Numerical study on local scour characteristics around submarine pipelines in the Yellow River Delta silty sandy soil under waves and currents

Due to their high reliability and cost-efficiency,submarine pipelines are widely used in offshore oil and gas resource engineering.Due to the interaction of waves,currents,seabed,and pipeline structures,the soil around submarine pipelines is prone to local scour,severely affecting their operational safety.With the Yellow River Delta as the research area and based on the renormalized group(RNG)k-εturbulence model and Stokes fifth-order wave theory,this study solves the Navier-Stokes(N-S)equation using the finite difference method.The volume of fluid(VOF)method is used to describe the fluid-free surface,and a threedimensional numerical model of currents and waves-submarine pipeline-silty sandy seabed is established.The rationality of the numerical model is verified using a self-built waveflow flume.On this basis,in this study,the local scour development and characteristics of submarine pipelines in the Yellow River Delta silty sandy seabed in the prototype environment are explored and the influence of the presence of pipelines on hydrodynamic features such as surrounding flow field,shear stress,and turbulence intensity is analyzed.The results indicate that(1)local scour around submarine pipelines can be divided into three stages:rapid scour,slow scour,and stable scour.The maximum scour depth occurs directly below the pipeline,and the shape of the scour pits is asymmetric.(2)As the water depth decreases and the pipeline suspension height increases,the scour becomes more intense.(3)When currents go through a pipeline,a clear stagnation point is formed in front of the pipeline,and the flow velocity is positively correlated with the depth of scour.This study can provide a valuable reference for the protection of submarine pipelines in this area.

Spatiotemporal distribution of fish eggs and larvae in the Huanghe(Yellow) River estuary, China in 2005–2016

Decreasing fish resources in estuaries is a subject of anthropogenic activities. Studies of the spatiotemporal distribution of fish eggs and larvae can help identify the status and processes underlying recruitment in a fishery. As the fifth largest river estuary in the world, the Huanghe (Yellow) River estuary (HRE) is a typical estuary that has been seriously aff ected by human activities. Annual surveys on ichthyoplankton and environmental factors were conducted in the months of May of 2005 and 2009-2016 in the HRE to investigate the spatiotemporal distribution of fish eggs and larvae and the associated infl uencing factors. A total of 23 and 20 species of eggs and larvae, respectively, were collected. The dominant orders were Perciformes (51.2%) and Clupeiformes (25.6%). The average number of fish species eggs and larvae were 6.0 and 4.1 in average abundance of 0.91 and 0.13 ind./m^3 , respectively. The dominant species were mainly low-commercial-value small-sized fishes, such as Clupanodon punctatus , Harengula zunasi, and Acanthogobius, whereas certain traditional commercial fishes, such as Trichiurus lepturus , and Clupea pallasii, were not seen. Analysis of the fish egg and larval community revealed four temporal assemblages and two spatial assemblages. Salinity was the main factor on the spatial distribution of ichthyoplankton communities, the species number and Shannon-Weiner diversity index (H′) of the fish egg and larval community near the river mouth with lower salinity were signifi cantly lower than the community far away from the river mouth with higher salinity. In addition, increases of water temperature promoted the number and abundance of fish species eggs, and the areas of abundant prey tended to have a more diversified and abundant of ichthyoplankton species. In overall, overfishing, dam construction, and other human activities were the main drivers that led to the substantial decline in fishery resources in the HRE.

Examining the evolution of tidal creeks in the Huanghe River delta using multi-temporal Landsat images

Coastal tidal creeks are important channels for exchanges of material and energy between sea and land,and play an important role in the ecological protection of tidal flats.Although tidal creeks have evolved differently in various regions,the evolutionary process of tidal creeks in the Huanghe(Yellow)River delta of China,one of the most active deltas worldwide,is not entirely clear.Therefore,the evolution of tidal creeks in the delta from 1981 to 2021 was investigated by quantitatively analysing the tidal creeks and developing a standard for dividing their evolution periods.Visual interpretation and supervised classification methods were applied to the Landsat images to extract the tidal creek network,and 17 groups of tidal creek systems were selected.Results indicate that Creek S 1 was the most developed creek for having 113 tidal creeks totaling 65.8 km in length,while Creek E 3 had the fastest growth rate for having average annual increase of 1.9 km.Meanwhile,the level of tidal creeks increased,the average and median lengths of tidal creeks increased,and the number of tidal creeks decreased since 1981.The evolution of the tidal creek system could be divided into four stages,namely,rising,developing,stabilizing,and degrading.Analyses of a representative tidal creek show that there was no degenerated tidal creek during the rising period,with an increase in the number of 50 and a length increase of 57.9 km between 1981 and 1989.The proportion of new tidal creeks in the developing period was more than 50%and the new tidal creeks in the stabilizing period were equal to the degraded tidal creeks.Extinct tidal creeks were greater than 50%during the degrading period.There was no fixed order of tidal creek evolution in each period,and there may be a skip in evolution.Our findings provided a reference for studying the evolution of tidal creeks.

Assessing the benthic habitat quality in the Huanghe(Yellow River) Estuary and its adjacent areas using AMBI and M-AMBI

The protection of the biological diversity and the maintenance of the regional ecological integrity for the Huanghe （Yellow River） Estuary and its adjacent areas are practically significant and valuable. However, frequent human activities and natural climate changes have caused vigorous disturbances on the ecosystem in these sea areas. An objective assessment on the benthic habitat quality （BHQ） of the Huanghe Estuary and its adjacent areas is conducted, using AZTI＇s Marine Biotic Index （AMBI） and multivariate AMBI （M-AMBI） based on the data of macrobenthos in May and August 2011. The results show that both the indices do not correlate significantly, and their assessment results are greatly different. All of the samples assessed using the AMBI were ＂high＂ or ＂good＂, because the ecological group I （EGI） and the ecological group II （EGII） were dominant macrobenthic ecological groups in the research area. Owing to a low species＇ richness and a high individual abundance in some samples, the BHQ levels using the M-AMBI were worse than those of the AMBI. Significant correlations are observed between the M-AMBI, water depth, bottom water salinity and dissolved inorganic nitrogen, thus the M-AMBI could sensitively respond to environmental changes and distinguish influences from uninfluenced stations, but the AMBI could not. The consistent results between the AMBI and the M-AMBI mainly appeared in the uninfluenced （undisturbed or slightly disturbed） sta- tions. Therefore, the M-AMBI is more effective than the AMBI in assessing the benthic habitat quality in the Huanghe Estuary and its adjacent areas. Using the M-AMBI to assess the BHQ of the Huanghe Estuary and its adjacent areas, the results show that 3% of the stations are undisturbed and the BHQs are ＂high＂, and 61% of the stations are slightly disturbed and those of the BHQ are ＂good＂, and the rest are meanly disturbed and those of the BHQ are ＂moderate＂.

Nitrogen Biological Cycle Characteristics of Seepweed(Suaeda salsa) Wetland in Intertidal Zone of Huanghe(Yellow) River Estuary

From April 2008 to November 2009, the nitrogen （N） cycle of plant-soil system in seepweed （Suaeda salsa） wetland in the intertidal zone of the Huanghe （Yellow） River estuary was studied. Results showed that soil N had sig- nificant seasonal fluctuations and vertical distribution, and the net N mineralization rates in topsoil were significantly different in growing season （p 〈 0.01）. The N/P ratio （9.87 ±1.23） of S. salsa was less than 14, indicating that plant growth was limited by N. The N accumulated in S. salsa litter at all times during decomposition, which was ascribed to the N immobilization by microbes from the environment. Soil organic N was the main N stock of plant-soil system, accounting for 97.35% of the total N stock. The N absorption and utilization coefficients of S. salsa were very low （0.0145 and 0.3844, respectively）, while the N cycle coefficient was high （0.7108）. The results of the N turnovers among compartments of S. salsa wetland showed that the N uptake amount of aboveground part and root were 7.764 g/m2and 4.332 g/m2, respectively. The N translocation amounts from aboveground part to root and from root to soil were 3.881 g/m2 and 0.626 g/m2, respectively. The N translocation amount from aboveground living body to litter was 3.883 g/m2, the annual N return amount from litter to soil was more than 0.125（-） g/m2 （minus represented immobili- zation）, and the net N mineralization amount in topsoil （0-15 cm） in growing season was 1.190 g/m2. The assessment of N biological cycle status orS. salsa wetland indicated that N was a very important limiting factor and the ecosystem was situated in unstable and vulnerable status. The S. salsa was seemingly well adapted to the low-nutrient status and vulnerable habitat, and the N quantitative relationships determined in the compartment model might provide scientific base for us to reveal the special adaptive strategy orS. salsa to the vulnerable habitat in the following studies.

Modeling of suspended sediment transport with wave-induced longshore current in Huanghe (Yellow) River Delta

A three-dimensional suspended sediment model （SED） developed by the present authors is coupled with the combinatorial model of COHERENS （Luyten et al., 1999） （the three-dimensional coupled hydrodynamical-ecological model for Regional and Shelf Seas） and SWAN （Holthuijsen et al., 2004） （the third generation wave model）. SWAN is regarded as a subroutine of COHERENS and gets time- and space-varying current velocity and surface elevation from COHERENS. COHERENS gets time- and space- varying wave relevant parameters provided by SWAN. Effects of wave on current are applied in bottom shear stress, wave-induced depth-dependent radiation stress and surface drag coefficient calculation. At the same time, the damping function of suspended sediment on turbulence is introduced into COHERENS. So the sediment model SED has feedback on circulation model COHERENS. The SED obtains current associated parameters from COHERENS. Then a coupled hydrodynamic-sediment model COHERENS-SED being able to account for interaction between wave and current is obtained. COHERENS-SED is adopted to simulate three-dimensional suspended sediment transport in the Huanghe River delta. In terms of simulation results, there is obvious difference between top and bottom layer of wave-induced longshore current. The values of time series of sediment concentration gotten by COHERENS-SED have, generally, an accepted agreement extent with measurement. Significant wave heights and wave periods obtained by COHERENS-SED show that wave simulation case with currentts effect can give better agreement extent with measurement than case without current＇s effect. In the meantime, suspended sediment concentration distributing rule obtained by COHERENS-SED is similar to former researches and measurement.

The distribution and variation of elements in sediments off the Huanghe (Yellow) River mouth

Surface sediment samples collected off the Huanghe （Yellow） River mouth during the period 2007-2009 were analyzed for major and trace element concentrations. Concentrations of 16 elements were measured using X-ray fluorescence spectrometry. Results demonstrate that sediment grain size is the dominant factor controlling the spatial variations of elemental concentrations. Correlation and cluster analyses allowed classification of the study area into four geochemical regions： Regions Ⅰ and Ⅲare characterized by high concentrations ofAl2O3, Fe2O3, MgO, Na2O, K2O, Cr, Cu, Mn, Ni, Pb, V, and Zn, and contain fine-grained sediments with mean grain size （Mz）〈22 μm; and; Regions Ⅱ and Ⅳcontain mostly coarse-grained sediments, and are characterized by high concentrations of SiO2, Na2O, and Zr. The sediment entering the sea from the Huanghe River and its tributaries is enriched in Ca. Thus, the Ca/Al ratio was used as an indicator of the proportion of sediments in the study area that originated from the Huanghe River. Ca/Al ratios decrease from Regions Ⅰ and Ⅱ（located in the nearshore zone of the Huanghe River delta） to Regions Ⅲand Ⅳ（distributed in the offshore zone of the northern Huanghe River delta, southern and southeastern Laizhou Bay area）.

Comparison of detrital mineral compositions between stream sediments of the Yangtze River (Changjiang) and the Yellow River (Huanghe) and their provenance implication

A comparative comparative study on the detrital mineral composition of stream sediments of the Yangtze River (Changjiang) and Yellow River (Huanghe) shows that, light minerals of the Yangtze River basin were mainly quartz, feldspar, and detritus, the compositional characteristics of light minerals differed among tributaries, the main stream had a generally higher maturity index than tributaries;heavy mineral content tended to decrease progressively from the upper stream to lower stream of the Yangtze River, the primary assemblage was magnetite-hornblende-augite-garnet-epidote, and diagnostic minerals of different river basins were capable of indicating the nature and distribution of the source rock. Detrital mineral assemblages in sediments of tributaries and the main stream of the Yellow River were basically similar, Primary heavy mineral assemblage was opaque mineral-garnet-epidote-carbonate mineral and alteration mineral. Variations in the contents of garnet, opaque mineral, and hornblende mainly reflected the degree of sedimentary differentiation in suspended sediment and the hydrodynamic intensity of a drainage system. The heavy mineral differentiation index F revealed sedimentary differentiation of diagnostic detrital mineral composition due to changes in regional hydrodynamic intensity and can serve as an indicator for studying the dynamic sedimentary environment of a single-provenance river and the degree of sedimentary differentiation of its detrital minerals. Changes in detrital mineral content of the Yellow River was not completely controlled by provenance but reflected gravity sorting of the detrital mineral due to variations in the ephemeral river hydrodynamic intensity and sedimentary environment, however the index changing of Yangtze River were mainly influenced by the complex sediment sources. Therefore caution must be exercised in using the detrital mineral composition of marginal sea to determine the contribution of the Yangtze River and Yellow River.

SEDIMENT DISCHARGE OF THE HUANGHE RIVER AND ITS EFFECT ON SEDIMENTATION OF THE BOHAI SEA AND THE YELLOW SEA

The Huanghe (Yellow) River, with annual sediment discharge about 11 ×108tons, contributes about 17% of the fluvial sediment discharge of world’s 21 major rivers to the ocean because its middle reaches flow across the great Loess Plateau of China. Sediment discharge of the Huanghe River has a widespread and profound effect on sedimentation of the sea. The remarkable shift of its outlet in 1128-1855 A.D. to the South Yellow Sea formed a large subaqueous delta and provided the substrate for an extensive submarine ridge field.The shift of its outlet in the modern delta every 10 years is the main reason why with an extremely heavy sediment input and a micro- tidal environment, the Huanghe River has not succeeded in building a birdfoot delta like the Mississippi. The Huanghe River has consistently brought heavy sediment input to sea at least since 0.7 myr.B.P. Paleochannels, paleosols, cheniers and fossils on the sea bottom indicate that the Yellow Sea was exposed during the late Quaternary glacial low-sea

Water discharge variability of Changjiang(Yangtze) and Huanghe(Yellow) Rivers and its response to climatic changes

Influences of large-scale climatic phenomena, such as the E1Nifio/La Nifia-Southem Oscillation （ENSO） and the Pacific Decadal Oscillation （PDO）, on the temporal variations of the annual water discharge at the Lijin station in the Huanghe （Yellow） River and at the Datong station in the Changjiang （Yangtze） River were examined. Using the empirical mode decomposition-maximum entropy spectral analysis （EMD- MESA） method, the 2- to 3-year, 8- to 14-year, and 23-year cyclical variations of the annual water discharge at the two stations were discovered. Based on the analysis results, the hydrological time series on the inter- annual to interdecadal scales were constructed. The results indicate that from 1950 to 2011, a significant downward trend occurred in the natural annual water discharge in Huanghe River. However, the changes in water discharge in Changjiang River basin exhibited a slightly upward trend. It indicated that the changes in the river discharge in the Huanghe basin were driven primarily by precipitation. Other factors, such as the precipitation over the Changjiang River tributaries, ice melt and evaporation contributed much more to the increase in the Changjiang River basin. Especially, the impacts of the inter-annual and inter-decadal climate oscillations such as ENSO and PDO could change the long-term patterns of precipitation over the basins of the two major rivers. Generally, low amounts of basin-wide precipitation on interannual to interdecadal scales over the two rivers corresponded to most of the warm ENSO events and the warm phases of the PDO, and vice versa. The positive phases of the PDO and ENSO could lead to reduced precipitation and consequently affect the long-term scale water discharges at the two rivers.

The influence of water-sediment regulation on macrobenthic community structures in the Huanghe River(Yellow River)Estuary during 2012–2016

To determine if water-sediment regulation has affected macrobenthic community structure in the Huanghe River Estuary,China,macrobenthic samples were collected following regulation events from 2012 to 2016.We identify seven phyla and 138 macrobenthic species from within samples throughout the survey area,over time.Species richness and abundance in 2012 were significantly higher than in 2016.Biomass did not differ significantly during 2012–2016.Dominant species were mostly small polychaetes,with mollusks,arthropods,and echinoderms all being relatively rare.In 2016,dominant species were small polychaetes.MDS reveals macrobenthic communities at all surveyed distances from the estuary to have become the same community structure over time.Shannon-Wiener diversity and Margalef richness indexes trended down over time.CCA reveals the most dominant sediment-dwelling species to prefer lower dissolved oxygen,sulfides,and pH,and sediments with high D50 and low clay content.We speculate that water-sediment regulation has affected seabed communities,particularly Region A in our survey area.

Landsat Image-Based Spatiotemporal Variation Analysis of Erosion and Deposition off the Qingshuigou of the Yellow River Delta from 1984 to 2021

Owing to climate change and human activity,the Qingshuigou of the Yellow River Delta(YRD)has undergone dynamic changes in erosion and deposition.Therefore,studying these changes is important to ensure ecological protection and sustainable development.In this study,the trend of erosion-deposition evolution in the Qingshuigou was investigated based on 38 coastline phases extracted from Landsat series images of the YRD at one-year intervals from 1984 to 2021.The periodicity of the scouring and deposition evolution was also analyzed using wavelet analysis.Results showed that the total area of the Qingshuigou was affected by deposition and erosion and that the fluctuation first increased and then decreased.The total area reached a maximum in 1993.The depositional area first increased and then decreased,whereas the overall erosion area decreased.Deposition and erosion areas showed periodic changes to some extent;however,the periodic signal intensity decreased.Furthermore,factors including channel morphological evolution and variations in water and sediment discharge affect the spatiotemporal dynamics of erosion and deposition processes.The application of nonconsistency tests finally revealed that deposition area and flushing magnitude exhibited non-stationarities,which are potentially attributed to impacts from climatic change drivers.

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.

Occurrence,Spatial Distribution,Sources and Risk Assessment of Per-and Polyfluoroalkyl Substances in Surface Sediments of the Yellow River Delta Wetland

Per-and polyfluoroalkyl substances(PFASs)are emerging persistent organic pollutants(POPs).In this study,47 surface sediment samples were collected from the Yellow River Delta wetland(YRDW)to investigate the occurrence,spatial distribution,potential sources,and ecological risks of PFASs.Twenty-three out of 26 targeted PFASs were detected in surface sediment samples from the YRDW,with totalΣ23PFASs concentrations ranging from 0.23 to 16.30 ng g^(-1) dw and a median value of 2.27 ng g^(-1) dw.Perfluorooctanoic acid(PFOA),perfluorobutanoic acid(PFBA)and perfluorooctanesulfonic acid(PFOS)were the main contaminants.The detection frequency and concentration of perfluoroalkyl carboxylic acids(PFCAs)were higher than those of perfluoroal-kanesulfonic acids(PFSAs),while those of long-chain PFASs were higher than those of short-chain PFASs.The emerging PFASs substitutes were dominated by 6:2 chlorinated polyfluoroalkyl ether sulfonic acid(6:2 Cl-PFESA).The distribution of PFASs is significantly influenced by the total organic carbon content in the sediments.The concentration of PFASs seems to be related to human activities,with high concentration levels of PFASs near locations such as beaches and villages.By using a positive matrix factorization model,the potential sources of PFASs in the region were identified as metal plating mist inhibitor and fluoropolymer manufacturing sources,metal plating industry and firefighting foam and textile treatment sources,and food packaging material sources.The risk assessment indicated that PFASs in YRDW sediments do not pose a significant ecological risk to benthic organisms in the region overall,but PFOA and PFOS exert a low to moderate risk at individual stations.

Runoff change in the Yellow River Basin of China from 1960 to 2020 and its driving factors

Analysing runoff changes and how these are affected by climate change and human activities is deemed crucial to elucidate the ecological and hydrological response mechanisms of rivers.The Indicators of Hydrologic Alteration and the Range of Variability Approach(IHA-RVA)method,as well as the ecological indicator method,were employed to quantitatively assess the degree of hydrologic change and ecological response processes in the Yellow River Basin from 1960 to 2020.Using Budyko's water heat coupling balance theory,the relative contributions of various driving factors(such as precipitation,potential evapotranspiration,and underlying surface)to runoff changes in the Yellow River Basin were quantitatively evaluated.The results show that the annual average runoff and precipitation in the Yellow River Basin had a downwards trend,whereas the potential evapotranspiration exhibited an upwards trend from 1960 to 2020.In approximately 1985,it was reported that the hydrological regime of the main stream underwent an abrupt change.The degree of hydrological change was observed to gradually increase from upstream to downstream,with a range of 34.00%-54.00%,all of which are moderate changes.However,significant differences have been noted among different ecological indicators,with a fluctuation index of 90.00%at the outlet of downstream hydrological stations,reaching a high level of change.After the mutation,the biodiversity index of flow in the middle and lower reaches of the Yellow River was generally lower than that in the base period.The research results also indicate that the driving factor for runoff changes in the upper reach of the Yellow River Basin is mainly precipitation,with a contribution rate of 39.31%-54.70%.Moreover,the driving factor for runoff changes in the middle and lower reaches is mainly human activities,having a contribution rate of 63.70%-84.37%.These results can serve as a basis to strengthen the protection and restoration efforts in the Yellow River Basin and further promote the rational development and use of water resources in the Yellow River.

A flume test on erosion mechanism for an abandoned section of the Huanghe(Yellow)River Delta

The erosion mechanisms of abandoned coastal section are understood detailedly by flume experiment, which play an important role to the offshore engineering facilities. A movable-bed physical model has been used to investigate the coastal erosion of an abandoned section of the Huanghe （Yellow） River Delta. The theory of physical scale models is discussed and a method for constructing the representative seabed section is developed. The results indicate that during the period initially after the abandonment of the delta the entire bed experienced rapid erosion because the seabed was steep and prone to liquefaction that resulted from storm wave action. After this initial period, a balance of erosion and accretion was established, and the beach profllc equilibrated with a point of balance present on the profile. The experimental results indicate that the volume of deposition was about half that of the erosion. Wave action may also induce significant stratal changes through its interaction with the soft seabed. The major morphological features developed in the model delta section were found to be qualitatively comparable with those observed in the prototype. A distorted modeling law that maintains the similarity of the modeled and prototype equilibrium beach profiles is proposed. Experimental results show that the distorted modeling is able to reproduce the beach-face slope in nature, and the model also successfully reproduced three historical evolutionary stages of erosion.

Changes in Huanghe (Yellow) River estuary since artificial re-routing in 1996

With the combination of historical data, field observations and satellite remotely sensed images (Landsat TM/ ETM+ and CBERS), changes in Huanghe (Yellow) River estuary since 1996 when artificial Chahe distributary was built up were studied, mainly including water and sediment discharge from the river, tides, tidal currents, suspended sediment diffusion, coastline changes and seabed development. During following six and half years (up to the end of 2002), runoff and sediment loads into the river mouth declined dramatically. At the beginning of the re-routing, abundant sediment loads from the river filled up nearshore shallow water areas so that the newborn delta prograded quickly. With rapid decrease of sediment loads transported to the estuary, the delta retrograded. In 1997, subaerial tip of the abandoned delta receded 1.5km; its annual mean recession rate was about 150 m in following years. In addition, marine dynamic condition near the artificial outlet had also changed. Under the interaction of ocean and river flow, most of incoming sediment loads deposited in the vicin- ity of the outlet. Seabed erosion occurred at the subaqueous delta front. Between 1999 and 2002, erosion thick- ness averaged at 0.3 m in the subaqueous delta of 585.5 km2.

Wave-induced seepage and its possible contribution to the formation of pockmarks in the Huanghe(Yellow) River delta

Wave-induced seepage and its possible contribution to the formation of pockmarks in the Huanghe(Yellow) River delta were investigated experimentally and numerically. Laboratory experiments were carried out to explore the response of a layered silty seabed with various saturation conditions under cyclic wave loads,in which the pore pressure and seepage-related phenomena were particularly monitored. Numerical models to simulate wave-induced seepage in the seabed were presented and evaluated,then applied to the Huanghe River delta. The experimental results show that the excess pore pressure decreases more rapidly at the surface layer,while the seepage-related phenomena are more pronounced when large cyclic loads are applied and the underlying layer is less saturated. The proposed numerical models were verified by comparing with the experiments. The calculated seepage depth agreed well with the depth of the pockmarks in the Huanghe River delta. The experimental and numerical results and the existing insitu investigations indicate that the wave-induced seepage may be a direct cause of the pockmarks in the Huanghe River delta. Extreme storm waves and the dual-layered structure of hard surface layer and weak underlying layer are essential external and internal factors,respectively. Wave- or current-induced scour and transport are possible contributors to the reformation of pockmarks at a later stage.

Activity Pattern and Habitat Use of Shorebirds in an Artificial Wetland Complex:A Case Study of Breeding Pied Avocet in the Yellow River Delta,China

With the loss of substantial natural wetlands in coastal zones,artificial wetlands provide alternative habitats for many shorebirds.Scientific management of artificial wetlands used by shorebirds plays an important role in maintaining the stability of shorebird population.Satellite tracking technique can obtain high-precision location information of individuals day and night,providing a good technical support for the study of quantitative relationship between waterfowls and their habitats.In this study,satellite tracking method,Remote Sensing(RS)and Geographic Information System(GIS)technology were used to analyze the activity pattern and habitat utilization characteristics of Pied Avocet during breeding period in an artificial wetland complex in the Yellow River Delta(YRD),China.The results showed that the breeding Pied Avocets had a small range of activity,with a total core and main home range of 33.10 km^(2) and 216.30 km^(2),respectively.This species tended to forage in the pond and salt pan during the day and night,respectively,with an unfixed staying time in the breeding ground.The distance between breeding ground and feeding ground was less than 6 km.It is emphasized that in addition to improving the conditions of the remaining natural habitats,effective managing artificial habitats is a priority for shorebird conservation.This research could provide reference for the management of artificial wetlands in coastal zones and supply technique support for the protection of shorebirds and their habitats,and alleviate human-bird conflicts and sustainable development of coastal zones.

Bioturbation Patterns in the Modern Subaqueous Yellow River Delta and Their Implication for Sedimentary Environment Changes

Bioturbation is one of the important processes that affect the structure and function of sedimentary environments.The particle mixing and element migration processes caused by bioturbation can interfere with the circulation of matter and the explanation of sedimentary records.Therefore,the quantitative characterization of bioturbation structures in the sedimentary sequence is of great significance in the field of sedimentology.Estuaries,where fresh and saltwater mix,exhibit high ecological heterogeneity and biodiversity,making them ideal places to explore bioturbation.This paper targets the subaqueous Yellow River Delta to quantitatively characterize bioturbation structures and their spatial distribution patterns using computed tomography(CT)scanning and three-dimensional reconstruction technology.By combining sediment characteristics and sedimentary environment analysis,the main factors affecting bioturbation structures are elucidated.The results show that bioturbation structures in the subaqueous Yellow River Delta can be divided into four types based on their morphology:uniaxial type,biaxial type,triaxial type,and multiaxial type.Skolithos,Palaeophycus in the uniaxial type,and Thalassinoides in the multiaxial type are the most developed structures.Different types of bioturbation may be constructed by trace-making organisms belonging to the same category or functional group.The intensity of bioturbation in this area ranges from 0 to 4%,with a decreasing trend from nearshore to offshore.There is a downward decreasing trend in the intensity of bioturbation overall in the sedimentary cores,with three vertical distribution patterns:exponential decay pattern,fluctuating decay pattern,and impulsive pattern.The impulsive pattern of bioturbation in a core may indicate the abrupt change in sedimentary environment induced by the Yellow River channel shift in 1996.These results suggest that factors affecting the development of bioturbation include grain size,porosity,consolidation,organic matter content of sediments,and sedimentation rate that is mainly influenced by local hydrodynamic conditions.The environment with clayey silt(average grain size 10μm)and moderate sedimentation rate(around 0.5 cm yr^(-1))is the most suitable area for the development of bioturbation in the Yellow River subaqueous delta.