Search

Wave- and current-supported fluid mud on gently sloped continental shelves represents a type of sediment gravity flow capable of rapidly transporting substantial sediment over short periods, significantly contributing to coastal geomorphic evolution. To investigate the dynamics of intertidal fluid mud events, in-situ observations were conducted from May 9 to May 18, 2017, using a seabed tripod system at the lower intertidal flat of the central Jiangsu coast, China. Fluid mud was observed following a medium wind-wave event, with a maximum significant wave height of 0.42 m. The liquefied seabed, loosened by liquefaction, facilitated bed erosion and sediment resuspension. Fluid mud layers, with mean suspended sediment concentrations (SSCs) exceeding 10 g/L, periodically formed during high slack tide, early flood, and late ebb phases. These layers varied in thickness from 4 cm to 20 cm and exhibited strong stratification caused by suspended sediment. Fluid mud disappeared when the bottom turbulence kinetic energy exceeded a threshold of 0.00045 m2/s2 due to an increase in current velocity. The downslope movement of intertidal fluid mud was estimated using a theoretical buoyancy-friction model and validated by observed offshore-directed velocity jets at 0.1 m above the seabed during high slack tide phases. Additionally, onshore winds favored fluid mud formation during early flood phases, while offshore winds favored it during late ebb phases. These observations suggest that fluid mud can form on intertidal flats under conditions where tidal flows and winds align, contributing to a deeper understanding of the formation mechanisms of shallow gravity flows and the improvement of sediment transport models. [ABSTRACT FROM AUTHOR]

Introduction: This study investigates the characteristics of sediment disturbance caused by impeller rotation in reservoirs of inland rivers with high sediment content in China. A scaled experimental model, reflecting typical environmental conditions of inland water reservoirs in Northwest China, was established in Lanzhou, Gansu Province, following the principle of similarity. Methods: The study integrates numerical simulations using Ansys Fluent software and corroborates the findings through hydraulic experiments. Computational Fluid Dynamics (CFD) and the κ-ε Realizable model were employed to simulate the solid-liquid mixing process, which was verified against the experimental model. Results: The results indicate that increasing the impeller velocity from 2 rad/s to 8 rad/s, while submerged at a depth of 1000 mm in the flow field, enhances the rate of bottom sediment suspension. Furthermore, the rate of suspended sediment discharge from the model outlet increased with inflow velocity ranging from 0.1 m/s to 0.8 m/s. A decrease in the impeller's submersion depth from 600 mm to 1200 mm was found to reduce the maximum disturbance radius affecting the bottom sediment. Discussion: The reliability of the simulation was confirmed by comparing the software results with experimental data. This study provides insights into the mechanisms of sediment-laden flow disturbance in the reservoir areas of inland rivers in China and lays the groundwork for more comprehensive investigations into sediment discharge in these environments. [ABSTRACT FROM AUTHOR]

This article extracts the Qiantang River tidal bore, analyzing the water environment characteristics in front of the tidal line of the Qiantang River tidal bore and behind it. The Qiantang River tidal bore Index (QRI) was established using HY-1C, HY-1D, and Gao Fen-1 wide field-of-view (GF-1 WFV) satellite data to precisely determine the location and details of the Qiantang River tidal bore. Comparative analyses of the changes on the two sides of the Qiantang River tidal bore were conducted. The results indicate the following: (1) QRI enhances the visibility of tidal bore lines, accentuating their contrast with the surrounding river water, resulting in a more vivid character. QRI proves to be an effective extraction method, with potential applicability to similar tidal lines in different regions. (2) Observable roughness changes occur at the tidal bore location, with smoother surface textures observed in front of the tidal line compared to those behind it. There is a discernible increase in suspended sediment concentration (SSC) as the tidal bore passes through. (3) This study reveals the mechanism of water environment change induced by the Qiantang River tidal bore, emphasizing its significance in promoting vertical water body exchange as well as scouring the bottom sediments. This effect increases SSC and surface roughness. [ABSTRACT FROM AUTHOR]

In‐situ observations of hydrodynamics and suspended sediment concentrations (SSCs) were conducted on an abandoned lobe in the northern part of the modern Yellow River Delta, China. The SSC record at the site is found to be the superposition of a general trend (fast increase and slow decrease cycle) caused by storm waves (SubSSC1) and relatively smaller fluctuations caused by tidal currents (SubSSC2). Physically, this indicates that storm waves eroded the bottom sediments while tidal currents then re‐suspended and advected the suspended sediments in the study area. To further obtain the suspended sediment transport parameters, first, SubSSC1 is modeled with significant wave height which incorporates a "memory curve" to consider the remaining impacts of historical waves. It is detected that waves in the past 75 hr still influence the present SSC which is reasonable because 75 hr is roughly the typical duration of a normal storm. Second, SubSSC2 is modeled with tidal excursion and trigonometric functions with measured periodicities. Finally, some sediment transport parameters, for example, the background SSC, the horizontal SSC gradient, the tidal constituents that advect it, and their relative time lags are optimized from the best fits of the measured and modeled SSC time series. The proposed framework for model construction and parameter optimization can be extended to other sea areas for inferring sediment transport parameters from field SSC time series at a specific station. Plain Language Summary: The evolution of our coastal zone fundamentally depends on the transport volume and direction of sediment, and understanding them is very beneficial for our coastal engineering construction and long‐term planning. Conducting in situ observations on‐site is one of the most reliable methods, but its observation cost is expensive. Therefore, we hope to extract as much information as possible from as few observation points as possible. This article successfully extracted the above information from the observation data of a station. First, we analyzed the data to preliminarily clarify that the suspended sediment in the area mainly comes from local erosion resuspension and advection transport from other regions. Furthermore, we conducted data modeling (i.e., constructed mathematical expressions of suspended sediment components from different sources, but with undetermined coefficients). Finally, we adjusted the model parameters to approximate the measured results, determined the undetermined coefficients, and explained the practical significance of the undetermined coefficients in physics. The analysis method we proposed can be extended to other sea areas. Key Points: Storm wave‐induced suspended sediment concentration (SSC) variation is modeled with a "memory curve" of wave heightTidally‐induced SSC variation is modeled with tidal excursion and trigonometric functionsSediment transport parameters are estimated from the optimal matching of measured and modeled SSC time series [ABSTRACT FROM AUTHOR]

Since the 1970s, extensive land reclamation has been carried out in the Bohai Sea. However, reclamation activities were prohibited in 2018. Using the MIKE3 numerical model, this study selected 1976 and 2018 as representative years before and after reclamation, respectively, and developed a highly accurate three‐dimensional hydrodynamic and sediment transport model for the Bohai Sea. The model was employed to access the effects of reclamation on tidal waves, tidal prism, residual current, tidal flux (TF), and suspended sediment flux (SSF). The results revealed that after reclamation, the amphidromic points of M2 and S2 shifted southward near Qinhuangdao, and eastward near the Yellow River estuary. The M2 amplitude in the Bohai Bay exhibited a maximum increase of 30 cm. In the Bohai Sea, the tidal prism decreased by 3.95%, suggesting a decrease in water exchange capacity. The TF in the Bohai Sea and Laizhou Bay decreased by 0.7% and 12%, respectively, while increasing by 16% in Bohai Bay and 12% in Liaodong Bay, primarily due to the variations in tidal waves. Furthermore, SSF decreased by 6% in the Bohai Sea, but increased by 125% in Bohai Bay and 114% in Laizhou Bay. The significant increase in SSF in Bohai Bay and Laizhou Bay was mainly attributed to the higher suspended sediment concentrations and the stronger residual current velocities near the Yellow River estuary. This study provides comprehensive insights into the impacts of reclamation on TF and SSF in the Bohai Sea, which could contribute to marine resource development and the planning of environmental restoration projects. Plain Language Summary: In the Bohai Sea, land reclamation has been accelerated since 1970s. Due to negative effects on aquaculture and channel, reclamation activities were prohibited in 2018. However, no research on annual tidal flux (TF) and suspend sediment flux (SSF) in the Bohai Sea has been reported. We have established high‐precision hydrodynamic and sediment transport model to analyze the impacts of reclamation on TF and SSF in the Bohai Sea. The findings revealed that reclamation led to a decrease in TF in the Bohai Sea and Laizhou Bay, while caused an increase in TF in Bohai Bay and Liaodong Bay. After reclamation, the SSF decreased in the Bohai Sea, while increased in Bohai Bay, Laizhou Bay and Liaodong Bay. After reclamation, the suspended sediment concentration and residual current velocity near the Yellow River estuary increased significantly, which was the main reason for the significant increase of SSF in Bohai Bay and Laizhou Bay. The Bohai Sea served as both the "source" of Yellow Sea muddy area and the "sink" of Yellow River which carried a large amount of sediment. The research on how reclamation affecting the TF and SSF in the Bohai Sea was essential for the sedimentation system of the East China Seas. Key Points: After reclamation, the area of Bohai Bay reduced, however, the tidal prism increased by nearly 10% due to the increase of tidal rangeAfter reclamation, tidal flux and water exchange capacity decreased in the Bohai Sea and Laizhou Bay, while increased in Bohai BayAfter reclamation, sediment flux decreased in the whole Bohai Sea and increased in three bays, particularly in Bohai Bay and Laizhou Bay [ABSTRACT FROM AUTHOR]

A thorough understanding of the evolutionary trends of river bifurcation channels is crucial for effective estuarine management in China's Greater Bay Area due to significant morphological changes observed in river mouth channels. At this tide‐influenced river mouth, where suspended sediment transport is dominant, how river mouth bifurcated channels that have different angles to the major axis of the incoming tidal flow in the receiving basin evolve on decadal scales remains unclear. Based on a comparative analysis of historical bathymetric data and numerical experiments using a validated morphodynamic model, we developed a conceptual model to illustrate the two end members of the morphological evolution of river mouth channels: a low‐angle (<45°) main channel and a high‐angle (>45°) secondary channel relative to the major axis of tidal flow in the receiving basin. If the mouth outflow also has a low angle with the main channel, the incoming tidal discharge fluxes have first‐order control over changes in the evolutionary trend of the bifurcated channels by changing the partition of residual sediment discharges between the two bifurcated channels. For example, a high incoming tidal discharge that varies around the mean flow increases the partitioning of residual sediment discharges from the upstream channel to the low‐angle channel, facilitating tide‐induced erosion in the low‐angle channel. By contrast, a low incoming tidal discharge decreases the partitioning of residual sediment discharges from the upstream channel to the low‐angle channel, which facilitates fluvial‐induced erosion in the high‐angle channel. Thus, high tidal discharges usually coincide with the river mouth adopting a single channel, and low tidal discharges facilitate the formation of fluvial‐induced bifurcation. The historical evolution of the river mouth and modern velocity measurements corroborated results derived from model experiments. The conceptual model applies to river mouths where suspended sediment transport is dominant and influenced by angled incoming tides. [ABSTRACT FROM AUTHOR]

Total suspended solids (TSS) can be a useful indicator of environmental change in nearshore coastal environments. Understanding the mechanisms of TSS variations in response to environmental drivers is of broad interest for ecology and geomorphology. The Yellow River Delta (YRD) in China is a fragile coastal region that has been affected by human activities and climate change. Here, we investigated TSS along the YRD shoreline over two decades with time‐series satellite data (2002–2020). We observed that TSS concentration decreased significantly in nearshore waters (5‐m isobath) surrounding the YRD, especially in the LaiZhou Bay. During the same time period, wave height (WH) along the deltaic shoreline and sediment load from the Yellow River have decreased, while sea surface height (SSH) has displayed a positive trend. Our results indicate that WH and SSH play a major role in sediment resuspension and dispersion, while the YSD mildly affected TSS variability along the coast. Monthly bed shear stress triggered by waves was then computed using WH, wave period (WP), and SSH. Bed shear stress and TSS displayed a positive correlation. We concluded that seasonal oscillations in SSH in conjunction with wind waves are responsible for TSS variability in the shallow waters in front of the YRD. [ABSTRACT FROM AUTHOR]

Suspended sediment fronts (SSFs) significantly affect water quality, ecology, and geomorphological evolution of estuarine and coastal waters. Based on 10‐year suspended sediment concentration data derived from satellite images, the multiscale spatio‐temporal variability of SSFs in the Bohai Sea was studied. Frontal probability (FP) was used to quantify the intensity of frontal activity. The 10‐year averaged FP was higher near the coast and decreased with increasing offshore distance. The arc‐shaped distributions of FP near the Yellow River Estuary revealed two tidal shear frontal zones. In the eastern Bohai Sea, 13 finger‐shaped high‐FP areas reflected the spatial pattern and fine structures of tidal sand ridges. The complex topography and strong tidal dynamics provided the essential conditions for frontogenesis. The seasonality of frontal activity was dominantly regulated by the change in wind waves associated with monsoons and stratification. The direct or indirect effects of sediment discharges from the Yellow River and Liaohe River on seasonal and annual variations of frontal activity only existed within close proximity to the estuaries. Frontal activity generally showed an interannual weakening trend, especially in the Laizhou Bay (−0.27%/yr), while an opposite trend was identified in the Liaodong Bay (0.10%/yr). This phenomenon was related to the interannual variations of wind speeds. Meanwhile, wind speed anomalies caused by El Niño‐Southern Oscillation events could explain the significant interannual fluctuations in frontal activity such that, frontal activity was significantly enhanced (suppressed) when El Niño (La Niña) events occurred, especially during 2015–2016 (2017–2018). Plain Language Summary: Suspended sediment fronts, one of the most common phenomena in estuarine and coastal waters, are defined as narrow zones with large spatial changes in suspended sediment concentration over relatively short distances. The Frontogenesis and frontal variability of the Bohai Sea, east coast of mainland China have unique patterns because of its complex hydro‐sedimentary environment, but no relevant studies have been systematically conducted yet. In this study, the intensity of frontal activity in the Bohai Sea was quantified by using satellite observation data spanning 10 years. Our analyses revealed that strong frontal activity mainly occurred in areas with dramatic changes in topography and shoreline and distinct tidal features. The seasonal and year‐to‐year variations of frontal activity were closely related to wind waves, stratification, riverine sediment input, and El Niño‐Southern Oscillation events. Nevertheless, their influence mechanisms varied in different regions. The new findings are of significance to further investigate the sedimentary patterns and the ecological effects of sub‐mesoscale processes in the Bohai Sea, and can also shed light on frontal variability of semi‐enclosed shallow seas worldwide. Key Points: Geostationary Ocean Color Imager remote sensing data were used to quantify suspended sediment front variations in the Bohai SeaSpatial patterns and seasonal‐to‐interannual variability of frontal activity were revealedEffects of dynamic factors on the spatio‐temporal variations of frontal activity were analyzed [ABSTRACT FROM AUTHOR]

[Display omitted] [ABSTRACT FROM AUTHOR]

The ecology of the aquatic environment in Poyang Lake, the largest fresh lake in China, is notably impacted by the backflow from the Yangtze River, which conveys a high flux of sediments. This study employs a widely recognized numerical model to replicate the backflow in 2007 (the strongest backflow after the operation initiation of the Three Gorges Dam) to investigate the contributions of wind and backflow to the sediment transport process. The results show that the influences of wind and backflow on flow patterns and sediment transport processes have significant spatial heterogeneity. In the narrow waterway leading to the central lake area, hydrodynamics is mainly driven by backflow. Conversely, the hydrodynamics of the open expanse of the lake is primarily influenced by wind forces. Dominant wind leads to the formation of gyres, which significantly alter flow paths and push sediment into the upstream areas. As a result, the suspended sediment area expands at an average rate of 20.1-21.3 km² daily, marking a 75-85% surge compared to the no wind condition (11.5 km2). The study facilitates a deeper understanding of sediment transport processes in large lakes. [ABSTRACT FROM AUTHOR]

Effective management of reservoir sedimentation necessitates the characterization of flood events, especially in relation to the propagation of the flow peak (Qpeak) and the suspended sediment concentration peak (SSCpeak). This study, based on a one‐dimensional river network hydro‐sediment model together with field data, presents an exploration of the flood events in the Three Gorges Reservoir (TGR) with focus on the propagating characteristics of Qpeak and SSCpeak. The findings reveal that the main flood season (from July to September) contributed over 80% of the annual sediment load into the TGR, with the mainstream Yangtze and its tributary, the Jialing River, being the primary sediment sources. After the impoundment of the TGR, the propagation time of Qpeak decreases with the raise of the water level in front of dam (WLdam). The increases in Qpeak discharge extends the range of river reach dominated by kinematic wave, resulting in an increase trend in Qpeak propagation time. The propagating speed of SSCpeak is closely related to the ratio of sediment concentration to flow discharge and WLdam. Finally, the propagating durations of Qpeak and SSCpeak in the TGR are compared, and empirical formulas are proposed for quantifying their difference. [ABSTRACT FROM AUTHOR]

Suspended sediments have profound impacts on marine primary productivity and the ecological environment. The Yellow River estuary and its vicinity waters, with a high dynamic range of suspended sediment concentration (SSC), have important eco-environmental functions for the sustainable development in this region. The multispectral imager (MI) on board China's first Sustainable Development Goals Science Satellite 1 (SDGSAT-1) features seven high-resolution bands (10 m). This study employs multispectral imagery obtained from SDGSAT-1 with single-band and band-ratio models to monitor the SSC in the Yellow River estuary and its vicinity waters. The results show that SDGSAT-1 images can be used to estimate the SSC in the Yellow River estuary and its vicinity waters. The overall pattern of the SSC exhibits a notable pattern of higher concentrations in nearshore areas and lower concentrations in offshore areas, and the retrieved SSC can attain values surpassing 1000 mg/L in nearshore areas. The R2 values of both the single-band and the band-ratio models for SSC inversion exceed 0.7. The single-band model R(854) demonstrates superior performance, achieving the highest R2 value of 0.93 and the lowest mean absolute percentage error (MAPE) of 44.04%. The single-band model based on SDGSAT-1 R(854) tends to outperform the band-ratio models for waters with algal blooms, which may be used for inversions of SSC and/or suspended particulate matter (SPM) in the waters full of algal blooms and suspended sediments. The monitoring results by SDGSAT-1 suggest that the complex SSC distributions in the Yellow River estuary and its vicinity waters were highly impacted by the river sediments discharge, tide, currents and wind-induced waves. [ABSTRACT FROM AUTHOR]

Agricultural nonpoint source (NPS) pollution is still the main factor that affects the quality of rivers, lakes, and reservoirs. Starting from the study of the mechanism of NPS, taking the Yangliu small watershed in the Shaanxi section of the Hanjiang River Basin in China as an example, and based on the combination of measured data and models, this paper focused on the analysis of the characteristics of NPS between the runoff plot and small watershed. The results showed that with the rainfall and surface runoff, the nutrient concentration increased first and then decreased, and the highest occurred in the first half of the whole rainfall process. Rainfall, maximum rainfall intensity at 60 min (I60), runoff, and suspended sediment (SS) were all related to nutrient diversion loss. However, the correlation among rainfall, I60 , and runoff and the content of various forms of nitrogen and phosphorus were significantly higher than that of SS. Crop interplanting and terrace planting could play a significant role in reducing sediment and nutrient loss. For the analysis of NPS pollution in small watersheds, the time-variant gain model (TVGM) was used to simulate the missing flow in some months of the basin during the flood season. The average concentration method was used to calculate the NPS pollution load in flood season. It was found that total nitrogen (TN) and total phosphorus (TP) accounted for more than 92% and 69%, respectively. This study is expected to provide scientific basis for NPS pollution control in areas both regionally and worldwide. [ABSTRACT FROM AUTHOR]

Retrogressive thaw slumps (RTSs), which frequently occur in permafrost regions of the Qinghai-Tibet Plateau (QTP), China, can cause significant damage to the local surface, resulting in material losses and posing a threat to infrastructure and ecosystems in the region. However, quantitative assessment of ground ice ablation and hydrological ecosystem response was limited due to a lack of understanding of the complex hydro-thermal process during RTS development. In this study, we developed a three-dimensional hydro-thermal coupled numerical model of a RTS in the permafrost terrain at the Beilu River Basin of the QTP, including ice–water phase transitions, heat exchange, mass transport, and the parameterized exchange of heat between the active layer and air. Based on the calibrated hydro-thermal model and combined with the electrical resistivity tomography survey and sample analysis results, a method for estimating the melting of ground ice was proposed. Simulation results indicate that the model effectively reflects the factual hydro-thermal regime of the RTS and can evaluate the ground ice ablation and total suspended sediment variation, represented by turbidity. Between 2011 and 2021, the maximum simulated ground ice ablation was in 2016 within the slump region, amounting to a total of 492 m3, and it induced the reciprocal evolution, especially in the headwall of the RTS. High ponding depression water turbidity values of 28 and 49 occurred in the thawing season in 2021. The simulated ground ice ablation and turbidity events were highly correlated with climatic warming and wetting. The results offer a valuable approach to assessing the effects of RTS on infrastructure and the environment, especially in the context of a changing climate. [ABSTRACT FROM AUTHOR]

Purpose: Substantial quantities of sedimentary materials are transported from the Yangtze River toward the water level fluctuation zone (WLFZ) of the Three Gorges Reservoir (TGR). Sediment and riparian soil coring across the elevation gradient in the WLFZ of the TGR over a 6-year period are used to interpret deposition patterns, particle size properties, total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP), and nutrient ratios using fluvial and suspended sediment data from upstream under flow regime manipulation of the reservoir. Materials and methods: Sediment and associated riparian soil cores were extracted in 2013 and 2019 across various elevation gradients in the WLFZ of the TGR. A total of 15 sediments and 24 soil cores were extracted. The sectioned sediment and soil subsamples were analyzed for particle size distribution (PSD) (including sand, silt, and clay fractions); median particle size (MPS) distributions, TOC, TN, TP, and various nutrient ratios were calculated. Upstream suspended sediment and hydrological data were used to interpret sediment deposition, carbon, associated nutrient deposition, and storage dynamics across the elevation gradient. Results and discussion: Sediment deposition and relative fining of sediment and riparian soil were irregular, decreased with an increase in elevation, and increased with time. In 2013, the distributions of TOC, TN, TP, and nutrient ratios were irregular, and comparatively stable distributions were observed in 2019, which increased from lower to upper elevation gradient. With a few exceptions, similar trends were also observed in riparian soil core profiles. We conclude that water level fluctuations, water residence time, suspended sediment dynamics, time, and topography played a significant role in determining changes in sediment and riparian soil properties over time. Fine sediment-induced carbon and nutrient lateral translocations and subsequent interactions in sediment and soil layers due to repeated inundation cycles change the sediment and soil properties over time. Conclusions: This study interprets sedimentary carbon and nutrient redistribution and translocation processes. The concentrations of carbon and nutrients in sediments and soils change over time due to various fluvial, sedimentary, and geochemical processes, including the hydrological regime, flow regulation manipulation, repeated inundation cycles, water residence time, and suspended sediment dynamics. Fine sediment-associated lateral translocations cause the enrichment of these components in sediments and riparian soils. Sediment deposition is declining in this region due to environmental protection and conservation initiatives. [ABSTRACT FROM AUTHOR]

This paper uses the finite-volume community ocean model (FVCOM) coupled with the simulating waves nearshore (SWAN) in a wave–current–sediment model to simulate the tidal current field, wave field, and suspended sediment concentration (SSC) field in the sea area near Weifang Port, China. The three-dimensional water-and-sediment model was modified by introducing a sediment-settling-velocity formula that considers the effect of gradation. Next, the SSCs calculated by the original and modified models were compared with the measured data. The SSCs calculated by the modified model were closer to the measured data, as evidenced by the smaller mean relative error and root-mean-square error. The results show that the modified coupled wave–current–sediment model can reasonably describe the hydrodynamic characteristics and sediment movement in the sea area near Weifang Port, and the nearshore SSCs calculated by the modified model were higher than those calculated by the original model. [ABSTRACT FROM AUTHOR]

The Rouse formula and its variants have been widely used to describe the vertical distribution of the sediment concentration in sediment-laden flows in equilibrium. Han's formula extends the Rouse formula to non-equilibrium regimes, where the diffusive flux is still assumed to be Fickian. The turbulent flow and suspension regimes downstream of a mega-reservoir, e.g., the Three Gorges Reservoir, usually exhibit fractal and unsaturated properties, respectively. To characterize the non-Fickian dynamics of suspended sediment and the non-equilibrium regime in natural dammed rivers, this study proposes a new formula for the concentration profile of unsaturated sediment based on the Hausdorff fractal derivative advection–dispersion equation. In addition, we find that the order of the Hausdorff fractal derivative is related to the sizes of the sediment and the degrees of non-equilibrium. Compared to Rouse and Han's formulae, the new formula performs better in describing the sediment concentration profiles in the Jingjiang Reach, approximately 100 km below the Three Gorges Dam. [ABSTRACT FROM AUTHOR]

Sediment transport in coastal waters has an important impact on the siltation of port channels and changes in the estuary ecological environment. The southeast coast of China is often hit by typhoons, which can affect the suspended sediment concentration (SSC) in coastal waters. In this study, we used Geostationary Ocean Color Imager (GOCI) data to analyze SSC variations in Hangzhou Bay during Typhoon Maria (2018), and the influencing factors were also analyzed. The results showed that: (1) During the typhoon's transit, the SSC in Hangzhou Bay (HZB) increased by 200–800 mg/L, which was one-fold higher than the day before the typhoon. The variation of SSC on the south bank was noticeable, and the typhoon effect on SSC lasted for 2–3 days; (2) The wind speed and significant wave height (SWH) increased during the typhoon. In general, in the early stage of the typhoon, the SSC in HZB was affected by the wind, and in the interim and late period, SSC was influenced by the effect of wind and wave height; (3) Typhoon "Maria" accelerated the transport of sediment and land-based pollutants from land to sea; the effect of residual current and wind stress are the driving mechanisms for seaward sediment transport. However, mechanisms and driving factors of sediment transport in coast water are complex and diverse. The results of this study can help to understand the processes of riverbed erosion and deposition in Hangzhou Bay and adjacent waters. They are also significant for the study of nearshore hydrodynamic characteristics of typhoons and channel engineering. [ABSTRACT FROM AUTHOR]

The water level fluctuation zone (WLFZ) of the Three Gorges Reservoir (TGR) acts as an important sink for inflowing suspended sediment loads over the inundation periods following regular dam operations. This study depicts the sedimentary geochemical dynamics along a sedimentary profile based on the determined chronology and explores its links to the specific hydrological regime created by dam flow regulation and riverine seasonal suspended sediment dynamics. A compact 345-cm-long sediment core was extracted near the base water level (145.3 m) from the WLFZ of the TGR and sectioned at 5-cm intervals. Extracted sediment subsamples were analyzed for grain size composition, organic matter (OM), total nitrogen (TN), and geochemical elements (Na, K, Ca, Mg, Pb, Zn, Ni, Co, Mn, Cr, Fe, and Cu). The sediment core chronology was determined using 137Cs elemental analysis. Sedimentary geochemistry and grain size properties of extracted sediment core exhibited greater variations during initial submergence years till the first complete impoundment of the TGR (2006–2010). Afterward (2011–2013), although upstream inflowing suspended sediments and reservoir water level were comparable, sediment deposition and concentrations of sedimentary geochemical constituents showed considerably fewer variations. Seasonal variations in sediment deposition and geochemical composition were also observed during the rainy (October–April) and dry (May–September) seasons, in addition to annual variations. Grain size, OM, and other sediment geochemical constituents all had significant correlations with each other and with sediment core depth. The concentrations of geochemical elements in various sediment stratigraphic layers exhibited staggering associations with each other and were dependent on each other in several ways. The arrangement of geochemical elements in various stratigraphic layers of the extracted core illustrated amalgamation with inputs from upstream seasonal suspended sediment dynamics and reservoir water levels. During shortened submergence periods and higher input sediment loads, geochemical elements demonstrated impulsive distributions. Alternatively, during longer submergence periods, elemental distributions were relatively uniform attributed to higher settling time to deposit according to grain size and geochemical affinities. Higher suspended sediment loads in association with seasonal floods also resulted in rough sediment deposition patterns, imparting variations in the distributions of geochemical elements. Interim mediations in geochemical element concentrations are associated with seasonal distal flash floods and local terrace bank collapses, which generate significant amounts of distal sediment loads that are quickly deposited and are not sorted hydrodynamically. Overall, although a specific mechanism was devised to circumvent the siltation process, a considerable amount of sediment is trapped at pre-dam sites. In addition, siltation caused nutrients and geochemical elements' enrichment. [ABSTRACT FROM AUTHOR]

The scientific and accurate prediction of suspended sediment concentrations is of great importance for river management in the lower reaches of the Yellow River and for the scheduling of water conservancy projects in the upper and middle reaches. In order to solve the influence of the non-linear and non-smooth characteristics of the suspended sediment concentration series in the lower Yellow River on the prediction results and improve the prediction accuracy, this paper proposes a coupled model based on Complementary Ensemble Empirical Mode Decomposition (CEEMD) and non-linear autoregressive (NAR) model. Take the predicted suspended sediment concentrations in the lower reaches of the Yellow River at the Huayuankou hydrographic station as an example. The accuracy and stability of the coupled CEEMD-NAR model were verified through the Gaocun and Lijin hydrological stations. The CEEMD-NAR model predicted suspended sediment concentrations with a Nash–Sutcliffe efficiency (NSE) factor of 0.93. The three statistical evaluation indicators of the CEEMD-NAR model, mean absolute error (MAE), mean relative error (MRE), and root mean square error (RMSE) were 2.12 kg/m3, 1.07, and 3.75 kg/m3 respectively. In contrast to the NAR, EMD-NAR, and EEMD-NAR models, the coupled CEEMD-NAR model has good stability and high prediction accuracy and can be used in non-linear, non-smooth suspended sediment concentration long series prediction. [ABSTRACT FROM AUTHOR]

An estuarine turbidity maximum (ETM) functions as a filter and plays a key role in transporting suspended sediment. The features of ETM and their formation mechanisms vary with different types of estuaries. Their responses to morphological factors require further study. In this study, the Modaomen Estuary of the Pearl River was selected to examine the formation mechanisms of the ETM and roles of the mouth bar. Hydrodynamics, suspended sediment concentration, and sediment size distribution were measured via cruise shipboard in the mouth bar zone during the dry season of 2020, which indicated that the ETM occurred in the central and western bars. Furthermore, numerical modeling of an idealized estuary based on Delft3D was performed to explore the effects of the existence of a mouth bar on the dynamic structures causing the ETM, including saltwater intrusion, residual longitudinal circulation, and bed sediment resuspension. The results indicated that the existence of a mouth bar contributed to the occurrence of double residual circulations and enhanced bed shear stress on the mouth bar, which favor the ETM formation. In general, two different dynamic regimes were responsible for the ETM formation, that is, sediment trapping by saltwater intrusion and sediment resuspension induced by tidal currents. The mouth bar played a key role in these two mechanisms, including altering the estuarine circulation and bed shear stress. The results contribute to a better elucidation of the ETM formation in estuaries and provide scientific guidelines for estuarine management and engineering. Plain Language Summary: In estuaries, sediment can accumulate forming a sediment‐rich zone with high suspended sediment concentration. The occurrence and distribution of sediment‐rich zones affect water quality and ecological systems in estuary, as well as dredging and shipping needs, which has attracted significant interests of scientists and engineers. We have conducted a field survey to investigate the locations of the sediment‐rich zone and their causes. And we find that high sediment concentration mainly occurs on a shallow depth zone in estuary, which is caused by saltwater intrusion and sediment resuspension. Furthermore, we use a computer model to explore the roles of shallow topography on the accumulation of massive sediment. The results indicate that the shallow topography enhances the impacts of saltwater intrusion and sediment resuspension on sediment accumulation, favoring the occurrence of sediment‐rich zones. These findings have important scientific implications for estuarine management and engineering efforts. Key Points: Formation of turbidity maximum in different mouth bar zones was caused by estuarine circulation and sediment resuspension varying with timeSill topography favored the formation of double estuarine circulation and subsequently trapped sediment on the mouth barExistence of mouth bar enlarged the bed shear stress and then strengthened sediment resuspension caused by tidal current scouring [ABSTRACT FROM AUTHOR]

Lake Taihu is an important drinking water source for cities in the Yangtze River Delta region, while the dramatic fluctuation in turbidity has caused severe problems for local waterwork management. The effects of sediment resuspension and migration on turbidity of water intake in a waterworks located in the south of Lake Taihu are studied. Because the sediment behavior induced by wind disturbance was believed to be the main factor for the matter, the effect of wind field on the hydrodynamics and sediment distribution of Lake Taihu was conducted based on a wind-driven numerical model. The obtained results indicate that wind direction was more influential on the structure of flow and wave fields, while wind speed contributed more to the field intensity. The suspended sediment concentration (SSC) of water intake area was most sensitive to onshore winds, which led to significant increase in suspended sediment concentration at 3 m/s, while for alongshore winds, the incipient speed was 4 m/s, and offshore winds were less influential. In addition, the suspended sediment of the water intake area was primarily migrated from other erosion regions rather than local suspended particles. A 7-h lag was found between SSC and the measured turbidity confirmed the lag effect of wind disturbance on turbidity change. The high consistency between the 2 series demonstrated the potential of this method to turbidity prediction when combined with the weather forecast technique. [ABSTRACT FROM AUTHOR]

The rapid expansion of Porphyra farming in China lends considerable urgency to developing a satellite remote sensing retrieval method to monitor its cultivation, in order to promote sustainable economic development and protective utilization of ecosystem-oriented marine natural resources. For medium-resolution satellite imagery such as HY-1C images, pixel-by-pixel techniques are appropriate; however, many factors affect the retrieval accuracy of the Porphyra cultivation area. In coastal regions, Porphyra and suspended sediment radiate a similar spectrum, which inevitably causes errors in the identification of the Porphyra. To improve the overall retrieval accuracy of Porphyra cultivation area from medium-resolution HY-1C images, we considered suspended sediment concentration (SSC) as an independent variable and constructed a new model in conjunction with high-resolution Sentinel-2 satellite images using a linear regression method in Haizhou Bay, China. A comparative analysis was performed with a traditional random forest classification algorithm and pixel-based dichotomy model in different SSC seawater. The results showed that the new model expressed the best ability to supervise Porphyra cultivation area, and its overall relative error and root mean square deviation, whether in area or in validation sample points, were the lowest among the models. The experiment was performed by removing the SSC variable while using the same processes as in the new model, and the results indicate that the SSC played an important role in new model, which is suitable to be applied to coastal seawater containing more suspended sediment, as in the HY-1C coastal zone image. The application of the new model on temporal change in the retrieved results was indirectly verified as effective. This study provides an effective method to exactly extract Porphyra cultivation area in the coastal sea using medium-resolution HY-1C satellite imagery. [ABSTRACT FROM AUTHOR]

Han, Z.; Li, H.; Xie, H.; Yang, H.; Ouyang, Q., and Gong, S., 2022. Dredging of the Shenzhen-Zhongshan Link in the Pearl River Estuary, China: Short-term siltation mechanism for a trial trench. Journal of Coastal Research, 38(5), 988–998. Coconut Creek (Florida), ISSN 0749-0208. Understanding the short-term, particularly daily, siltation mechanism of a dredged trench is critical for immersed tunnel construction, as well as for offshore engineering and coastal management. This study explored the short-term siltation mechanism of the trial trench dredged for the Shenzhen-Zhongshan Link in the Pearl River Estuary, China. Monthly silting characteristics over a period of ∼11 months indicate that the silting intensity during the flood season was much larger than during the dry season. Local suspended sediment concentrations (SSCs) also varied on a flood–dry seasonal cycle, which were impacted by the suspended load from the Pearl River. Daily silting characteristics indicate that the silting intensity during spring tides were higher than during neap and moderate tides and that the local SSCs and flow velocities also varied on a spring–neap tidal cycle, which was dominated by periodic variations in the astronomical tide. The flow velocity deceased substantially from the surface to the bottom of the trench, and flow circulation occurred at the bottom of the trench, which aided the silting process. Seasonal changes in the sediment load from the Pearl River were the dominant cause of the changes in suspended sediment around the trench, which produced seasonal siltation changes in the trench. Daily changes in trench siltation were directly caused by the amount of sediment that entered the trench, which was affected by changes in the flow velocity and bottom SSC around the trench during the neap–spring tidal cycle. Although the high-siltation intensity during the flood season was unhelpful, the low-siltation intensity during neap and moderate tides was helpful for the construction of immersed tunnel during the flood season. [ABSTRACT FROM AUTHOR]

Sediment flocculation is a key process for the deposition of fine-grained sediments in the Three Gorges Reservoir (TGR) of China. Sediment flocculation influences the evolution of the river regime, but also hampers the smooth navigation in the long term. However, the flocculation process and its controlling factors are poorly understood. We experimentally determined the flocculation properties of cohesive sediment of samples from the TGR (predominantly a mixture of clay and silt) over a range of turbulent shear rates and sediment concentrations. The experiments were conducted in an almost isotropic turbulence field, which was simulated by an array of horizontal oscillating grids in a water tank. Sediment flocculation was recorded by a camera and investigated by image analysis. Our new data indicate that flocculation is generally a response in equilibrium median floc size (df,50) to the increase of the shear rate G. The peak value is attained at G = 16.5 s−1, where df,50 is 81.3 μm (for the suspended sediment concentration (ssc) = 0.4 g/L) and 107 μm (for ssc=0.7 g/L), respectively. At low shear rates (G < 16.5 s−1), the equilibrium floc sizes df,50 increase with rising shear rate G and is inversely related to the Kolmogorov micro length scale η. We attribute this variability to an insufficient deposition time of the sediment flocs in the water tank. Settling velocities, calculated from our experimental data of the floc sizes, are almost consistent with in-situ measured settling velocities, and are ten times larger than the terminal settling velocity of primary particles as calculated from Stokes' law. [ABSTRACT FROM AUTHOR]

Resuspended sediment is an important carrier of underwater material circulation, and bed shear stress is usually considered to be closely related to sediment resuspension. To analyze the resuspension dynamics in severely eutrophic Lake Chaohu, China, three fixed stations were set up to collect wave, current, and suspended sediment concentrate (SSC) data under windy weather, and two significant sediment resuspension events were recorded. Based on the Gaussian-shaped spectrum characteristics of waves in Lake Chaohu, the wave orbital velocity was estimated by using the wave parameter method. The selection of the general wave spectrum is important for the accurate estimation of wave orbital velocity. The results of the simple linear wave method were very similar to those of the wave parameter method with a Gaussian-shaped spectrum in Lake Chaohu. The total bed shear stress combining waves and currents during the observation period was calculated, and most of it was contributed by wind-driven waves. The bed material of Lake Chaohu has silt-enriched and weak cohesive features, and an examination of critical shear stress showed that the modified Shields curve method was still applicable to Lake Chaohu. When a sediment resuspension event occurred, the vertical gradient of SSC increased significantly, and the peak SSC value depended on the peak value of bed shear stress. As a predictor, bed shear stress only showed a good linear relationship during sediment resuspension events. At other times, the prediction of SSC using bed shear stress may be biased, especially at the time after a significant sediment resuspension event. [ABSTRACT FROM AUTHOR]

Marsh creeks are perceived as important conduits for transporting water and sediment between mudflats and marshes. In order to advance the understanding of the transport mechanisms in creeks, the source and ultimate sink of sediment which moves between mudflats and marshes through creek channels need further investigation. Therefore, two field campaigns were conducted in two intertidal systems with varying sediment availability. The water depth, flow velocity, suspended sediment concentration, and bed level change were measured simultaneously in a marsh creek and on the adjacent mudflat in Chongming Island (China) and in Paulina Saltmarsh (the Netherlands). Paulina Saltmarsh is much smaller, more frequently flooded, and has lower sediment concentration than Chongming. These contrasting conditions allow for a comparison of transport mechanisms and functioning of the creek. Both systems first show that the high suspended sediment concentration (SSC) measured in marsh creeks is mainly the consequence of sediment advection rather than local erosion. In addition, erosion in marsh creeks is usually limited during ebb tides, reducing the export of sediment through these creeks. However, differences have been observed between two systems. The measured SSC was highly asymmetric between flood and ebb tides in Chongming. Large peaks in SSC during the flood period can be observed for most tidal cycles. The marsh creeks in Chongming therefore function as conduits for sediment import. Additionally, there are distinct overbank and underbank tides in Chongming. Sediment was trapped and retained in creeks during underbank tides, which can then be eroded and transported to the marsh during subsequent overbank tides. We also observed that mudflats in Chongming quickly recovered after erosion. These mechanisms have not been observed in Paulina Saltmarsh, where net sediment export via the marsh creek was observed due to a lack of abundant sediment in suspension during flood tides. Furthermore, the remaining bed surface of mudflats after an erosion event was stronger than before, limiting further erosion in Paulina Saltmarsh. These findings from the two systems indicate that the role of creeks in sediment import/export depends on the availability of sediment from mudflats, shedding light on nourishment strategies for salt marshes. • High SSC during flood tides in the studied marsh creeks is attributed to advection of sediment rather than local erosion. • Ebb tides were limited in suspended sediment by various mechanisms, reducing the export of sediment via marsh creeks. • Roles of marsh creeks in sediment delivery depend on the sediment supply from mudflats and hydrodynamic forcing in creeks. [ABSTRACT FROM AUTHOR]

Rivers are important sites for nitrogen (N) cycling processes. N removal is thought to occur predominantly in the benthic zone and the role of the water column is frequently neglected. Here, we find that the water‐air and sediment‐water fluxes of N2 and N2O decreased, while the water column production increased with stream order through 4‐year observations across six river networks in China. The water column contribution increased with stream order and accounted for more than 50% in rivers above fifth order. The increase in the contact area of suspended sediment (SPS)‐water caused by higher SPS concentrations and river depths resulted in the shift as river size increased. N removal and N2O emissions would be underestimated approximately by 50% if neglecting water column processes for the six river networks. This study highlights the necessity and provides a pathway to incorporate water column processes into models to balance the global N budget. Plain Language Summary: The entire global N budget remains out of balance, with total N inputs exceeding N losses. Streams and rivers serve as substantial recipients and processors of reactive N transported from terrestrial landscapes. The benthic zone is traditionally identified as a hotspot for N processing in fluvial systems. However, the role of the water column is poorly understood. Here, we found that the water column area‐basis production rates of N2 and N2O increased with stream order although volumetric‐basis production rates did not change significantly with stream order through 4‐year observations across six river networks in China. The water column contribution increased with stream order and became dominant in large rivers. The increase in the contact area of SPS‐water caused by higher SPS concentrations and water volume accounted for the shift as river size increased. The current estimates would underestimate riverine N removal and N2O emissions by approximately 50% if neglecting water column processes based on the upscaling results for the six large river networks ranging from first to eighth order. Thus, our findings provide insight into the understanding of riverine N dynamics and highlight the important role of water column processes in N upscaling for closing regional and global N budgets. Key Points: Water column contribution in N removal and N2O emissions increased with stream order and it played a dominant role in large riversThe increase in the contact area of suspended sediment‐water accounted for the increasing water column contribution with river sizeRiverine N removal and N2O emissions would be underestimated approximately by 50% if neglecting water column processes [ABSTRACT FROM AUTHOR]

Soil erosion has presented a major environmental threat to sustainable agricultural production in karst areas. Scientific control of soil erosion depends mainly on the sources of suspended sediment on the surface and suspended sediment in the underground rivers in the small watersheds in karst valleys. Among them, the typical karst areas are characterized by dual lithologic structures on the surface and underground. Taking the small watershed of Qingmuguan karst valley in Chongqing of southwest China as an example, accurate and rapid identification of the sediment sources was proposed for the targeted prevention and control measures of soil erosion. Soil samples were collected from four sediment sources, including carbonate rocks, clastic rocks, channels, and fissures. 41 soil physical and chemical properties were measured as the fingerprint factors, such as the radionuclide 137Cs, magnetic susceptibility (χ), Li, and As. The bilateral range and mean test were utilized to screen the 33 fingerprint factors. Further screening was performed on the 33 fingerprint factors to differentiate the sediment sources using the Kruskal-Wallis H nonparametric test. The fingerprint factors were screened with significant differences (P<0.05) among different sediment sources. A stepwise multivariate discriminant analysis was performed on the fingerprint factors with the significant differences between groups using the premise of Wilks' lambda minimization. The best combination of fingerprint factors was achieved in the Fe, 137Cs, Pb, V, and χfd. The composite fingerprint identification was finally used to quantitatively analyze the sources of suspended sediment in the surface and underground river outlets. The results show that there were certain regularities between rainfall, rainfall duration, rainfall intensity, and the contribution rate of potential sediment sources in the basin. The variation in the contribution rate of suspended sediment on the surface of carbonate rocks was proportional to the rainfall and rainfall duration. Specifically, the contribution rate of carbonate rocks increased gradually with the increase of rainfall and rainfall duration. There was no significant change in the contribution rate of suspended sediment on the surface of the channel with the rainfall. There was a gradual increase in the contribution rate of the carbonate underground suspended sediment, as the rainfall and rainfall duration increased. The contribution rate of fissures to the underground suspended sediment sources was inversely proportional to the rainfall, indicating a gradual decrease with the increase in rainfall. The average contribution rates of potential sediment sources in the watershed to the surface suspended sediment were ranked in the descending order of the carbonate rocks (43.62%) > channels (27.34%) > clastic rocks (17.30%) > fissures (11.74%). The average contribution rates of potential sediment sources in the basin to the suspended sediment at the outlet of the underground river were ranked as carbonate rocks (36.14%) > fissures (24.02%) > channels (22.93%) > clastic rocks (16.91%). There were totally different characteristics of soil erosion in the karst areas from those non-karst ones. In addition to the surface soil erosion and channel erosion, there was also soil leakage. The goodness of fit was greater than 80% for the surface and underground suspended sediment sources in the small watershed of Qingmuguan karst trough valley. Consequently, the credible model and composite fingerprint can be expected to effectively identify the main sources of the suspended sediment on the surface of the karst trough valley and the outlet of underground rivers. The finding can also provide a strong reference for the comprehensive management of small watersheds in the karst troughs. [ABSTRACT FROM AUTHOR]

Most of the existing results were related to the impact of land storms on sediment, and few explained the impact of storms on sediment movement and its formation law from the mechanism. At present, the research on the impact of storm on sediment suspension on the North Bank of Longkou City in the south of Bohai Sea was not clear. Therefore, this study aimed to explore the formation and mechanism of storm on suspended sediment from the perspective of hydrodynamic characteristics and sediment distribution by monitoring the impact of storm on sediment suspension in the south of Bohai Sea. A storm with wind speeds of 4.5–13.5 m/s occurred in the coastal area of the north side of Longkou City located in Southern Bohai Sea in April, 2015. Suspended sediment samples were obtained using automatic samplers, and the results showed that the suspended sediment content was 7.8 mg/L under normal weather conditions, which reached 121.2 mg/L at the highest during the storm event. Waves and tides were synchronously observed by acoustic Doppler current meter. Wave height was more closely correlated with wind speed when the wind veered to north, and the maximum wave height was 243 cm. The reciprocating motion of the current at the sampling site was strong, with the maximum current speed of 43.8 cm/s and a water depth of 10 m. The results of laser analysis showed that the bottom sediments were composed of 92% sand and 8% silt, with a medium diameter of 0.102 mm. From the experimental observation and result analysis, it was known that the strong dynamic process during storm surge led to the movement of sediment surface and the resuspension of sediment. [ABSTRACT FROM AUTHOR]

Natural and anthropogenic factors have led to a series of fluvial sedimentation and hydrological changes in the lower West River, China. To evaluate the influence of human activities on the channel's morphology and examine the hydrological responses, we analyzed channel adjustments and changes of low water levels in the main river channel between Wuzhou and Zhaoqing that occurred over the recent decades. Due to a remarkable decrease in the suspended sediment concentration, the suspended sediment outputs during this period were larger than the sediment inputs for 27 consecutive years from 1987 to 2013. Therefore, the riverbed became a sediment source, with a high scouring of riverbed material. Between 2004 and 2014, the channel capacity of the lower reaches increased by 302.02 × 106 m3, and the average riverbed elevation decreased by 2.21 m, approximately 11.8% of which was caused by bed sediment loss induced by natural scour through sediment depletion; the remainder was caused by waterway engineering and sand mining, accounting for 0.8 and 87.4%, respectively. Approximately 91.3% of 1,312 river cross‐sections exhibited downcutting, indicating significant adjustment of the riverbed. This resulted in a substantial decline in the low water level in the 44‐km upstream section above Ducheng, which is located at the end of the tidal limit during dry seasons. However, this change was not noticeable in the section below Ducheng owing to the small water surface gradient and tidal influence. These findings reveal that human activities are a major driving force in the evolution of large rivers and the complexity of the hydrological responses to riverbed downcutting in a tidal reach, providing useful information for future river sand mining management and navigable engineering design of the lower West River and other rivers. [ABSTRACT FROM AUTHOR]

Coastal turbidity maxima (CTMs) have been recognized on open coastal seas with elevated suspended sediment concentrations. Tidal pumping is often considered the major contributor to turbidity maxima in well‐mixed estuaries. However, its role in CTM formation on well‐mixed coasts remains unclear. Here, we propose a two‐dimensional depth‐averaged analytical model to explore residual sediment transport influenced by interactions between cross‐shore and along‐shore tidal currents. Observation data collected on the well‐mixed central Jiangsu coast (southern Yellow Sea), China, are analyzed by the model. The results display a persistent CTM close to the shore and show that the large along‐shore tidal velocity strongly influences the cross‐shore tidal pumping flux. The model calculation presents landward tidal pumping flux under horizontally homogeneous bed sediment distribution, illustrating the dominant role of tidal pumping in CTM formation within well‐mixed coastal water bodies. The model suggests that the significance of alongshore tidal current to cross‐shore sediment transport should be addressed in similar coastal environments. Plain Language Summary: Like estuaries, muddy coasts can also trap fine sediments and form zones with high suspended sediment concentration, which can impact water quality, nutrient exchange, and coastal ecosystem dynamics, as well as navigation and dredging needs. The formation and distribution of these sediment‐rich zones are of significant interest to engineers and scientists. In this study, we report a persistent area with massive fine sediments close to the coast where tidal mixing is intense (central Jiangsu coast, China), and develop a model to investigate the formation mechanism for high turbidity. Our model further shows that, in this area, the landward flood current carried more fine sediment than the seaward ebb current during a tidal cycle, which led to the accumulation of fine sediments near the coast. In addition, the nonlinear interaction between tidal currents along and across the shoreline enhanced this accumulation. These findings will enable more effective sediment and ecosystem management near muddy coasts. Key Points: The mechanism for coastal turbidity maximum (CTM) on a well‐mixed coast is revealed by a two‐dimensional analytical solutionTidal pumping dominates CTM formation in well‐mixed coastal seasInteractions between alongshore and cross‐shore tidal currents play an important role in cross‐shore sediment transport [ABSTRACT FROM AUTHOR]

Environmental factors of projects in the sea area, such as tidal current characteristics and sediment transport patterns, play a decisive role in the safe operation of the harbor. Based on the observation data of tide level, tidal current, suspended sediment, and surface sediment in the Port of Shenquan, this paper focuses on the study of the characteristics of tidal current and sediment of projects in the sea area. According to the measured tide hydrograph, it can be concluded that the tide in the Port of Shenquan is irregular diurnal, and the flow of rising and falling tides is basically rectilinear. The velocity of the neap tide is higher than that of spring tide, which is mainly related to the strong winds and waves. The sand source is limited, and the sediment concentration in the water is very low. The hourly sediment concentration in each station fluctuates within a narrow range, independent of hourly velocity change. The sediment is coarse and fine, with a distribution pattern of coarse near shore, fine in deep water, coarse in East and West, and fine in the middle, and the sorting coefficient of sediment is medium to well. [ABSTRACT FROM AUTHOR]

Bohai Sea, with the highest suspended sediment concentration in the world, has experienced a sharp decrease in sea surface suspended sediment concentration (SSSC) in the latest two decades. However, limited by the shortage of long‐term field observations, the spatiotemporal characteristics and mechanisms of the long‐term variation in the SSSC are still unclear. Based on remote sensing data, this study reconstructed the spatiotemporal SSSC distribution from 2003 to 2016, and found significant spatial difference in decadal SSSC variation in the Bohai Sea. The largest decadal SSSC decrease was observed in the southern Bohai Sea with an average annual decrease of 1.3 mg/L (decrease of 4.4% per year), while significant SSSC increase was observed in the central Bohai Sea with largest annual increase of 0.4 mg/L (increase of 5.0% per year). Significant seasonal differences in the SSSC decreasing were also revealed, and the SSSC decrease in winter and spring (0.46 mg/L/a) was 27.8% higher than that in summer and autumn (0.36 mg/L/a). Decadal wind speed data measured at 14 meteorological stations around the Bohai Sea indicated that wind speed reduction played the most important role in the decadal decrease in SSSCs, and significant SSSC decrease can only be found in sea areas with a significantly reduced wind speed. In addition, although the runoff and sediment discharge of the Yellow River also decreased during 2003–2016, they were not related to the spatiotemporal variation of SSSCs and their direct impact was limited to the range of 15 km from the estuary. Plain Language Summary: Long‐term and drastic changes in suspended sediment concentration (SSC) have been observed in the seas all over the world. The drastic changes of SSC inevitably have a significant impact on the marine ecological environment, geomorphic evolution, and biogeochemical cycle, and their variation mechanism have become the focus of geoscience research. It is generally believed that the long‐term changes of SSC in the seas near the large rivers were mainly affected by the changes of river runoff and sediment discharge. However, taking the Bohai Sea of China as an example, based on the data of satellite remote sensing, meteorological and river hydrological stations, this study clarifies that although the sediment discharge of the Yellow River, which ranks second in the world, has decreased greatly, its direct impact on SSC variation is limited to the adjacent estuarine areas. This work also points out that wind speed reduction plays the most important role in the decadal SSC decrease in the Bohai Sea. Influenced by climate change and human activities, estuaries and coastal seas around the world are facing the same problem of long‐term SSC variation. The conclusions of this work provide useful information for the long‐term SSC variation and regulation mechanism study. Key Points: Decadal decreasing trend of the suspended sediment concentration in the Bohai Sea was revealed using MODIS remote sensing dataWind speed reduction played the most important role in the decadal decrease in SSSCsThe direct impact of the Yellow River discharge decreasing on the decadal SSSC variations was limited to within 15 km from the estuary [ABSTRACT FROM AUTHOR]

River runoff and suspended sediment play a critical role in the chemical, physical, biological processes of Earth's ecosystems. We assessed the temporal changes in runoff and sediment load at both the annual and event scales in the Gushanchuan watershed in the middle reaches of the Yellow River. A total of 330 events, from 1955 to 2018, were selected to evaluate the relationships between rainfall, runoff, and suspended sediment load at the Gaoshiya gauging station. Significant reductions were examined in the maximum runoff peaks, suspended sediment concentration, total runoff, suspended sediment yield, and ratio of event runoff to annual total, whereas the ratio of event sediment yield to annual total remained relatively stable. Hysteresis analysis suggested that the complex loops, anti‐clockwise, and figure‐eight loops accounted for 93.7% of the total events in the watershed. High positive correlations were observed between the flood‐event sediment yield, runoff volume, maximum runoff peaks, and total rainfall amount. The flow‐sediment relationship can be well fitted by the proportional model, and was weaker in 1997–2018 than those in the periods of 1955–1979 and 1980–1996. Runoff during the rising limb of the event significantly contributed to the total runoff and sediment yield. Land use changes and various soil conservation practices were responsible for the decrease in the flood frequency and magnitude. The results of this study provide useful insights into the relationships between rainfall, runoff, and suspended sediment dynamics, and their responses to soil conservation practices. [ABSTRACT FROM AUTHOR]

Long-chain alkenones (LCAs) produced by phylogenetically classified Groups 1 and 3 Isochrysidales are increasingly used for paleotemperature and/or paleosalinity reconstructions in oligohaline lakes and marine environments. However, there are considerable difficulties in the paleoenvironmental interpretation of LCAs from Group 2 Isochrysidales thriving in saline lakes. The biggest challenge lies in our poor understanding of the complexity and ecological niches of individual Group 2 subclades in saline lakes. Here, we perform comprehensive analysis of haptophyte-specific 18S rRNA sequences and distributions of LCAs, and long-chain alkenoates (LCEs) in surface sediments and suspended particulate matter (SPM) from 37 saline lakes in northern China. These lakes span a large salinity gradient from 0.5 to 308‰. Combined with published genomic data of Group 2 Isochrysidales, our phylogenetic analysis reveals three Group 2 subclades occupying distinct ecological niches: one ice-related bloomer Group 2i and two warm-season bloomers Groups 2w1 and 2w2. Group 2i, the earliest seasonal bloomer, frequently co-occurs with Group 2w1 in sediments from saline lakes with relatively low to intermediate salinity waters, whereas Group 2w2 blooms in hypersaline waters. Based on existing data, C 39:4 methyl alkenone is a chemotaxonomic biomarker for Group 2i. %C 37:4 (relative abundance of C 37:4 to the total C 37 alkenones) values in the three Group subclades follow the order: Group 2i > Group 2w2 > Group 2w1. The %C 37:4 in sediment cores of saline lakes does not directly record past salinity changes, but instead reflects variable contributions in production by these three subclades. This could indirectly and partially reflect overall salinity changes in some lakes dominated by Groups 2i and 2w1, but can be more complicated in lakes dominated by other assemblages. For our sites, we also demonstrate that direct use of C 37 alkenone unsaturation indices (U 37 K , U 37 K ' , and U 37 K ' ' ) for paleotemperature reconstructions in saline lakes is generally not feasible, except for cases where alkenone-producing Isochrysidales are dominated by one single species/subclade and seasonal production effects can be circumvented. We propose two possible alternative proxies for paleotemperature reconstructions in saline lakes: 1) unsaturation ratios of C 41 and C 42 alkenones, as these compounds are predominantly produced by a limited number of Group 2 species, such as Isochrysis nuda (Liao et al., 2020); 2) C 38 Et/C 36 OEt ratio (ratio of C 38 ethyl alkenones and C 36 ethyl alkenoates), which appears to have similar temperature sensitivity for Groups 2w1 and 2w2, in lakes with no Group 2i inputs. Our study provides new insights into the phylogenetic classifications of Group 2 Isochrysidales and their ecological/environmental niches, which are fundamental for more quantitative and rigorous applications of LCAs and LCEs in saline lakes as paleosalinity and paleotemperature proxies. [ABSTRACT FROM AUTHOR]

Purpose: The effective removal of internal pollution is of great importance for lake management and eutrophication control in shallow lakes. A new technology for collecting internal pollution was tested in a shallow lake. Methods: The surface sediments of shallow lakes have a low density and flow easily. Under the disturbance of wind-induced waves, such sediments will resuspend and enter the water body from the bottom of the lake and move horizontally with lake currents. Based on these characteristics, bottom traps were installed in the bottom of Lake Chaohu, China, to capture the internal pollutants in suspended sediments. Results: Static water environments can be formed inside the traps. The amount of chlorophyll a and organic matter in the sediments inside the traps was approximately 3.0–4.0 times and 1.5–2.0 times greater than in the surrounding sediments, respectively. After long-term collection by traps, the average reduction of chlorophyll a, organic matter, total nitrogen, and total phosphorus in the surrounding sediments were approximately 8–14%, 9–14%, 27–48%, and 0.5–2%, respectively. A trap with a width of 4 m can collect surface sediments within a 400 m wide area (200 m on both sides of the trap). Conclusion: Bottom traps can collect a large amount of surface sediment, which can be treated with desilting, which have little impact on the lake bottom ecosystem and biological community. Compared with ecological dredging, an investment of more than 50% can be saved. It has a broad application potential for the collection and removal of internal pollutants in shallow lakes. [ABSTRACT FROM AUTHOR]

Understanding sediment sorting and bedding dynamics has high value to unravelling the mechanisms underlying geomorphological, geological, ecological and environmental imprints of tidal wetlands and hence to predicting their future changes. Using the Nanhui tidal flat on the Changjiang (Yangtze) Delta, China, as a reference site, this study establishes a schematized morphodynamic model coupling flow, sediment dynamics and bed level change to explore the processes that govern sediment sorting and bedding phenomena. Model results indicate an overall agreement with field data in terms of tidal current velocities, suspended sediment concentrations (SSCs), deposition thicknesses and sedimentary structures. Depending on the variation of tidal current strength, sand‐dominated layers (SDLs) and mud‐dominated layers (MDLs) tend to form during spring and neap tides, respectively. Thinner tidal couplets are developed during daily scale flood–ebb variations. A larger tidal level variation during a spring–neap tidal cycle, associated with a stronger tidal current variation, favours the formation of SDLs and tidal couplets. A larger boundary sediment supply generally promotes the formation of tidal bedding, though the bedding detail is partially dependent on the SSC composition of different sediment types. Sediment properties, including for example grain size and settling velocity, are also found to influence sediment sorting and bedding characteristics. In particular, finer and coarser sediment respond differently to spring and neap tides. During neap tides, relatively small flow velocities favour the deposition of finer sediment, with limited coarser sediment being transported to the upper tidal flat because of the larger settling velocity. During spring tides, larger flow velocities transport more coarser sediment to the upper tidal flat, accounting for distinct lamination formation. Model results are qualitatively consistent with field observations, but the role of waves, biological processes and alongshore currents needs to be included in further studies to establish a more complete understanding. [ABSTRACT FROM AUTHOR]

Accurate estimate of riverine material fluxes in dissolved and suspended particulate forms is a fundamental issue in monitoring water environments of large basins. Here we collected sub-daily observations of dissolved pollutants (NO3−-N, NH4+-N, and DOC) and daily data of suspended sediment (SS) at eight gauging stations with controlling areas varied from 694,700 to 1,705,400 km2 located in the Yangtze River basin of China, and selected optimal estimates for both dissolved and suspended particulate material fluxes from five time-averaging methods and two regression methods. The results showed that time-averaging methods generally performed better in estimating dissolved pollutants, while regression methods were more applicable for suspended particulate materials. Compared with the selected optimal methods, the conventional method generally overestimated material fluxes by 0.09–49.75% in most cases. Longer sampling interval and smaller controlling area often led to larger uncertainty in estimation and critical values of sampling interval and controlling area were generally found to be 10–20 days and 1.3 million km2 in the Yangtze River basin. [ABSTRACT FROM AUTHOR]

Purpose: The geochemistry of rare earth elements (REEs, La to Lu) in suspended sediments (SS) is generally controlled by weathering processes and the water environment. Although the concentrations and fractionations of REEs in SS have been reported in the Zhujiang River, China, their variations and controlling factors have not been researched. Thus, the objective of this study was to identify the REE controlling factors in SS through their variations of concentrations and fractionations during 14 years (from 2000 to 2014). Material and methods: The concentrations of REEs, light REE (LREE, La to Nd), middle REE (MREE, Sm to Ho), and heavy REE (HREE, Er to Lu) in the SS of the Zhujiang River were investigated, and REE fractionation proxies including ∑LREE/∑HREE, ∑MREE/∑HREE, and Ce and Eu anomalies were calculated. Furthermore, the Pearson correlation relationships between physicochemical parameters, REE concentrations, and REE fractionation proxies were analyzed. Results and discussion: The ∑REE concentrations of SS in the Zhujiang River varied from 35.9 to 396.4 mg kg−1 (mean 229.6 mg kg−1), higher than the world's rivers (mean 174.8 mg kg−1). Moreover, ∑REE, ∑LREE, ∑MREE, and ∑HREE concentrations increased along the flow direction. PAAS-normalized REE ratios showed that MREE in SS were enriched relative to LREE and HREE. The concentrations of all REEs in SS significantly correlated with Fe, Al, and K concentrations positively, while significantly correlating with Ca and Na concentrations in a negative trend. These correlation relationships between the concentrations of REEs and major metal elements were attributed to the spatial variation of rock distribution based on the same source (weathering processes and soil erosion) of REEs and major metal elements in SS. The physicochemical properties affected REE fractionation in SS, such as clay minerals, water pH, and dissolved oxygen (DO). During 14 years from 2000 to 2014, the decrement of soil erosion reduced the REE concentrations of SS in the upper reaches. Meanwhile, river water acidification resulted in the weakening negative Ce anomaly and positive Eu anomaly of SS. These results suggested that the variations of REE concentrations and fractionations in SS were mainly controlled by soil erosion and water pH in the Zhujiang River from 2000 to 2014. Conclusions: The concentrations of REEs in SS mainly depend on weathering processes, while REE fractionations are closely associated with river water physicochemical properties in the Zhujiang River. [ABSTRACT FROM AUTHOR]

Phosphorus is the primary eutrophication cause of river, lake, reservoir and estuary and it may be one of the principal pollutants for the agricultural watershed with middle and small cities. The sediment and phosphorus loads, related migration paths and contribution of source regions to receiving waters at different sections of a river basin are not clear. The modified Soil and Water Assessment Tool (SWAT) model was utilized to investigate the phosphorus loads and the relationships among water resources, sediment, and phosphorus loads in one of the important tributaries of the Three Gorge Reservoir (TGR) of China, and to investigate the retention dynamics of phosphorus in the river continuum and the influencing factors. It showed that under the scenario of rice terraces and ponds, the annual sediment loss and total phosphorus load were 125t and 2.5t, being reduced by 40%–80% compared to the natural slope scenario; the daily peak value of suspended sediment load was reduced by 30%–75%, and the relationship between the rainfall and runoff was weakened slightly; the retention rate of phosphorus sources reached 40%–78%. The results confirm that the rice terraces and ponds have altered local hydrological conditions, enhanced a substantial water, sediment, and phosphorus retention capacity that is highly consistent over time and space scales, thereby altering the predominant forms of phosphorus and improving the environmental resilience in soil and nutrition loss for the hilly watershed of the TGR. • Phosphorus and sediment loads are quantitative analyzed in a typical hilly watershed of TGR. • Rice terraces and ponds reduce the particle phosphorus concentration and flux up to 80%. • Response relationship among the flow, sediment and TP in different land use are altered at different degree. • Rice terraces and ponds improved the local environment residence at moderate and relative heavy rainfall. [ABSTRACT FROM AUTHOR]

Previous research methodologies for quantifying Suspended Sediment Concentration (SSC) have encompassed in-situ observations, numerical simulations, and analyses of remote sensing datasets, each with inherent constraints. In this study, we have harnessed Convolutional Neural Networks (CNNs) to create a deep learning model, which has been applied to the remote sensing data procured from the Geostationary Ocean Color Imager (GOCI) spanning April 2011 to March 2021. Our research indicates that on a small time scale, wind and hydrodynamic forces both have a significant impact on the prediction results of CNNs model. Considering both wind and hydrodynamic forces can effectively improve the model's prediction efficiency for SSC. Moreover, we have employed CNNs to interpolate absent values within the remote sensing datasets, yielding enhancements superior to those attained via linear or multivariate regression techniques. Finally, the correlation coefficient between CNN-derived SSC estimates for Jiaozhou Bay (JZB) and its corresponding remote sensing data is 0.72. Correlation coefficient and root mean square error differ in different regions. In the shallow water of JZB, due to water level changes, there is limited data, and the correlation coefficient in this area is about 0.5–0.6. In the central region of JZB with sufficient data, the correlation coefficient is generally higher than 0.75. Therefore, we believe that this CNNs model can be used to predict the hourly variation of SSC. When juxtaposed with alternative methodologies, the CNN approach is found to economize computational resources and enhance processing efficiency. • The missing values of remote sensing data were filled by deep learning model. • We analyzed the spatial distribution of SSC in Jiaozhou Bay and accurately simulated the hydrodynamics. • A simple and efficient CNNs model was established for predicting suspended sediment concentration. [ABSTRACT FROM AUTHOR]

Increasing the power generation and reducing the sediment deposition in a reservoir are two contradictory and incommensurable objectives. Hence, these two operational objectives rarely are considered simultaneously in reservoir optimization. This study proposes a method to balance sediment desilting and power generation in reservoirs, and to study their quantitative relationship. First, a formula to calculate the suspended sediment transport rate for reservoirs was established. Second, based on that formula, a multiobjective model was built that considers simultaneously, the sediment transporting efficiency and the power generation efficiency. The nondominated sorting genetic algorithm (NSGA-II) along with Pareto optimality was used to find the Pareto front of the model. The proposed method was applied to the Three Gorges project in China. The research results not only provide the Pareto front of the reservoir operation scheme, but also imply that the maximum annual sediment runoff was improved by 6% at the expense of 9% of the annual power generation. [ABSTRACT FROM AUTHOR]

Suspended sediment is a key driving factor in river evolution and ecosystem stability. However, there is a significant change in the annual suspended sediment loads in many basins under a current rapidly changing environment. Therefore, it is highly demanding to clarify the influencing factors and their attributions for the suspended sediment, thereby improving control measures of soil and water loss in basins. Taking the Ganjiang River in the Poyang Lake Basin of China as an example, the forest coverage rate increased by nearly 40% in the last 30 years, where there were 139 large and medium-sized reservoirs in 2014. In this study, the annual suspended sediment of the Ganjiang River Basin was firstly determined during the period of 1958-2014. Then, time-varying moment models were constructed for different types of probability distributions, where the factors of rainfall erosivity, forest coverage, and reservoir regulation were taken as explanatory variables. Finally, the Bayesian Model Averaging (BMA) was selected to combine four time-varying moment models for the simulation of annual suspended sediment load, and thereby to separate the attributions of different factors. The results were as follows: 1) Rainfall erosivity, forest coverage, and reservoir regulation were all key factors affecting the suspended sediment load. The time-varying moment model was constructed using four probability distributions (Gamma, Pearson-Ⅲ, Weibull, Lognormal) considering the time-varying of location and scale parameters, where the rainfall erosivity (Re), forest coverage rate (Fc), and reservoir regulation coefficient (Rc) were utilized as physical covariables. The distribution characteristics and process changes of annual sediment load were reasonably described in the study areas, with a Nash-Sutcliffe Efficiency coefficient (NSE) of 0.93; 2) BMA improved the simulation effect, while reduced model uncertainty, compared with the single time-varying moment model. The Root Mean Square Error (RMSE) and Relative Error (RE) of simulated value were 125.96×104 t/a, and 11.41%, respectively. The Containing Ratio (CR) and average band-width (B) of uncertainty interval were 94.47%, and 481.38×104 t/a, respectively. A fixing-changing method was selected to perform the attribution analysis of suspended sediment load using BMA under various scenario combinations. 3) The annual suspended sediment load showed a local trend in the study area from 1958 to 2014, with the change point year of 1989. There was a significant decreasing trend of annual suspended sediment load at the 5% significance level during the period from 1990 to 2014, due possibly to the increase of forest coverage during the regulation of large and medium-sized reservoirs. Specifically, the decreased sediment loads were 414.87×104 and 261.45×104 t/a, for the increase of forest coverage and reservoirs in 1958-1989, indicating a great contribution of 59.72% and 37.63%, respectively. The factor of rainfall erosivity increased the suspended sediment load by about 42.99×104 t/a, whereas, the forest coverage and reservoir regulation caused the decrease of 61.40×104t/a. Furthermore, the decrease of suspended sediment load was actually caused by human activities, indicating better agreement with the conclusions obtained by the double cumulative curve and sediment yield function. The dynamic characteristics of the first and second moment were well elucidated in the observed samples using the BMA based on time-varying moment models, with an exact description for the mean value and variance. Therefore, the attribution analysis on the suspended sediment load was more objective and reliable in practice. Some recommendations were made here to strengthen the protection of forest resources, and the scientific regulation of large and medium-sized reservoirs, further to improve the control ability of water and soil loss in the Ganjiang River Basin. [ABSTRACT FROM AUTHOR]

Suspended sediments, one of the most important factors affecting the water environments of inland lakes, are closely related to the migration and interaction of various pollutants. Existing studies show that the suspended sediment concentration can be accurately predicted based on assimilation methods coupled with hydrodynamic models. However, in the hydrological assimilation simulation process, the existing perturbation generation methods consider the perturbation error to follow a random Gaussian distribution, which does not consider the spatial variation characteristics of errors. Thus, in this paper, we proposed a new method that generates a hybrid perturbation field for the assimilation simulation instead of using random error. The proposed approach was validated through assimilation simulations of the suspended sediment concentration of Taihu Lake, China, and five assimilation experiments were conducted. The proposed method was compared with the existing methods for generating the perturbation field. After three days and 72 time steps of assimilation simulation based on the hybrid perturbation field, the proposed assimilation method provided results that were more consistent with the buoy-measured data. These findings demonstrate that the proposed method for generating a hybrid perturbation field has a higher simulation accuracy than other methods and is therefore effective and provides a new idea for the assimilation simulation of suspended sediment concentrations in inland lakes. [ABSTRACT FROM AUTHOR]

Confluences act as critical nodes in a river network as they affect flow, sediment transport, water quality, and ecological patterns. A complete knowledge about hydro‐morpho‐sedimentary processes at river confluences is still incompleted and it has been usually accepted that secondary flows are weak because of the significant role of form roughness in large rivers. In this study, two field surveys were conducted on the flow structure, suspended sediment transport and morphology of the confluence between the Yangtze River (the largest river in China) and the Poyang Lake (the largest freshwater lake in China). Dual counter‐rotating cells were observed during high flow conditions and a single secondary cell appeared in low flow conditions. These helical cells restricted the core size of high sediment concentration and downwelling flows acted as a barrier hindering the exchange of sediment between the two rivers. Furthermore, the observed large scour hole was likely related to the downwelling and upwelling flows caused by helical motions. In low flow conditions, the scour hole looked like a deep channel, which was likely related to a long‐surviving helical cell. The scour hole disappeared further downstream, when either the helical motion got weak during low flow conditions, or when a reverse helical cell occurred during high flow conditions. Hydrodynamics, suspended sediment transport and morphological features observed at such a large confluence demonstrated that river planform geometry and discharge ratio affected the flow structure, especially the helical motion. This in turn affected sediment transport as well as the local bed morphology. Key Points: Two field surveys on the river confluence of Yangtze River and the outflow channel of Poyang Lake were conductedFlow structure, suspended sediment transport, and morphology of this large river confluence have been studiedLarge‐size helical motions were observed that likely played important roles in suspended sediment transport and local morphology [ABSTRACT FROM AUTHOR]

Karst aquifers are highly heterogeneous, and non-stationary systems in terms of hydrodynamic properties. The investigation of the different transport properties and characteristics of a karst aquifer system (KAS) is of great significance for the management and protection of karst aquifers. To investigate the response of discharge (Q), suspended sediment (SS), and temperature (T) to the precipitation (P), we performed correlation, spectral, and wavelet analyses on the hydrologic time series that included mean daily value from 2009/1/1 to 2015/12/31 from the Nandong underground river system (NURS), a large (> 1600 km2) karst-groundwater basin in southern China. The long memory effects can be determined from the autocorrelation functions of the Q, SS and T implied that the NURS has a significant amount of storage. The sharp and narrow cross-correlation function (CCF) peaks and the cross-wavelet transform (XT) power spectrum of the SS vs. P indicated that the response of the SS to P was shorter than that of the Q and T, and also indicated that the weak memory effect and small inertia of the karst systems with regard to SS. The CCF and XT power spectrum indicated that an increase in Q was the main factor triggering the increase in SS, not precipitation, which is contrary to results determined for other karst springs. Furthermore, the XT and cross-wavelet coherence (TC) of T vs. the air temperature (Ta) was used to demonstrate that Ta is not a direct control on the T in the NURS, which can be misinterpreted when using the traditional correlation and spectral analyses. [ABSTRACT FROM AUTHOR]

An estimation of daily suspended sediment concentration (SSC) is required for water resource and environmental management. The traditional methods for simulating daily SSC focus on modeling the SSCs themselves, whereas the cross-correlation structure between SSC and streamflow has received only minor attention. To address this issue, we propose a stochastic method to generate long-term daily SSC using multivariate copula functions that account for temporal and cross dependences in daily SSCs. We use the conditional copula method to construct daily multivariate distributions to alleviate the complications and workload of parameter estimations using high-dimensional copulas. The observed daily streamflow and SSC data are normalized using the normal quantile transform method to relax the computationally intensive model of building daily marginal distributions. Daily SSCs can thus be simulated through the multivariate conditional distribution using previous daily SSC and concurrent daily streamflow values. The proposed method is rigorously examined by application to a case study at the Pingshan station in the Jinsha River Basin, China, and compared with the bivariate copula method. The results show that the proposed method has a high degree of accuracy, in preserving the statistics and temporal correlation of daily SSC observations, and better preserves the lag-0 cross correlation compared with the bivariate copula method. The multivariate copula framework proposed here can accurately and efficiently generate long-term daily SSC data for water resource and environmental management, which play a critical role in accurately estimating the frequency and magnitude of extreme SSC events. [ABSTRACT FROM AUTHOR]

Poyang Lake, the largest freshwater lake in China, is distinguished by complicated suspended sediment (SS) dynamics. Apart from lake currents, wind is an important form of natural disturbance in driving SS transport. Combining field data, laboratory experiments, and numerical simulations, we gained valuable insight into wind impacts on SS dynamics in Poyang Lake. (1) Lake current patterns exert great influence on the level of wind impacts. Due to reduced sediment carrying capacity, SS under weak current suffers from stronger wind influence than under strong currents. (2) Wind speed determines the degree of wind impact, not only affecting horizontal SS transport, but also regulating vertical dynamics. Winds exceeding critical intensity can enhance horizontal transport through both surface drift and Stokes drift at different water depths, triggering sediment suspension to feed the loads in overlying water. (3) Wind impact is influenced by lake morphology. The broad water surface in the central lake permits formation of continuous waves, leading to the largest SS fluctuation, from -10.05 mg·L-1 to +20.17 mg·L-1, while average variation in the south and north part of the lake is only -6.59 mg·L-1 to þ10.36 mg·L-1. (4) SS in four reserves are characterized by notable wind impact, while in the other two reserves SS show no obvious departure from values without wind. [ABSTRACT FROM AUTHOR]

The Lancang-Mekong River is one of the largest transboundary river shared by China and Southeast Asian countries. In recent years, the sediment issue in this large river has received extensive attention due to nutrient-rich sediment decreasing which is critical to ecological health, aquatic habitats, shipping, coastal erosion and agricultural and fisheries production. A wide range of studies on sediment yield, transportation and trapped by reservoirs are summarized. The main controversial topics include where the most sediment comes from, how to explain the abnormal relationship among suspended sediment loads observed along the mainstream, and the quantification of effect of human activities on sediment load change. There are five main issues unsolved, including unreliable observed sediment data in Lower Mekong River, weak basis of total sediment load of 160 x 106 t/a, low spatiotemporal resolution in model simulation, insufficient study of the land use change impacts in recent decades and inadequate research on sediment except for suspended sediment. Several possible ways to overcome these difficulties are also discussed. [ABSTRACT FROM AUTHOR]