Sediment flux and source in northern Yellow Sea by ^(210)Pb technique

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.

Estimation of suspended sediment flux from acoustic Doppler current profiling along the Jinhae Bay entrance

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.

Effects of hydrodynamics processes on phosphorus fluxes from sediment in large,shallow Taihu Lake

The turnover of phosphorus （P） in lake sediments, a major cause of eutrophication and subsequent deterioration of water quality, is in need of deep understanding. In this study, effects of resuspension on P release were studied in cylindrical microcosms with Yshape apparatus. The results indicated that there was a positive correlation between flux of suspended substance across sediment-water interface （Fss） and the wind speed, and an increasing Fss during each wind process followed by a steady state. The maximal Fss under fight, moderate, and strong wind conditions were 299.9±41.1,573.4±61.7, and 2093.8±215.7 g/m^2, respectively. However, flux of P across sediment-water interface （Fp） did not follow a similar pattern as Fss responding to wind intensity, which increased and reached the maximum in initial 120 rain for fight wind, then decreased gradually, with maximal flux of 9.4±1.9 mg/m^2. A rapid increase of Fp at the first 30 rain was observed under moderate wind, with maximal flux of 11.2±0.6 mg/m^2. Surprisingly, strong wind caused less Fp than under light and moderate wind conditions with maximal flux of 3.5±0.9 mg/m^2. Fss in water column declined obviously during the sedimentation process after winds, but Fp varied with wind regime. No obvious difference was detected on Fp after 8 h sedimentation process, compared with the initial value, which means little redundant P left in the water column after winds.

Anthropogenic Impacts on the Sediment Flux in the Dry-hot Valleys of Southwest China—an Example of the Longchuan River

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.

Distribution and fluxes of suspended sediments in the offshore waters of the Changjiang (Yangtze) Estuary

The offshore waters of the Changjiang Estuary are the transitional areas where river-supplied water and sediment are transported to the sea, and material exchanges occur with the neighbored Hangzhou Bay and the Jiangsu waters. Field observations of currents and sediment properties were conducted to study temporal and spatial distributions of suspended sediments under various dynamical conditions. The high sediment concentrations were found to occur in the western and southern waters of the offshore, and the low concentrations occurred in the eastern and northern waters. This pattern of the suspended sediment concentration （SSC） distribution is obviously influ- enced by the runoff and tidal current. The significant difference of along-estuary SSC distribution indicates that the SSC is reduced gradually from the west to the east, and that in the spring tide is obviously higher than in the neap tide. The methods of mechanism analysis and equal-area grids were used to calculate the suspended sediment fluxes at the typical cross sections. It was found that 44 percent of total suspended sediments from the Changjiang River were deposited in the submarine delta, and more than 27 percent of sediments were transported southernly into the Hangzhou Bay, and only 9 percent of sediments was supplied and exchanged with the northern Jiangsu waters, and about 20 percent of sediments was delivered offshore to the sea.

Calculating the sediment flux of the small coastal watersheds:a modification of global equations

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.

Using seismic surveys to investigate sediment distribution and to estimate burial fluxes of OC, N, and P in a canyon reservoir

As a high-precision survey method,seismic surveying has been increasingly applied to inland water research,although its application to artificial reservoirs has remained limited.As a special artificial water body,reservoirs have important effects on the fluvial transport of material from land to ocean,and inevitably have complex terrain which can complicate and distort the results of seismic surveys.Therefore,there are still some problems need to be resolved in the application of seismic surveys in reservoirs with complex terrain.For this study,the Dongfeng Reservoir located in the upper reaches of the Wujiang River was chosen as an example to test the seismic survey method.Our testing showed that(1)because of the complex underwater terrain,the signal-to-noise ratio of the echo signal in canyon reservoir is low,making it difficult to determine sediment layers thicknesses in some areas;and(2)due to the large spatial heterogeneity of sediment distribution,insufficient density of cross-sections can lead to inaccurate interpolation results.To improve the accuracy of calculations,a mathematical method was used.Ultimately,the total burial mass of sediment was estimated at 2.85 x 107 tons,and the average burial rates of total organic carbon,total phosphorus,and total nitrogen were estimated at 0.194,0.011,and 0.014 g cm-2 year-1,respectively.These values were close to the results of previous studies and hydrographic station data,indicating that seismic survey can be a reliable and efficient method for the mapping of reservoirs.

Cross-shore suspended sediment flux in the salt marsh pioneer zone of Chongming eastern beach in the Chang- jiang Estuary in China

Between April 2002 and April 2003,in situ measurements of water depth,current velocity and suspended sediment content were carried out in edge region of East Chongming salt marsh and neighboring bald flat in the Changjiang （Yangtze） Estuary under different weather conditions.Cross-shore suspended sediment flux was calculated and analyzed.The results show that under calm weather conditions,the current velocity process in bald field and salt marsh area varied differently during semidiurnal tidal cycles.Owing to current velocity asymmetry,mean SSC during flood tide phase was 1.8 times higher than that of ebb tide phase.As a result,net onshore sediment flux controlled cross-shore suspended sediment transport process and salt marsh pioneer zone was generally accreting.There was significant positive correlation between total sediment flux and quartic power of maximum water depth.It indicates that tidal ranges dominate suspended sediment transport and sedimentation process in the salt marsh pioneer zone under the calm weather condition.The sedimentation rate on the adjacent mudflat was higher than the salt marsh,which induced stable accreting of salt marsh towards the sea.The wind events enhanced SSC and current velocity during the semidiurnal tides.And the remarkable onshore net sediment flux could occur on the high marsh and mudflat close to the marsh fringe during the short period under the rough weather condition.

The Effect of Bioturbation Activity of the Ark Clam Scapharca subcrenata on the Fluxes of Nutrient Exchange at the Sediment–Water Interface

Filter-feeding shellfish are common benthos and significantly affect the biogeochemical cycle in the shallow coastal ecosystems.Ark clam Scapharca subcrenata is one of the widely cultured bivalve species in many coastal areas owing to its tremendous economic value.However,there is little information regarding the effects of the bioturbation of S.subcrenata on the fluxes of nutrient exchange in the sediment-water interface(SWI).In this regard,S.subcrenata was sampled during October 2016 to determine the effects of its bioturbation activity on the nutrient exchange flux of the SWI.The results showed that the biological activity of S.subcrenata could increase the diffusion depth and the rate of the nutrients exchange in the sediments.The bioturbation of S.subcrenata could allow the nutrients to permeate into the surface sediments at 6-10cm and increase the release rate of nutrients at the SWI.The releasing fluxes of DIN and PO43−-P in the culture area were found to be around three times higher than that in the non-cultured region.The culture of S.subcrenata has been proved to be an important contributor to nutrient exchange across the SWI in the farming area of Haizhou Bay.Nutrients exchange in the SWI contributes a part of 86%DIN,71%PO43−-P and 18%SiO32−-Si for the aquaculture farm.

Predicting sediment flux from continental shelf islands,southeastern China

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.

Water Flow and Sediment Flux Forecast in the ChókwèIrrigation Scheme, Mozambique

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.

Re-evaluating the vertical mass-flux profiles of aeolian sediment at the southern fringe of the Taklimakan Desert, China

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.

Exchange fluxes of nutrients between sediment and sea water in the Bohai Sea

Investigations of sediment-water fluxes of nutrients in the Bohai Sea were carried out in September - October 1998 and April - May 1999. The exchange fluxes of nutrients between sediment and sea water were determined by incubating the core-top sediments with overlying water aerated with air. The benthic fluxes of NO3- , NO2- , NH4+ , DIN, DON and TON in the first cruise and the flux-es of NO3 , NO2- , NH4+ , DIN, DON, TDN, PO43- , DOP and TDP in the second cruise were measured. The exchange fluxes of nutrients in fall were higher than in spring. The benthic nutrient fluxes represented 15% -55% of nutrient budgets in the Bohai Sea.

Nutrient Fluxes and Sediments Composition in El Mex Bay and Surround Drains, Alexandria, Egypt

The regeneration of pore water (PW) nutrients was investigated and the contribution of benthic nutrient fluxes to the overlying bottom water (BW) was examined. Dissolved inorganic nutrients (NO-2, NO-3, PO3-4 and SIO4-4) were measured in PW and BW in El Mex Bay and surround drains during spring 2010. Nutrient concentrations gradiance in PW with overlying seawater were evaluated according to Fick’s Law. Average inorganic nutrient fluxes were estimated using the pore water gradient concentration across the sediment-water interface. Calculated nutrient fluxes had averages of ﹣7.24, ﹣1.36, ﹣7.86 and ﹣1.33 in El Mex Bay. Additionally, the fluxes in the drains were ﹣34.39, ﹣32.28, ﹣53.20 and ﹣117.6 mg·m﹣2·day﹣1 for NO-3, NO-2, PO3-4 and SIO4-4, respectively. Mineralogical studies of sediment samples by using IR, X-ray analysis were carried out to identify the chemical structure of sediments. The results revealed that calcite, aragonite and quartz are the dominant minerals. On the other hand, differential thermal analysis (DTA) was used to evaluate and discuss different kinetic parameters such as Ea#, ΔG#, ΔH#, ΔS#, Z and Tm support the view of the extra stability of these sediments.

Comparison of depth-averaged concentration and bed load flux sediment transport models of dam-break flow

This paper presents numerical simulations of dam-break flow over a movable bed. Two different mathematical models were compared: a fully coupled formulation of shallow water equations with erosion and deposition terms(a depth-averaged concentration flux model), and shallow water equations with a fully coupled Exner equation(a bed load flux model). Both models were discretized using the cell-centered finite volume method, and a second-order Godunov-type scheme was used to solve the equations. The numerical flux was calculated using a Harten, Lax, and van Leer approximate Riemann solver with the contact wave restored(HLLC). A novel slope source term treatment that considers the density change was introduced to the depth-averaged concentration flux model to obtain higher-order accuracy. A source term that accounts for the sediment flux was added to the bed load flux model to reflect the influence of sediment movement on the momentum of the water. In a onedimensional test case, a sensitivity study on different model parameters was carried out. For the depth-averaged concentration flux model,Manning's coefficient and sediment porosity values showed an almost linear relationship with the bottom change, and for the bed load flux model, the sediment porosity was identified as the most sensitive parameter. The capabilities and limitations of both model concepts are demonstrated in a benchmark experimental test case dealing with dam-break flow over variable bed topography.

Release Flux Estimation of Sediment Phosphorus in Shiwuli River Estuary of Chao Lake in Summer

[Objective] The study aimed to estimate the release flux of sediment phosphorus in Shiwuli River estuary of Chao Lake in summer. [Method] Under static and dynamic conditions, we analyzed the release characteristics of sediment phosphorus in Shiwuli River estuary of Chao Lake in summer, and estimated the release flux of sediment phosphorus in the studied area in summer. [Result] Disturbance had great effects on the release of sediment phosphorus in Shiwuli River estuary of Chao Lake in summer. When phosphorus concentration in overlying water was 0 mg/L, the amount of released phosphorus under dynamic conditions was 2.3 times as much as that under static conditions; as phosphorus concentration in overlying water was 0.05 mg/L, the amount of released phosphorus under dynamic conditions was 1.3 times as much as that under static condi- tions. In a word, the amount of released phosphorus under dynamic conditions was higher than that under static conditions. In summer, the release flux of sediment phosphorus in Shiwuli River estuary of Chao Lake was very high, namely 0.2 t/km2. Therefore, besides controlling exogenous phosphorus pollution, we should pay more attention to the release of sediment phosphorus. [ Conclusion] The research could provide theoretical ref- erences for dredging sediment and controlling lake eutrophication in future.

黄河水沙监测数据分析与模型构建

对黄河水沙监测数据进行分析研究,使用相关性分析、回归分析、Mann-Kendall非参数检验、奇异谱分析等方法构建数学模型.分析含沙量与各因素的关系、水沙通量变化规律、水沙通量趋势预测、河底高程变化规律预测等问题,并提出水沙通量监测的优化策略.在环境治理、调水调沙、防洪减灾等方面具有一定的现实意义.

海水多品种养殖池塘沉积物-水界面氮磷通量

为探明生源要素氮、磷在沉积物与水体间的迁移过程,比较3种不同养殖模式下、不同时间养殖池塘沉积物-水界面的氮、磷通量变化,2014年6—10月,在3种综合养殖池塘:海蜇+凡纳滨对虾+菲律宾蛤仔、海蜇+凡纳滨对虾+缢蛏和海蜇+凡纳滨对虾的整个养殖周期内,采集检测3口池塘沉积物-水界面样品中的亚硝态氮、硝态氮、氨氮和活性磷酸盐含量,分析沉积物-水界面的亚硝态氮+硝态氮、氨氮和活性磷酸盐的通量变化。试验结果显示,6—10月,3种综合养殖池塘沉积物上覆水中亚硝态氮和硝态氮均以向沉积物中扩散为主,仅10月海蜇+凡纳滨对虾池塘沉积物中亚硝态氮和硝态氮向上覆水释放。海蜇+凡纳滨对虾+菲律宾蛤仔、海蜇+凡纳滨对虾+缢蛏池塘沉积物上覆水中氨氮向沉积物扩散,6月海蜇+凡纳滨对虾+缢蛏池塘沉积物中氨氮向上覆水扩散;与海蜇+凡纳滨对虾+菲律宾蛤仔和海蜇+凡纳滨对虾+缢蛏池塘相比,海蜇+凡纳滨对虾池塘氨氮通量变化幅度较大,6—7月上覆水中氨氮向沉积物扩散,且扩散速率逐渐降低,9—10月沉积物中氨氮向上覆水释放,释放速率逐渐上升。6、7、10月海蜇+凡纳滨对虾+菲律宾蛤仔池塘沉积物中活性磷酸盐向上覆水释放,8—9月上覆水中活性磷酸盐向沉积物扩散;6—10月,海蜇+凡纳滨对虾+缢蛏池塘沉积物中活性磷酸盐向上覆水释放;海蜇+凡纳滨对虾池塘上覆水中活性磷酸盐向沉积物扩散,10月沉积物中活性磷酸盐向上覆水释放。试验结果表明,配养底栖贝类,可以通过改变综合养殖池塘沉积物-水界面的氮、磷通量,改善池塘的底质和水质环境。

1958-2022年黄河头道拐水文站水沙特征分析及预测

[目的]探究黄河头道拐水文站径流量与输沙量演变特征,为区域水资源合理规划提供理论依据。[方法]基于1958—2022年径流输沙数据,采用非参数检验方法与CEEMDAN法研究了头道拐水文站水沙趋势、突变及周期变化特征,并通过水沙月值数据构建Informer预测模型。[结果](1)年径流量与年输沙量的M-K统计量分别为-3.380,-5.067。年径流量和年输沙量分别于1986年、1968年和1986年发生突变,下降率分别为36%,44.38%和61.32%。(2)使用CEEMDAN法对径流量与输沙量年值序列进行分解后均得到3个IMF分量与1个RES分量,水沙序列的3个IMF分量平均周期分别为3.69 a,7.67 a,30 a和3.41 a,7.5 a,26 a;水沙月值序列经过分解后得到7个IMF分量,短周期为3.46月与3.61月,长周期为226.33月与184.50月,主导周期为7.25月和8.09月。(3)模型构建后发现径流的预测精度高于输沙,原因是输沙量受影响因素众多,变动幅度更大,较径流量预测难度大。[结论]黄河头道拐水文站水沙存在显著下降趋势,主要归因于降水影响,且序列突变节点与上游水库建成密切相关。

深时源-汇系统要素的常用定量分析方法

源-汇系统研究是构造地质学、沉积学和层序地层学的综合,因其整体性、动态化和半定量-定量的特点受到了广泛关注。首先阐述了目前深时(前第四纪)源-汇系统的关键问题是物质平衡的定量表征及搬运过程对沉积物的控制,由于地层记录缺失和参数获取困难等原因,研究仍极具挑战。随后综述了深时源-汇系统定量分析方法,可分为地质年代学法、将今论古法和沉积学法。各方法通过获取地貌要素、水力学参数、侵蚀速率、沉积通量等信息,建立“源”“汇”之间的定量关系,进而重建盆地沉积充填演化史。通过系统介绍不同方法的基本原理、相关参数,对比其优越性及局限性,认为地质年代学法应用较广,核心在于物源示踪;将今论古法关键是地质背景的类比及地质参数的选择;沉积学法受多变量控制,需兼顾构造-气候背景及研究尺度。最后对深时源-汇系统定量分析的发展进行了展望,在“将今论古”这一重要思想指导下,需着眼于物源体系、沉积物搬运路径、沉积物分配关系、系统内的各要素及其耦合作用,需注重多时间尺度的定量表征、多学科交叉的动态研究。而相较于大陆边缘源-汇系统,陆相湖盆源-汇系统模式与预测模型有待进一步完善。