Sedimentation of fine-grained deposits on coastal zones and continental shelves are important because of the association with chemical pollutants, and the implication to the impact on biological processes, the stratig...Sedimentation of fine-grained deposits on coastal zones and continental shelves are important because of the association with chemical pollutants, and the implication to the impact on biological processes, the stratigraphic correlations, and changes in sedimentary environments. The Yellow Sea continental shelf receives large quantities of sediment from the Huanghe （Yellow） River. Unfortunately, little attention has been yet paid to the sedimentation on the shallow shelf and its features, and the vertical sediment flux in the area is poorly understood. In this study, nine cores were collected in northern Yellow Sea by the R/V Science 1 in September, 1998 and 1999 to examine the sedimentation rate, sediment flux and the provenance with ^210Pb analysis. The 2^210Pb activity profiles showed that the vertical sediment flux ranged from 0.06 to 1.18 g/cm^2·a in the region. In central part of the area, there was a patch of fine-grained mud, with the flux below 0.33 g/cm^2·a. Most profiles were featured in two-segment model. Differences in the profiles reflected spatial and temporal variations in hydrodynamic and sedimentary processes. In order to determine the provenance and sedimentary setting in the area, the geochemistry of Ca, Fe, Sr, Cu, Ti and Rb in 11 surficial sediment samples were studied, which showed that in the central northern Yellow Sea, the mud deposit was from multi-source but mainly from the Huanghe River.展开更多
A Nortek acoustic Doppler current profiler (NDP) was installed on a moving vessel to survey the entrance to the Jinhae Bay on August 22~23, 2001. The current velocity and acoustic backscattering signal were collected ...A Nortek acoustic Doppler current profiler (NDP) was installed on a moving vessel to survey the entrance to the Jinhae Bay on August 22~23, 2001. The current velocity and acoustic backscattering signal were collected along two cross-sections; water samples were also collected during the measurement. The acoustic signals were normalized to compensate for the loss incurred by acoustic beam spreading in the seawater. The in situ calibration shows that a significant relationship is present between suspended sediment concentrations (SSC) and normalized acoustic signals. Two acoustic parameters have been determined to construct an acoustic-concentration model. Using this derived model, the SSC patterns along the surveyed cross-sections were obtained by the conversion of acoustic data. Using the current velocity and SSC data, the flux of suspended sediment was estimated. It indicates that the sediment transport into the bay through the entrance has an order of magnitude of 100 t per tidal cycle.展开更多
The sediment flux data, measured from a dry-hot valley of the Longchuan River, a tributary of the lower Jinsha River, were analyzed with Mann-Kendall test, Seasonal Mann-Kendall test and Sen’s test. In both the upper...The sediment flux data, measured from a dry-hot valley of the Longchuan River, a tributary of the lower Jinsha River, were analyzed with Mann-Kendall test, Seasonal Mann-Kendall test and Sen’s test. In both the upper reaches (Xiaohekou) and the lower reaches (Xiaohuangguayuan), the sediment fluxes showed a significant increase from 1970 to 2001, despite the fact that the water discharge did not change significantly during the period and numerous reservoir constructions which contribute to the trap of sediment. This can be attributed to the intensification of human activities, especially the activities related to land surface disturbances such as deforestation and afforestation, expansion of agriculture land, and road constructions. This increase is more significant in the lower reaches of the river observed at the place of Xiaohuangguayuan due to the dry-hot climate. The profound increase in sediment flux has significant implications for effective management of the sedimentation problems of the on-going Three Gorges Reservoir.展开更多
The Lanzhou-Xinjiang High-speed Railway runs through an expansive windy area in a Gobi Desert, and sand-blocking fences were built to protect the railway from destruction by wind-blown sand. However, the shielding eff...The Lanzhou-Xinjiang High-speed Railway runs through an expansive windy area in a Gobi Desert, and sand-blocking fences were built to protect the railway from destruction by wind-blown sand. However, the shielding effect of the sand-blocking fence is below the expectation. In this study, effects of metal net fences with porosities of 0.5 and 0.7 were tested in a wind tunnel to determine the effectiveness of the employed two kinds of fences in reducing wind velocity and restraining wind-blown sand. Specifically, the horizontal wind velocities and sediment flux densities above the gravel surface were measured under different free-stream wind velocities for the following conditions： no fence at all, single fence with a porosity of 0.5, single fence with a porosity of 0.7, double fences with a porosity of 0.5, and double fences with a porosity of 0.7. Experimental results showed that the horizontal wind velocity was more significantly decreased by the fence with a porosity of 0.5, especially for the double fences. The horizontal wind velocity decreased approximately 65% at a distance of 3.25 m（i.e., 13 H, where H denotes the fence height） downwind the double fences, and no reverse flow or vortex was observed on the leeward side. The sediment flux density decreased exponentially with height above the gravel surface downwind in all tested fences. The reduction percentage of total sediment flux density was higher for the fence with a porosity of 0.5 than for the fence with a porosity of 0.7, especially for the double fences. Furthermore, the decreasing percentage of total sediment flux density decreased with increasing free-stream wind velocity. The results suggest that compared with metal net fence with a porosity of 0.7, the metal net fence with a porosity of 0.5 is more effective for controlling wind-blown sand in the expansive windy area where the Lanzhou-Xinjiang High-speed Railway runs through.展开更多
Two kinds of regression equations are used to reproduce the sediment flux of the 26 small coastal watersheds in southeastern China.The first kind is the global equations suggested by Milliman and Syvitski(1992),Mulder...Two kinds of regression equations are used to reproduce the sediment flux of the 26 small coastal watersheds in southeastern China.The first kind is the global equations suggested by Milliman and Syvitski(1992),Mulder and Syvitski(1996),Syvitski et al.(2003),and Syvitski and Milliman(2007).The second kind is the modified equations revised by the characteristics of the coastal watersheds,including the drainage area,mean water discharge,and mean sediment discharge.Compared with the observations of the hydrometric stations,the global equations overestimate the sediment flux by 1–2 orders of magnitude.By using the modified equations,the accuracy of the estimated sediment flux is significantly improved,with the relative error in the range of 7%–24%.The reason for the overestimation mainly caused by different parameters’domain and regression coefficients between global rivers and study coastal watersheds.This study demonstrates that modification needs to be considered when using global regression equations to reproduce the sediment flux of the small coastal watersheds in southeastern China.展开更多
Continental shelf islands are contributors of terrestrial sediment supply to shelf regions,and the sediment flux from these islands shall be quantified.We calculated the sediment flux of continental shelf islands in t...Continental shelf islands are contributors of terrestrial sediment supply to shelf regions,and the sediment flux from these islands shall be quantified.We calculated the sediment flux of continental shelf islands in the southeastern China using two empirical equations under two preconditions.The first,the sediment load/yield of the islands has the same pattern as the adjacent small,mountainous rivers along the coastline;and the second,each of the islands was treated as a single catchment.The results show that the sediment supply from these islands reached an order of magnitude of 1 Mt/a,which is comparable to the supply from the local smaller rivers.A sensitivity analysis indicates that this value represents the lower limit of estimate;if the accurate amount of sub-catchments of any island is considered,then this value will be enhanced slightly.This study demonstrates that the sediment supply from continental shelf islands to oceans is an important factor affecting the regional sedimentation and,therefore,should be paid with attention.展开更多
This study sought to forecast water flow and sediment flux in the scheme as potential contributions for improved management in the Chókwè Irrigation Scheme (CIS). Fieldwork data was collected during dry (DS)...This study sought to forecast water flow and sediment flux in the scheme as potential contributions for improved management in the Chókwè Irrigation Scheme (CIS). Fieldwork data was collected during dry (DS) and wet (WS) seasons. Flow measurement was performed at 9 stations using a calibrated flow meter OTT C31. Water flow and sediment flux from 2004 to 2019 were used. Hydrodynamic forecast simulations were performed using Mann-Kendall test and ARIMA model for determination of temporal trends. Findings suggest higher values during DS for water discharge and sediment flux. Mann-Kendall test for sediment discharge trends was not significant at 95% significance level, except for the Offtake in WS. ARIMA test for the sediment discharges, at the Intake, for DS and WS, sediments were well described by the ARIMA model and gave a good result for the sediments. Good fit between the observed and the predicted ARIMA model was found. ARIMA model for sediment discharge at CIS based on AIC has a good fit for AR (p = 1), whereby, at the Intake the ARIMA p-value was 0.822 and 0.932, for WS and DS, respectively. Whilst in the Offtake, the ARIMA p-value was 0.877 and 0.893, respectively. These results can be used to improve the CIS management, both for water flow and sediment flux.展开更多
Reliable estimation of the mass-flux profiles of aeolian sediment is essential for predicting sediment transport rates accurately and designing measures to cope with wind-erosion. Vertical mass-flux profiles from seve...Reliable estimation of the mass-flux profiles of aeolian sediment is essential for predicting sediment transport rates accurately and designing measures to cope with wind-erosion. Vertical mass-flux profiles from seventeen wind-erosion events were re-evaluated using five typical models based on observed data obtained from a smooth bare field at the southern fringe of the Taklimakan Desert, China. The results showed that the exponential-function model and the logarithmic-function model exhibited the poorest fit between observed and predicted mass-flux profiles. The power-function model and the modified power-function model improved the fit to field data to an equivalent extent, while the five-parameter combined-function model with a scale constant（σ） of 0.00001 m（different from the σ value proposed by Fryear, which represented the height above which 50% of the total mass flux occurred） was verified as the best for describing the vertical aeolian sediment mass-flux profiles using goodness of fit（R2） and the Akaike Information Criterion（AIC） values to evaluate model performance. According to relationships among model parameters, the modified power model played a prominent explanatory role in describing the vertical profiles of the observed data, whereas the exponential model played a coordinating role. In addition, it was found that the vertical profiles could not be extrapolated using the five selected models or easily estimated using an efficient model without field observations by a near-surface sampler at 0 to 0.05 m.展开更多
In this study,a two-dimensional hydrodynamic and sediment transport model is established to quantify the influences of sea level rise on sediment transport in the Yangtze River Estuary(YRE).After validation,the model ...In this study,a two-dimensional hydrodynamic and sediment transport model is established to quantify the influences of sea level rise on sediment transport in the Yangtze River Estuary(YRE).After validation,the model was employed to investigate the sediment transport and seabed evolution under four different scenarios of sea level rise,specifically,0,0.5,1 and 1.5 m.The results reveal that there exists a‘transition point(TP)'of SSC in each main channel of YRE.Upstream of the transition point,the suspended sediment concentration(SSC)increases along with the rise in sea level,while downstream of the transition point,SSC decreases as sea level rises.Similarly,there are also transition points for topography evolution.The maximum scouring rate upstream of the transition points exceeds 4.32% for a 1.5 m rise in sea level,while the maximum deposition rate downstream of the transition points is 2.48%.The sediment fluxes from upstream to downstream in the branches of YRE are enhanced by the rise in sea level.The direction of sediment flux in the North Branch reverses downstream as sea level rises.The sediment flux from the North Channel towards downstream increases significantly,while there is no significant change in sediment flux for South Channel.Sediment deposition in the North Passage is also accelerated by sea level rise.In addition,the sediment flux from YRE to northern Jiangsu and Hangzhou Bay is also weakened by the rise in sea level.展开更多
Wind erosion is a key global environmental problem and has many adverse effects.The Mu Us Sandy Land of northern China is characterized by an arid climate,where vegetation patches and bare sand patches are usually dis...Wind erosion is a key global environmental problem and has many adverse effects.The Mu Us Sandy Land of northern China is characterized by an arid climate,where vegetation patches and bare sand patches are usually distributed mosaically,and aeolian activities occur frequently.Vegetation plays a significant role in controlling wind erosion.Artemisia ordosica is the most dominant native plant species in the Mu Us Sandy Land.It is urgent to study the wind-proof and sand-fixing effects of Artemisia ordosica in the Mu Us Sandy Land.This study analyzed the wind-proof and sand-fixing effects of Artemisia ordosica based on the field data of wind regimes,aeolian sediment transport,and surface change of Artemisia ordosica plots with four coverages(denoted as site A,site B,site C,and site D)in the Mu Us Sandy Land during the period from 1 June 2018 to 29 June 2019.The coverages of Artemisia ordosica at site A,site B,site C,and site D were 2%,16%,29%,and 69%,respectively.The annual average wind speeds at 2.0 m height above the ground for site A,site B,site C,and site D were 3.47,2.77,2.21,and 1.97 m/s,respectively.The annual drift potentials were 193.80,69.72,15.05,and 6.73 VU at site A,site B,site C,and site D,respectively.The total horizontal aeolian sediment fluxes during the period from 2-3 June 2018 to 6 June 2019 at site A,site B,site C,and site D were 4633.61,896.80,10.54,and 6.14 kg/m,respectively.Site A had the largest surface changes,and the surface changes at site B were significantly weaker than those at site A,whereas the surface changes at site C and site D were minimal.The results indicated that Artemisia ordosica significantly reduced the wind speed,drift potential,aeolian sediment transport,and surface changes.The higher the coverage of Artemisia ordosica is,the more obvious the effects of wind-proof and sand-fixing.Wind erosion would be effectively controlled in the Mu Us Sandy Land if the coverage of Artemisia ordosica is greater than 29%.These results provide a scientific basis for evaluating the ecosystem service function of Artemisia ordosica and the vegetation protection and construction projects in the Mu Us Sandy Land.展开更多
Based on the 2-D flow and sediment numerical model of the Yangtze Estuary and the Hangzhou Bay, the characteristics of water and sediment exchange in their joint waters is studied through quantitative calculation and ...Based on the 2-D flow and sediment numerical model of the Yangtze Estuary and the Hangzhou Bay, the characteristics of water and sediment exchange in their joint waters is studied through quantitative calculation and analysis of the characteristics of water flow and sediment transportation. The results show that there is periodical water and sediment exchange in this joint waters, that the net water exchange appears mainly between 0 - 6 m depth （theoretical datum plane, the same below） offshore and the maximum is near the depth of 2 m, and that the net sediment exchange mainly appears between 0 - 5 m depth and the maximum is near the depth of 3 m, indicating that the range of water flow passage is different from that of sediment transport from the Yangtze Estuary to the Hangzhou Bay. Combined with the results of numerical simulation, this paper also analyzes the hydrodynamical mechanism influencing water and sediment exchange between the Yangtze Estuary and the Hangzhou Bay, including tidal fluctuation, tidal current kinetic energy, tide-induced residual current and the trace of water particles. Finally, the sediment transportation passage on the Nanhui tidal fiat is discussed, and the results show that sediment is transported into the Hangzhou Bay from the south side of Shipilei, while sediment is brought back to the South Channel of the Yangtze Estuary from the north side.展开更多
The radionuclide ^（210） Pb is suitable for century-scale dating and has been used to calculate the sedimentation rate in a variety of environments. However, two common ways to apply 210 Pb dating techniques may give...The radionuclide ^（210） Pb is suitable for century-scale dating and has been used to calculate the sedimentation rate in a variety of environments. However, two common ways to apply 210 Pb dating techniques may give misleading results. One is ＂prolonging of age＂, i.e., using the calculated sedimentation rate to date back to 200 or 300 years.This practice must be treated with caution because the 210 Pb dating techniques do not guarantee direct dating for ages much older than 100 years. Another is ＂loss of age＂, i.e., the calculated time span between the topmost layer and the 210 Pb background layer in cores is less than 100 years when an apparent sedimentation rate is used in the calculation. Here, we propose that based on the principle of 210 Pb dating, the upper limit of age suitable for direct210 Pb dating is between 110 and 155 years. The ＂prolonging＂ application is acceptable only if the sedimentary environment in the past several hundred years was stable and the sedimentation rate was generally constant, and verification with independent evidence（such as historical records or biomarker methodology） is needed.Furthermore, after analyzing many published and collected data, we found four possible reasons for the ＂loss of age＂. First, the compaction effect of sediment should be corrected in laboratory analysis or else the calculated age will be underestimated. Second, the accuracy and uncertainty of 210 Pb activity measurement affect the judgment of the background. To be cautious, researchers are apt to choose a background activity with a younger age. Third,use of a slightly smaller value of supported 210 Pb activity in a calculation will lead to considerable underestimation of the time span. Finally, later-stage erosion and migration are common for sedimentation, which lead to loss of sedimentary records and are often reflected as a ＂loss of age＂ in cores. We believe that proper use of 210 Pb dating data may provide helpful information on our understanding of sediment records and recent environmental changes.展开更多
Tree uprooting is an important process which leads to many geomorphic consequences.Some of the most important are the transport of sediment and mixing of soil.The aim of this article is to make a detailed examination ...Tree uprooting is an important process which leads to many geomorphic consequences.Some of the most important are the transport of sediment and mixing of soil.The aim of this article is to make a detailed examination of the magnitude of sediment transport caused by an extreme windthrow event in three severely affected catchments.Also,a comparison is made of the windthrow event with a mass movement event in the aspect of the magnitude of sediment transport and soil mixing.The study was conducted in three second-to third-order catchments in the Tatra Mountains,where a strong foehn wind event caused extensive windthrow in 2013,and a high-magnitude rainfall event triggered mass movements in 2007.The volume of sediment uplifted by the uprooting event was calculated based on the mapping of root plates using high-resolution(0.04 m)aerial images and measurements of root plate volumes conducted in the field.The volume of sediment transported by shallow landslides was determined based on a Digital Elevation Model(DEM1-m resolution).Windthrows affected 34%,76%,and94%of the area of the investigated catchments.Most of the trees had fallen downslope.The direction of treefall was influenced by the slope aspect and steepness.Root plates and pits covered 1.3%,4.8%,and 5.4%of the area of the catchments.Sediment flux generated by the uprooting event,calculated for the entire area of each investigated catchment ranged from 8.1×10^(–4) to 9.9×10^(–3) m^(3) m^(–1) event^(–1).This was notably lower than the sediment flux generated by the mass movement event(also calculated for the entire area of each catchment),which was 1.8-6.1×10^(–2)m^(3) m^(–1) event^(–1).By contrast,uprooting affected a much larger area than the mass movement event,which underlines its significant role in the mixing of soil.展开更多
Foreset profiles of deltaic topography change corresponding to hydraulic conditions,and are influenced by water discharge and change rates of water discharge.To investigate the correlation between the transition of de...Foreset profiles of deltaic topography change corresponding to hydraulic conditions,and are influenced by water discharge and change rates of water discharge.To investigate the correlation between the transition of deposition rates on the foreset and the change rate of water discharge of temporary waxing and subsequent waning flows,we perform experiments on silty deltas that developed under several different hydrographic patterns.The findings are as follows:(1) Under flows with constant discharge,the deposition rate on the foreset was low at high water discharge and high at low water discharge because the separated flow became vigorous at high water discharge and prevented sediment supply onto the foreset.If the water discharge is not constant,the deposition rate shifted concurrently with water discharge only at extremely low change rate.(2i) In a waxing flow at low(but not extremely low) increase rate,the deposition rate gradually decreased with some time lag.(2ii) In the case of high increase discharge,intense erosion on the topset caused by rapid waxing made a large amount of silt move onto the foreset and the deposition rate temporary increased.(3) With ample time after waning stage,the deposition rate recovered to that at constant low water discharge in all runs.However,the transitional processes depended on not only waning rate but also waxing rate at before waning stage.(3i) In the case of high decrease rate of water discharge,the deposition rate abruptly decreased regardless of increase rate.(3ii) Even in the case of low decrease rate of water discharge,if the increase rate before waning stage was high,the deposition rate abruptly decreased.(3iii) Only in the case where both the increase rate and the decrease rate were low,deposition rate gradually increased.展开更多
Internal solitary waves can generate intense bottom currents and turbulent mixing over continental slopes, influencing the redistribution of sediments and pollutants, as well as driving changes in marine geomorphology...Internal solitary waves can generate intense bottom currents and turbulent mixing over continental slopes, influencing the redistribution of sediments and pollutants, as well as driving changes in marine geomorphology and ecosystems. However,owing to the lack of detailed quantitative measurements of the bottom boundary layer, the mechanisms and impacts of internal solitary waves in resuspending and transporting seafloor sediments remain poorly understood. In this study, we present highresolution in situ observations of hydrodynamics in the upper layer(14–265 m) and the bottom boundary layer(<1 m) in the continental shelf slope break zone. Our results reveal that strongly nonlinear internal solitary waves, which occur at the peak of semidiurnal tidal currents, trigger benthic storms at the seafloor. Unlike previously proposed global instability mechanisms, the suspended sediment concentration caused by these strongly nonlinear internal solitary waves reaches 60 times higher than the background value and exhibits sudden, transient peaks. The bottom shear stress(τ) is an order of magnitude greater than that in laboratory measurements, and the observed fluctuating pressure is approximately 2.3 to 7 times greater than that in previous coastal observations. The sediments stirred by benthic storms are transported vertically to more than 100 m above the seabed,with lateral transport extending tens of kilometres beyond the study area. This process is driven by the dynamic mechanism of“strongly nonlinear internal solitary waves lifting sediments, weakly nonlinear internal solitary waves assisted by internal tides,and contour currents transporting sediments.” The suspended sediment flux induced by internal solitary waves in the South China Sea is on the same order of magnitude as that of global dust storm emissions, 21.9 times the volume of Asian dust storms entering the sea, and approximately 21 times the fluvial sediment flux entering the northern South China Sea. These findings are significant for evaluating sedimentary processes and ecological–geochemical impacts in the northern South China Sea, offering a novel perspective on marine ecological environments and carbon sequestration processes.展开更多
Sediment fingerprinting technology is widely used to differentiate sediment sources.However,despite its long-recognized benefits,there it has been seldom applied to assess the variability of sediment sources during st...Sediment fingerprinting technology is widely used to differentiate sediment sources.However,despite its long-recognized benefits,there it has been seldom applied to assess the variability of sediment sources during storm events.In this study,sediment fingerprinting is used for four storm events to determine the dynamic changes in sediment sources throughout them in the black soil region in Northeast China.Three potential sediment sources—cultivated land,unpaved roads,and gullies—were effectively differentiated using four geochemical tracers(As,Be,Cs,and Cu),with an accuracy of 100%.The relative sediment contribution from each source was determined using linear and Bayesian mixing models.The mean absolute fit(MAF)values of the linear mixing model(MAF_(mean)=0.976–0.949)were higher than those of the Bayesian mixing model(MAF_(mean)=0.921–0.992),indicating that the first performed better.Cultivated land was the primary source of the sediment load,accounting for 59.03%of it(load-weighted mean=68.29%),followed by the gullies(37.15%,load-weighted mean=28.09%),and unpaved roads(3.90%,load-weighted mean=3.69%)for the four storm events.In addition,a high variability in sediment source contribution was observed during the storm events.Cultivated land was the dominant sediment source during storm events with higher sediment concentrations(logarithmic function,r^(2)=0.878,p<0.01),discharge(linear function,r^(2)=0.452,p<0.05),and sediment flux(logarithmic function,r^(2)=0.857,p<0.01),whereas the reverse was observed for gullies.Contrastingly,the contribution of sediment from unpaved roads remained relatively stable during rainfall events.This provides a potential means to assess dynamic changes in sediment contributions from different erosion units.Moreover,it provides data support for exploring soil erosion mechanisms and effective erosion control in the black soil region in Northeast China.展开更多
New high-resolution 3D seismic data image a submarine channel complex in the northern slope of the South China Sea. The channel complex stretches hundreds of kilometers across the slope and flows into the deepsea from...New high-resolution 3D seismic data image a submarine channel complex in the northern slope of the South China Sea. The channel complex stretches hundreds of kilometers across the slope and flows into the deepsea from the siliciclastic shelf margin, linking neritic environment to the pelagic plain. The evolution of the channel complex developed two sedimentary stages, stage Ⅰ （19.1-18.5 Ma） and stage Ⅱ （18.5-17.5 Ma）, separated by erosional surfaces. In the first stage, the complex was rifled with pure siliciclastic sediments, forming thick-massive sandstone intercalated by thin layers of mudstone. During the stage Ⅱ, the channel complex was deposited five carbonate-siliciclastic cycles. The unexpected channel-fifl carbonate deposits present allochthonous characteristics, suggesting the siliciclastic channel was surprisingly used to transport carbonate sediment from the adjacent neritic carbonate platform. By analyzing the periodical carbonate sedimentary process in the siliciclastic channel complex, we infer that it was related to the in situ carbonate production of the neritic carbonate platform and was most likely to be controlled by the relative sea-level changes. Unlike line-source carbonate slope aprons or smafl-sized carbonate channels, the large-sized siliciclastic channel complex links directly neritic carbonate platform to deepwater basin and can transport large volumes of neritic carbonates to the pelagic environment in a short period. The new findings help to estimate the contributions of neritie siliciclastic shelf and carbonate platform to deepwater slope more accurately. This study suggests that channel systems are more complex than expected and have significant implications on the conceptual models describing the deepwater sedimentary theory.展开更多
For the Hengsha East Shoal Promoting Siltation Project in the Yangtze River Estuary, this work developed a formula for calculating sediment carrying capacity based on variable coefficients and a mathematical model for...For the Hengsha East Shoal Promoting Siltation Project in the Yangtze River Estuary, this work developed a formula for calculating sediment carrying capacity based on variable coefficients and a mathematical model for suspended sedimentation using variable saturation recovery coefficients. Not only does the model yield good verification, preferably give the hydrodynamics and the sediment concentration, but also reach a good agreement between the simulation results andlux by tide for studying the effect the measured topographical changes in the promoting siltation zone of the Hengsha East Shoal. Moreover, this article proposes a method for examing the net sediment tran- sportation fs of the project of promoting siltation and comparatively analyzes the current siltation of the Hengsha East Shoal and siltation mouth layouts, entrance widths, entrance bottom elevations, and the impact of the South Main Dike on promoting siltation through calculating the net sediment transportation flux by tide over the fixed bed and the direct movable bed numerical simulations. The results are in good agreement with each other, indicating that the method for calculating the net sedi- ment transportation flux by the tide is also useful for assessing the project in promoting siltation. Finally, we use the modeling results to analyze the water and sediment diversion ratios and the changes in silting and scouting in riverbeds and draw the conclusion that the completion of the Hengsha East Shoal Promoting Siltation Project would not adversely affect the Yangtze River Estuary Deepwater Channel Project.展开更多
Two field campaigns in Dafeng and Jianggang were organized to compare spatial variations of hydrodynamic characteristics and sediment transport patterns on intertidal flats of different types with distinct human inter...Two field campaigns in Dafeng and Jianggang were organized to compare spatial variations of hydrodynamic characteristics and sediment transport patterns on intertidal flats of different types with distinct human interferences along middle Jiangsu coast, China. The major contributors to the different patterns of sediment dynamics between the two tidal flats were offshore tidal current field and human interference. Offshore tidal force provide the basic setup of tidal current patterns on tidal flats, which is then modified by local morphology. Seawalls parallel to coast reduce tidal flat width, forcing tidal energy to dissipate within a shorter distance and thus influencing tidal flat morphology. Seawalls vertical to coast and major tidal current significantly reduce tidal current speed, which favors sediment deposition on tidal flats. Two seawalls built on both sides of the observational tidal flat profile caused much reduced current speed at Dafeng tidal flat, comparing to the offshore station. Being exposed to offshore radial tidal currents, hydrodynamics at Jianggang was much stronger than that at Dafeng. Residual currents at both areas showed net landward transport at the lower flat and net seaward transport at the upper flat, in favor to sediment accumulation at the middle flat. Sediment flux over tidal cycles showed net landward sediment transport at Dafeng, and net seaward transport at Jianggang, consistent with the convex-up accretion-dominated profile observed at Dafenge, and concave-up erosion-dominated profile observed at Jianggang. The instantaneons sediment flux changed significantly due to variations in velocity and sediment concentrations, but these terms counteracted with each other within tidal cycles, leading to the dominant role of Eulerian flux in determining net sediment flux over tidal cycles.展开更多
In AD1128,the Yellow River shifted its course from the Bohai Sea to the South Yellow Sea(SYS)due to anthropogenic dike excavation,starting the development of the Abandoned Yellow River Delta(AYRD)that lasted for more ...In AD1128,the Yellow River shifted its course from the Bohai Sea to the South Yellow Sea(SYS)due to anthropogenic dike excavation,starting the development of the Abandoned Yellow River Delta(AYRD)that lasted for more than 700 years(AD1128-1855).However,the sediment flux of the abandoned Yellow River into the sea is in a state of change due to human activities,and the growth process of the AYRD is not well understood.Here,we investigate the growth process of the AYRD and its sedimentary record characteristics over the last millennium based on three cores collected from the AYRD.The results show that the main sediment types in the AYRD are silt,mud and sandy silt.After AD1128,the grain size components in the sediments of the AYRD showed significant stage changes with the sand content first starting to decrease.The clay content increased and remained at a high percentage in the middle to late 14th century,followed by a sharp increase from the mid-16th to the mid-17th century,due to a further increase in sediment flux from the abandoned Yellow River into the sea.A slight increase in the proportion of sand content during the final stage of the transition from subaqueous delta to terrestrial delta is a distinctive feature of the sedimentary record,and this change persists for 10~90 years in different core records.This study further proposes a schematic model of the development of the AYRD:(a)before the 16th century,the sediments were deposited mainly in the estuary and nearshore,with rapid vertical accretion;(b)After the 16th century,the horizontal land formation was the main focus,and the rate of seaward extension increased rapidly.This model also reflects the following pattern:when the sediment flux from the river into the sea is certain,the rate of land formation is inversely proportional to the rate of vertical accretion.The dominant factors affecting the evolution of the AYRD are the sediment flux into the sea and initial submerged topography,with less influence from sea level changes.Hydrodynamic erosion by wave and tidal forces from the outer delta began to dominate after the interruption of sediment supply due to the Yellow River mouth northward to the Bohai Sea in AD1855.This study has important implications for understanding the growth and evolution of deltas under the influence of human activities.展开更多
基金Supported by Qingdao Special Program for Outstanding Scientists (No.04-3-JJ-03), the "100 Talents Program" of the Chinese Academy of Sciences (CAS), the Knowledge Innovation Program of CAS (Nos. KZCX1-SW-01-08 and KZCX3-SW-214) and the NSF for Outstanding Young Scientists (Nos. 49925614 and 49725612), and the NSF of Shan-dong Province (No. H74990247).
文摘Sedimentation of fine-grained deposits on coastal zones and continental shelves are important because of the association with chemical pollutants, and the implication to the impact on biological processes, the stratigraphic correlations, and changes in sedimentary environments. The Yellow Sea continental shelf receives large quantities of sediment from the Huanghe （Yellow） River. Unfortunately, little attention has been yet paid to the sedimentation on the shallow shelf and its features, and the vertical sediment flux in the area is poorly understood. In this study, nine cores were collected in northern Yellow Sea by the R/V Science 1 in September, 1998 and 1999 to examine the sedimentation rate, sediment flux and the provenance with ^210Pb analysis. The 2^210Pb activity profiles showed that the vertical sediment flux ranged from 0.06 to 1.18 g/cm^2·a in the region. In central part of the area, there was a patch of fine-grained mud, with the flux below 0.33 g/cm^2·a. Most profiles were featured in two-segment model. Differences in the profiles reflected spatial and temporal variations in hydrodynamic and sedimentary processes. In order to determine the provenance and sedimentary setting in the area, the geochemistry of Ca, Fe, Sr, Cu, Ti and Rb in 11 surficial sediment samples were studied, which showed that in the central northern Yellow Sea, the mud deposit was from multi-source but mainly from the Huanghe River.
文摘A Nortek acoustic Doppler current profiler (NDP) was installed on a moving vessel to survey the entrance to the Jinhae Bay on August 22~23, 2001. The current velocity and acoustic backscattering signal were collected along two cross-sections; water samples were also collected during the measurement. The acoustic signals were normalized to compensate for the loss incurred by acoustic beam spreading in the seawater. The in situ calibration shows that a significant relationship is present between suspended sediment concentrations (SSC) and normalized acoustic signals. Two acoustic parameters have been determined to construct an acoustic-concentration model. Using this derived model, the SSC patterns along the surveyed cross-sections were obtained by the conversion of acoustic data. Using the current velocity and SSC data, the flux of suspended sediment was estimated. It indicates that the sediment transport into the bay through the entrance has an order of magnitude of 100 t per tidal cycle.
基金National BasicResearch Program of China(also called 973program)(project No.2003CB415105-6)National University of Singapore(NUS grantnumber R-109-000-034-112).
文摘The sediment flux data, measured from a dry-hot valley of the Longchuan River, a tributary of the lower Jinsha River, were analyzed with Mann-Kendall test, Seasonal Mann-Kendall test and Sen’s test. In both the upper reaches (Xiaohekou) and the lower reaches (Xiaohuangguayuan), the sediment fluxes showed a significant increase from 1970 to 2001, despite the fact that the water discharge did not change significantly during the period and numerous reservoir constructions which contribute to the trap of sediment. This can be attributed to the intensification of human activities, especially the activities related to land surface disturbances such as deforestation and afforestation, expansion of agriculture land, and road constructions. This increase is more significant in the lower reaches of the river observed at the place of Xiaohuangguayuan due to the dry-hot climate. The profound increase in sediment flux has significant implications for effective management of the sedimentation problems of the on-going Three Gorges Reservoir.
基金financially supported by the Scientific and Technological Services Network Planning Project of Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences (HHS-TSS-STS-1504)the Technological Research and Developmental Planning Projects of China Railway Corporation (2015G005-B)the National Natural Science Foundation of China (41501010, 41401611)
文摘The Lanzhou-Xinjiang High-speed Railway runs through an expansive windy area in a Gobi Desert, and sand-blocking fences were built to protect the railway from destruction by wind-blown sand. However, the shielding effect of the sand-blocking fence is below the expectation. In this study, effects of metal net fences with porosities of 0.5 and 0.7 were tested in a wind tunnel to determine the effectiveness of the employed two kinds of fences in reducing wind velocity and restraining wind-blown sand. Specifically, the horizontal wind velocities and sediment flux densities above the gravel surface were measured under different free-stream wind velocities for the following conditions： no fence at all, single fence with a porosity of 0.5, single fence with a porosity of 0.7, double fences with a porosity of 0.5, and double fences with a porosity of 0.7. Experimental results showed that the horizontal wind velocity was more significantly decreased by the fence with a porosity of 0.5, especially for the double fences. The horizontal wind velocity decreased approximately 65% at a distance of 3.25 m（i.e., 13 H, where H denotes the fence height） downwind the double fences, and no reverse flow or vortex was observed on the leeward side. The sediment flux density decreased exponentially with height above the gravel surface downwind in all tested fences. The reduction percentage of total sediment flux density was higher for the fence with a porosity of 0.5 than for the fence with a porosity of 0.7, especially for the double fences. Furthermore, the decreasing percentage of total sediment flux density decreased with increasing free-stream wind velocity. The results suggest that compared with metal net fence with a porosity of 0.7, the metal net fence with a porosity of 0.5 is more effective for controlling wind-blown sand in the expansive windy area where the Lanzhou-Xinjiang High-speed Railway runs through.
基金The National Natural Science Foundation of China under contract Nos 41625021,41676079 and 41906021the Project of Enhancing School with Innovation of Guangdong Ocean University under contract No.Q18307the Program for Scientific Research Start-up Funds of Guangdong Ocean University under contract No.060302112010
文摘Two kinds of regression equations are used to reproduce the sediment flux of the 26 small coastal watersheds in southeastern China.The first kind is the global equations suggested by Milliman and Syvitski(1992),Mulder and Syvitski(1996),Syvitski et al.(2003),and Syvitski and Milliman(2007).The second kind is the modified equations revised by the characteristics of the coastal watersheds,including the drainage area,mean water discharge,and mean sediment discharge.Compared with the observations of the hydrometric stations,the global equations overestimate the sediment flux by 1–2 orders of magnitude.By using the modified equations,the accuracy of the estimated sediment flux is significantly improved,with the relative error in the range of 7%–24%.The reason for the overestimation mainly caused by different parameters’domain and regression coefficients between global rivers and study coastal watersheds.This study demonstrates that modification needs to be considered when using global regression equations to reproduce the sediment flux of the small coastal watersheds in southeastern China.
基金Supported by the National Natural Science Foundation of China(Nos.41625021,41876092,41576095,41906021)。
文摘Continental shelf islands are contributors of terrestrial sediment supply to shelf regions,and the sediment flux from these islands shall be quantified.We calculated the sediment flux of continental shelf islands in the southeastern China using two empirical equations under two preconditions.The first,the sediment load/yield of the islands has the same pattern as the adjacent small,mountainous rivers along the coastline;and the second,each of the islands was treated as a single catchment.The results show that the sediment supply from these islands reached an order of magnitude of 1 Mt/a,which is comparable to the supply from the local smaller rivers.A sensitivity analysis indicates that this value represents the lower limit of estimate;if the accurate amount of sub-catchments of any island is considered,then this value will be enhanced slightly.This study demonstrates that the sediment supply from continental shelf islands to oceans is an important factor affecting the regional sedimentation and,therefore,should be paid with attention.
文摘This study sought to forecast water flow and sediment flux in the scheme as potential contributions for improved management in the Chókwè Irrigation Scheme (CIS). Fieldwork data was collected during dry (DS) and wet (WS) seasons. Flow measurement was performed at 9 stations using a calibrated flow meter OTT C31. Water flow and sediment flux from 2004 to 2019 were used. Hydrodynamic forecast simulations were performed using Mann-Kendall test and ARIMA model for determination of temporal trends. Findings suggest higher values during DS for water discharge and sediment flux. Mann-Kendall test for sediment discharge trends was not significant at 95% significance level, except for the Offtake in WS. ARIMA test for the sediment discharges, at the Intake, for DS and WS, sediments were well described by the ARIMA model and gave a good result for the sediments. Good fit between the observed and the predicted ARIMA model was found. ARIMA model for sediment discharge at CIS based on AIC has a good fit for AR (p = 1), whereby, at the Intake the ARIMA p-value was 0.822 and 0.932, for WS and DS, respectively. Whilst in the Offtake, the ARIMA p-value was 0.877 and 0.893, respectively. These results can be used to improve the CIS management, both for water flow and sediment flux.
基金financially supported by the Special Scientific Research Fund of Meteorological Public Welfare Profession of China (GYHY201106025)the National Natural Science Foundation of China (41471031)
文摘Reliable estimation of the mass-flux profiles of aeolian sediment is essential for predicting sediment transport rates accurately and designing measures to cope with wind-erosion. Vertical mass-flux profiles from seventeen wind-erosion events were re-evaluated using five typical models based on observed data obtained from a smooth bare field at the southern fringe of the Taklimakan Desert, China. The results showed that the exponential-function model and the logarithmic-function model exhibited the poorest fit between observed and predicted mass-flux profiles. The power-function model and the modified power-function model improved the fit to field data to an equivalent extent, while the five-parameter combined-function model with a scale constant（σ） of 0.00001 m（different from the σ value proposed by Fryear, which represented the height above which 50% of the total mass flux occurred） was verified as the best for describing the vertical aeolian sediment mass-flux profiles using goodness of fit（R2） and the Akaike Information Criterion（AIC） values to evaluate model performance. According to relationships among model parameters, the modified power model played a prominent explanatory role in describing the vertical profiles of the observed data, whereas the exponential model played a coordinating role. In addition, it was found that the vertical profiles could not be extrapolated using the five selected models or easily estimated using an efficient model without field observations by a near-surface sampler at 0 to 0.05 m.
基金funded by the Key Laboratory of Ocean Space Resource Management Technology,MNR(No.KF-2021-106)the National Natural Science Foundation of China(No.42006143)+1 种基金the Natural Science Foundation of Zhejiang Province(No.LY22E090011)the Open Research Fund Program of Marine Ecological Restoration and Smart Ocean Engineering Research Center of Hebei Province(No.HBMESO2312)。
文摘In this study,a two-dimensional hydrodynamic and sediment transport model is established to quantify the influences of sea level rise on sediment transport in the Yangtze River Estuary(YRE).After validation,the model was employed to investigate the sediment transport and seabed evolution under four different scenarios of sea level rise,specifically,0,0.5,1 and 1.5 m.The results reveal that there exists a‘transition point(TP)'of SSC in each main channel of YRE.Upstream of the transition point,the suspended sediment concentration(SSC)increases along with the rise in sea level,while downstream of the transition point,SSC decreases as sea level rises.Similarly,there are also transition points for topography evolution.The maximum scouring rate upstream of the transition points exceeds 4.32% for a 1.5 m rise in sea level,while the maximum deposition rate downstream of the transition points is 2.48%.The sediment fluxes from upstream to downstream in the branches of YRE are enhanced by the rise in sea level.The direction of sediment flux in the North Branch reverses downstream as sea level rises.The sediment flux from the North Channel towards downstream increases significantly,while there is no significant change in sediment flux for South Channel.Sediment deposition in the North Passage is also accelerated by sea level rise.In addition,the sediment flux from YRE to northern Jiangsu and Hangzhou Bay is also weakened by the rise in sea level.
基金the Fundamental Research Funds of Chinese Academy of Forestry(CAFYBB2019MA009)the National Natural Science Foundation of China(41701010)+1 种基金the Key Special Project on'Science and Technology Promoting the Development of Inner Mongolia Autonomous Region'(KJXM-EEDS-2020006)the Youth Innovation Promotion Association of Chinese Academy of Sciences(2018459)。
文摘Wind erosion is a key global environmental problem and has many adverse effects.The Mu Us Sandy Land of northern China is characterized by an arid climate,where vegetation patches and bare sand patches are usually distributed mosaically,and aeolian activities occur frequently.Vegetation plays a significant role in controlling wind erosion.Artemisia ordosica is the most dominant native plant species in the Mu Us Sandy Land.It is urgent to study the wind-proof and sand-fixing effects of Artemisia ordosica in the Mu Us Sandy Land.This study analyzed the wind-proof and sand-fixing effects of Artemisia ordosica based on the field data of wind regimes,aeolian sediment transport,and surface change of Artemisia ordosica plots with four coverages(denoted as site A,site B,site C,and site D)in the Mu Us Sandy Land during the period from 1 June 2018 to 29 June 2019.The coverages of Artemisia ordosica at site A,site B,site C,and site D were 2%,16%,29%,and 69%,respectively.The annual average wind speeds at 2.0 m height above the ground for site A,site B,site C,and site D were 3.47,2.77,2.21,and 1.97 m/s,respectively.The annual drift potentials were 193.80,69.72,15.05,and 6.73 VU at site A,site B,site C,and site D,respectively.The total horizontal aeolian sediment fluxes during the period from 2-3 June 2018 to 6 June 2019 at site A,site B,site C,and site D were 4633.61,896.80,10.54,and 6.14 kg/m,respectively.Site A had the largest surface changes,and the surface changes at site B were significantly weaker than those at site A,whereas the surface changes at site C and site D were minimal.The results indicated that Artemisia ordosica significantly reduced the wind speed,drift potential,aeolian sediment transport,and surface changes.The higher the coverage of Artemisia ordosica is,the more obvious the effects of wind-proof and sand-fixing.Wind erosion would be effectively controlled in the Mu Us Sandy Land if the coverage of Artemisia ordosica is greater than 29%.These results provide a scientific basis for evaluating the ecosystem service function of Artemisia ordosica and the vegetation protection and construction projects in the Mu Us Sandy Land.
基金This study was supported bythe National Natural Science Foundation of China (Grant Nos 40476039 and 50339010)
文摘Based on the 2-D flow and sediment numerical model of the Yangtze Estuary and the Hangzhou Bay, the characteristics of water and sediment exchange in their joint waters is studied through quantitative calculation and analysis of the characteristics of water flow and sediment transportation. The results show that there is periodical water and sediment exchange in this joint waters, that the net water exchange appears mainly between 0 - 6 m depth （theoretical datum plane, the same below） offshore and the maximum is near the depth of 2 m, and that the net sediment exchange mainly appears between 0 - 5 m depth and the maximum is near the depth of 3 m, indicating that the range of water flow passage is different from that of sediment transport from the Yangtze Estuary to the Hangzhou Bay. Combined with the results of numerical simulation, this paper also analyzes the hydrodynamical mechanism influencing water and sediment exchange between the Yangtze Estuary and the Hangzhou Bay, including tidal fluctuation, tidal current kinetic energy, tide-induced residual current and the trace of water particles. Finally, the sediment transportation passage on the Nanhui tidal fiat is discussed, and the results show that sediment is transported into the Hangzhou Bay from the south side of Shipilei, while sediment is brought back to the South Channel of the Yangtze Estuary from the north side.
基金The National Natural Science Foundation of China under contract Nos 41376068 and 41776068
文摘The radionuclide ^（210） Pb is suitable for century-scale dating and has been used to calculate the sedimentation rate in a variety of environments. However, two common ways to apply 210 Pb dating techniques may give misleading results. One is ＂prolonging of age＂, i.e., using the calculated sedimentation rate to date back to 200 or 300 years.This practice must be treated with caution because the 210 Pb dating techniques do not guarantee direct dating for ages much older than 100 years. Another is ＂loss of age＂, i.e., the calculated time span between the topmost layer and the 210 Pb background layer in cores is less than 100 years when an apparent sedimentation rate is used in the calculation. Here, we propose that based on the principle of 210 Pb dating, the upper limit of age suitable for direct210 Pb dating is between 110 and 155 years. The ＂prolonging＂ application is acceptable only if the sedimentary environment in the past several hundred years was stable and the sedimentation rate was generally constant, and verification with independent evidence（such as historical records or biomarker methodology） is needed.Furthermore, after analyzing many published and collected data, we found four possible reasons for the ＂loss of age＂. First, the compaction effect of sediment should be corrected in laboratory analysis or else the calculated age will be underestimated. Second, the accuracy and uncertainty of 210 Pb activity measurement affect the judgment of the background. To be cautious, researchers are apt to choose a background activity with a younger age. Third,use of a slightly smaller value of supported 210 Pb activity in a calculation will lead to considerable underestimation of the time span. Finally, later-stage erosion and migration are common for sedimentation, which lead to loss of sedimentary records and are often reflected as a ＂loss of age＂ in cores. We believe that proper use of 210 Pb dating data may provide helpful information on our understanding of sediment records and recent environmental changes.
基金This research is part of the project“Impact of extensive windthrow areas on the dynamics of slopefluvial system”funded by the National Science Centre,Poland(Grant No.UMO-2017/27/N/ST10/00802)。
文摘Tree uprooting is an important process which leads to many geomorphic consequences.Some of the most important are the transport of sediment and mixing of soil.The aim of this article is to make a detailed examination of the magnitude of sediment transport caused by an extreme windthrow event in three severely affected catchments.Also,a comparison is made of the windthrow event with a mass movement event in the aspect of the magnitude of sediment transport and soil mixing.The study was conducted in three second-to third-order catchments in the Tatra Mountains,where a strong foehn wind event caused extensive windthrow in 2013,and a high-magnitude rainfall event triggered mass movements in 2007.The volume of sediment uplifted by the uprooting event was calculated based on the mapping of root plates using high-resolution(0.04 m)aerial images and measurements of root plate volumes conducted in the field.The volume of sediment transported by shallow landslides was determined based on a Digital Elevation Model(DEM1-m resolution).Windthrows affected 34%,76%,and94%of the area of the investigated catchments.Most of the trees had fallen downslope.The direction of treefall was influenced by the slope aspect and steepness.Root plates and pits covered 1.3%,4.8%,and 5.4%of the area of the catchments.Sediment flux generated by the uprooting event,calculated for the entire area of each investigated catchment ranged from 8.1×10^(–4) to 9.9×10^(–3) m^(3) m^(–1) event^(–1).This was notably lower than the sediment flux generated by the mass movement event(also calculated for the entire area of each catchment),which was 1.8-6.1×10^(–2)m^(3) m^(–1) event^(–1).By contrast,uprooting affected a much larger area than the mass movement event,which underlines its significant role in the mixing of soil.
基金Grants-in-Aid for Scientific Research from Ministry of Education,Science and Culture(Japan)to K.Kashiwaya[(A2)20253002]
文摘Foreset profiles of deltaic topography change corresponding to hydraulic conditions,and are influenced by water discharge and change rates of water discharge.To investigate the correlation between the transition of deposition rates on the foreset and the change rate of water discharge of temporary waxing and subsequent waning flows,we perform experiments on silty deltas that developed under several different hydrographic patterns.The findings are as follows:(1) Under flows with constant discharge,the deposition rate on the foreset was low at high water discharge and high at low water discharge because the separated flow became vigorous at high water discharge and prevented sediment supply onto the foreset.If the water discharge is not constant,the deposition rate shifted concurrently with water discharge only at extremely low change rate.(2i) In a waxing flow at low(but not extremely low) increase rate,the deposition rate gradually decreased with some time lag.(2ii) In the case of high increase discharge,intense erosion on the topset caused by rapid waxing made a large amount of silt move onto the foreset and the deposition rate temporary increased.(3) With ample time after waning stage,the deposition rate recovered to that at constant low water discharge in all runs.However,the transitional processes depended on not only waning rate but also waxing rate at before waning stage.(3i) In the case of high decrease rate of water discharge,the deposition rate abruptly decreased regardless of increase rate.(3ii) Even in the case of low decrease rate of water discharge,if the increase rate before waning stage was high,the deposition rate abruptly decreased.(3iii) Only in the case where both the increase rate and the decrease rate were low,deposition rate gradually increased.
基金the National Natural Science Foundation of China for supporting open scientific expeditions in the northern South China Sea (NORC2020-05, NORC2022-05)supported by the National Natural Science Foundation of China (Grant Nos. 41831280, 42207173)the Natural Science Foundation of Shandong Province (Grant No. ZR2022QD002)。
文摘Internal solitary waves can generate intense bottom currents and turbulent mixing over continental slopes, influencing the redistribution of sediments and pollutants, as well as driving changes in marine geomorphology and ecosystems. However,owing to the lack of detailed quantitative measurements of the bottom boundary layer, the mechanisms and impacts of internal solitary waves in resuspending and transporting seafloor sediments remain poorly understood. In this study, we present highresolution in situ observations of hydrodynamics in the upper layer(14–265 m) and the bottom boundary layer(<1 m) in the continental shelf slope break zone. Our results reveal that strongly nonlinear internal solitary waves, which occur at the peak of semidiurnal tidal currents, trigger benthic storms at the seafloor. Unlike previously proposed global instability mechanisms, the suspended sediment concentration caused by these strongly nonlinear internal solitary waves reaches 60 times higher than the background value and exhibits sudden, transient peaks. The bottom shear stress(τ) is an order of magnitude greater than that in laboratory measurements, and the observed fluctuating pressure is approximately 2.3 to 7 times greater than that in previous coastal observations. The sediments stirred by benthic storms are transported vertically to more than 100 m above the seabed,with lateral transport extending tens of kilometres beyond the study area. This process is driven by the dynamic mechanism of“strongly nonlinear internal solitary waves lifting sediments, weakly nonlinear internal solitary waves assisted by internal tides,and contour currents transporting sediments.” The suspended sediment flux induced by internal solitary waves in the South China Sea is on the same order of magnitude as that of global dust storm emissions, 21.9 times the volume of Asian dust storms entering the sea, and approximately 21 times the fluvial sediment flux entering the northern South China Sea. These findings are significant for evaluating sedimentary processes and ecological–geochemical impacts in the northern South China Sea, offering a novel perspective on marine ecological environments and carbon sequestration processes.
基金supported by the National Key R&D Program of China[Grant number 2021YFD1500700]the National Natural Science Foundation of China[Grant number 42007050]+1 种基金the Basic Scientific Research Projects of Liaoning Province[Grant number LJKMZ20221049]the Scientific Research Foundation of Liaoning Province[Grant number LSNPT202002].
文摘Sediment fingerprinting technology is widely used to differentiate sediment sources.However,despite its long-recognized benefits,there it has been seldom applied to assess the variability of sediment sources during storm events.In this study,sediment fingerprinting is used for four storm events to determine the dynamic changes in sediment sources throughout them in the black soil region in Northeast China.Three potential sediment sources—cultivated land,unpaved roads,and gullies—were effectively differentiated using four geochemical tracers(As,Be,Cs,and Cu),with an accuracy of 100%.The relative sediment contribution from each source was determined using linear and Bayesian mixing models.The mean absolute fit(MAF)values of the linear mixing model(MAF_(mean)=0.976–0.949)were higher than those of the Bayesian mixing model(MAF_(mean)=0.921–0.992),indicating that the first performed better.Cultivated land was the primary source of the sediment load,accounting for 59.03%of it(load-weighted mean=68.29%),followed by the gullies(37.15%,load-weighted mean=28.09%),and unpaved roads(3.90%,load-weighted mean=3.69%)for the four storm events.In addition,a high variability in sediment source contribution was observed during the storm events.Cultivated land was the dominant sediment source during storm events with higher sediment concentrations(logarithmic function,r^(2)=0.878,p<0.01),discharge(linear function,r^(2)=0.452,p<0.05),and sediment flux(logarithmic function,r^(2)=0.857,p<0.01),whereas the reverse was observed for gullies.Contrastingly,the contribution of sediment from unpaved roads remained relatively stable during rainfall events.This provides a potential means to assess dynamic changes in sediment contributions from different erosion units.Moreover,it provides data support for exploring soil erosion mechanisms and effective erosion control in the black soil region in Northeast China.
基金financially supported by the National Basic Research Program of MOST of China(No.2015CB251201)the National Natural Science Foundation of China(Nos.91228208,41506055)the China Geological Survey(Nos.GZH201400210,DD20160140)
文摘New high-resolution 3D seismic data image a submarine channel complex in the northern slope of the South China Sea. The channel complex stretches hundreds of kilometers across the slope and flows into the deepsea from the siliciclastic shelf margin, linking neritic environment to the pelagic plain. The evolution of the channel complex developed two sedimentary stages, stage Ⅰ （19.1-18.5 Ma） and stage Ⅱ （18.5-17.5 Ma）, separated by erosional surfaces. In the first stage, the complex was rifled with pure siliciclastic sediments, forming thick-massive sandstone intercalated by thin layers of mudstone. During the stage Ⅱ, the channel complex was deposited five carbonate-siliciclastic cycles. The unexpected channel-fifl carbonate deposits present allochthonous characteristics, suggesting the siliciclastic channel was surprisingly used to transport carbonate sediment from the adjacent neritic carbonate platform. By analyzing the periodical carbonate sedimentary process in the siliciclastic channel complex, we infer that it was related to the in situ carbonate production of the neritic carbonate platform and was most likely to be controlled by the relative sea-level changes. Unlike line-source carbonate slope aprons or smafl-sized carbonate channels, the large-sized siliciclastic channel complex links directly neritic carbonate platform to deepwater basin and can transport large volumes of neritic carbonates to the pelagic environment in a short period. The new findings help to estimate the contributions of neritie siliciclastic shelf and carbonate platform to deepwater slope more accurately. This study suggests that channel systems are more complex than expected and have significant implications on the conceptual models describing the deepwater sedimentary theory.
基金supported by the Commonweal Program of Chinese Ministry of Water Resources (Grand No. 200701026)
文摘For the Hengsha East Shoal Promoting Siltation Project in the Yangtze River Estuary, this work developed a formula for calculating sediment carrying capacity based on variable coefficients and a mathematical model for suspended sedimentation using variable saturation recovery coefficients. Not only does the model yield good verification, preferably give the hydrodynamics and the sediment concentration, but also reach a good agreement between the simulation results andlux by tide for studying the effect the measured topographical changes in the promoting siltation zone of the Hengsha East Shoal. Moreover, this article proposes a method for examing the net sediment tran- sportation fs of the project of promoting siltation and comparatively analyzes the current siltation of the Hengsha East Shoal and siltation mouth layouts, entrance widths, entrance bottom elevations, and the impact of the South Main Dike on promoting siltation through calculating the net sediment transportation flux by tide over the fixed bed and the direct movable bed numerical simulations. The results are in good agreement with each other, indicating that the method for calculating the net sedi- ment transportation flux by the tide is also useful for assessing the project in promoting siltation. Finally, we use the modeling results to analyze the water and sediment diversion ratios and the changes in silting and scouting in riverbeds and draw the conclusion that the completion of the Hengsha East Shoal Promoting Siltation Project would not adversely affect the Yangtze River Estuary Deepwater Channel Project.
基金supported by This study was financially supported by the National Natural Science Foundation of China(41625021,42006149)Jiangsu Special Program for Science and Technology Innovation(JSZRHYKJ202106)Jiangsu coastal geological resources and environmental multi-factor monitoring network optimization and dynamic controlling(202146).
文摘Two field campaigns in Dafeng and Jianggang were organized to compare spatial variations of hydrodynamic characteristics and sediment transport patterns on intertidal flats of different types with distinct human interferences along middle Jiangsu coast, China. The major contributors to the different patterns of sediment dynamics between the two tidal flats were offshore tidal current field and human interference. Offshore tidal force provide the basic setup of tidal current patterns on tidal flats, which is then modified by local morphology. Seawalls parallel to coast reduce tidal flat width, forcing tidal energy to dissipate within a shorter distance and thus influencing tidal flat morphology. Seawalls vertical to coast and major tidal current significantly reduce tidal current speed, which favors sediment deposition on tidal flats. Two seawalls built on both sides of the observational tidal flat profile caused much reduced current speed at Dafeng tidal flat, comparing to the offshore station. Being exposed to offshore radial tidal currents, hydrodynamics at Jianggang was much stronger than that at Dafeng. Residual currents at both areas showed net landward transport at the lower flat and net seaward transport at the upper flat, in favor to sediment accumulation at the middle flat. Sediment flux over tidal cycles showed net landward sediment transport at Dafeng, and net seaward transport at Jianggang, consistent with the convex-up accretion-dominated profile observed at Dafenge, and concave-up erosion-dominated profile observed at Jianggang. The instantaneons sediment flux changed significantly due to variations in velocity and sediment concentrations, but these terms counteracted with each other within tidal cycles, leading to the dominant role of Eulerian flux in determining net sediment flux over tidal cycles.
基金provided by the National Natural Science Foundation of China(Nos.41876092 and 42006151)the Open Research Fund of Key Laboratory of Coastal Salt Marsh Ecosystems and Resources,Ministry of Natural Resources(No.KLCSMERMNR2021001).
文摘In AD1128,the Yellow River shifted its course from the Bohai Sea to the South Yellow Sea(SYS)due to anthropogenic dike excavation,starting the development of the Abandoned Yellow River Delta(AYRD)that lasted for more than 700 years(AD1128-1855).However,the sediment flux of the abandoned Yellow River into the sea is in a state of change due to human activities,and the growth process of the AYRD is not well understood.Here,we investigate the growth process of the AYRD and its sedimentary record characteristics over the last millennium based on three cores collected from the AYRD.The results show that the main sediment types in the AYRD are silt,mud and sandy silt.After AD1128,the grain size components in the sediments of the AYRD showed significant stage changes with the sand content first starting to decrease.The clay content increased and remained at a high percentage in the middle to late 14th century,followed by a sharp increase from the mid-16th to the mid-17th century,due to a further increase in sediment flux from the abandoned Yellow River into the sea.A slight increase in the proportion of sand content during the final stage of the transition from subaqueous delta to terrestrial delta is a distinctive feature of the sedimentary record,and this change persists for 10~90 years in different core records.This study further proposes a schematic model of the development of the AYRD:(a)before the 16th century,the sediments were deposited mainly in the estuary and nearshore,with rapid vertical accretion;(b)After the 16th century,the horizontal land formation was the main focus,and the rate of seaward extension increased rapidly.This model also reflects the following pattern:when the sediment flux from the river into the sea is certain,the rate of land formation is inversely proportional to the rate of vertical accretion.The dominant factors affecting the evolution of the AYRD are the sediment flux into the sea and initial submerged topography,with less influence from sea level changes.Hydrodynamic erosion by wave and tidal forces from the outer delta began to dominate after the interruption of sediment supply due to the Yellow River mouth northward to the Bohai Sea in AD1855.This study has important implications for understanding the growth and evolution of deltas under the influence of human activities.
