Modern Yellow River Delta Research Articles

Mechanisms and Morphological Time Scales of Avulsed Channel Process on the Modern Yellow River Delta

AbstractThe modern Yellow River Delta (YRD) has witnessed frequent channel avulsions followed by the morphological processes of “wandering‐ short‐lived braiding ‐merging” in history. However, process‐based investigation and relevant physics behind these processes remain poorly constrained. The present study complements the understanding for this evolution through numerical experiments. This is achieved by applying a two‐dimensional (2‐D) depth‐averaged fully coupled morphodynamic model that considers the feedbacks of sediment‐laden flow and bed deformation to a schematized fan‐shaped YRD. Under an uneven bed of uniform sediment, the avulsed processes of “wandering‐ short‐lived braiding ‐merging” during new channel routing on the YRD are satisfactorily reproduced by the present modelling in terms of the time evolution of planar channel pattern and channel length. Moreover, the mechanisms of the avulsed evolution have been elucidated through factor analysis on delta slope, incoming flow‐sediment conditions and artificial trenching, etc. It is suggested that morphological stability could be reached when a single meandering channel is finally sustained, of which the time scale is 4–8 years echoing the documented data of abandoned channels on the YRD. In addition, quantitative criteria have been advocated to help distinguishing the sub‐stages of the avulsed evolution together with the characteristic pattern judgement. Based on the above, implications for the YRD management are discussed.

Geochemical characteristics of the modern Yellow River Delta sediments and their response to evolution of the sedimentary environment

IntroductionSedimentary evolution and river channel changes of large river delta (e.g. Huang River, Changjiang River) in response to environmental changes have been one of the key issues in global change research.MethodsThis study reconstructed sedimentary environment changes in the modern Yellow River Delta (YRD), based on grain size and elemental chemical analysis of two short cores (YDC and YDG) from the southern region of the Qing 8 course delta of the modern YRD. ResultsThe results indicated that the cores YDC and YDG sediment were dominated by silt (58.47% and 67.6%, respectively) with varied grain-size variations and poor sediment sorting. The cores YDC and YDG sediments are both predominantly composed of the major element SiO2, and have an average content of 55.53% and 58.45%, respectively. The R-mode factor analysis showed the content of chemical substances of core sediments was controlled by three factors: grain size, sedimentary provenance, and marine sedimentary dynamics. DiscussionBefore the diversion of the Yellow River to the Qing 8 course in 1996, the two cores sediment were mainly sources from the Yellow River, and both cores were in the delta-front sedimentary environment under weak hydrodynamic conditions. After the Yellow River was diverted to the Qing 8 course, the cores YDC and YDG experienced significant erosion under the nearshore strong waves and tides. And then the sedimentary environment of the YRD changed from siltation to erosion. The results of the study would be helps to further our understanding of the changes in sediment grain size and geochemical element characteristics in the Yellow River estuary, and reveal the evolution of its sedimentary environment.

Estimation of Sediment Transport Parameters From Measured Suspended Concentration Time Series Under Waves and Currents With a New Conceptual Model

AbstractIn‐situ observations of hydrodynamics and suspended sediment concentrations (SSCs) were conducted on an abandoned lobe in the northern part of the modern Yellow River Delta, China. The SSC record at the site is found to be the superposition of a general trend (fast increase and slow decrease cycle) caused by storm waves (SubSSC1) and relatively smaller fluctuations caused by tidal currents (SubSSC2). Physically, this indicates that storm waves eroded the bottom sediments while tidal currents then re‐suspended and advected the suspended sediments in the study area. To further obtain the suspended sediment transport parameters, first, SubSSC1 is modeled with significant wave height which incorporates a “memory curve” to consider the remaining impacts of historical waves. It is detected that waves in the past 75 hr still influence the present SSC which is reasonable because 75 hr is roughly the typical duration of a normal storm. Second, SubSSC2 is modeled with tidal excursion and trigonometric functions with measured periodicities. Finally, some sediment transport parameters, for example, the background SSC, the horizontal SSC gradient, the tidal constituents that advect it, and their relative time lags are optimized from the best fits of the measured and modeled SSC time series. The proposed framework for model construction and parameter optimization can be extended to other sea areas for inferring sediment transport parameters from field SSC time series at a specific station.

Investigating soil layers with ground penetrating radar in the modern Yellow River Delta of China

AbstractSoil layers affect the vertical movement of moisture and salt, eventually resulting in land cover and land use pattern changes. This study explored the ability of ground penetrating radar (GPR) to detect soil layers in the modern Yellow River Delta of China and assessed its accuracy. It was found that soil moisture and salt had a strong dampening effect on the electromagnetic wave signal which resulted in blurred GPR images of the soil profile below 1 m. The cultivated soil layers of different crop types, such as rice, wheat, corn and cotton, were accurately identified in GPR images. To estimate an individual soil layer thickness, the propagation velocity of the electromagnetic wave was calculated using soil mass moisture content, and the propagation time was confirmed by comparing the GPR image with the amplitude–time plot of the soil profile. The estimated thickness was 1.02 times the thickness determined in the field and the average estimation error was 0.04 m, which was 24.09% of the soil layer thickness determined in the field. The second derivative value of envelope amplitude energy with time (SDEA) was used to describe the amplitude change in the soil layers. The SDEA has negative logarithmic and power function relationships with soil mass moisture content and electrical conductivity, respectively. The present results provide a reference database for future quantitative soil investigation in the sedimentary plain area using GPR.

Wave-supported fluid mud and sediment vertical mixing under winter storm

Data from 5 monthly field observations of the modern Yellow River delta demonstrate the formation of the fluid mud layer (FML) above the seabed under continuous storms and the sediment resuspension and vertical mixing over the FML. It was observed that the storm wave-related oscillatory flows during winter were mainly in energetic regime (400<ReΔ<1200). The high concentration sediment is trapped in a thin layer stably stratified above the seabed due to the formation of the wave-supported fluid mud (WSFM) layer. Above the WSFM, the total velocity spectral flux E(f) at z=0.7 m is decreased by approximately 14%∼22%, indicating a significantly decreased sediment carrying capacity of the flow. To explore detailed flow and sediment dynamics within the WSFM, a series of experiments in a wide wave flume with WSFM generated were carried out. The velocity and sediment concentration profiles measured over the water depth suggested that the sediment was confined in a thin FML even in high ReΔ regimes (ReΔ>480), and the behavior of FML can transition between a laminar to turbulent with varying wave orbital velocity and Rib. Laminar fluid mud dominates when uw<45 cm/s and ReΔ<518, resulting in exceptionally high viscous dissipation of wave energy. This can explain the observed significant decrease of E(f) during the onset of storm wave recession. Once the fluid mud layer forms, stronger flow with uw>45 cm/s (Rib<0.2) can disturb the interfacial wave of the fluid mud and the flow above it, which cause strong entrainment of the fluid mud layer and sediment mixing into the water column.

The salinization process and its response to the combined processes of climate change–human activity in the Yellow River Delta between 1984 and 2022

Within the context of global change, the evolution of salinization in the Yellow River Delta has undergone dramatic changes. However, it is not clear how it responds to the combined processes of climate change and human activity（reclamation projects, changes in land-use types, and increases in fertilizer use）Based on the optimal soil salinization monitoring index model, this study retrieved the annual time series data set for salinization from 1984 to 2022 and then analyzed the spatial and temporal evolution patterns of salinization in the modern Yellow River Delta. The mechanism of the response of salinization evolution to climate change and human activities was investigated using Geodetector. The main conclusions were as follows: (1) From 1984 to 2022, the salinization intensity in the northeastern coastal zone of the Yellow River Delta showed an increasing trend, while that in the southwestern inland area showed an improving trend. (2) The high-frequency salinization zones were mainly concentrated near the mainstream and tributaries of the Yellow River, while zones with desalinization, re-salinization, and new salinization zones were mainly distributed in the main stream of the Yellow River. (3) There were obvious differences in the dominant factors in the evolution of salinization in different historical periods. In 1984, soil component factors and vegetation coverage were the dominant factors in the evolution of salinization. In 2022, vegetation coverage and land-use types had the strongest explanatory power for the salinization process. (4) The influence of natural and human activity factors on the salinization process was not independent, but a mutually reinforcing process. The interaction between NDVI and other factors has dominated the evolution of salinization in the Yellow River Delta. From 1984 to 2022, human activities were the dominant factors that promoted the improvement or intensification of salinization in the region.

End-member characteristics of sediment grain size in modern Yellow River delta sediments and its environmental significance

IntroductionThe sediments of the Yellow River delta record the environmental changes in the Yellow River basin on a long time scale and are sensitive to the river diversion and sedimentary environment evolution.MethodsIn this study, cores YDC and YDG in the delta near the estuary of the Yellow River since 1976 were taken as the research object, and the parameterized end-member analysis model was used to analyze the grain-size data of the cores.ResultsThe results show that: The main sediments were silty and sand (58% and 77.9%). The grain-size parameters showed opposite changes with wide grain-size ranges and mixed sizes obviously. End member 1 (EM1) and end member 2 (EM2) were composed of clay and fine silt with fine particle sizes of 0.04 mm and 9.8 mm, respectively, and were deposited under weak hydrodynamic conditions during long-distance transport along the Yellow River. End member 3 (EM3) and end member 4 (EM4) were coarse silt with mode particle sizes of 40.14 mm and 66.89 mm, respectively. These were deposited by waves and tidal currents under strong dynamic conditions.DiscussionAccording to the channel changes and the sedimentary facies data of the modern Yellow River delta, before the Yellow River was diverted in 1996, the cores YDC and YDG were both in the estuary-front bar sedimentary environment. In 1996, the Yellow River was diverted to the Qing 8 course. Subsequently, the core YDC changed to the delta-plain sedimentary facies, and the core YDG changed to the delta-front facies. The sediment sources of the two cores changed from the Yellow River sediments to coastal sediment erosion and resuspension. The sedimentary environment changed from siltation to erosion. The results of this study are of great practical significance for estuary management and coastal engineering construction in the modern Yellow River delta and can provide a scientific basis for ecological protection and high-quality development of the Yellow River basin.

Increased discharge of Yellow River sediments into the western Bohai Sea since 0.71 Ma

AbstractThe Yellow River originates on the Tibetan Plateau and transports vast amounts of terrestrial sediment to the ocean. However, previous studies have not reached a consensus as to when and how the Yellow River first began to flow into the sea. Here we present Sr-Nd-Pb isotope data and a high-resolution clay mineral record of a 200-m-long sediment core recovered from the modern Yellow River delta. The changes in Sr-Nd-Pb isotopic compositions and clay minerals at 0.71 Ma suggest that a larger proportion of sediment was derived from the Yellow River after this time. We propose that the Yellow River has influenced the Bohai Sea since 1.9 Ma (or even earlier), which provides important evidence for an older Yellow River than 1.2 Ma. A significant increase in discharge of Yellow River sediments since 0.71 Ma is due to continuing subsidence of the eastern China coast, the large amplitude of Quaternary sea-level changes, and increased supply of eroded loess during the last 1.0 Ma. After this time, the contribution of local rivers surrounding the Bohai Sea became negligible due to dilution by the huge amounts of Yellow River sediments. These results provide improved constraints on the evolution of the Yellow River and subsequent land-sea fluxes.

Geomorphologic evolution of the shallow-buried abandoned Yellow River delta during the last 2000 years

Different from the continuous development of many river deltas since the major Holocene transgression, the modern Yellow River delta (YRD) remained for nearly 1000 years (from 893 AD to 1855 AD) in an abandonment state, until after 1855 AD when it was buried after the Yellow River entered the sea via Lijin. In this study we used optically stimulated luminescence (OSL) dating and grain size and sedimentary facies analysis of four borehole cores, combined with an analysis of landform morphology, to reconstruct the history of the ancient abandoned YRD. The results indicate that after the delta was abandoned due to the reduced sediment supply by the Yellow River in 893 AD, a sandy coast developed under the influence of wave erosion, and offshore shell ridges were formed beyond the coastline. During the interval from the Medieval Warm Period (MWP) to the Little Ice Age (LIA), driven by climate change and storm surges, the shell ridges migrated laterally, widened and rose, while sediment accumulation in the landward-side interfluvial floodplains was relatively weak. This configuration subsequently constituted a coastal highland – plain depression system. After 1077 AD, this system, together with the abandoned delta, was eroded by the Daqing River estuary. After 1855 AD, the abandoned delta landform system was completely buried by Yellow River sediments, and the wave-controlled sandy coast was transformed to a tide-controlled silt-mud coast. We summarize these findings in the form of a geomorphic model of the evolution of the abandoned delta from the MWP to the LIA. Overall, our results highlight the geomorphic effects of the sediment-laden river delta and the response of the abandoned delta geomorphic system on the millennial timescale, and they provide a theoretical foundation for predicting the geomorphic evolution of a major river delta on different timescales, against the background of global change.

Timing of Sedimentary Evolution and Transgressions in the Bohai Sea During the Last ∼200 ka: Constraints from Luminescence Dating of a Core from the Yellow River Delta

The southwestern coast of the Bohai Sea is a favorable area to study land-sea interactions and palaeoenvironmental changes. The Bohai Sea hosts vast volumes of sediment discharged from rivers of mainland China and has undergone large-scale sea-level fluctuations during the Quaternary. Three transgressions have been previously determined for the Bohai Sea since the late Pleistocene. However, the timings of the two earlier transgressions are still unclear. Here we present chronological, micropalaeontological, and sedimentological data for an 80-m-long sediment core recovered from the modern Yellow River delta. The changes in grain size and foraminiferal assemblages suggest the occurrence of three marine sedimentary units, M-3, M-2, and M-1, that represent transgressions of the Bohai Sea. We applied optically stimulated luminescence dating using both quartz and feldspar minerals on 15 samples obtained from core YRD-1401 and eight radiocarbon ages using fragments of microfossils shells and organic carbon. Our quartz optically stimulated luminescence ages for M-2 (ca. 60 ka), are consistent with K-feldspar post-infrared stimulated luminescence ages, suggesting that M-2 on the southwestern coast of the Bohai Sea was deposited during early MIS 3. The sea level of the Bohai Sea during early MIS 3 is estimated to have ranged from 26.8 to 19.9 m below the present sea level. Luminescence ages and foraminiferal assemblages indicate that M-3 was likely formed during MIS 5 and a tidal-river environment prevailed on the southwestern coast of the Bohai Sea during MIS 6 or earlier.

Numerical study on the morphological evolution of the Qingshuigou channel on the Yellow River Delta in response to changing water and sediment regimes

The Qingshuigou channel is the longest channel in the modern Yellow River Delta since its diversion in 1976. To explore the morphological evolution of the Qingshuigou channel on the Yellow River Delta in response to changing water and sediment regimes, we applied the two-dimensional hydro-sediment-morphodynamic coupling model to simulate the characteristics of bed erosion and deposition in Qingshuigou channel and its estuary in different water and sediment regimes. The results demonstrate that regarding the seasonal difference of the year, the sediment deposition in the estuary during the flood season is larger than the non-flood season, and the former accounts for 88% of the annual estuary deposition. On a long-term scale, the erosion of the river channel becomes considerable and the sediment deposits rapidly in the estuary with high water discharge and sediment concentration.

The modern Yellow River Delta in transition: Causes and implications

Sustainable development of megadeltas worldwide has recently been the focus of international socioeconomic and environmental concerns. Long-term geomorphic sustainability of deltas is crucial for sustaining coastal resources and marine ecosystems. The modern Yellow River Delta (YRD), which has been developed since 1855, is increasingly facing erosion threats under natural and human-induced changes. Utilizing long-term hydrological data, remote-sensing satellite images and bathymetric survey data, the transition processes of the modern YRD (including both the subaerial and subaqueous delta) during 1855–2015 from the perspective of morphodynamics are examined. The results show that over the past 160 years, the evolution of the Yellow River subaerial delta is under rapid accretion before 2000, and transitioned to slight erosion state after 2000, which is believed to be associated with the reduced sediment supply. Correspondingly, the Yellow River subaqueous delta is also believed to transition from the accretion into net erosion since 2000, with a net volume change rate of −1.5 × 108 m3/yr. As the primary source for deltaic deposits, at least 2.6 × 108 t/yr of sediment supply is required to sustain the erosion-accretion balance of both the subaerial and subaqueous delta. Compared with the previous research, we present that the 160-year morphological evolution of the modern deltaic system is strongly influenced by the reduction of sediment input. Within this time frame the changes in the partition of sediment load among frequent migrations of the deltaic channel could have a direct impact on variations of the long-term erosion-deposition patterns of the modern YRD. Extreme events of storm surges and frequent strong winds caused significant short-term fluctuations in the erosion/deposition of the subaqueous delta that would affect long-term changes. The insights gained from this study may help to set scientific guidelines for the sustainable development of other river deltas worldwide that are subject to climate change and human interventions.

Distribution and Assessment of Cr, Pb, Ni and Cd in Topsoil of the Modern Yellow River Delta, China

Modern Yellow River Delta (MYRD) is a typical petrochemical and agricultural industrial area of China. To effectively assess the current status of the four heavy metals (Cr, Pb, Ni and Cd) of topsoil residues, soil samples (0 ~ 20 cm) (n = 104) in the MYRD were collected and analyzed. The results showed that the contents of the four heavy metals were all below or equal to the level 1 background content as specified in the National Environmental Quality Standard for Soils, while the content of Cd and Pb were 1.68 and 1.41 times higher than the background value of soil in Shandong province, respectively. The difference of four heavy metal contents between different kinds of land types existed. Geoaccumulation index and potential ecological risk index methods were used to evaluate the risk of the four heavy metal pollution in the MYRD. The results showed that there was a light or moderate pollution of heavy metals Cd and Pb, which were a strong ecological hazard. Therefore, it is necessary to enhance the monitoring and controlling of heavy metal Cd and Pb pollution in the MYRD.

Monitoring and analysis of land subsidence in modern Yellow River Delta using SBAS-InSAR Technology

Modern Yellow River Delta has become one of the areas with serious land subsidence disaster in the plain area of Shandong Province. In this paper, Small Baseline Subsets - Interferometry Synthetic Aperture Radar (SBAS-InSAR) technology was used to process the Sentinel-1A data from August 2018 to October 2019 in the modern Yellow River Delta, in order to obtain the range and rate of land subsidence in the study area. At the same time, use the Leveling results of the same period to verify the accuracy. By selecting four larger land subsidence rate as feature points to analyze the characteristics of surface time series deformation, the influencing factors of land subsidence in this area are found out. The results show that during the past 2018-2019 years, the land subsidence in the the Yellow River Delta area was mainly distributed in Xianhe Town, southern the Huanghekou Town, Hubin Town, Guangrao County and its surrounding areas, DaWang Town, Yingli Town, Yangkou Town and the western part of Binhai Township, the most serious subsidence area is located in Xianhe Town, with an annual settlement rate of -204.7 mm/a. The land subsidence in the Yellow River Delta is mainly affected by groundwater overdraft, and the distribution characteristics of land subsidence funnel and deep groundwater depression funnel are basically consistent. In addition, natural factors such as consolidation of Quaternary loose sediments and regional tectonic movement also exacerbate the occurrence of land subsidence.

Land subsidence of the Yellow River Delta in China driven by river sediment compaction

Many of the world's largest deltas are sinking due to multiple natural and anthropogenic causes. This is particularly evident for the modern Yellow River Delta (YRD) in China, which is one of the most dynamic coastal systems on Earth. The YRD has experienced complicated patterns of accretion and erosion as well as significant compaction settlements. However, spatiotemporal variability and the long-term settlement rates law in this complex delta system remain poorly understood. Evidently, the surface settlement is supposedly controlled by a long-term natural compaction process of sediments. We first combined the Small Baseline Subset (SBAS) Interferometric Synthetic Aperture Radar (InSAR) method with a geotechnical model and geological, geomorphological, hydrogeological, and geotechnical data to assess the delta-wide long-term spatiotemporal settlement triggered by the consolidation and compaction of river sediments. The combination of satellite and field observations allows us to gain insights into the primary processes controlling surface movement. A total of seventy-five SAR images acquired by ERS and Envisat from 1992 to 2010 are used to generate three independent interferometric subsets calibrated with leveling to unveil spatiotemporal settlement variability. The densely distributed spatiotemporal measurements enable us to acquire the characteristics of the spatiotemporal variations of land movements. Moreover, the annual average settlement rates are observed within a range of 0 to >30 mm. Results suggest that the relative inland stability of the delta contrasts with the decreasing coastal margin trend at an average annual rate of 15 mm. Moreover, the variability is significantly correlated with the delta evolution and variations in subsoil architecture. A comparative analysis has also been conducted between time series InSAR measurements and the theoretical estimates of settlement derived from the geotechnical model. The strong agreement between the InSAR measurements and the geotechnical modeled results indicates that long-term settlement (in a decade-to-century scale) is primarily driven by the compaction of river sediments. The more the delta sub-lobe was newly formed, the more significant the settlement. Decreasing trends in annual settlement rates from approximately 70 mm to 0 mm in the long-term deposit compaction process are also identified. These findings are useful to understand the YRD morphological evolution and may provide insights into the changes in other deltas worldwide.

Historical change of carbon burial in Late Quaternary sediments of the ancient Yellow River delta on the west coast of Bohai Bay, China

The ancient Yellow River Delta (YRD) on the west coast of the Bohai Bay is possibly a huge carbon sink due to the high runoff and sediment load of the Yellow River, which transfers huge amounts of particulate carbon from terrestrial sources to the Bohai Sea. In this study, a 30.76 m long core (BXZK11), drilled in 2016, has been analyzed for AMS 14C dating, grain size, foraminifera, organic carbon (OC), total nitrogen (TN), and stable carbon isotope ratios (δ13C) to provide insights into the historical changes of carbon burial in Late Quaternary sediments of the ancient YRD. The results show that the sedimentary environments are divided into six depositional units in core BXZK11. The biggest contributor to organic carbon apparent mass accumulation rate (OCAMAR) is the negative covariance between apparent sedimentation rate (ASR) and OC. The average of OCAMAR is 20.76 g/(m2 yr) during the Holocene. The rates are highest in delta front deposits and lowest in shallow sea environments. Compared with the modern YRD, BXZK11 exhibits rather low ASR and OCAMAR, indicative of the enormous variations of Yellow River sediment load into the sea and the significant difference of carbon sequestration capacity of YRD at different periods. C3 plants of the delta wetland gradually develop without C4 plant input as the delta transgresses after sea level stabilization. The sediments have been characterized by decreasing terrestrial organic matter (TOM) since 6500 cal. a BP, reflecting the decline of Yellow River freshwater discharge. Both the 8.2 ka event and the weak Asian monsoon summer event at 6265 cal. a BP correspond well with the low TOM in BXZK11. The implication is that climate may affect the dynamics of carbon burial by regulating terrestrial inputs.

Mineralogy of the core YRD-1101 of the Yellow River Delta: Implications for sediment origin and environmental evolution during the last ~1.9Myr

In this study, we report the high-resolution heavy mineral records from a 200.30 m long borehole (YRD-1101) on the northern coast of modern Yellow River delta (YRD), covering the last ~1.90Myr. The results show that the heavy mineral assemblages are dominated by epidote, followed by hornblende, garnet and hematite-limonite. In the Yellow River (YR) sediments, the content of hornblende is higher than the epidote, and the epidote to hornblende ratios (E/H) are lower than the core YRD-1101. The E/H show two distinct lower values at depositional unit (DU) 4–2 (117.9–125.6 m) and DU 4–1 to DU 2 (13.5–99.3 m), indicating the obvious influence of YR sediments. The heavy mineral composition of DU 5 is distinct from YR sediments and interpreted as the result from heterogeneous provenance of the adjacent ancient rivers, while DU 4 to DU 1 resemble the upper-middle reaches of the YR sediments. The different sediment types (mud, sandy silt and silt) of core YRD-1101 do not contain markedly different transparent-heavy-mineral assemblages in terms of concentration and mineral ratios. No matter how sedimentary environment changes, the ratios of epidote and hornblende show very stable values in DU 4–1 and DU 3 due to the influence of YR sediments. The transparent-heavy-minerals such as hornblende, epidote and other stable minerals, which were relatively stable, are controlled primarily by provenance, while the sedimentary environment mostly influences the flaky minerals and the authigenic minerals. This study provides evidence regarding the history of the lower reaches of the YR and YRD since the early Pleistocene, highlighting river's important role for the evolution of the western coast of the Bohai Sea (BS).

Monitoring the Invasion of Smooth Cordgrass Spartina alterniflora within the Modern Yellow River Delta Using Remote Sensing

Ren, G.-B.; Wang, J.-J.; Wang, A.-D.; Wang, J.-B.; Zhu, Y.-L.; Wu, P.-Q.; Ma, Y., and Zhang, J.B., 2019. Monitoring the invasion of smooth cordgrass Spartina alterniflora within the modern Yellow River Delta using remote sensing. In: Jung, H.-S.; Lee, S., and Ryu, J.-H. (eds.), Advances in Remote Sensing and Geoscience Information Systems of the Coastal Environments. Journal of Coastal Research, Special Issue No. 90, pp. 135-145. Coconut Creek (Florida), ISSN 0749-0208.The Smooth Cordgrass, Spartina alterniflora, was introduced into the modern Yellow River Delta in 1989 to protect banks and beaches within the intertidal zone. By 2018, its distribution area had expanded to 4005.89 ha, which was 2557 times its initial colonization area. The distribution of S. alterniflora in the modern Yellow River Delta at given times and its ecological and biological effects have been studied previously; however, its invasion rate and characteristics, which affect its comprehensive management, are not known. Using multi-resolution and multi-platform remote sensing time series data from 1989 to 2018, combined with years of field data, the invasion of S. alterniflora within the modern Yellow River Delta was studied. These data show that S. alterniflora began to expand rapidly in 2011, after a 22-y incubation period within the modern Yellow River Delta. Its expansion mainly occurred via seed reproduction. In addition, S. alterniflora preferentially invaded intertidal deltaic areas, using local seagrass beds as colonization sites. There was a significant correlation between the increase in area of S. alterniflora and the decrease in pollutant concentration of the Yellow River. Clearly, the improvement in water quality of the Yellow River accelerated the invasion of S. alterniflora within the delta.

Estimation of sediment compaction and its relationship with river channel distributions in the Yellow River delta, China

The geomechanical properties of the stratigraphic sequences strongly influence the land surface subsidence, as the latter can be caused by the sediment compaction. Depositional units of transitional environments such as coastal plain and deltas are characterized by a high lithological variability due to the history and complexity of the sedimentary processes. Therefore, detailed modeling of the stratigraphic architecture is necessary to better understand the land surface subsidence process and accurately estimate its rates. The frequent avulsion and rearrangement of the channel network in the modern Yellow River delta since 1855 has led to the rapid accumulation and deposition of large amounts of sediment in the delta plain. The compaction of the substratum sediment due to the new sediment load and the consolidation of younger deposits caused land surface subsidence. We used 108 sediment core data covering the delta and obtained detailed stratigraphic structural information. A detailed distribution of clay and soft clayey soils, which are the primary contributors to land subsidence, was identified. Furthermore, the compaction rates and the consolidation at time of the subaerial area and neritic area for the entire modern Yellow River delta were estimated. We also analyzed the characteristics of present land subsidence by combining a ground movement dataset obtained by high-resolution topographic surveys with Synthetic Aperture Radar (SAR) Interferometry (InSAR) of satellite images. The results show that during the early stages of the development of the active deltaic lobe, the compaction of neritic sediments was the primary contributor to initial subsidence. Furthermore, combined with the relevant sedimentary age and environment determined by previous studies, we found that the spatial variation in compaction-induced subsidence in the subaerial deltaic area over time is closely related to the historical distributions of the river channels in the modern Yellow River delta. Our findings, providing a better characterization of the spatial and time heterogeneity of the land surface subsidence of both subaerial and submarine areas, significantly improved the previous knowledge on land subsidence of the Yellow River delta. Our results also demonstrate that the subaerial delta becomes increasingly stable over time with the gradual decrease in the average subsidence rate of each deltaic lobe.

Inversion and Prediction of Consolidation Settlement Characteristics of the Fluvial Sediments Based on Void Ratio Variation in the Northern Modern Yellow River Subaqueous Delta, China

The modern Yellow River delta is formed near the estuary of the Yellow River with the characteristics of short formation time, efficient sedimentation rate and loose structure which make sediments prone to be compacted and consolidate under the geostatic stress and overburden stress. It is one of the key areas with land subsidence disasters in China, bringing a series of safety hazards to production and living. Based on the data of massive surface cores and ten drill holes ranging from 12 to 40 m obtained from the northern modern Yellow River subaqueous delta, the inversion method suitable for the calculation of consolidation settlement characteristics of the modern Yellow River subaqueous delta is discussed, and the consolidation settlement characteristics of the delta sediments are inversed and predicted in this paper. The actual void ratio of the delta sediments at the depth from 3 to 15 m shows a significant power function relationship with the depth, while the void ratio of the sediments below 15 m changes little with depth. The pre-consolidation settlement (from deposition to sampling) of the delta sediments is between 0.91 and 1.96 m, while the consolidation settlement of unit depth is between 9.6 and 14.0 cm m−1. The post-consolidation settlement (from sampling to stable) of the subaqueous delta sediments is between 0.65 and 1.56 m in the later stage, and the consolidation settlement of unit depth is between 7.6 and 13.1 cm m−1 under the overburden stress. The delta sediments with a buried depth of 3 to 7 m contribute the most to the possible consolidation settlement in the later stage.