Using Natural Radionuclides to Trace Sources of Suspended Particles in the Lower Reaches of the Yellow River

Natural radionuclides are powerful tools for understanding the sources and fate of suspended particulate matter(SPM).Particulate matter with different particle sizes behaves differently with respect to adsorption and desorption.We analyzed the activi-ties and distribution characteristics of multiple natural radionuclides(238U,226Ra,40K,228Ra,7Be and 210Pbex)on size-fractionated SPM at the Lijin Hydrographic Station(Huanghe or Yellow River)every month over a one-year period.Results showed that medium silt(16–32µm)was the main component.As expected,the activity of each radionuclide decreased with an increase of particle size.We examined the sources of SPM with different particle sizes using activity ratios of 226Ra/238U,228Ra/226Ra,40K/238U and 7Be/210Pbex,and concluded that SPM with different particle sizes originated from different sources.Our results indicate that fine SPM(<32µm)was mainly from the erosion of soil along the lower reaches of the Yellow River,while coarse SPM(>32µm)was mainly derived from resuspension of riverbed sediment.During high runoff periods,the concentration of SPM increased significantly,and the pro-portion of fine particles originating upstream increased.Naturally occurring radioactive isotopes,especially on size-fractionated par-ticles,are therefore seen as useful tracers to understand the sources and behaviors of riverine particles transported from land to sea.

Using Rn-222 to Study Human-Regulated River Water-Sediment Input Event in the Estuary

The implementation of the water sediment regulation scheme(WSRS)is a typical example of artificially controlling land-source input.During WSRS,the water discharge of the Yellow River will increase significantly,and so will the input of terri-genous materials.In this study,we used a natural geochemical tracer 222Rn to quantify terrestrial inputs under the influence of the 2014 WSRS in the Yellow River Estuary.The results indicated that during WSRS the concentration of 222Rn in the estuary increased by about four times than in the period before WSRS.The high-level 222Rn plume disappeared quickly after WSRS,indicating that 222Rn has a very short‘memory effect’in the estuary.Based on the investigation conducted from 2015 to 2016,the concentration of 222Rn tended to be stable in the lower reaches of the Yellow River.During WSRS,the concentrations of 222Rn in the river water in-creased sharply at about 3–5 times greater than in the non-WSRS period.Based on the 222Rn mass balance model,the fluxes of 222Rn caused by submarine groundwater discharge(SGD)were estimated to be(3.5±1.7)×10^(3),(11±3.9)×10^(3),and(5.2±1.9)×10^(3)dpm m^(-2)d^(-1)in the periods before,during,and after WSRS,respectively.This finding indicated that SGD was the major source of 222Rn in the Yellow River Estuary,which can be significantly increased during WSRS.Furthermore,the SGD-associated nutrient fluxes were estimated to be 9.8×10^(3),2.5×102,and 1.1×10^(4)μmolm^(-2)d^(-1)for dissolved inorganic nitrogen,phosphorus,and silicon,respectively,during WSRS or about 2–40 times greater than during the non-WSRS period.

Response of delta sedimentary system to variation of water and sediment in the Yellow River over past six decades

In order to find out the variation process of water-sediment and its effect on the Yellow River Delta, the water discharge and sediment load at Lijin from 1950 to 2007 and the decrease of water discharge and sediment load in the Yellow River Basin caused by human disturbances were analyzed by means of statistics. It was shown that the water discharge and sediment load into the sea were decreasing from 1950 to 2007 with serious fluctuation. The human activities were the main cause for decrease of water discharge and sediment load into the sea. From 1950 to 2005, the average annual reduction of water discharge and sediment load by means of water-soil conservation practices were 2.02×10^9 m^3 and 3.41×10^8 t respectively, and the average annual volume by water abstraction for industry and agriculture were 2.52×10^10 m^3 and 2.42×10^8 t respectively. The average sediment trapped by Sanmenxia Reservoir was 1.45×10^8 t from 1960 to 2007, and the average sediment retention of Xiaolangdi Reservoir was 2.398×10^8t from 1997 to 2007. Compared to the data records at Huanyuankou, the water discharge and sediment load into the sea decreased with siltation in the lower reaches and increased with scouring in the lower reaches. The coastline near river mouth extended and the delta area increased when the ratio of accumulative sediment load and accumulative water discharge into the sea （SSCT） is 25.4-26.0 kg/m^3 in different time periods. However, the sharp decrease of water discharge and sediment load into the sea in recent years, especially the Yellow River into the sea at Qing 8, the entire Yellow River Delta has turned into erosion from siltation, and the time for a reversal of the state was about 1997.

Numerical Study on Seasonal Transportation of the Suspended Sediments in the Modern Yellow River Mouth Effected by the Artificial Water and Sediment Regulation

Since 2002, an artificial water and sediment regulation(AWSR) has been carried out, which largely reduced water and sediment discharged from the Yellow River into the Bohai Sea. Although the sediment transport in the Yellow River Mouth(YRM) has been observed and modeled intensively since AWSR, but preferentially for the non-storm conditions. In this study, a three-dimensional current-wave-sediment coupled model, DHI-MIKE numerical model, was used to examine the seasonal suspended-sediment transport in the YRM after the AWSR. Results show that the seasonal distribution of suspended-sediments in the YRM is dominated by wind and wave rather than river input. The major transport pathway of suspended-sediments is from the western Laizhou Bay to the Bohai Strait during the winter monsoon, especially in storm events. In addition, about 66% of the river sediments deposit within 30 km of the YRM, which is smaller than previous estimations. It suggests that the YRM has been eroded in recent decades.

Changes in sediment discharge in a sediment-rich region of the Yellow River from 1955 to 2010: implications for further soil erosion control

The well-documented decrease in the discharge of sediment into the Yellow River has attracted considerable attention in recent years. The present study analyzed the spatial and temporal variation of sediment yield based on data from 46 hydrological stations in the sediment-rich region of the Yellow River from 1955 to 2010. The results showed that since 1970 sediment yield in the region has clearly decreased at different rates in the 45 sub-areas controlled by hydrological stations. The decrease in sediment yield was closely related to the intensity and extent of soil erosion control measures and rainstorms that occurred in different periods and sub-areas. The average sediment delivery modulus（SDM） in the study area decreased from 7,767.4 t/（km^2·a） in 1951–1969 to 980.5 t/（km^2·a） in 2000–2010. Our study suggested that 65.5% of the study area with the SDM below 1,000 t/（km^2·a） is still necessary to control soil deterioration caused by erosion, and soil erosion control measures should be further strengthened in the areas with the SDM above 1,000 t/（km^2·a）.

Sediment transport following water transfer from Yangtze River to Taihu Basin

To meet the increasing ：need of fresh water and to improve the water quality of Taihu Lake, water transfer from the Yangtze River was initiated in 2002. This study was performed to investigate the sediment distribution along the river course following water transfer. A rainfall-runoff model was first built to calculate the runoff of the Taihu Basin in 2003. Then, the flow patterns of river networks were simulated using a one-dimensional river network hydrodynamic model. Based on the boundary conditions of the flow in tributaries of the Wangyu River and the water level in Taihu Lake, a one-dimensional hydrodynamic and sediment transport numerical model of the Wangyu River was built to analyze the influences of the inflow rate of the water transfer and the suspended sediment concentration （SSC） of inflow on the sediment transport. The results show that the water transfer inflow rate and SSC of inflow have significant effects on the sediment distribution. The higher the inflow rate or SSC of inflow is, the higher the SSC value is at certain cross-sections along the ：river course of water transfer. Higher inflow rate and SSC of inflow contribute to higher sediment deposition per kilometer and sediment thickness. It is also concluded that a sharp decrease of the inflow velocity at the entrance of the Wangyu River on the river course of water transfer induces intense sedimentation at the cross-section near the Changshu hydro-junction. With an increasing distance from the Changshu hydro-junction, the sediment deposition and sedimentation thickness decrease gradually along the river course.

Effect of water-sediment regulation and its impact on coastline and suspended sediment concentration in Yellow River Estuary

Implementation of the water-sediment regulation(WSR) scheme, mainly focused on solving the sedimentation problems of reservoirs and the lower reaches of the Yellow River, has inevitably influenced the sediment distribution and coastal morphology of the Yellow River Estuary.Using coastline delineation and suspended sediment concentration(SSC) retrieval methods, this study investigated water and sediment changes,identified detailed inter-annual and intra-annual variations of the coastline and SSC in the normal period(NP: 1986-2001, before and after the flood season) and WSR period(WSRP: 2002-2013, before and after WSR). The results indicate that(1) the sedimentation in the low reaches of the Yellow River turned into erosion from 2002 onward;(2) the inter-annual coastline changes could be divided into an accretion stage(1986-1996), a slow erosion stage(1996-2002), and a slow accretion stage(2002-2013);(3) an intra-annual coastline extension occurred in the river mouth in most years of the WSRP; and(4) the mean intra-annual accretion area was 0.789 km^2 in the NP and 4.73 km2 in the WSRP,and the mean SSC increased from 238 mg/L to 293 mg/L in the NP and from 192 mg/L to 264 mg/L in the WSRP.

Effect of Water and Sediment Regulation on Lower Yellow River

According to the results of the water and sediment regulations of the Yellow River in year 2002—2007,the effect of erosion and deposition on the lower reaches,the amount and distribution of erosion and deposition in the river mouth area,the adjustment of river regime,the effect of river regulation projects and changes of flowing capacity of the channel are analyzed.It is revealed that the water and sediment regulation is efficient to reduce deposition and improve the flowing capacity and the conditions of sediment transport.

Impact of Water-Sediment Regulation on Variations of Amino Acids in the Middle-Lower Yellow River, China

In order to examine the impacts of water-sediment regulation on regional carbon cycling,we collected water,particulate and sediment samples from the middle-lower Yellow River in late June and early July,2015 and analyzed their specific amino acids(AA),DOC,POC,and bacteria abundance.Summarized by 14 specific AA,the total hydrolysable AA(THAA),particulate AA(PAA),and sediment AA(SAA)varied in ranges of 2.29-9.05μmol L^-1,5.22-22.96μmol L^-1,and 81.7-137.19μg g^-1 dry weight.After the regulation,dissolved free AA(DFAA)decreased by 29%while DCAA increased by 72%.These variations suggested that DFAA were further degraded,while DCAA molecules were further activated.Meanwhile,PAA increased almost 4 times as many as those before regulation,and SAA increased as well.After regulation,the amounts of bioactive amino acids(Asp,Glu and Gly)increased in THAA but decreased in PAA,with little changes in SAA.The ratios of Asp/Gly in different phases increased after regulation,indicating the AA contributions were promoted by calcareous organisms rather than by siliceous organisms.Multiple correlation analysis showed that PAA was primary representatives of AA and organic carbon,followed by DCAA and POC.Moreover,bacterial reproduction played a key role in shaping the AA compositions and properties,followed by the redox condition and acid-base balance.The results of this study provided a clear evidence for the effects of water-sediment regulation on regional biogeochemistry of organic carbon in the middle-lower Yellow River.

Effects of muddy water irrigation with different sediment gradations on nitrogen transformation in agricultural soil of Yellow River Basin

Muddy water irrigation has been widely practiced in the Yellow River Basin for agricultural production and is an important method of economical and intensive utilization of water resources.In this study,the effects of sediment gradation,sand content,and soil moisture content on nitrogen(N)transformation were studied through a series of experimental tests.The results indicated that muddy water irrigation significantly affected agricultural soil physical and biological properties as well as N transformation.Soil bulk density,total porosity,pH,and microbial enzyme activities significantly correlated with N transformation as affected by the interaction between sediment and soil moisture.Sediment addition generally increased the soil bulk density and reduced the soil porosity and pH significantly,and the optimum moisture for promotion of the N transformation rate was 80%of the water-filled pore space.Therefore,muddy water irrigation has a potentially long-term influence on agricultural N cycles in semi-arid regions of northwestern China.This could provide a theoretical basis for scientific and rational use of muddy water for irrigation.

Study on the Operation Mechanism and Effect of the Yellow River Water and Sediment Regulation System

In order to scientifically deal with the problems of less water and more sediment in the Yellow River and the uncoordinated relationship between water and sediment,it is necessary to establish a perfect water and sediment regulation system.Through the calculation of the sediment transport capacity of the Yellow River and the application of the water and sediment regulation system,it is found that the sediment transport efficiency of the Yellow River will increase with the increase of water flow,and there will be an obvious inflection point near the flat discharge.The joint regulation of the backbone reservoir group can discharge the large discharge close to the minimum flat discharge of the downstream river,which improves the sediment transport capacity of the river and alleviates the problem of sediment deposition.In this paper,through the introduction of the Yellow River water and sediment regulation project system,regulation indicators and mechanisms,the author discusses in detail the Yellow River water and sediment regulation scheme and its operation effect,hoping to provide help promote the improvement of the Yellow River governance effect.

TRANSFERABLE PHOSPHORUS IN SEDIMENTS OF THE HUANGHE RIVER ESTUARY'S ADJACENT WATERS

Based on a new idea for research on cycling of marine biogenic elements, this study showed that only the leachable form phosphorus in natural grain sizes marine sediments constitutes the transferable phosphorous in the sediments. The transferable phosphorus content in the natural grain sizes surface sediments in the Huanghe River estuary adjacent waters ranges from 58.5-69.8 μg/g, accounting for only 9.1%-11.0% of the total phosphorus content, whereas the leachable form (“transferable") phosphorus content in the sediment after it was totally ground into powder was found to be 454.8-529.2 μg/g, accounting for 73.4%-89.1% of the total phosphorus. Analysis of the correlation between the biomass of benthos and the leachable form (“transferable") phosphorus showed that most of the leachable form (“transferable") phosphorus in the totally ground sediment did not participate in the marine biogeochemical cycling. Furthermore, a synchronous survey on benthos showed that the biomass of meio and macro benthos exhibited good positive correlation with the leachable form of phosphorus in the natural grain sizes sediment, but poorer correlation with the leachable form (“transferable") phosphorus in the totally ground sediment, indicating that transferable phosphorus in marine sediment is the leachable form of phosphorus in the natural grain sizes sediments, and is not the previously known leachable form (“transferable") phosphorus obtained from the totally ground sediment.

Equilibrium sediment transport in lower Yellow River during later sediment-retaining period of Xiaolangdi Reservoir

The Xiaolangdi Reservoir has entered the later sediment-retaining period, and new sediment transport phenomena and channel re-estab- lishing behaviors are appearing. A physical model test was used to forecast the scouring and silting trends of the lower Yellow River. Based on water and sediment data from the lower Yellow River during the period from 1960 to 2012, and using a statistical method, this paper analyzed the sediment transport in sediment-laden flows with different discharges and sediment concentrations in the lower Yellow River. The results show that rational water-sediment regulation is necessary to avoid silting in the later sediment-retaining period. The combination of 3 000 m^3/s 〈 Q 〈 4 000 m^3/s and 20 kg/m^3 〈 S 〈 60 kg/m^3 （where Q is the discharge and S is the sediment concentration） at the Huayuankou section is considered an optimal combination for equilibrium sediment transport in the lower Yellow River over a long period of time.

Remote Sensing Retrieval of Surface Suspended Sediment Concentration in the Yellow River Estuary

Accurate assessment of surface suspended sediment concentration(SSSC) in estuary is essential to address several important issues: erosion, water pollution, human health risks, etc. In this study, an empirical cubic retrieval model was developed for the retrieval of SSSC from Yellow River Estuary. Based on sediments and seawater collected from the Yellow River and southeastern Laizhou Bay, SSSC conditions were reproduced in the laboratory at increasing concentrations within a range common to field observations. Continuous spectrum measurements of the various SSSCs ranging from 1 to 5700 mg/l were carried out using an Ava Field-3 spectrometer. The results indicated the good correlation between water SSSC and spectral reflectance(Rrs) was obtained in the spectral range of 726–900 nm. At SSSC greater than 2700 mg/L, the 740–900 nm spectral range was less susceptible to the effects of spectral reflectance saturation and more suitable for retrieval of high sediment concentrations. The best correlations were obtained for the reflectance ratio of 820 nm to 490 nm. Informed by the correlation between Rrs and SSSC, a retrieval model was developed(R2 = 0.992). The novel cubic model, which used the ratio of a near-infrared(NIR) band(740–900 nm) to a visible band(400–600 nm) as factors, provided robust quantification of high SSSC water samples. Two high SSSC centers, with an order of 103 mg/l, were found in the inversion results around the abandoned Diaokou River mouth, the present Yellow River mouth to the abandoned Qingshuigou River mouth. There was little sediment exchange between the two high SSSC centers due to the directions of the residual currents and vertical mixing.

Response of the distributary channel of the Huanghe River estuary to water and sediment discharge regulation in 2007

The water and sediment discharge regulation(WSDR) project,which has been performed since 2002 before flood season every year,is of great significance to the river management in China.Until 2007,six experiments have been fulfilled to evaluate the effect of the project on the natural environment.To fill the gap of investigations,a study on flood and suspended sediment transportation and channel changing along the distributary channel of the Huanghe(Yellow) River was conducted during the WSDR project period in 2007.The lower channel was scoured rapidly and the channel became unobstructed gradually several days after the flood peak water was discharged from the Xiaolangdi Reservoir.Within four days after the flood peak at 3 000 m3/s entered the distributary,the channel in the river mouth area was eroded quickly.Both the mean values of area and depth of the main channel were tripled,and the maximum flood carrying capacity increased to 5 500 m3/s or more.Then,the river channel was silted anew in a very short time after completion of the WSDR.Favored by the WSDR project,the river status in April 2008 became better than that of the year before.The adjustment ranges of main channel parameters were about 30%,10%,and 10% at sections C2,Q4,and Q7,respectively.The process of rapid erosion-deposition was more active 15 km away in the channel from the river mouth due to the marine influence.It is reasonable for discharging sediment at concentration peak from Xiaolangdi Reservoir at the end of the flood peak.As a result,the sediment peak reached the river mouth about two days later than that of the water current.In addition,the WSDR project has improved the development of the estuarine wetland.Wetland vegetation planted along the river banks restrained the water flow as a strainer and improved the main channel stability.It is suggested to draw water at mean rate of 150 m3/s from the Huanghe River during flood periods,because at the rate the water in the wetland would be stored and replenished in balance.Moreover,we believe that cropland on the river shoal of the lower Huanghe River should be replaced by wetland.These activities should achieve the Huanghe River management strategy of "To concentrate flow to scour sediment,stabilize the main channel,and regulate water and sediment".

A STUDY ON THE WATER RESOURCES AND SEDIMENT PROBLEMS IN THE IRRIGATED AREA OF NORTHWEST SHANDONG PROVINCE

There are very serious water and sediment problems in the irrigated areas of northwest Shandong Province. In upper reaches of the irrigated area, the Yellow River water are widely used for farmland watering while leaving the ground water unusedion. But in the lower reaches, there is not enough surface water to be channeled for irrigation, so the ground water has always been over extracted, in some parts of the lower reaches, the descending water table caused the formation of funnel. Siltation in canals are very difficult to be cleared up, the drop of agriculture yield in the sandy land close to the channel head and along the main channels impair the living conditions of the local people. The conflicts between the excessive dependence on the Yellow River and the decreasing tendancy of water amount provided by the Yellow Ricer forces the local government to find new ways to solve the water resource problems. The answer could be: Using new technique for the irrigated system, pay more attention to the ground water development, and the construction and maintenance of wells.

水土保持生态建设下的黄土高原典型流域水沙响应

为探讨黄土高原多沙粗沙区流域水沙关系演变特征及其对水土流失治理的响应,以黄河中游无定河流域为研究对象,综合采用水沙关系曲线、数理统计等多种方法,系统分析1956—2019年间无定河流域水沙关系多时间尺度演变特征及其与水土流失治理的协同响应。研究结果表明:1)研究时段内,无定河流域年径流及年输沙量呈锐减趋势(P<0.05),且均在1970年左右发生减少突变;2)流域水沙关系在年际和场次洪水尺度上均发生深刻变化。2010年以后,暴雨频发导致流域内侵蚀物源头供应明显增加,流域河道泥沙输送能力小幅提高;3)水土保持措施实施对流域水沙锐减影响较大。2000年前后在相似降雨条件下,单位降雨量径流量和单位降雨量输沙量较20世纪70年代减少47%和62%。水土保持措施面积增加与流域径流输沙减少呈现较好的一致性,流域水土流失治理在提高黄河多沙粗沙区流域下垫面抗侵蚀能力等方面发挥重要作用。研究结果可为科学认知区域水土流失治理成效及入黄泥沙锐减成因提供参考。