean Sea by the Suez Canal.

Genetic Relationship Analysis of Genus Nomorhamphus from Lindu Lake, Central Sulawesi and Adaptive Responses to Exposure Different Light Wavelengths

Graphical Abstract Highlight Research Genus Nomorhamphusfrom three river inlets of Lindu Lake, Central Sulawesi was identified as Nomorhamphus with CO1 gene. Green wavelength can accelerate growth and maturation. Wild fish Nomorhamphus can complete life cycles in an aquaculture environment. Domestication level two is completed. Abstract Genus Nomorhamphus is an endemic fish that can be found in Sulawesi, Indonesia. This fish belongs to the halfbeak group and has diverse colors and morphology. It has economic value as an export commodity in the ornamental fish trade. Exploration of the genetic relationship of genus Nomorhamphus in Central Sulawesi is still limited. Nomorhamphus's fulfillment of export demand still comes from wild catches. This study aimed to identify the genetic relationship of genus Nomorhamphus in the inlet rivers of Lake Lindu, Central Sulawesi, and evaluate the adaptation response of genus Nomorhamphus to different wavelengths of light exposure. Caudal fin of six fish from the three inlet rivers of Lake Lindu were preserved in 95% ethanol for DNA extraction purposes. This research used a completely randomized design with three treatment, namely rearing under white (400 nm), green (525 nm), and red (625 nm) light for 60 days. Each treatment had three replications in the form of aquariums, with each aquarium being filled with four fish. A total of 42 fish were utilized in the study. CO1 sequence was amplified with universal primers of FISH-F2 and FISH-R2. The PCR amplification products were then sequenced and performed with phylogenetic tree analysis. The genetic diversity analysis suggests that the genus Nomorhamphus of all three rivers, Lindu Lake, Central Sulawesi is one species as Nomorhamphus sp.. Male and female growth length and gonad maturation were developed faster under green light exposure, while survival rate, blood glucose level, and color quality were not significantly different under different light. Exposure of wild fish to green light Nomorhamphus sp. can accelerate gonad maturation and growth to accelerate domestication.

Occurrence and ecological risks assessment of representative herbicides in a plateau alkali lake: Implications water management in prairie lakes

Herbicide residues in surface waters pose a potential hazard to aquatic ecosystems. Moreover, there is a scarcity of data regarding the occurrence of herbicide residues in lakes predominantly surrounded by non-agricultural land. This study aimed to monitor and assess seasonal variations in four commonly used herbicides (i.e., acetochlor, pretilachlor, butachlor, and atrazine) in the surface waters of the Hulun Lake Basin in China. The results indicated that the target herbicides were widely distributed throughout the study area.The residues of the four herbicides in surface water ranged from non-detectable levels to 1,978.60 ng L−1. Among the herbicides, atrazine had the highest detection rate (90.48 %). When considering the temporal factor, the median concentration of the selected herbicides in the lake was significantly higher during summer (102.68 ng L−1) than that during spring (97.59 ng L−1) and autumn (6.78 ng L−1). Furthermore, there were spatial variations in the surface waters of the Hulun Lake Basin. The residual levels in the lake exceeded those found in the inlet river, and the concentrations of herbicides in the estuary of the Kerulen River and central area of Hulun Lake were higher. The environmental risk assessment results indicated that the selected herbicides posed acceptable risks to fish in the aquatic environment of Hulun Lake. However, the risk quotient (RQ) values for acetochlor and atrazine in relation to algae exceeded 0.10. Similarly, the RQ values for butachlor in relation to algae and crustaceans exceeded 0.10 during the summer and autumn seasons and even surpassed 1.00 in certain samples. This can potentially endanger the survival of aquatic organisms. The findings of this study offer valuable insights to support efforts in pollution control, environmental safety assessments, and decision-making regarding water resource management in the Hulun Lake Basin.

River water injecting into sea: Movement of sediments in stable stratified flows

The study of sediment movement in a stably stratified (each layer is less dense than the one below it) fluid is important for applications such as airborne virus transport, contaminant transport, and sediment settling in river inlets. This project will quantify the effect of sediment-driven instability on the horizontal motion of sediment in a stably stratified fluid. Experiments are designed to analyze this process by adding sediment-rich brine-free water to sediment-free brine, where salinity differences are used to construct stably stratified fluids. The experiments are done with salinity same as salty water with concentration of sediments derived from linear stability analysis. This work provide baseline experiments for sediment settling in a stably stratified fluids for numerical validations in the future.

Can Turbidity Data from Remote Sensing Explain Modelled Spatial and Temporal Sediment Loading Patterns? An Application in the Lake Tana Basin

Understanding the spatial and temporal patterns of sediment loading in water bodies is crucial for effective water quality management. Remote sensing (RS) has emerged as a valuable and reliable tool for monitoring turbidity, which can provide insights into sediment dynamics in water bodies. In this study, we investigate the potential of turbidity data derived from RS to explain simulated spatial and temporal sediment loading patterns in the Lake Tana basin, Ethiopia. Utilizing existing RS lake turbidity data from Copernicus Global Land Service (CGLS) and simulated seasonal and multiyear trends of river sediment loadings into Lake Tana from the Soil and Water Assessment Tool (SWAT + model), we estimate correlations at different river inlets into Lake Tana. The results reveal a strong positive correlation (R2 > 0.66) between the multiyear monthly average sediment load from inflow rivers and RS lake turbidity at most river inlets. This indicates that the simulated river sediment loads and lake turbidity at river inlets exhibit similar seasonal patterns. Notably, higher turbidity levels are observed at the river inlet with the highest sediment load export. These findings highlight the potential of RS turbidity products in characterizing temporal and spatial patterns of sediment loadings, particularly in data-scarce regions, contributing to a better understanding of water quality dynamics in such areas.

Impact of urbanization and land use on wetland water quality: A case study in Mengxi town

Wetlands provide critical ecological functions but are facing increasing threats from urbanization. This study assessed the impact of differentiated urban development approaches on wetland water quality in Mengxi town, Hangzhou, China. Water samples were collected from 48 locations in the Wuchang and Hemu wetlands from September 2021 to March 2022, covering different seasons. Parameters including COD, TN, TP, and NH4+-N were analyzed. The results showed the inlet water quality was heavily degraded, with NH4+-N concentrations up to 4.8 mg/L in January. The Hemu wetland showed improved water quality due to dilution effects after convergence of the two inlet rivers. However, NH4+-N and TN remained problematic, with average concentrations of 5.49 mg/L and 5.13 mg/L, exceeding the controlled standards. Statistical analysis identified paddy fields as the dominant contributor of TN (51%) and TP (41%) loads. The area contained 73.5% of total paddy fields obsereverd highest pollution levels. The results highlight the need for targeted agricultural runoff control and land use planning to conserve wetland ecological functions. This study provides important insights on differentiated impacts of urban development models on wetlands in southern China. The findings contribute to effective policy making for wetland water quality protection under rapid urbanization.

Spatial and Temporal Distribution and Risk Assessment of Heavy Metals in Surface Water of Changshou Lake Reservoir, Chongqing

To understand the water pollution status and environmental risks of Changshou Lake, the concentrations of heavy metals (Cr, Cu, Zn, As, Cd, and Pb) in the water were collected and analyzed during different seasons. The study investigated temporal and spatial variations, distribution characteristics, pollution levels, and health risks associated with heavy metals in Changshou Lake. The results showed that all six heavy metals were below than the Class Ⅰ standard of the Surface Water Environmental Quality Standard (GB 3838-2002), but recent years have witnessed an increasing trend, with Cu, As, and Pb showing a significant increase (P<0.05). The temporal and spatial distributions of these heavy metals were different. Temporally, Cr and Cd concentrations in surface water were higher in summer, As and Zn were higher in spring, and Pb and Cu were higher in autumn and winter. Spatially, the concentrations of Cr, As, Cu, Zn, and Pb showed higher concentrations in the southern outlet of the reservoir, the northwestern Longxi River inlet, and the central part of the reservoir, whereas Cd was higher in the northern stagnant area. The overall levels of heavy metals in the water body of Changshou Lake were low, with Cr and Cu slightly polluted, while other heavy metals were identified as having an insignificant pollution level. Drinking water was the primary exposure pathway to carcinogenic and non-carcinogenic heavy metals in surface water bodies. The health risk values of Cr and As in water bodies were high, ranging from 6.2×10-10 to 3.0×10-4 and 5.1×10-8 to 3.9×10-5, respectively. The corresponding contribution rates for children and adults to the total health risk were high, with Cr accounting for 87.18% and 87.20%, respectively, while As accounted for 12.73% and 12.71%, respectively. Therefore, it is crucial to prioritize environmental risks associated with Cr and Cu, as well as the health risks associated with Cr and As in Changshou Lake These findings provide a scientific foundation for water pollution control and environmental quality improvement in Changshou Lake, and rational development and utilization of water resources.

Spatial-temporal Distribution and Source Analysis of Polycyclic Aromatic Hydrocarbons in the Sediments of Poyang Lake

The concentrations, spatial-temporal distribution, and influencing factors of 16 polycyclic aromatic hydrocarbons (PAHs) in the sediments of Poyang Lake were studied, and a quantitative source analysis of PAHs in different areas of the lake was conducted. PAHs were widespread within the sediments. The concentrations of ∑16PAHs in the surface sediments of all sites ranged from 203 to 2 318 μg·kg-1. The concentrations of PAHs in the surface sediments of the lake body were higher than those in the surface sediments of the inlet rivers. The ratio of PAHs in Poyang Lake was 4 rings > 5 rings > 6 rings > 3 rings > 2 rings; the composition of 4-ring PAHs was dominant, and its content accounted for 86.11% of ∑16PAHs. The 2- and 3-ring and some 4-ring PAHs, including Flua and Pyr, were more susceptible to SOM, and the 4 through 6-ring PAHs were more susceptible to ORP and heavy metals and other environmental factors. Spatially, the higher concentration of ∑16PAHs occurred in the area of the lake adjacent to Duchang County and Poyang County, where the terrain was relatively closed, and the water exchange with the surrounding area was less than that in other sections, which was not conducive to the migration, transformation, and degradation of pollutants. In the temporal distribution, the changes in PAHs concentration level and the development of GDP in Jiangxi Province showed high consistency, and the influence of economic development and human activities might have been the main reason for the increasing PAHs concentration level. The main sources of PAHs in surface sediments of Poyang Lake included petroleum pollution and oil and coal and biomass combustion sources, and there were some spatial differences in PAHs sources in different regions. This study can provide a reference for PAHs pollution in surface sediments of Poyang Lake, which is important for the ecological environmental protection and management of Poyang Lake.

Investigating Temporal and Spatial Variations of Nutrient and Trace Metal Loading in Utah Lake (Utah, USA)

Utah Lake is one of the largest freshwater bodies in the West and a valuable resource for agricultural and recreational activities in the region. However, it has suffered elevated trace metal and nutrient levels since the pioneer settlement in 1847. The objectives of this project were as follows: (1) investigate the temporal and spatial variations of trace metal and nutrient concentrations in Utah Lake and its tributaries; (2) model trace metal and nutrient concentrations across the lake using GIS spatial analysis techniques. We collected floc layer sediment samples quarterly as well as monthly water samples for trace metal and nutrient analyses at designated sites. GIS spatial analysis techniques were used to model the trace metal and nutrient concentrations in the lake. Elevated trace metal concentrations in river and lake water samples have been detected, especially in the month of June. The GIS modeling revealed that the highest trace metal and nutrient concentrations were located at the deepest part of the lake and near the Spanish Fork River inlet, respectively. Moreover, the results indicate that Utah Lake is not well mixed horizontally but well mixed vertically. Our findings can help state agencies address issues in water quality and management related to human–environment interactions.

Organochlorine pesticide residues in water and sediments in river Kibos-Nyamasaria in Kisumu County: An inlet river of Lake Victoria, Kenya

The misuse of organochlorine pesticides (OCPs) and the lack of adequate regulations have led to contamination of rivers and lakes. In this study, we determined the concentrations of OCPs that have either been banned or restricted for use in the Kibos-Nyamasaria River during two seasons: wet (April-May) and dry (February-March). OCPs were analyzed using GC–MS. Nineteen pesticide residues were detected in the river (water) and sediments. In water, aldrin had the highest concentration of 8.33 ± 0.58 μg/L, dieldrin (8.67 ± 0.5 μg/L), endosulfan sulphate (0.23 ± 0.00 μg/L), α-endosulfan (0.19 ± 0.00 μg/L), methoxychlor (4.57 ± 0.03 μg/L) and α-HCH (3.47 ± 0.00 μg/L) during the wet season, while dieldrin (6.03 ± 5.1 μg/L), methoxychlor (3.43 ± 0.06 μg/L), and α-HCH (8.27 ± 0.06 μg/L) were above 0.1 μg/L detection limit during the dry season. In sediments, aldrin, methoxychlor, and δ-HCH were not detected in either season; however, dieldrin and β-endosulfan were detected only during the dry season. Additionally, OCPs were above 0.2 μg/kg (maximum residue level (MRLs). The concentration of OCPs increased downstream as the river approached Lake Victoria. Because some pesticides were present at levels beyond the recommended limits, strategies must be developed to reduce them and identify potential sources of banned pesticides.

Prediksi Distribusi Sedimentasi Terhadap Usia Guna Waduk Ameroro, Sulawesi Tenggara

The Ameroro River experiences significant sedimentation rates from year to year, along with rapid land cover changes. Due to the considerable benefits of the Ameroro River for the sustainability of life in Konawe Regency, it was decided to construct the Ameroro Reservoir as a means to fulfill irrigation needs and provide raw water for the community. Given the high sedimentation in reservoirs in Indonesia, it rapidly accelerates the aging of the Reservoir. One of the issues is the inadequate representation of sediment distribution in the reservoir, reducing the effectiveness of sediment control and management in the Reservoir. Predictions using HEC-RAS 2D reveal the sediment distribution in the Ameroro reservoir at locations STA 13872 in the upstream river and STA 4446 at the inlet, which is 7.7 km from the main river length from the Reservoir's axis and 4.5 km from the inlet river length. Sedimentation rates, based on riverbed material modeling and land cover, show an influx of sediment into the reservoir at 1,192,015 m3/year, comprising 662,275 m3/year from the upstream river and 529,739 m3/year from the inlet river. Calculations using the sedimentation deposition composition method and Brune's trap efficiency method indicate that the original Reservoir's lifespan of 107 years will be reduced to 85 years, deviating by 22 years from the plan. This implies that the Reservoir will reach the end of its useful life sooner than anticipated.

Halospeciosus flavus gen. nov., sp. nov. and Haladaptatus caseinilyticus sp. nov., halophilic archaea isolated from saline soil of an inland solar saltern and offshore sediment.

Two novel halophilic archaeal strains (XZGYJ-43T and ZJ1T) were isolated from Mangkang ancient solar saltern (Tibet, PR China) and Zhujiang river inlet (Guangdong, PR China), respectively. The comparison of the 16S rRNA gene sequences revealed that strain XZGYJ-43T is related to the current species of the family Halobacteriaceae (89.2-91.7% similarity) and strain ZJ1T showed 94.7-98.3% similarity to the current species of the genus Haladaptatus. Phylogenetic analyses based on 16S rRNA genes, rpoB' genes and genomes indicated that strain XZGYJ-43T is separate from the related genera, Halocalculus, Salarchaeum and Halarchaeum of the family Halobacteriaceae, and strain ZJ1T tightly clusters with the current species of the genus Haladaptatus. The average nucleotide identity, digital DNA-DNA hybridization and average amino acid identity values between strain XZGYJ-43T and the current species of the family Halobacteriaceae were 71-75, 20-25 and 59-68 %, and these values between strain ZJ1T and the current species of the genus Haladaptatus were 77-81, 27-32 and 76-82 %, respectively, clearly below the thresholds for prokaryotic species demarcation. These two strains could be distinguished from their relatives according to differential phenotypic characteristics. The major polar lipids of strain XZGYJ-43T were phosphatidic acid (PA), phosphatidylglycerol (PG), phosphatidylglycerol phosphate methyl ester (PGP-Me), mannosyl glucosyl diether (DGD-1; DGD-PA) and sulphated mannosyl glucosyl diether (S-DGD-1; S-DGD-PA), and those of strain ZJ1T were PA, PG, PGP-Me, DGD-PA, S-DGD-1 (S-DGD-PA) and sulphated galactosyl mannosyl glucosyl diether. Based on phenotypic, phylogenetic and genomic data, strain XZGYJ-43T (=CGMCC 1.13890T=JCM 33735T) represents a novel species of a new genus within the family Halobacteriaceae, and strain ZJ1T (=CGMCC 1.18785T=JCM 34917T) represents a novel species of the genus Haladaptatus, for which the names Halospeciosus flavus gen. nov., sp. nov. and Haladaptatus caseinilyticus sp. nov. are proposed, respectively.

The morphodynamics and sedimentology of a seasonally controlled microtidal tidal inlet: the Nariva River tidal inlet, Cocos Bay, Trinidad

Abstract The geomorphology and sedimentology of the Nariva River tidal-inlet complex, a microtidal fluvially influenced tidal-inlet complex, was analyzed. The complex comprises a recurved spit, an ebb-tidal channel, and an ebb-tidal delta. Morphological trends in the spatio-temporal evolution of the inlet complex were observed and recorded from Google Earth™ timelapse satellite images taken from 2003 to 2019. The two-dimensional internal architecture of the inlet complex and the sedimentary succession of the recurved spit, an ebb spit, the swash platform (of the ebb-tidal delta), a mouth bar (associated with the wet-season river-dominated inlet complex erosion), the ebb-tidal channel, and the adjacent foreshore were observed and documented from six shallow sedimentary cores. The Nariva River inlet width ranges from 17 to 40 m through its seasonal evolution, has a tidal prism of ∼ 2.17 × 105 m3, a cross-sectional area of 29.52 m2, and a depth ∼ 1.4 m (calculated at peak dry season near the inlet throat). The inlet complex undergoes an annual geomorphological evolution linked to the seasonally induced migration of the fluvial-to-marine transition zone (FMTZ). Increased fluvial discharge during the wet and hurricane seasons results in the basinward migration of the FMTZ rendering the inlet river dominated and resulting in the erosion of the inlet complex. During the dry season, low fluvial discharge, tidal dominance, and fair-weather conditions promote sedimentation in the inlet and the redevelopment of the inlet complex. The inlet has a complex (CX) internal architecture (fill pattern) defined by the laterally migrating recurved spit and ebb spit on their updrift margin, and conformable, mounded elements on their downdrift (e.g., mouth bar, swash platform, and foreshore). Two sedimentary successions were developed for ebb-tidal-delta deposits: off-axis of the ebb-tidal channel and on-axis. The off-axis succession is considerably similar to the adjacent foreshore-to-shoreface succession which can pose a challenge when attempting to identify these deposits in the rock record. The on-axis succession, however, despite thickness variability, showed a positive correlation to studied mesotidal tide-dominated inlet successions.

Quantification of sedimentary organic carbon sources in a land–river–lake continuum combined with multi-fingerprint and un-mixing models

Identifying organic carbon (OC) sources in lake sediment is essential for elucidating biogeochemical cycling processes and effectively supporting watershed management. However, the complexity of sources as well as environments in the land–river–lake continuum makes it challenging to accurately identify OC sources. Accordingly, the current study utilized a systematic approach to identify and validate OC sources in a typical land–river–lake continuum. Two tracer groups (group 1: δ13C and δ15N; group 2: fluorescence index and biotic index, respectively (where C is carbon and N is nitrogen)) and one model (MixSIAR) were eventually selected from five tracer groups and two models to identify the OC sources in a land–river–lake continuum according to a consistency evaluation and virtual mixing test. The results showed that the distribution of OC sources in lake sediment was spatially heterogeneous. Closer to the lake center (from sampling site S1 to S3), the autochthonous contributions increased while the allochthonous contributions decreased. Downstream of the inlet river (site S1) was dominated by allochthonous contributions (78.6%), especially cropland (28.7% ± 0.5%, where ± indicates a standard deviation range) and urban land (30.5% ± 2.5%). From site S1 to S2, the allochthonous contribution decreased 11.4%. Autochthonous OC gradually became the major source closer to the lake center (site S3: phragmites: 48% ± 4.5%). This distribution of OC sources in the land–river–lake system was attributed to the mixing effect of the autochthonous sources, selective transport of sediment, and human activities. The current findings may aid in validating the ability of different tracers and models to identify OC sources in complex ecosystems and also provide a theoretical basis for watershed management.

Nutrients transport behavior in inlet river in the Yellow River Delta in winter

The nutrients such as dissolved inorganic nitrogen (DIN, NH4+-N, NO2−-N, and NO3−-N), dissolved inorganic phosphorus (DIP, PO43−) and dissolved SiO2 (DSi) funneled by the inlet river are the dominant factors to coastal eutrophication. This study investigated nutrient transport process in typical inlet rivers in the Yellow River Delta. The indicator of coastal eutrophication potential and concentration ratio between upstream and downstream stations were used to evaluate the influence of different sources to the nutrient risks. It showed that urban areas are the most important source of the nutrients in studied rivers. The harbor and mariculture would have greater risk because of their proximity close to the coastal area. Wetland was a vital conversion to eliminate the river nutrients, and the retention could reach 80 %. It is imperative to protect and construct wetlands to reduce the nutrient pollution in the inlet river.

Is water resources management at the expense of deteriorating water quality in a large river-connected lake after the construction of a lake sluice?

River-connected lakes with floodplain characteristics have substantial effects on terrestrial hydrologic cycles and are highly sensitive to external disturbances; thus, large-scale hydraulic projects are often constructed in such lakes to mitigate problems in the water environment. However, the spatiotemporal dynamics of the water environment in river-connected lakes and the differences in the water environment before and after the hydraulic project operation have received little attention. Here, a well-established coupled hydrodynamic–water quality model was applied to estimate the effects of the Chenglingji Sluice (CS) operation on the hydrodynamic features and water quality of Dongting Lake, a typical river-connected lake in China. The model successfully reproduced the water level and water quality dynamics of Dongting Lake, with a Root Mean Square Error (RMSE) of 0.29–1.24 m for water level and a Mean Relative Error (MRE) of 5.76–10.28% and 6.25–8.14% for total nitrogen (TN) and permanganate index (CODMn), respectively. The spatiotemporal fluctuation of lake water levels was observed over different hydrological periods. Water quality varied considerably spatially, with considerable pollution in East Dongting Lake and the Xiang River inlet. Concentrations of NH3-N (ammonia nitrogen), TN, and total phosphorus (TP) first decreased and then increased during the study period, whereas CODMn concentrations displayed the opposite trend. After the CS operation, the water level increased to 27.11 m and the water surface area increased by 19.29% in the dry period; furthermore, the water quality in the CS operation scenario had low concentrations compared to that of the baseline scenario in the dry period, with concentrations ranging from 0.03 to 0.24 mg/L for TN, 0.001 to 0.015 mg/L for TP, 0.006 to 0.09 mg/L for NH3-N, and 0.02 to 0.22 mg/L for CODM, effectively improving the water environment of Dongting Lake. However, the subsequent reaction of the lake environment to changes in hydrological conditions after the CS operation requires further attention.

Spawning habitat characteristics of pond smelt Hypomesus nipponensis in small inlet rivers to Lake Yogo, central Japan

Spawning habitat characteristics of pond smelt Hypomesus nipponensis in small inlet rivers to Lake Yogo, central Japan