Yellow River Mouth Research Articles

Spatiotemporal variations in the grain size distribution in the water column and sediments from the Yellow River Delta to distal areas under coastal currents

The differentiation of sediment grain size from large river deltas to distal areas in a coastal flow system and its evolution are vital because they greatly contribute to matter transport, pollution accumulation, and carbon cycling on the inner shelf. Here, the Yellow River sedimentary system in the adjacent seas is studied, including the proximal delta of the Yellow River and the distal mud patch. The grain size distributions of the suspended particulate matter (SPM), surface sediments, and core sediments in the Shandong Peninsula Coastal Current (SPCC) system were integrated and analyzed. The results show that apparent variations in the grain size distribution exist in the SPM and sediments in the SPCC system. The grain size distribution of the SPM near the proximal delta of the Yellow River is multimodal and variable with water depth, whereas that in the distal mud area is typically unimodal. The coarse-grained endmember of suspended sediments is restricted in the proximal area by ocean fronts under fair weather conditions in both summer and winter and is only transported to the distal mud area under strengthened coastal currents in winter. In contrast, fine-grained endmembers can be transported far away under tidal currents and coastal currents year-round. The temporal grain size variation near the proximal delta is also significantly affected by historical shifts in the Yellow River mouth, while the strength of coastal currents associated with the East Asian Winter Monsoon (EAWM) controls the grain size distribution in the distal mud area. The roles of river behaviors, ocean fronts, tides, and winds are all highlighted in the control of grain size differentiation. These results potentially have significance for understanding sediment dynamics and mass transport processes in similar coastal current systems involving large rivers worldwide.

Rapid change of vegetation cover in the Huanghe (Yellow River) mouth wetland and its biogeomorphological feedbacks

Vegetation plays a crucial role in the evolutionary process of coastal wetlands through its biogeomorphological feedbacks, and has become a hot topic of worldwide concern in the context of global climate change. However, as one of the youngest wetlands, the impact of vegetation expansion on the evolution of the Huanghe mouth wetland is currently unknown. In this study, we investigated the spatial and temporal variation of the vegetation cover in the Huanghe mouth wetland over the past twenty years and quantitatively examined its biogeomorphological feedbacks on the river mouth evolution. The results showed that the vegetation cover of the Huanghe mouth wetland has expanded rapidly since 2012 due to the invasion of the exotic species Spartina alterniflora. Its biogeomorphological feedbacks controlled the spatial distribution of surface sediments in the Huanghe mouth wetland and also altered the sediment budget in subaqueous and subaerial deltas. The land-building efficiency of the Huanghe sediment jumped to 101.76 km2/Gt, more than four times that of the pre-invasion period. Compared with other coastal wetlands in the world, the unique feature of high suspended sediment concentration (SSC) makes the Huanghe mouth wetland with high accretion rate under the influence of vegetation. The present study reveals the rapid changes of the vegetation cover and its biogeomorphological feedbacks in the Huanghe mouth wetland, and highlights that the vegetation plays a more critical role in the morphological evolution of the highly turbid river mouth.

Impact of tidal shear fronts on terrigenous sediment transport in the Yellow River Mouth: Observations and a synthesis

A tidal shear front (TSF) can be defined as an obvious horizontal gradient of flow velocity formed by opposing tidal currents (reversed TSF) or same-direction tidal currents (homogenous TSF) on both sides of the front with limited impact by river runoff. Observational and modeling studies have been conducted to investigate the impact of a reversed TSF on the transport of freshwater and sediment in the Yellow River Mouth (YRM). The reversed TSF existence period is only about 40% of a tidal cycle (around slack of flood and ebb); however, when this front disappears (around maximum flood and ebb), sediment transport across the frontal zone is still rare. This suggests that the dynamic mechanism of cross-frontal sediment transport in a tidal cycle remains unclear. In this study, synchronous observations of sea current and suspended sediment concentrations along the river mouth profiles at the YRM in 1995, 2003, and 2019 were used to investigate the long-term variation characteristics, mechanisms, and impacts of the TSF on cross-frontal sediment transport. The results indicate that in addition to the reversed TSF, there are also homogenous TSF during flood and ebb tides, with the ebb homogenous TSF being more significant due to tidal asymmetry in the YRM. The ebb homogenous TSF is located between shallow shoals and the slopes of the subaqueous delta front and lasts for about 3 h around the maximum ebb. Its maximum shear strength is similar to that of the reversed TSF, and the formation mechanism is also similar. The presence of the ebb homogenous TSF reduces the efficiency of cross-frontal sediment transport during the ebb. The reversed and homogenous TSFs alternately block sediment moving towards the sea. Thus, terrigenous sediment is difficult to cross the frontal zone to the central Bohai Sea by tidal currents solely. Over the past two decades of low discharge, with the Yellow River implementing artificial water and sediment regulation, the homogenous TSF during the ebb tide has become more and more important and cannot be neglected for cross-frontal sediment transport under normal conditions. Furthermore, from a long-term perspective, the shear strength of the TSF is positively correlated with the distance of river mouth siltation into the sea. Additionally, salinity and turbidity gradients are also positively correlated with the shear strength in the estuary. This indicates that the blocking of cross-frontal sediment transport by the TSF is a key process in river-sea interaction in the YRM.

Sedimentary evolution of the western North Yellow Sea mud patch: A Holocene perspective

The western North Yellow Sea mud patch has a unique location, abundant sediment supply and a complex sedimentary environment. Reconstructing its sedimentary evolution is crucial for a comprehensive understanding of source to sink process in the North Yellow Sea. Using core W03 collected from the mud patch, this study unravels its Holocene history through analysis of sedimentology, mineralogy and micropalaeontology. The results indicate that core W03 can be divided into three depositional units (DU). DU3 (538-461 cm) is composed of earthy yellow clayey silt and characterized by a hard layer. It was formed in the near-coast environment between 10.3 and 9.8 cal kyr BP, a hiatus period between Melt Water Pulse 1B and 1C events. DU2 (460-341 cm) was formed during the period of 9.8–6.5 cal kyr BP. As sea level rose, the westward retreat of the Yellow River mouth caused the transportation of Yellow River-derived sediment over longer distances, leading to an increase in flaky minerals. The rising sea level also induced a shift towards a reducing environment in the western North Yellow Sea. DU1 (340-0 cm) was formed after 6.5 cal kyr BP. During this period, the study area remained in a shelf shallow sea environment characterized by relatively strong chemical hydrolysis and reducing conditions. The intensification of the Yellow Sea Warm Current and an increase in Yellow River sediment transported to the sea led to an obvious increase in sedimentation rate after 2.3 cal kyr BP.

Pb and O isotopic characteristics of single minerals in the Jianggang radial sand ridges of the southwestern Yellow Sea: Implications for provenance and pathways of silt-size sediments

Understanding the sediment provenance of the Jianggang radial sand ridges (RSRs) along the Jiangsu coast in the southwestern Yellow Sea is crucial for sustainable coastal development and land resource management. In this study, the provenance and transport patterns of silt-size sediments in the Jianggang RSRs were explored using Quartz oxygen (O) and K-feldspar lead (Pb) isotopic compositions and their large ion lithophile elements (LILEs) concentrations. The Pb-O isotopic compositions and concentrations of most LILEs in RSRs sediments were between those of the Yangtze River Mouth (YTZ), Old Yellow River Delta (OYR), and Modern Yellow River Mouth (MYR). The Pb-O isotopic compositions and typical elemental ratios were similar between the onshore and northwest offshore RSRs sediments, implying shoreward transport of offshore silt-size sediments. Through multidimensional scaling and graphic methods, it was found that the sediments of onshore and offshore RSRs originate mainly from the YTZ and OYR. Furthermore, the MixSIAR model showed that the contributions of the YTZ to onshore and offshore RSRs reached 33 ± 4 % and 36 ± 3 %, respectively. Followed by the OYR with contributions of 36 ± 3 % and 25 ± 8 %, respectively, and the contributions of the MYR and Korean Peninsula were <21 % and 8 %, respectively. Meanwhile, contributions from the Northern Chinese Deserts (approximately 10 %) deserved attention. Through the distribution of indicators, the transport patterns of silt-size sediments were proposed and compared with those of other fractions for the first time. According to the correlation analysis, the change in the area of central Jiangsu coast was mostly affected by terrestrial river supply and coastal mariculture. Therefore, it was necessary to control the scale of river reservoir construction and strengthen mariculture for sustainable land development and management. In future, comprehensive interdisciplinary and large temporal–spatial scales are suggested to further understand the coastal development.

Sedimentary records reveal two stages of evolution of the Abandoned Yellow River Delta from AD1128 to AD1855: vertical accretion and land-forming

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.

Dynamic response of water flow and sediment transport off the Yellow River mouth to tides and waves in winter

Freshwater and sediments are transported from the Yellow River mouth downstream along the coast into Laizhou Bay under the northeasterly wind in winter. Numerical experiments indicate that sediment transport shows the tendency of convergence in the river mouth, divergence in the downstream area, and convergence in the north of Laizhou Bay. Tides and waves are the two main forcings affecting the transport of water and sediments off river mouths. For the high-turbidity Yellow River mouth and the adjacent sea, tidal forcing enhances the subtidal downstream transport of water and sediments off the river mouth into Laizhou Bay, whereas wave forcing has little effect on the advection of water and sediments. Sediment resuspension is controlled by the bottom shear stress induced by tides and waves. The tide-induced bottom shear stress is higher in the north of Laizhou Bay and south of Bohai Bay due to the stronger bottom tidal current. The wave-induced bottom shear stress plays a more important role in sediment resuspension, which is higher in the nearshore region along the Yellow River Delta away from the coast to some extent on account of the maximum near-bottom wave orbital velocity. Tidal mixing strengthens the upward diffusion of the bottom suspended sediments. Without tidal forcing, there is an interesting phenomenon along the Yellow River Delta. In the nearshore region, the decreased bottom shear stress suspends less sediment above the bed. However, in the offshore region, the enhanced stratification hinders the upward diffusion of the bottom sediment due to the lack of tidal mixing, resulting in higher suspended sediment concentration (SSC) in the bottom layer.

The distribution and speciation of dissolved Cd and Pb in the Bohai Sea and Yellow Sea, China

The speciation of dissolved trace metals is important due to its closely linkage with toxicity and bioavailability in seawater. We investigate the speciation of dissolved Pb (DPb) and Cd (DCd), and their spatial distributions in the Yellow Sea and Bohai Sea, China. The results showed that the organic complexation of DPb and DCd accounted for 35 ± 14 % and 75 ± 10 % of their dissolved concentrations, respectively. The measured free ion activity of Cd ({Cd2 +}) and organic ligand concentration of Cd ([LCd]) were highest near the Yellow River mouth, where the free ion activity of Pb ({Pb2+}) were also found to be the highest. In this study, both {Pb2+} and {Cd2+} did not exceed the toxicity threshold, and they were identified not toxic in the waters of the Yellow Sea and Bohai Seas, but biological accumulation effects potentially exist.

Identifying the clay-size sediment provenance of the radial sand ridges in the southwestern Yellow Sea using geochemical and Sr[sbnd]Nd isotopic tracers

Although the sediment provenance of the Jianggang radial sand ridges (RSRs) in the southwestern Yellow Sea has attracted much attention in recent years, the provenance of the clay-size fraction is rarely known. In this paper, the residual fraction of the clay-size sediments in the Jianggang RSRs was isotopically and geochemically determined to analysis their provenance contributions and transport patterns. The clay minerals of the sediments in the Jianggang RSRs, Yangtze River Mouth, Modern Yellow River Mouth and Old Yellow River Delta were characterized by high illite and low smectite contents, differing from those of the Korean rivers. The isotopic and geochemical data showed that 87Sr/86Sr ratios and εNd(0) values of the clay-size sediments ranged from 0.719 to 0.725 and from −14.5 to −12.2, respectively for the onshore RSRs, and from 0.715 to 0.724 and from −14.6 to −10.9, respectively for the offshore RSRs. The clay-size sediments in the offshore RSRs were represented by high concentrations of Sr, Co, Zr, Nb, Hf, Ta, while in the onshore RSRs were characteristic of high concentrations of other elements (except for Ba). The clay-size sediments showed partially similar Y/Hf and Rb/Sc ratios and upper continental crust (UCC)-normalized distribution patterns of trace elements between the onshore and offshore RSRs. However, there was a clearly SrNd isotopic boundary between the two RSRs, indicating that the offshore clay-size sediments were just partly transported to the onshore area. The UCC normalized patterns of the clay-size sediments in the onshore and offshore RSRs were close to those of the Yangtze River Mouth, Modern Yellow River Mouth and Old Yellow River Delta, but different from those of the Korean rivers and Cheju Island. Based on the analyses of SrNd isotopes and trace elements through MixSIAR model, the clay-size sediments of the onshore RSRs mainly originated from the Yangtze River Mouth, but those of the offshore RSRs were predominantly mixed by the Yangtze River Mouth, the Modern Yellow River Mouth and the Old Yellow River Delta, while the contributions of other sources were tiny. Through the SrNd isotopic comparisons, it was further found that there existed a large-scale transport of the clay-size sediment from the Yangtze River Mouth within the Yellow Sea to reach the Jianggang RSRs finally under the influence of the Changjiang Diluted Freshwater and the Yellow Sea Warm Current. This study not only gives deep insight into the formation and evolution theory of the Jianggang RSRs, but also enriches the sediment migration patterns in the Yellow Sea. Meanwhile, it demonstrates the effectiveness of the SrNd isotopic and geochemical tools for provenance analyses of the clay-size sediments, although 87Sr/86Sr should be used cautiously for provenance apportionment due to its indistinguishability between the Chinese and Korean rivers.

The spatio-temporal distribution and transport of suspended sediment in Laizhou Bay: Insights from hydrological and sedimentological investigations

Suspended sediment transport and deposition are crucial physical processes controlling the geomorphological evolution of estuaries and bays. Specially, under the context of worldwide coastal erosion, knowledge of the spatio-temporal distribution of suspended sediment concentration (SSC) and its associated sediment load have become increasingly important for bay management. However, our understanding of the mechanisms of suspended sediment dynamics continues to be hampered by the lack of high-resolution observations. Here, we present a study of the transport mechanisms and controlling factors of suspended sediment over Laizhou Bay. For this, we conducted continuous measurements of SSC, salinity, temperature, and flow velocity at nine stations throughout Laizhou Bay for one 25-h period during each of the spring and moderate tides. Based on these data, residual current, gradient Richardson numbers, and suspended sediment flux were calculated. Our results indicate that a strong current field occurs near the Yellow River mouth, corresponding to the zone with high SSC. The overall diffusion characteristics of suspended sediment are controlled by the tidal current field. Furthermore, our findings suggest that different degrees of stratification occur in the water column, which inhibit the effective vertical diffusion of suspended sediment; Higher water temperature was the main cause of stronger water column stratification of spring tide than moderate tide. Finally, our results reveal that the type of seabed sediment is an important factor controlling SSC by influencing resuspension flux. We conclude that the primary mechanisms controlling suspended sediment transport in Laizhou Bay are advection and tidal pumping, especially advection. Our research provides both a foundational reference for the sediment source-to-sink process from the Yellow River to the sea, as well as guideline implications for coastal engineering construction and channel dredging.

Environmental magnetic properties of core sediments in the Yellow River subaqueous delta and their chronologicalapplications

The Yellow River has shifted frequently in the downstream region since 1885; it has flowed into the sea through the Qingshuigou channel from 1976 onward, thus forming the latest delta lobe (1976–present). During the past ~40 years, the sediment load of the Yellow River has been greatly reduced because of human and natural activities, such as reservoir construction, soil and water conservation, and river avulsion. Beginning in 2002, the water-sediment regulation scheme (WSRS) has also changed the sediment loading patterns of the Yellow River. Several studies have reported on the erosion and deposition characteristics of the latest lobe of the Yellow River Delta over the past several decades, based on remote sensing methods and water-depth measurements. However, continuous sedimentary records of delta erosion and deposition and their responses to natural and human activities in the watershed are lacking. Here, we obtained three sediments cores, YD01, YD02, and YD03, from the subaqueous delta of the latest lobe of the Yellow River Delta. These cores contain sediments deposited from 1976 to 2018. We analyzed the environmental magnetism and lithological characteristics of these cores, and investigated their responses to natural and human activities in the watershed of the Yellow River, as well as possible applications to sediment dating in the Yellow River Delta. The results show that frequency-dependent susceptibility ( χ fd%) and anhysteretic remanent magnetization susceptibility ( χ ARM) values were high in core sediments deposited from 1976 to 1996, indicating abundant contents of fine single-domain (SD) and superparamagnetic (SP) magnetic particles, and therefore a dominant sediment supply from the Chinese Loess Plateau. Small decreases in χ fd% and χ ARM in sediments deposited after 1986 revealed slight reduction of the sediment load from the Yellow River, which was likely caused by sediment retention related to the construction of the Longyangxia Reservoir. Rapid rises in χ fd% and χ ARM occurred in core YD01 sediments deposited during 2002 and ~2007, likely in response to the implementation of the WSRS, which resulted in an increase in sediment transportation. Increases in hard isothermal remanent magnetization (HIRM) values, an indicator of high-coercivity magnetic minerals such as goethite and hematite, in cores YD02 and YD03 from 2002 to ~2007 may also represent the start of the WSRS. This is because the downstream riverbed of the Xiaolangdi Reservoir underwent intense erosion during the implementation of the WSRS, leading to large-scale transportation of coarse sediments enriched in goethite and hematite, which were deposited on the riverbed before the implementation of the WSRS. The lack of increased contents of fine SD and SP magnetic minerals in cores YD02 and YD03 compared with YD01 in the interval deposited between 2002 and ~2007 was attributed to erosion and redeposition in the areas around cores YD02 and YD03. Large drops in SD and SP contents after ~2007 were detected in all three cores, revealing intense erosion near the river mouth likely caused by river channel shift and reduced capability of the WSRS to remove sediments. Contents of SD and SP particles increased again in sediments deposited after 2014 in cores YD02 and YD03, likely related to erosion of the present (after 1996) Yellow River mouth and transportation of fine particles to the region near cores YD02 and YD03. In summary, the magnetic parameters χ fd% and χ ARM and the lithological characteristics of cores YD01, YD02, and YD03 recorded sediment delivery changes caused by four events in the Yellow River watershed: The main river channel shift in 1976, construction of the Longyangxia Reservoir in 1986, the beginning of the WSRS in 2002, and weakened capability of the WSRS to remove sediments after ~2007. The notable changes of χ fd%, χ ARM, and lithology at the 1976, 1986, 2002, and ~2007 horizons may be used as dating points in future research of sediment cores from the Yellow River Mouth.

Distribution of Phosphorus and Iron Species in the Sediments along the Path of Yellow River and Correlation of Contents of the Two Species

Lv, W.H. and Yang, H.W., 2020. Distribution of phosphorus and iron species in the sediments along the path of yellow river and correlation of contents of the two species. In: Guido Aldana, P.A. and Kantamaneni, K. (eds.), Advances in Water Resources, Coastal Management, and Marine Science Technology. Journal of Coastal Research, Special Issue No. 104, pp. 813–817. Coconut Creek (Florida), ISSN 0749-0208.We measured contents of total phosphorus (TP) and total iron (TFe) in the sediments from 21 samples along the path of Yellow river. TP content of the 21 sediments were from 0.87 to1.75 g·kg-1, and TP contents of sediments from Huayuankou section (H18) and Liulin section (H13) were maximum and minimum, respectively. TFe content were in the range of 15.50∼31.24 g·kg-1, correspondingly, Liulin section (H13) and Sanmenxia section (H17), were the maximum and minimum. It had a positive correlation relationship between TFe and TP by correlation analysis on Maduo section (H1), Xinghai section (H2), Zhongwei section (H5), Baotou section (H10), Xingxian section (H12), Dayudu section (H15), Sanmenxia section (H17), Jinan section (H19) and Yellow River Mouth section (H20), and the equation fits well (R2>0.93). The distribution of TP and TFe of the sediments from different sections in Yellow River related with regional environmental conditions and the geological environment.

Detachment of Low‐Salinity Water From the Yellow River Plume in Summer

AbstractHistorical hydrographic data reveal that low‐salinity water can detach from the Yellow River plume in summer. In this study, the mechanism of this detachment is examined using a three‐dimensional numerical model that reproduced the observed detachment, including the position and size of the detached low‐salinity water patch. Sensitivity experiments showed that tide‐induced residual currents and tidal mixing around the Yellow River mouth played key roles in the detachment during spring tide. During the transition from neap tide to spring tide, the intensification of the northward tide‐induced residual current and the weakening of the southward density‐driven current lead to a net northward residual current (0.03 m/s), transporting high‐salinity water to the southern area of low‐salinity water. Meanwhile, the gradually strengthened tidal mixing also increased surface salinity, which was apparent in the central area of low‐salinity water. With the combination of these two effects, the low‐salinity water was separated into two parts during spring tide; that is, detachment of low‐salinity water occurred. The above scenario works with a condition of no wind. With the prevailing southeasterly winds during summer, the northeastward wind‐induced surface current promoted detachment by moving the detached low‐salinity water northeastward and enlarging its size. In contrast, the northerly wind that prevails in the other seasons drove low‐salinity water southward, which then flowed along the coast and hindered detachment. Consequently, the detachment of low‐salinity water from the Yellow River plume occurs only in summer.

Remotely Sensed Retrieval of Extreme High Surface Suspended Sediment Concentration in the Yellow River Estuary from 1996 to 2017

Zhan, C.; Dong, C.; Wang, T.; Li, B.; Liu, Y., and Yu, X., 2020. Remotely sensed retrieval of extreme high surface suspended sediment concentration in the Yellow River estuary from 1996 to 2017. In: Zheng, C.W.; Wang, Q.; Zhan, C., and Yang, S.B. (eds.), Air-Sea Interaction and Coastal Environments of the Maritime and Polar Silk Roads. Journal of Coastal Research, Special Issue No. 99, pp. 221–226. Coconut Creek (Florida), ISSN 0749-0208.Remotely sensed retrieval provides an alternative for surface suspended sediment concentration (SSC) monitoring with its advantages of wide area survey and real-time monitoring. In situ measurements were precise, however, they were inherently accidental, both in time and space. Extreme high SSC in shoal remains hard to be mapped. Moreover, in situ measurements were of a normal distribution but discontinuous. This paper tried to retrieval SSC in the Yellow River estuary, especially in the Yellow River Mouth characterized by extreme high SSC. The inherent optical property of SSC was precisely obtained based on a control experiment. A calibration model was then developed based on a band ratio (R(820)/R(490)), and was used in SSC mapping in the Yellow River estuary. The suspended sediment generally distributed in a strip pattern parallel to the coast in the northern part of the Yellow River Delta. SSC was high near the current Yellow River estuary. SSC contours in the southwest of Laizhou Bay were elliptical, with the highest SSC in the elliptical center and the northwest-southeast trend in the long axis.

Grain-Size Distribution of Surface Sediments in the Bohai Sea and the Northern Yellow Sea: Sediment Supply and Hydrodynamics

The grain-size distribution of surface sediments in the Bohai Sea (BS) and the northern Yellow Sea (NYS), and its relationship with sediment supply and hydrodynamic environment were investigated based on grain-size compositions of surface sediments and modern sedimentation rates. The results showed that the surface sediments in the BS and the NYS were primarily composed of silty sand and clayey silt with a dominant size of silt. In addition, the Yellow River delivered high amount of water and sediments to the BS, and they are dominated in surface sediments (mainly silt) in the Bohai Bay, the Yellow River mouth, the center of the BS, and the north coast of Shandong Peninsula. The coarse-grained sediments were mainly deposited at the river mouth due to the estuarine filtration and physical sorting. Meanwhile, there was a significant relationship among the modern sedimentation rate, the surface sediment grain size distribution and sediment transport pattern. The areas with coarser surface sediments generally corresponded low sedimentation rates because of strong erosion; whereas the sedimentation rate was relatively high at the place that the surface sediments were fine-grained. Furthermore, the grain-size trend analysis showed that the areas with fine-grained surface sediments such as the mud area in the central BS and the upper Liaodong Bay were the convergent centers of surface sediments, except for the Bohai Bay and the subaqueous Yellow River Delta where offshore sediment transport was evident.

Pathways of suspended sediments transported from the Yellow River mouth to the Bohai Sea and Yellow Sea

The concentration of suspended particulate matter in the Yellow River is very high, and the Yellow River is one of the main sources of sediment in China's coastal waters. The diffusion of substances from the Yellow River into the sea is of great significance to the ecological environments of the Bohai Sea and the Yellow Sea. Thus, the transport pathways and mechanisms of sediment delivered by the Yellow River are hot topics. In this paper, transport pathways, seasonal variations and their relationship between them and wind direction and flow field in the Bohai Sea were investigated based on observational data (suspended sediment concentration, temperature, and salinity) and MODIS imagery and ocean current data from ROMS. This study shows that the sediments from the Yellow River are mainly transported outward along two pathways: along the west side of the central Bohai Shoal to the central part of the Bohai Sea and along the Bohai Strait to the Yellow Sea. Winter is the main season for outward expansion. The interannual variation in the pathway exhibits little correlation with the sediment transport volume of the Yellow River, so the re-suspended sediment from the seabed is the source of the outward diffusion of sediment from the Yellow River into the sea. The interannual variations in the two pathways are closely related to sea surface temperature (SST), flow field, wind speed and wind direction.

River base level change in mouth channel evolution: The case of the Yellow River delta, China

The base level is one of the key factors controlling river evolution. In the Yellow River mouth, a base-level rise takes place not only because of a relative sea-level rise, but also as a consequence of the increasing of river channel length associated with the large progradation rate of the delta. A change in river length results in a change in the gradient (slope) of the mouth channel, which further leads to a riverbed aggradation/degradation or a water level change at the deltaic apex. This process is principally associated with the morphodynamic backwater effect. The consequent water level change can be considered as a base-level change of the Yellow River. In this work, a relation was constructed between the water level at the deltaic apex and the riverine water and sediment inputs, as well as with the gradient of the mouth channel in the progradation period of each deltaic lobe. Also, for disclosing the importance of the base-level change due to variations of mouth channel length, it was estimated and compared with the relative sea-level change in the past decades, and for predicting the water level at the deltaic apex, the relation between mouth channel length and cumulative riverine sediment input was investigated. It was found that in the period 1953–2016, the base-level changes associated with variations of the mouth channel length could be larger than 1 m, or even larger than 2 m in one year, with a conservatively estimated annual mean of 34.8 mm/a, which is much larger than the relative sea-level change of 7.0 mm/a in the Yellow River mouth. The mouth channel length is closely and linearly related to the cumulative sediment discharge of the Yellow River. The relation for calculating the water level at the deltaic apex was found to be capable of giving a reliable result with the riverine water and sediment inputs, the relative sea-level, and the mouth channel length estimated from cumulative riverine sediment discharge. This relation was also used to estimate the equilibrium gradient of the mouth channel for sediment transport. The results show that after the year 2000, the equilibrium gradient has remained smaller than the actual gradient of the mouth channel, and both gradients decreased continuously with the decrease of riverine sediment inputs, but their values were becoming closer to each other. It is highly possible that the water level at the deltaic apex will be raised by the increase in sediment discharge of the river in the future.

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.

Quaternary sedimentary record in the northern Okinawa Trough indicates the tectonic control on depositional environment change

During the Quaternary, global sea level was characterized by large fluctuations in amplitude and increased frequency. However, the eastern marginal seas of China, especially the northern East China Sea and Yellow Sea did not experience large-scale transgression until the middle Pleistocene. The Zhe-Min (Zhejiang-Fujian) Uplift was an important barrier in the East China Sea preventing transgression of sea water into the northern marginal seas of China, but its Quaternary evolution is still poorly constrained. Here we present a thick sand layer record (the top age is ~416 ka) of the Integrated Ocean Drilling Program (IODP) Site U1428 from the northern Okinawa Trough to reconstruct the history of the Zhe-Min Uplift since the middle Pleistocene. Provenance analysis indicates that sediments from both sand and imbedded fine-grained calcareous-rich clay layers at the study site were mainly derived from the Yellow River, which for the first time indicates that the Yellow River sediments could influence the northern Okinawa Trough since at least the middle Pleistocene. Significant change of lithology at IODP Site U1428 at ~416 ka was attributed to the large-scale subsidence of the Zhe-Min Uplift, which is probably due to the rapid uplifting of Tibet during 0.52–0.38 Ma. Before ~416 ka, obstacle of the emersed Zhe-Min Uplift induced extremely severe reworking and promoted sand ridge formation in the shelf edge of southeastern Yellow Sea, and supplied sand sediments to the northern Okinawa Trough during transgression and high sea-level stages. After the subsidence of the Zhe-Min Uplift at ~416 ka, westward of tidal sand ridge and Yellow River mouth with the process of shelf transgressions favored fine-grained sediments input to the northern Okinawa Trough. Even during low sea-level stages, the flat terrain of the East Asian marginal sea shelf and low rainfall amount resulted in low discharge of Yellow River, and supplied fine-grained particles to the northern Okinawa Trough.

Four Decades of Estuarine Wetland Changes in the Yellow River Delta Based on Landsat Observations Between 1973 and 2013

Yellow River Delta wetlands are essential for the migration of endangered birds and breeding. The wetlands, however, have been severely damaged during recent decades, partly due to the lack of wetland ecosystem protection by authorities. To have a better historical understanding of the spatio-temporal dynamics of the wetlands, this study aims to map and characterize patterns of the loss and degradation of wetlands in the Yellow River Delta using a time series of remotely sensed images (at nine points in time) based on object-based image analysis and knowledge transfer learning technology. Spatio-temporal analysis was conducted to document the long-term changes taking place in different wetlands over the four decades. The results showed that the Yellow River Delta wetlands have experienced significant changes between 1973 and 2013. The total area of wetlands has been reduced by 683.12 km2 during the overall period and the trend of loss continues. However, the rates and trends of change for the different types of wetlands were not the same. The natural wetlands showed a statistically significant decrease in area during the overall period (36.04 km2·year−1). Meanwhile, the artificial wetlands had the opposite trend and showed a statistically significant increase in area during the past four decades (18.96 km2·year−1). According to the change characteristics revealed by the time series wetland classification maps, the evolution process of the Yellow River Delta wetlands could be divided into three stages: (1) From 1973–1984, basically stable, but with little increase; (2) from 1984–1995, rapid loss; and (3) from 1995–2013, slow loss. The area of the wetlands reached a low point around 1995, and then with a little improvement, the regional wetlands entered a slow loss stage. It is believed that interference by human activities (e.g., urban construction, cropland creation, and oil exploitation) was the main reason for wetland degradation in the Yellow River Delta over the past four decades. Climate change also has long-term impacts on regional wetlands. In addition, due to the special geographical environment, the hydrological and sediment conditions and the location of the Yellow River mouth also have a significant influence on the evolution process of the wetlands.