Yalu River Estuary Research Articles

Surface carbonate dynamics in a temperate coastal system in the Northern Yellow Sea, China

The carbon sink/source in estuaries and coastal seas may have significant implications for regional climate change. This study investigated seawater carbon dioxide partial pressure (pCO2), aragonite saturation state (Ωarag), and related carbonate parameters in the Yalu River estuary and the adjacent Northern Yellow Sea, China, in September 2023. The results indicate that seawater pCO2 ranged from 261 to 1121 μatm, while Ωarag ranged from 0.49 to 3.34 in the study area. High pCO2 were observed in the estuarine and northwestern areas, whereas low pCO2 were found in the southern offshore area. In the estuarine area, high pCO2 levels were attributed to the input of diluted water from the Yalu River. In the southern areas, low pCO2 were a result of primary production, while community respiration played an important role in increasing seawater pCO2 in the northwestern area. On the other hand, seawater Ωarag was extremely low in the estuarine area, and greater than 1.5 in the southern offshore area. Ωarag in the study area was mainly controlled by water mixing and temperature. The study area acted as a source of atmospheric CO2 with an average air-sea CO2 flux of 6.2 mmol m−2d−1 in autumn, which was relatively high compared with other marginal seas. The high pCO2 and low Ωarag associated with diluted water inputs and community respiration could weaken the ability of coastal oceans to uptake CO2. Therefore, it is crucial to explore ways to reduce CO2 levels in riverine and adjacent coastal seas.

Soil Microbial Community Structure and Its Contribution to Carbon Cycling in the Yalu River Estuary Wetland

Wetland microbial communities play a vital role in ecosystem functioning, particularly in the intricate processes of carbon cycling. This study employed metagenomic sequencing to investigate the diversity, composition, structural differences, carbon cycling functional gene, and microbial species of soil microbial communities in five distinct soil types of the Yalu River estuary wetland, including shoal soil, bog soil, paddy soil, meadow soil, and brown forest soil. We further explored the influence of environmental factors on both the microbial community structure and carbon cycling functional genes. Our results revealed a bacterial-dominated soil microbial community, constituting about 97.6%. Archaea and fungi represented relatively minor fractions, at 1.9% and 0.4%, respectively. While no significant differences were observed in Chao1 indices between bacterial and fungal communities, the Shannon index revealed notable differences. Both Chao1 and Shannon indices exhibited significant variations within the archaeal communities. The dominant bacterial phyla were Proteobacteria, Actinobacteria, Acidobacteria, Bacteroidetes, and Nitrospirae. Thaumarchaeota, Crenarchaeota, and Euryarchaeota formed the major archaeal phyla, while Ascomycota, Mucoromycota, and Basidiomycota were the dominant fungal phyla. Non-metric multidimensional scaling (NMDS) analysis based on Bray-Curtis distance revealed notable differences in the bacterial, archaeal, and fungal community structures across the samples. Redundancy analysis (RDA) identified key environmental factors for the major phyla. Soil pH, soil organic carbon (SOC), electrical conductivity (EC), and total phosphorus (TP) were the main influencing factors for bacteria, while soil TP, EC, total sulfur (TS), and SOC were the primary drivers for archaeal phyla. Soil total nitrogen (TN) and EC were the main influencing factors for fungal phyla. Analysis of key carbon cycling pathway genes utilizing the Kyoto Encyclopedia of Genes and Genomes (KEGG) database and clustering heatmap revealed some variations in functional gene composition across different soil types. Mantel test indicated that pH, TN, and SOC were the primary environmental factors influencing microbial functional genes associated with soil carbon cycling. Stratified bar chart analysis further demonstrated that the major contributors to carbon cycling originated from corresponding dominatnt phyla and genera of Proteobacteria, Thaumarchaeota, Actinomycetota, Euryarchaeota, and Bacteroidota. The species and relative abundance of microorganisms associated with carbon cycling pathways varied among the samples. These findings provide a crucial reference for informing the conservation and sustainable management of wetland ecosystems in the Yalu River estuary.

Assessment of carbon sink capacity and its value accounting for a farmed shellfish in the coastal wetland of the Yalu River Estuary

The carbon sink of cultivation shellfish in coastal wetlands is characterized as both highly ecological and economic value, thus making great contributions to achieving carbon neutrality. In this study, the main species of cultured shellfish (Ruditapes philippinarum, Meretrix meretrix, Sinonovacula constricta, Scapharca suberenata, and Grassostrea gigas) were selected as the research objects in the coastal wetland of the Yalu River Estuary to measure shellfish yields and carbon contents. Combined with the data from the cultured shellfish of fishery statistics of Donggang city, Dandong, Liaoning Province, China, the carbon sequestration capacity was calculated, and the carbon sink values of cultured shellfish also evaluated on the base of the diverse shellfish carbon sequestration ratios. The carbon sink conversion ratio of cultivation shellfish decreased in the following order: S. suberenata, R. philippinarum, G. gigas, S. constricta, and M. meretrix. The total carbon sequestration of cultured shellfish in the Yalu River Estuary Coastal Wetland from 2015 to 2019 was approximately 110,500 tC. The yield and the carbon sequestration quantity of R. philippinarum accounted for 76.60~83.30% of the total yield and 79.07~85.41% of the total carbon sequestration quantity. The value of the carbon sink was approximately 63,710,600 yuan. Among the species of cultured shellfish, R. philippinarum was the largest contributor to the carbon sink value. Based on Tapio’s decoupling model, R. philippinarum has the most ideal state of decoupling between carbon sink and economic growth of cultured shellfish, followed by M. meretrix and S. suberenata. Our results illustrate that the development of coastal wetland shellfish aquaculture has a positive contribution to reducing carbon emissions and increasing carbon sinks.

Coastline changes under natural and anthropogenic drivers in a macro-tidal estuary between 2000-2020

Coastline changes in estuarine areas can result from a combination of natural processes such as erosion, sedimentation, and sea-level rise, as well as human activities, including urbanization and infrastructure development. These changes have the potential to affect the local environment, including submarine groundwater discharge, wetlands, and navigation routes. The Yalu River Estuary (YRE), situated on the border between China and North Korea, has been experiencing significant changes in its coastline over recent years. This study aims to investigate the coastline dynamics in the YRE from 2000 to 2020. The study employs Landsat 5/7/8 satellite data and proposes a modified Normalized Difference Water Index (NDWI) to accurately delineate the coast boundary, particularly in areas with extensive tidal flats like the YRE. The research findings indicate that from 2010 to 2020, significant changes occurred in the YRE shoreline, with erosion being the dominant trend. Human activities and alternations in hydrological conditions are important factors affecting the YRE coastline changes, contributing to the formation of distinctive spatiotemporal patterns. An extreme flooding event in the year 2010 also altered the inner estuarine coastline in the YRE, indicating the impact of strong natural drivers. Findings from this study provide a comprehensive understanding of the evolving coastal environment, considering natural and anthropogenic drivers, and highlight the importance of continuous monitoring in a region of ecological and geopolitical significance.

Distributions, influencing factors and fluxes of dissolved methane in the North Yellow Sea, near the Yalu River estuary, China

Distributions, influencing factors and sea-to-air flux of dissolved methane (CH4) in the North Yellow Sea near the Yalu River estuary were investigated using a field survey conducted in October 2022. The dissolved CH4 concentration and degree saturation ranged from 3.4 to 34.2 nmol/L and 120%–1059%, respectively. The highest dissolved CH4 concentrations were observed in the northeast inshore areas, especially the area near the Yalu River estuary, and the CH4 concentrations were seen to decrease sharply from inshore to offshore areas. The processes controlling the variability of dissolved CH4 were identified using the two-end-member mixing model and factor analysis. The high dissolved CH4 concentrations in the North Yellow Sea, especially the northeast inshore areas, are ascribed to the input of river-diluted water, while the invasions of the North Yellow Sea Cold Water Mass and Warm Current are important sources of the dissolved CH4 in the bottom water in the southwest offshore area. Overall, the study area is a net source of atmospheric CH4, at a rate of 2.9–133.8 μmol/(m2·day), while the flux in the inshore area are significantly higher than in the offshore area. It is, therefore, the CH4 release from the estuary and marginal seas, which are impacted by human activities, that are a target hot-spot for CH4 emission reduction.

Processes controlling the aragonite saturation state in the North Yellow Sea near the Yalu River estuary: contrasting river input effects

Understanding the characteristics of the aragonite saturation state (Ωarag) is necessary for assessing impacts of ocean acidification, especially in coastal oceans. Based upon surveys conducted in August and October 2022, the distribution and controlling processes of Ωarag were investigated in the North Yellow Sea near the Yalu River estuary. Surface water Ωarag values exhibited substantial variations of 1.14 to 3.79 for the input of river-diluted water and community production, whereas bottom water Ωarag values ranged from 1.82 to 2.40 in August. In addition, surface water Ωarag was further reduced to 1.07–2.37 in October due to the combined effects of seawater temperature decreasing and the upwelling of bottom water with low Ωarag values, while Ωarag values lowed to 1.04–2.14 in bottom water. Considerably low Ωarag values during summer and autumn in nearshore areas, especially in the Yalu River estuary, were resulted from the input of river-diluted water, while the net community respiration and remineralization induced the low bottom water Ωarag values in offshore areas. We suggest that integrated and multidisciplinary studies are required to quantify the trends and dynamics of acidification and its synergistic effects on the marine ecosystem in estuarine and coastal oceans.

Morphological changes in a macro-tidal estuary during extreme flooding events

River discharge is a controlling factor in estuarine morphological changes; estuarine topography can be significantly altered even by only one flooding event. However, the mechanism of morphological changes in mountain-stream macro-tidal estuaries during wet seasons is not fully understood. Taking the Yalu River Estuary (YRE), China, as an example, this study aims to explore the effects of extreme flooding events on estuarine morphology. An improved Finite Volume Coastal Ocean Model (FVCOM) was applied in the YRE to reproduce the distribution of bed sediment erosion and deposition during dry years, normal years, and wet years. Sensitivity tests were conducted to assess the responses of the estuarine system to river discharge. The influence of the Yalu River on the magnitude of estuarine bed change was examined. With an increase in river discharge, the bed thickness in the main estuarine channel first increased and then decreased after reaching a threshold of 0.4 × 104m3/s. Simultaneously, density stratification became stronger with the increase in runoff. Subsequently, vertical mixing of water was weakened after a certain threshold, which in turn, enhanced the density stratification and changed the location of the Estuarine Turbidity Maxima (ETM). In addition, river effects contributed to nearly half of the bed erosion under 0.6 × 104m3/s (flooding with 50-year return period). The ETM extended and moved approximately 8 km seaward during flooding events. The West River channel experienced strong siltation, which was more significant during flood events. The results of this study demonstrate that estuarine circulation plays a key role in morphology change. The magnitude of bed thickness erosion can reach 22% of the total initial thickness during one flooding event. This rapid change is a threat to the stability of port infrastructures, and actions should be taken to maintain the safety of coastal construction.

Spatiotemporal distribution of size-fractioned phytoplankton in the Yalu River Estuary, China

ABSTRACT The grain size structure of phytoplankton has great influence on shellfish culture. The present study aimed to assess the spatial and temporal variation in the phytoplankton community structure in the Yalu River Estuary and to explore the relationship between the phytoplankton community structure and various environmental parameters in 2020. High-throughput sequencing was used in this study. The results showed that nanophytoplankton, especially Karlodinium veneficum, dominated the estuary throughout the year. The biomass ratio of picophytoplankton, nanophytoplankton, and microphytoplankton were 20:63:17 in spring, 30:44:26 in summer, 1:38:61 in autumn, and 2:45:53 in winter, respectively. Meanwhile, Dinophyta had the greatest biomass throughout the year, followed by Bacillariophyta. On the spatial dimension (Station average), COD, T, SST had a positive impact on total phytoplankton communities, and Dep had a negative impact. In the time dimension (Monthly average), the environmental factor that significantly controlled the phytoplankton community structure were NO2 and SST.

Feeding Selectivity of Ruditapes philippinarum on Phytoplankton

A monthly survey of the feeding selectivity of Ruditapes philippinarum in the Yalu River Estuary in 2020–2021 was conducted using high-throughput sequencing identification and visual grading technology. The results showed that the most-dominant species in the water of the shellfish culture area and in the stomachs of R. philippinarum was Karlodinium veneficum in those years. The selectivity index (E) indicated that R. philippinarum avoided consuming Bacillariophyta, Chrysophyta and Cryptophyta throughout the year and preferentially consumed Dinophyta and Chlorophyta. In 2020, the annual average biomass of Dinophyta, Bacillariophyta, Chlorophyta, Dictyochophyta, Cryptophyta and Chrysophyta in the stomach contents of R. philippinarum was 54:14:16:1:10:4; it was 41:12:28:0:1:17 in 2021. The annual average biomass ratio of picophytoplankton, nanophytoplankton and microphytoplankton in the stomachs of R. philippinarum was 13:48:39 in 2020; it was 14:66:20 in 2021. R. philippinarum actively fed on nanophytoplankton and avoided picophytoplankton. Among the phytoplankton of different sizes and groups that R. philippinarum prefer to feed, chemical oxygen demand (COD) and organic phosphorus (DOP) have a significant negative effect on the nanophytoplankton community, pH has a positive effect on the Dictyochophyta community and COD and the inorganic nitrogen to phosphorus ratio (DI-N/P) have a significant positive effect on the Chlorophyta community.

Anthropogenic influences on genetic diversity and differentiation of the clearhead icefish (Protosalanx hyalocranius), as revealed by mitochondrial and microsatellite DNA markers

The clearhead icefish, Protosalanx hyalocranius, is an economically important fishery species in China. For the past few decades, the wild resources of P. hyalocranius have markedly decreased due to human activities such as overfishing, hydro-projects and water pollution. Meanwhile, P. hyalocranius has been widely introduced into lakes and reservoirs of northern China and some have become established, invasive populations, leading to detrimental effects on ecosystems. Using mitochondrial control region sequences and nine microsatellite DNA markers, the aim of this study was to assess to what extent human activities could impact the genetic diversity and population structure of P. hyalocranius, and explore the sources of the invasive Heilong River population based on genetic characterization. Based on mitochondrial DNA, the average haplotype diversity and nucleotide diversity among six populations were 0.737 and 0.0029 respectively. Based on microsatellite markers, the observed (HO) and expected (HE) heterozygosities in each population ranged from 0.481 to 0.565 and 0.478 to 0.565, respectively. Both mitochondrial and microsatellite markers indicated the genetic diversity in Chaohu Lake was the lowest. HO and HE of the two anadromous populations (Liao River Estuary and Yalu River Estuary) were close to Chaohu Lake and relatively low among all populations. The pairwise Dest values showed high and significant genetic differentiation between Taihu Lake and other populations. There was no evidence of genetic differentiation between Chaohu Lake and the two anadromous populations. No significant reduction of genetic diversity was observed in the Heilong River population. Bottleneck analysis showed that the two anadromous populations may have experienced a recent genetic bottleneck. DIYABC analysis suggested that the sources of the invasive Heilong River population were Taihu and Hongze lakes, with a greater genetic contribution from Hongze Lake. Therefore, the anadromous populations of P. hyalocranius may have suffered more impacts from human activities than the strictly freshwater populations. Among freshwater populations, Chaohu Lake should also be paid more attention in fisheries management. In addition, our study demonstrated that multiple introductions can give rise to high genetic diversity in an invasive population.

Seasonal and regional differences in migration patterns and conservation status of Swan Geese (Anser cygnoides) in the East Asian Flyway

BackgroundThe Swan Goose (Anser cygnoides) breeds across Mongolia and adjacent China and Russia and winters exclusively in China. It is globally threatened, showing long-term major range contractions and declining abundance, linked to habitat loss and degradation. We remain ignorant about the biogeographical subpopulation structure of the species and potential differences in their migration timing, stopovers and schedules, information that could be vital to effective conservation of different elements of the species population, which we address here with results from a telemetry study.MethodsIn 2017–2018, we attached GPS/GSM telemetry devices to 238 Swan Geese on moulting sites in three discrete parts of their summering area (Dauria International Protected Area, Central Mongolia and Western Mongolia), generating 104 complete spring and autumn migration episodes to compare migration speed and nature between birds of different summer provenances.ResultsBirds from all three breeding areas used almost completely separate migration routes to winter sympatrically in the Yangtze River floodplain. Although many features of the spring and autumn migrations of the three groups were similar, despite the significantly longer migration routes taken by Western Mongolian tagged birds, birds from Dauria Region arrived significantly later in winter due to prolonged staging in coastal areas and took longer to reach their breeding areas in spring. Among birds of all breeding provenances, spring migration was approximately twice as fast as autumn migration. Areas used by staging Swan Geese (mainly wetlands) in autumn and spring almost never fell within national level protected areas, suggesting major site safeguard is necessary to protect these critical areas.ConclusionsThis study showed the discreteness of migration routes taken by birds of different summer provenances and differences in their migratory patterns, highlighting key staging areas (Yalu River Estuary in China/North Korea for Dauria Region breeding birds, Daihai Lake for Central Mongolian and Ordos Basin for Western Mongolian birds). Based on this new knowledge of the biogeographical subpopulation structure of the Swan Goose, we need to combine data on subpopulation size, their distribution throughout the annual life cycle and conservation status, to develop more effective conservation strategies and measures to reverse population decline throughout the range.

Emergence, Evolution, and Pathogenicity of Influenza A(H7N4) Virus in Shorebirds in China.

ABSTRACTA 2-year surveillance study of influenza A viruses in migratory birds was conducted to understand the subsequent risk during the migratory seasons in Dandong Yalu River Estuary Coastal Wetland National Nature Reserve, Liaoning Province, China, a major stopover site on the East Asian-Australasian flyway. Overall, we isolated 27 influenza A viruses with multiple subtypes, including H3N8 (n = 2), H4N6 (n = 2), H4N7 (n = 2), H7N4 (n = 9), H7N7 (n = 1), H10N7 (n = 7), and H13N6 (n = 4). Particularly, a novel reassortant influenza A(H7N4) virus was first identified in a woman and her backyard poultry flock in Jiangsu Province, China, posing a serious threat to public health. Here, we describe the genetic characterization and pathogenicity of the nine influenza A(H7N4) isolates. Phylogenetic analysis indicated that complex viral gene flow occurred among Asian countries. We also demonstrated a similar evolutionary trajectory of the surface genes of the A(H7N4) isolates and Jiangsu human-related A(H7N4) viruses. Our A(H7N4) isolates exhibited differing degrees of virulence in mice, suggesting a potential risk to other mammalian species, including humans. We revealed multiple mutations that might affect viral virulence in mice. Our report highlights the importance and need for the long-term surveillance of avian influenza virus in migratory birds combined with domestic poultry surveillance along migratory routes and flyways and, thereby, the development of measures to manage potential health threats.IMPORTANCE The H7 subtype avian influenza viruses, such as H7N2, H7N3, H7N4, H7N7, and H7N9, were documented as being capable of infecting humans, and the H7 subtype low pathogenicity avian influenza viruses are capable of mutating into highly pathogenic avian influenza; therefore, they pose a serious threat to public health. Here, we investigated the evolutionary history, molecular characteristics, and pathogenicity of shorebird-origin influenza A(H7N4) viruses, showing a similar evolutionary trajectory with Jiangsu human A(H7N4) viruses in HA and NA genes. Moreover, our isolates exhibited variable virulence (including moderate virulence) in mice, suggesting a potential risk to other mammalian species, including humans.

Modelling study on estuarine circulation and its effect on the turbidity maximum zone in the Yalu River Estuary, China

The along-channel, lateral estuarine circulation and the related baroclinic effects on the turbidity maximum zone (TMZ) of the Yalu River Estuary (YRE) were explored in our study based on the Finite Volume Coastal Ocean Model (FVCOM). The results show that along-channel estuarine flow in YRE had a two-layer-structure with seaward flow in the surface layer and landward flow in the bottom layer. The along-channel bottom landward flow can transport sediment to the upper estuary and influence the location of the TMZ, which was mainly induced by asymmetric tidal mixing. Then, for the variation in cross-channel circulation (lateral circulation), the TMZ moved westwards after reclamation, due to the decreased eastward residual flow resulting from weakened eastward barotropic and baroclinic pressure gradient forcing. This study qualitatively demonstrated the baroclinic effects and human-induced impacts on estuarine subtidal flow and sedimentation. Although site-specific, these findings have wider implications for sediment transport in other medium-scale estuaries.

Impacts of land reclamation on sediment transport and sedimentary environment in a macro-tidal estuary

During the past decades, extensive coastal areas have been reclaimed along the coastline of China, while the physical mechanisms of human pressures on estuarine-sedimentation are largely unknown. This study investigates the impacts of a land reclamation activity on estuarine sedimentation in the Yalu River Estuary (YE), China. For this purpose, we perform a multidisciplinary approach that combines rare earth element (REE) sediment records and numerical simulations. REE pattern of two sediment core samples from the main estuarine branch changed from diverse to homogenous after the early 1970s, which indicates that the estuarine sedimentary environment experienced dramatic change after the land reclamation activity completed in 1975. In order to explore physical drivers behind this change, hydro-sedimentary dynamics were simulated using Finite Volume Coastal Ocean Model (FVCOM) and an improved Track Marine Plastic Debris (TrackMPD) models. After the land reclamation, model results show that: (1) the degree of flood dominance decreased, and the tidal-choking effect was enhanced in the main branch. (2) The estuary became more well-mixed due to the stronger tidal current; (3) Suspended-sediment concentration (SSC), especially SSC in the bottom layer was increased. (4) The landward sediment flux caused by tidal pumping decreased significantly and the YE may turn into a sediment source instead of a sink if more land is reclaimed in the future. Furthermore, sediments in the main branch were likely from different sources before reclamation but became a homogenous mixture afterwards. This study qualitatively demonstrates the human-induced impacts on estuarine sedimentation using a multidisciplinary method.

Reconstruction of sedimentation changes under anthropogenic influence in a medium-scale estuary based on a decadal chronological framework

The present study uses sedimentary records from the Yalu River Estuary (YRE) over the past five decades to establish a regional age framework and investigate the influence of anthropogenic activity. Ten sediment core samples collected from various locations in the estuary were analysed. Core-averaged sediment accumulation rates calculated based on the 210Pb and 137Cs profiles of these samples were in the range 1.09–2.83 and 0.94–3.11, respectively. Accordingly, a regional age framework with major environmental events was established assuming the deposition rate in a sub-section was constant. The age framework showed that most of the sediments in the YRE were deposited from the 1960s, and a grain size analysis also evidenced that the sedimentary environment experienced dramatic change after 1963. Changes in sedimentary environment in the estuary due to human activity (e.g. dam construction, deforestation and large mining activities) were also discussed: (1) the mean grain size at sites near the main channel became finer after 1963 due to the contemporaneous reduction in sediment discharge caused by upstream reservoir construction; (2) abnormal 137Cs signals in the records during the 1980s probably reflected a concurrent deforestation, and the 137Cs signals in the 1990s were related to mixing of sediments caused by mining activities. Results of this study demonstrate that sedimentation processes in a medium-scale estuary can be greatly changed under anthropogenic influence. The feasibility of using 137Cs time markers (especially auxiliary time markers in 1975 and 1986) in a dynamic estuary is confirmed in this study. Furthermore, the regional age framework established in this study can provide a chronological reference for future studies in the YRE and adjacent areas.

The response of sedimentary record to catchment changes induced by human activities in the western intertidal flat of Yalu River Estuary, China

The response to the catchment changes of the sedimentary environment of the western intertidal flat of Yalu River Estuary was investigated by analyzing the vertical variations of the grain size of sediment cores, along with the hydrologic data and human activities in the catchment. The results demonstrated a stepwise decreasing trend for the variations of both the sediment load and water discharge into the sea, which could be divided into three stages as 1958–1970, 1971–1990 and 1991–2009. Reservoir construction and the changes of catchment vegetation coverage turned out to be the two predominant contributors to the changes. There are four periods for the variation of the sensitive components of the sediment cores from 1940 to 2010, i.e., 1940–1950, 1951–1980, 1981–1990 and 1991–2010. The vertical distribution of grain size in the cores mainly varied with the changes of vegetation coverage in the catchment and reservoir construction from 1960 to 1980, whereas it varied depending on the intensity of water and soil erosion in the catchment from 1980 to 1990. Despite the further reduction of the water and sediment input into the sea from 1990 to 2009, this period was characterized by coarsening trends for the grain size of sediment in the estuarine intertidal flat and correspondingly, the significantly increased silt contents of the sensitive component.

Spatial distribution and potential ecological risk assessment of heavy metals in sediments of Yalu River estuary wetland mudflat.

Kriging interpolation analysis was conducted with ArcGIS to find out the distribution characteristics of heavy metals concentrations in the surface sediments of the coastal wetland mudflat on the Yalu River estuary, environmental risk index and Hakanson potential ecological risk index were used to assess their extents of pollution in this area.The concentrations of heavy metals in the surface sediments of the study area were at a relatively high level compared with the typical estuarine wetland. The concentration of heavy metals in the east was higher than that in the west, and in the human activity area, the concentration was higher. Cu was found to contribute the most to the pollution status based on environmental risk index method, while Hg and Cd produced the greatest potential ecological harm according to Hankanson Potential ecological risk index method. The average potential ecological risk index (RI) of the Yalu River estuary wetland was 189.30 (ranged from 93.65-507.20), suggesting a moderate ecological risk. However, the potential ecological risk was highest in the east and should be treated as the major heavy metal pollution prevention area in the future.

Application of the Geostationary Ocean Color Imager to Mapping the Diurnal and Seasonal Variability of Surface Suspended Matter in a Macro-Tidal Estuary

Total suspended particulate matter (TSM) in estuarine and coastal regions usually exhibits significant natural variations. The understanding of such variations is of great significance in coastal waters. The aim of this study is to investigate and assess the diurnal and seasonal variations of surface TSM distribution and its mechanisms in coastal waters based on Geostationary Ocean Color Imager (GOCI) data. As a case study, dynamic variations of TSM in the macro-tidal Yalu River estuary (YRE) of China were analysed. With regard to diurnal variability, there were usually two peaks of TSM in a tidal cycle corresponding to the maximum flood and ebb current. Tidal action appears to play a vital role in diurnal variations of TSM. Both the processes of tidal re-suspension and advection could be identified; however, the diurnal variation of TSM was mainly affected by a re-suspension process. In addition, spring-neap tides can affect the magnitude of TSM diurnal variations in the YRE. The GOCI-retrieved TSM results clearly showed the seasonal variability of surface TSM in this area, with the highest level occurring in winter and the lowest in summer. Moreover, although river discharge to the YRE was much greater in the wet season than the dry season, TSM concentrations were significantly higher in the dry season. Wind waves were considered to be the main factor affecting TSM seasonal variation in the YRE.

Provenance tracking of macroelements in surface sediments from the Yalu River estuary, China

ABSTRACTThe sources of macroelements SiO2, Al2O3, Fe2O3, K2O, Na2O CaO, Fe2O3, TiO2, MgO, P2O5, and MnO can be traced using provenance discrimination functions and by analyzing background values, coefficient of variations, and enrichment factors as well as performing Q and R cluster analyses. In this study, the surface sediments in shallow sea adjacent to the Yalu River estuary were determined to be the “sources” of macroelements rather than the “sinks”. The sediments obtained from the downstream regions of the Yalu River and East Branch were comprised of not only materials transported from the Yalu River to the sea, but also materials transported from adjacent shallow sea toward the land. The sediments obtained from the West Branch were influenced by “re-suspension” as well as modern fluvial transport. The “re-suspended” sediments primarily resembled the characteristics of sediments from the West Branch, which acted as the main channel before 1941. The sediments collected from the Northern Yellow Sea coast predominantly consisted of sediments from the Ai River and Dayang Rivers, followed by “re-suspended” sediments and sediments from the shallow sea.

Provenance discrimination of surface sediments using rare earth elements in the Yalu River estuary, China

Rare earth elements (REE) are important tracers with which to explore sediment provenance. This study analyzed the distribution features of REE in surface sediments of the Yalu River estuary and determined their provenance. Estuarine systems of small rivers such as the Yalu River are suitable “target areas” to understand sediment transport and transfer processes. The fractional characteristics of REE distribution plots, La/Yb(UCC), Eu and Ce anomalies, La/Yb − ∑REE dendrograms, and discriminant functions can all be used for provenance discrimination of the surface sediments in the Yalu River estuary. All these indicate that REE can be one of the most important tools for the study of the coupling mechanism between the watershed and coast, either as a provenance tracer or as a signal of environmental change. The results from this study show that the middle and upper reaches of the Yalu River do not directly supply sediments to the estuarine delta. The western branch transported most material before the construction of the Shuifeng Reservoir in 1941, and these sediments have diffused to other sections via re-suspension. The Dayang River directly supplies sediments to the coasts of the northern Yellow Sea, which is transported toward land under the action of tidal currents or storm surges. These findings also reveal that anthropogenic activities have halted Yalu River estuarine delta preservation and dominated regional landform development in the last 100 years.