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Over the past 30 years, reclamation projects and related changes have impacted the hydrodynamics and sediment transport in the Bohai Sea. Three-dimensional tidal current models of the Bohai Sea and the Yellow Sea were constructed using the MIKE 3 model. We used a refined grid to simulate and analyze the effects of changes in coastline, depth, topography, reclamation, the Yellow River estuary, and coastal erosion on tidal systems, tide levels, tidal currents, residual currents, and tidal fluxes. The simulation results show that the relative change in the amplitude of the half-day tide is greater than that of the full-day tide. The changes in the tidal amplitudes of M2, S2, K1, and O1 caused by coastline changes accounted for 27.76-99.07% of the overall change in amplitude from 1987 to 2016, and water depth changes accounted for 0.93-72.24% of the overall change. The dominant factor driving coastline changes is reclamation, accounting for 99.55-99.91% of the amplitude changes in tidal waves, followed by coastal erosion, accounting for 0.05-0.40% of the tidal wave amplitude changes. The contribution of changes in the Yellow River estuary to tidal wave amplitude changes is small, accounting for 0.01-0.12% of the amplitude change factor. The change in the highest tide level (HTL) is mainly related to the amplitude change, and the correlation with the phase change is small. The dominant factor responsible for the change in the HTL is the tide amplitude change in M2, followed by S2, whereas the influence of the K1 and O1 tides on the change in the HTL is small. Reclamation resulted in a decrease in the vertical average maximum flow velocity (VVAM) in the Bohai Sea. Shallower water depths have led to an increase in the VVAM; deeper water depths have led to a decrease in the maximum flow velocity. The absolute value of the maximum flow velocity gradually decreases from the surface to the bottom, but the relative change value is basically constant. The changes in the tidal dynamics of the Bohai Sea are proportional to the degree of change in the coastline. The maximum and minimum changes in the tidal flux appear in Laizhou Bay (P-LZB) and Liaodong Bay (P-LDB), respectively. The changes in the tidal flux are related to the change in the area of the bay. Due to the reduced tidal flux, the water exchange capacity of the Bohai Sea has decreased, impacting the ecological environment of the Bohai Sea. Strictly controlling the scale of reclamation are important measures for reducing the decline in the water exchange capacity of the Bohai Sea and the deterioration of its ecological environment. [ABSTRACT FROM AUTHOR]

This paper investigates sediment trapping in coastal embayments during summer seasons based on observation data obtained from two instrumented tripods that were placed at the mouth of Weihai Bay on north coast of Shandong Peninsula, China, over a 15-day period between 5 and August 20, 2018. The data consisted of time series of water depths, current profiles, wave parameters, near-bed flow velocities, turbidity, water salinity and temperature. Distributions of suspended sediment concentration (SSC) and water temperature in the bay and adjacent sea areas were also investigated at 87 grid stations from July 31 to August 4, 2018. From these data the bed shear stresses, residual currents and suspended sediment fluxes (SSF) were calculated. The results indicated that the variability in the SSC at the northern mouth was mainly controlled by local sediment resuspension while at the southern mouth horizontal advection due to the SSC gradient was the dominant mechanism. To identify the main drivers of the sediment transport, the SSF was analyzed using the decomposition method. The seaward advective transport due to residual flow and landward tidal pumping effect dominated the total near-bed sediment transport at the northern and southern mouths, respectively. Therefore, trapping processes occurred mainly through the southern mouth. The suspended sediment fluxes (SSF) during neap and spring tides at the southern mouth were 0.053 and 0.321 g m−2 s−1, respectively, while during moderate wave conditions (H s > 0.8 m), the SSF was two times larger than the spring tide. In summer, the fine-grained sediments trapped in the bay were mainly derived from resuspension off the eastern tip of the Shandong Peninsula and thus is indirectly from the Yellow River. During such sediment transport and trapping processes, upwelling and winds can also play important roles. • SSC variations at the northern and southern bay mouth were controlled by local resuspension and horizontal advection. • Trapping occurred mainly through the southern mouth via tidal pumping as the SSC gradient dominated the net sediment flux. • Sediments trapped in the bay were mainly derived from resuspension off the eastern tip of the Shandong Peninsula. [ABSTRACT FROM AUTHOR]

• Sediment resuspension drives refractory organic carbon (OC) transfer into seawater. • OC transfer results in the enhancement of dissolved OC bioavailability. • Refractory OC accumulates on particles during sediment resuspension. • The magnitudes of OC transfer are affected by sediment grain sizes. The transfer of particulate organic carbon (POC) to dissolved organic carbon (DOC; OC transfer P-D) is crucial for the marine carbon cycle. Sediment resuspension driven by hydrodynamic forcing can affect the burial of sedimentary POC and benthic biological processes in marginal sea. However, the role of sediment grain size fraction on OC transfer P-D and the subsequent impact on OC cycling remain unknown. Here, we conduct sediment resuspension simulations by resuspending grain-size fractionated sediments (< 20, 20–63, and > 63 μm) into filtered seawater, combined with analyses of OC content, optical characteristics, 13C and 14C isotope compositions, and molecular dynamics simulations to investigate OC transfer P-D and its regulations on OC bioavailability under sediment resuspension. Our results show that the relative intensities of terrestrial humic-like OC (refractory DOC) increase in resuspension experiments of < 20, 20–63, and > 63 μm sediments by 0.14, 0.01, and 0.03, respectively, likely suggesting that sediment resuspension drives refractory DOC transfer into seawater. The variations in the relative intensities of microbial protein-like DOC are linked to the change of terrestrial humic-like OC, accompanied by higher DOC content and reactivity in seawater, particularly in finer sediments resuspension experiments. This implies that transferred DOC likely fuels microbial growth, contributing to the subsequent enhancement of DOC bioavailability in seawater. Our results also show that the POC contents increase by 0.35 %, 0.66 %, and 0.93 % in < 20, 20–63, and > 63 μm resuspension experiments at the end of incubation, respectively. This suggests that the re-absorption of OC on particles may be a significant process, but previously unrecognized during sediment resuspension. Overall, our findings suggest that sediment resuspension promotes the OC transfer P-D , and the magnitudes of OC transfer P-D further influence the DOC and POC properties by inducing microbial production and respiration. These processes significantly affect the dynamics and recycling of biological carbon pump in shallow marginal seas. [Display omitted] [ABSTRACT FROM AUTHOR]

Estuarine deltas play a critical role in the interaction between the ocean and land and serve as the primary location for the deposition of terrestrial organic carbon and pollutants. However, many deltas are increasingly at risk of erosion due to natural processes and human activities. In particular, abandoned estuarine deltas are extremely prone to erosion in the absence of sediment replenishment. The erosion of sediment in these deltas is crucial in comprehending the evolution of delta erosion as it directly impacts coastal geomorphology, ecological environments, geochemical cycling, and carbon sequestration dynamics. Therefore, determining accurately the erosion characteristics of estuarine deltaic sediments is essential for assessing and managing these evolving coastal systems. Therefore, this study conducted erosion experiments on undisturbed sediment samples collected from the subaqueous delta of the abandoned Yellow River Estuary (Old Qingshuigou Estuary) utilizing the UMCES-Gust Erosion Microcosm System. The aim was to reveal the spatial distribution characteristics of sediment erodibility and explore the erosion process, characteristics, and influencing factors of the surface sediments in the area. Erosion characteristics exhibited a spatial distribution pattern of increased erodibility in nearshore sediment and reduced erodibility in offshore sediments. The critical erosion shear stress of surface sediments ranged from 0.2 to 0.68 N/m2, while the erosion rate increased linearly with an increase in erosion shear stress and reached a maximum value of 2.119 g/m2 s, suggesting that nearshore sediments exhibited strong erodibility. Furthermore, the erosion characteristics exhibited a strong correlation with the type of sediment. Silt exhibited surface erosion and Type I erosion (depth-limited erosion), whereas silty sand primarily underwent volume erosion and Type II erosion (steady-state erosion). Particle size characteristics played a crucial role in influencing erosion. Additionally, our results revealed that the effective particle size of sediment aggregates and the scale effect of turbulence were also important factors that affected sediment erosion characteristics. These findings not only enhance our understanding of the erosion characteristics of silty sediments but also provide valuable parameters for sediment transport models in large river deltas such as the Yellow River Delta, thus facilitating the release of buried organic carbon and heavy metals from estuaries. • The subaqueous delta of the abandoned Yellow River Estuary sediments were assessed. • UMCES-Gust Erosion Microcosm System was employed for erosion experiments. • Sediment erodibility distribution and erosion process characteristics were analyzed. • Particle size characteristics represented the most important influencing factors. • Erosion characteristics were closely related to the sediment type. [ABSTRACT FROM AUTHOR]

The waters offshore the Shandong Peninsula separate the North Yellow Sea from the South Yellow Sea, and receive a large amount of terrestrial material from Chinese and Korean rivers, making it an ideal area for studying land-sea interactions. However, little attention has been given to measuring sediment transportation in most previous studies. Based on an analysis in composition of major and trace elements and particle size characteristics from 62 surface sediment samples from the northeastern region off Shandong Peninsula, the type, element composition, and controlling factors of the surface sediments were investigated. In addition, the transportation of sediments from source to sink was described from measured thermohaline data. The results show two types of surface sediments: sandy silt and silt. The sediments were mainly terrestrial; and marine carbonate had little effect on sediment composition. Shown on a binary diagram of Rb/Sc to Co/Sc, the Huanghe (Yellow) and Changjiang (Yangtze) rivers are the main sources of surface sediments in the study area. The component mixing model showed that the relative contribution of sediment from the Huanghe River was up to 92%, followed by the Changjiang River (8%). The Yellow Sea Warm Current and the North Shandong Peninsula Coastal Current met at ∼37.7°N in the study area, and were the main forces carrying sediment from the two main river sources. However, there was a deficit of transported material into the study area in summer. The secondary distribution of sediment from the two river sources was controlled by tidal currents and waves. [ABSTRACT FROM AUTHOR]

The eastern Nanhui mudflat (ENM), located in the southern flank of the Changjiang (Yangtze River) Estuary, plays a key role in storm protection, defense against sea level rise, and land resource provision for Shanghai, China's largest city. Recently, there has been a great deal of concern for its evolutionary fate, since a drastic reduction in the Changjiang sediment discharge rate and an increased number of estuarine enclosures might negatively impact the environmental protection functions that this mudflat provides. In this paper, a novel method, which employed the envelope lines of instantaneous shoreline positions identified in 436 Landsat satellite images from 1975 to 2016, was used to demonstrate the evolution of the mudflat high and low tide lines in a detailed, quantitative way. Our study reveals the southeast progradation rate of the mudflat doubled from 24 m/yr in 713–1974 CE to 49 m/yr in 1975–1995 CE, probably due to the influence of the estuarine turbidity maximum zone shifting to the ENM. Under the ample sediment input directly from the turbidity maximum zone, the spatial evolution of the ENM was governed predominantly by the changing morphology of the South Passage due to the quick progradation of the ENM, which narrowed the South Passage by pushing the South Passage Trumpet southeastward. Therefore, the ENM experienced rapid accretion during 1975–2016. The accretion rate of the high tide line increased 2–13 times due to vegetation and intertidal enclosures, resulting in the rapid reduction of the intertidal area. The area decreased from 97 km 2 in 1976 to 66 km 2 in 1995, mainly due to vegetation, and continued decreasing to 12 km 2 in 2006 due to the intertidal enclosures. In contrast, the accretion rate of the low tide line increased by 25 times due to subtidal enclosures and caused the intertidal area increased to 78 km 2 in 2015. The almost disappeared intertidal zones in 2006 reappeared. However, this reappearance might be a temporary transitional state, and once the subtidal enclosures are completed, most of the intertidal zones will be replaced by enclosure land. Our study reveals that the drastic reduction in the Changjiang sediment flow to the sea has not caused a decline in the ENM. In contrast, the ENM has experienced rapid accretion in the past 40 years, resulting in the strengthening of its functional abilities to protect Shanghai, an unexpected outcome. [ABSTRACT FROM AUTHOR]

The provenances and transport mechanisms of marine sediments are of significance to understanding the oceanic material cycle. Here we examine the rare earth elements (REE) contents and differentiation characteristics as revealed by the analysis of 62 surface sediment samples collected from the offshore muddy area of the Shandong Peninsula. We identify the sediments' provenances and reveal the transport mechanisms based on the REE results and measured temperature and salinity data. The REE concentration of the surface sediments in the study area varies between 153.81 and 205.57 μg/g. Discriminant function and (ΣREE) N *-(Sm/Nd) N scatter diagrams both show that these sediments are mainly from the Huanghe River, and are also impacted upon by the Changjiang River. The North Shandong Peninsula Coastal Current and the Yellow Sea Warm Current, which meet at 37.7°N, drive the lateral sediment transport. • REE differentiation pattern might be similar in global marginal sea sediments. • The contribution of Changjiang River sediments to the NYS must be concerned. • The NSCC and the YSWC are the main driving force for source materials. [ABSTRACT FROM AUTHOR]

The Miaodao Archipelago, located in the southern Bohai Strait, serves as a major route for the exchange of energy and materials between the Yellow and Bohai seas and is distinguished by a complicated hydrodynamic environment and provenance. Based on the grain size and elemental data of 107 surface sediment samples from the archipelago waters, and 58 coastal erosional sediment and bedrock samples, this study investigated the factors influencing the geochemical elemental distribution, discusses the provenance of the surface sediments and relative contributions, as well as proposes a sediment source–sink model for the region. The distribution of major and trace elements in the surface sediments, typically characterized by "high in the north, low in the south" patterning (except for SiO 2 , Ba, and Sr), with their contents primarily controlled by the input of terrestrial materials. The surface sediments in the study area are separated into the geochemical subdivisions of north and south. The main provenances of the study area include the Yellow River, the nearshore Miaodao Archipelago, and the north side of nearshore Penglai, whose sediments were transported under the combined action of the Shandong Peninsula's tidal current, waves, and longshore current. Deposition occurred under the capturing action of the archipelago. The relative contributions of the three provenance areas were 74.7%, 15.5%, and 9.8%, respectively; the relative contribution of coastal erosion reaches 1/3 of the river. Studies have demonstrated that the contribution of coastal erosion provenances to sea surface sediments is non-negligible, and in fact, it may even be quite important; thus, in the context of decreasing riverine inputs to the sea and enhanced coastal erosion processes, the contribution of coastal erosion requires special attention. • In the context of decreasing riverine inputs to the sea, the contribution of coastal erosion requires special attention. • The relative contribution of coastal erosion to sediment sources reaches 1/3rd of the river. • The sea area of Miaodao Archipelago is both an important source and a sink of sediment. [ABSTRACT FROM AUTHOR]

• The diversity of microbial communities in resuspended sediments is largely influenced by hydrodynamic intensity. • Hydrodynamic processes selectively influence the erosion and dispersion of OC within the sediment-water interface. • Hydrodynamic processes can control the lateral transport of microbes and OC in marginal sea sediments. Hydrodynamic processes play a crucial role in driving the transmission of sediments, likely harboring diverse microbes and heterogeneous organic carbon (OC) in the ocean. Here we conducted continuous micro-erosion experiments on surface sediments retrieved from shallow marginal seas, and analyzed the microbial community structures, OC content, and isotope compositions (δ13C and Δ14C) of resuspended sediments to investigate the effects of hydrodynamics on microbial assembly and OC composition in marginal seas. Our results showed that gene abundance and major microbial compositions in resuspended sediments changed with varying benthic shear stresses, which evolved towards diversification after continuous hydrodynamic erosion. Aerobic bacteria were more likely to be eroded out from sediments under lower shear stresses compared with anaerobic bacteria. Our study provides evidence that hydrodynamic disturbances shape the assembly of microbial communities with different metabolic functions, especially for bacteria, which may spatially influence the microbial-mediated biogeochemical transformation in marginal seas. Isotopic results revealed that more terrestrial OC was resuspended under initial erosion, while more marine OC was eroded out with increasing shear stresses, suggesting that hydrodynamics may control the redistribution of different sourced OC and contribute to the dispersion and degradation of terrestrial OC during transport process. Our findings further suggest that the nature of resuspended OC may influence the assembly of sediment-attached microbes due to their metabolic preference for carbon sources, as evidenced by correlations between OC compositions and microbial diversity and abundance. We thus suggest that hydrodynamic disturbance is an extrinsic physical driver of OC redistribution and microbial reassembly, whereas OC may be an intrinsic factor influencing microbial colonization, helping to interpret the spatial heterogeneity of microbes and OC compositions observed in marginal sea sediments. Our study underscores the significant roles of hydrodynamic-driven sediment resuspension in shaping diverse microbial communities and redistributing OC in aquatic systems, and highlights the importance of this process in biogeochemical cycles and ecological environment evolution in shallow marginal sea systems. [Display omitted] [ABSTRACT FROM AUTHOR]

In this paper, 342 Landsat satellite images were used to study the evolution of the Qingshuigou and Qing8 Lobes during 1976–2016. Sea-level correction and statistical analysis were used to eliminate the effect of sea-level fluctuations on the shoreline positions. The results revealed that the evolution of the two newborn Huanghe Delta lobes was mainly influenced by the river sediment discharges, river channel changes, course shifts, floods, droughts, and marine hydrodynamic forces. During 1976–2016, the total land gain of the two lobes was 377 km 2 according to mean-tide line, and the average epeirogenetic efficiency of river sediment discharge was 0.020 m 2 /ton, which was greatly less than that when the channels were natural. The artificial stabilization of the deltaic channels had negative impact on the land gain. Assuming no artificial adjustment to the deltaic channels, the total land gain would increase 435 km 2 . The land gain of the two lobes was a function of the cumulative sediment discharges, shoreline lengths and Course Shift Bonuses under the circumstance of historical river channel changes. The critical sediment discharge maintaining the area balance of the two lobes was a function of historical shoreline lengths, which increased linearly from 61 M ton in 1976 to an average of 163 M ton during 1996–2016. In the future, there are two ways to increase the land gain under the less Huanghe sediment discharge: reducing artificial disturbance of deltaic channels and letting the river enter the sea through the southwest coast of Qingshuigou Lobe. [ABSTRACT FROM AUTHOR]

Organic and Elemental Carbon (OEC) is widely applied in the atmospheric sciences for determining carbon content and distinguishing black carbon contents of aerosols, with an advantage that OEC-based approach can provide thermograms derived from carbonaceous material. It is potential to adopt the advantage to measure the content and composition of organic carbon (OC)% in marine sediments. Here, we utilized the OEC analyzer to measure the OC% in marine sediment based on the pyrolytic oxidation principle, and obtain the OC-derived carbon dioxide (CO 2) thermograms. We examined marine sediments and reference materials to understand the stability and reproducibility of OC% measurements using our approach. The findings indicate that the OC% results (ranging from 1.44 to 1.59%, ave. 1.55 ± 0.03%, n = 64) based on this approach are accurate. In addition, CO 2 concentration thermograms obtained by repeated measurements exhibit a strong reproducibility. Our approach can thus provide the concentrations of thermally-evolved CO 2 with increasing heating temperature to deeply understand the reactivities of OC and the compositions in sediments. We suggest that the OEC-based OC% measurement is credible when samples preparation is well-performed (e.g., suitable sample mass and uniformly distributed loading). To sum up, we provide a means to accurately determine the OC% in marine sediments in terms of the ramped-pyrolysis principle. • OEC analyzer can be used for determining OC% in marine sediments. • Our methodology for determining C% of carbonaceous material is reliable. • Our approach provides a means to decipher reactivity of OC in sediments. [ABSTRACT FROM AUTHOR]

Under the influence of glacial-interglacial climate change and regional tectonic activities in the Quaternary, the sedimentary environments of the Bohai Sea changed greatly, providing significant information on transgression-regression events, East Asian monsoon changes and regional tectonic activities. This study analyzed the sedimentological characteristics of the BH1302 core (water depth of 12.3 m, length of 70.2 m) in the southern Bohai Sea based on grain size, foraminiferal assemblages, carbon and oxygen isotopes in foraminiferal shells and element geochemistry, and established a chronological framework based on AMS 14C, optically stimulated luminescence dating and Oxcal age-depth model using Bayesian modeling. The results showed that three interglacial transgressions and one interstadial transgression were revealed in BH1302 since the late Quaternary, corresponding to marine isotope stages (MIS) 7, 5, 3 and 1, and three subinterglacial transgressions were further identified during MIS 7. The sedimentary environments of Laizhou Bay transitioned from an estuary environment dominated by rivers to a neritic environment dominated by marine conditions because of subsidence of the Miaodao uplift in late MIS 7.1. Three subinterstadial transgressions occurred in both MIS5 with two subinterstadial in MIS 3, and the highstand sea level of MIS 3 reached approximately −18 ∼ −21 m. Under the influence of sea level fluctuations and the East Asian monsoon, the sedimentary environments of MIS 1 can be divided into a low salinity tidal-flat environment (12.0–7.0 kyr BP), a low salinity neritic environment (7.0–4.5 kyr BP) and a modern neritic environment (∼4.5 kyr BP). • The isotopes in the foraminifera shells have good indications to the impact of freshwater input on the neritic environments. • Except for 4 interglacial transgressions, the paper further identifies 3 sub-interglacial transgressions in the MIS7 period. [ABSTRACT FROM AUTHOR]

As a key sedimentary body connecting the north and South Yellow Sea, the subaqueous clinoform off Shandong Peninsula plays an important role in the sedimentary system of China seas, and it is also a studied example in the study among the major "source to sink" systems. Based on AMS 14C dating, sediment grain size, major and trace element contents from core WH-05 located at the edge of the clinoform, we discuss changes in the deposition rate, analyze sediment provenance and controlling factors, and reveal the environmental evolution of the source area since the Holocene. Results from core WH-05 show that marine sedimentation began at about 8.5 ka B.P. The deposition rate decreased from the initial 28.37 m/ka to 0.52 m/ka. Sediment provenance suggests that the Huanghe river sediments have been the main source for the study area since the Holocene. The As/Al, V/Sc indicators show that the environmental oxidation environment was gradually weakened and then increased slightly starting from 7.0 ka B.P. The change in redox is consistent with the change in sea level, the deposition rate, and depositional depth. [ABSTRACT FROM AUTHOR]

Based on the Cr, Pb, Zn, Cd, and As content and grain data from the surface sediments of 56 sampling sites in the coastal waters off the northern Shandong Peninsula, the distribution characteristics of heavy metals in sediments were analyzed, and the sources of these elements were discussed. The results show that the distributions of Cr, Pb, and Zn were similar to each other, while the distributions of As and Cd differed from the other three, with Cr, Pb, Cd, and As all showing high concentrations in the Dengzhou shoal. Cr, Pb, and Zn, which are controlled by fine-grained components of surface sediments, mainly originated from natural processes, As mainly originated from aquaculture, and Cd originated from both natural and human sources. The high concentrations of heavy metals were mostly in areas of residual current convergence and coastal current action, and the distribution of heavy metals can be well correlated to the sedimentary dynamic environment. Human activities, grain size and hydrodynamic conditions are therefore important factors that influence the distribution of heavy metals in this study area. [Display omitted] • The average concentration of heavy metals is relatively low, while the content of As and Cd is higher in some areas. • The heavy metal concentrations can correspond closely to the regional sedimentary dynamic environment. • Cr, Pb, and Zn mainly originate from natural sources, As is mainly from aquaculture, and Cd comes from both. [ABSTRACT FROM AUTHOR]

This paper devises a set of simple and practical method for interpreting hundreds of free medium-resolution satellite images to study beach evolution. The method focuses on beach transects, integrates the computer-aided and subpixel recognition technologies, and derives multiple shoreline indicators and historical beach profile shape. This paper also introduces how to use the method with a case study. The case study uses 880 Landsat images from 1984 to 2020 to examine the historical evolution of the complex Haiyang Beach in China as well as its responses to onshore and offshore engineering projects. The results not only show the detailed temporal and spatial changes of the upper beach based on dry/wet and high-water lines, but also the changes of the middle and lower beach based on mean-water, low-water, and low boundary lines, as well as the changes of beach profile shape, beach slope, and intertidal width. The random errors of the dry/wet, high-water, mean-water, and low-water lines are 7.8 m, 10.5 m, 15.9 m, and 19.2 m, respectively. The random errors not only result from the geo-reference process of satellite images and the recognition process of shoreline positions, but are also affected by random water level fluctuations and irregular undulations of the beach profile. This paper also discusses the similarities, differences, and applicability of these shoreline indicators. It is found that the evolution of dry/wet and high-water lines are similar and mainly affected by onshore engineering projects while the evolution of mean-water, low-water, and low boundary lines are similar and mainly affected by offshore engineering projects. The method provided in this paper can comprehensively evaluate beach evolution based on free satellite images, and would be helpful for understanding and protection of the beaches affected by intensified or intensifying engineering projects and human activities. • Transect-focused software and method for studying beach evolution are shared. • The software integrates subpixel and human-computer interaction technologies. • The method can derive beach profile shape based on hundreds of satellite images. • Six beach shoreline indicators were identified/calculated and evaluated. • Responses of the indicators to onshore and offshore engineering vary greatly. [ABSTRACT FROM AUTHOR]

Coastal wetlands, especially broad mudflats, are facing an unprecedented crisis due to combined influence of intensified coastal development activities, drastic river sediment reduction and rapid relative sea level rise. However, it is still a huge challenge to accurately assess the evolution of mudflats for the lack of reliable shoreline indicators on satellite images, especially the indicators for shoreline at low tide. This study, based on instantaneous shoreline positions derived from 430 Landsat satellite images during 1983–2019, uses sea level correction and statistical analysis methods to study the evolution of Laizhou Mudflat, and the intertidal mudflat loss in Laizhou Mudflat was accurately assessed and the effects of multiple factors, especially the effects of various coastal hard structures, on the evolution of Laizhou Mudflat were quantitatively estimated for the first time. The results show that the intertidal mudflat loss caused by the construction of cofferdams was 98 km2, 93% of the total intertidal mudflat loss. Although the previous intertidal mudflat loss caused by shore-parallel structures was less, the shore-parallel structures will cause great mudflat loss in the future, and the broad Laizhou Mudflat will disappear in 110 years owing to the barrier effect of the widespread shore-parallel structures if the current rapid shoreline retreat is not improved. The construction of shore-normal structures can slow the shoreline retreat of adjacent mudflat but accelerate downstream shoreline retreat. As far as coastal protection is concerned, the construction of shore-normal structures in Laizhou Mudflat is inadvisable. Diverting 13 M ton/year of Huanghe sediment can totally offset the mudflat loss on the upstream of Dongying Pier, however, the mudflat located on the downstream of Dongying Pier is hard to restore owing to the block effect of the shore-normal structures to the alongshore transported sediment. Another option is demolishing the shore-parallel structures to recover the landward movement of shoreline, avoiding the mudflat loss at the expense of land loss. • Effects of various factors on mudflat evolution were quantitatively estimated. • Previous mudflat loss was mainly caused by the construction of cofferdams. • Shore-parallel structures will cause great mudflat loss in future. • Construction of shore-normal structures in the mudflat is inadvisable. [ABSTRACT FROM AUTHOR]