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Current contamination trends and historical records of traditional and emerging polycyclic aromatic hydrocarbons in sediments from Yeongil Bay and Hupo Region, East Sea
No full textThis study investigated the distribution, potential sources, and ecological risks of traditional and emerging polycyclic aromatic hydrocarbons (t-PAHs and e-PAHs) in sediments from Yeongil Bay (n = 17), the Hupo Basin (n = 20), and the Hupo Bank (n = 6) in the East Sea of Korea. Sediment properties were characterized using carbon and nitrogen stable isotope ratios, grain size, total organic carbon (TOC), and total nitrogen (TN) contents. Concentrations of 15 t-PAHs and 8 e-PAHs were significantly higher in Yeongil Bay (490 ng g−1 dm), while similar levels were found in the Hupo Basin (160 ng g−1 dm) and the Hupo Bank (96 ng g−1 dm). Multivariate analysis revealed that these regions were primarily distinguished by TN, TOC, and 3-ring PAHs. Positive matrix factorization identified vehicle emissions, coal combustion, and steel production as the main sources of PAHs in Yeongil Bay. In the Hupo region, vehicle emissions, biomass combustion, and coal combustion were the dominant sources, with coal combustion being the most influential in the Hupo Basin and vehicle emissions in the Hupo Bank. Hazard quotient analysis indicated that benzo[g,h,i]perylene and indeno[1,2,3-cd]pyrene were the primary contributors to ecological risk. Temporal trends in core sediments from the Hupo Basin revealed a continuous presence of PAHs since the pre-industrial period, with either long-term persistence or recent increases across different cores. This study provides insights into the spatiotemporal distribution and environmental behavior of PAHs, offering a scientific basis for environmental monitoring and management.11Nsciescopu
Satellite-observed first large-scale Sargassum bloom in the northern South China Sea
No full textA large-scale Sargassum bloom occurred in 2024 in the South China Sea (SCS), with many scientific issues of spatio-temporal patterns, origins, and possible driving factors being still unclear. Here, we investigated these questions by using 5,121 optical satellite images from January to April 2024 (including Sentinel-2A/B MSI, HY-1C/D CZI, GF-1/6 WFV, Landsat-8/9 OLI, and HJ-2A/B CCD, with spatial resolutions from 10 to 50 m), and various environment data of sea surface temperature (SST), photosynthetically active radiation (PAR), sea surface wind field, sea surface current, and Pearl River runoff. The Sargassum patches, mainly found in the northern SCS, spanned 630 km east–west and 227 km north–south, with the maximum daily coverage of 6.40 km2. On January 9, the patches were first spotted from satellite images, and after April 28, they were no longer detectable from space, lasting 111 days. An intensive retrospective survey from 2015 to 2023 by using 115,019 Sentinel-2A/B MSI satellite images and 6,506 Landsat-8/9 OLI images (<20 % cloud coverage) indicated that 2024 may mark the first large-scale Sargassum bloom in the SCS during the past decade, implying that all the 4 marginal Seas around China have experienced large-scale floating macroalgae bloom events. Potential bloom origins were identified and consecutive positive SST anomaly for four months (from December 2023 to March 2024) may be an important contributing factor to the unprecedent regional large-scale bloom. In the context of global warming, Sargassum blooms in the SCS may occur in a larger scale in the foreseeable future, urgently requiring efforts for monitoring and early warning to be strengthened.11Nsciescopu
Seasonal and antifoulant effects on microbial-metazoan interactions in biofouling communities revealed by comprehensive eDNA metabarcoding
No full textBiofouling is the undesired accumulation of organisms on submerged or wet surfaces of ship hulls, marine structures, and even the shells of marine organisms, such as bivalves. To prevent this, various coating technologies and antifouling agents have been developed. To assess the impact of biofouling patterns and antifoulants on biofilm and biofouling formation, we deployed untreated control plates and antifoulants-coated plates in Jangmok Bay and analyzed the interactions between bacteria and metazoans. Result showed minimal impact of biofouling patterns, while antifouling agents influenced both bacterial and metazoan biofouling. However, biofouling formation was species-specific, with gram-negative bacteria, particularly copper-tolerant ones, being more dominant on antifouling plates. Although the genus Pseudomonas had a lower abundance, its metabolic pathways were highly enriched. Instead of preventing barnacle settlement, increased settlement of other macrofoulers, including non-indigenous species like Perna viridis, was detected due to competitive interactions. Our findings suggest that antifouling effect may lead to increased dominance of certain organisms, rather than preventing biofouling. The development of more effective antifoulants coatings is crucial, as organisms with antifouling resistance can pose new hazards. Our study also confirmed the efficiency of metabarcoding approach, demonstrating a correlation between bacteria and metazoans through species level detection, as well as predicting potential hazardous factors.11Nsciescopu
Intensified sediment transport by breakdown of discharge-induced two-layer circulation in a contaminated, macro-tidal bay
No full textFreshwater discharge from sluice gates can enhance tidal asymmetry and form a two-layer circulation. In-situ observations using acoustic Doppler current profiler and CTD were conducted to investigate the effects of discharge on the sediment dynamics in a contaminated, macro-tidal Asan Bay. Continuous discharge during the early flood tide induced a two-layer circulation, characterized by a seaward surface current and a landward bottom current. During neap tide, as the two-layer circulation broke down after discharge was nearly complete, the landward current velocity near the bed reached up to 0.53 m s−1, comparable to spring tide, and the landward sediment flux was approximately twice that during spring tide. The enhanced vertical mixing likely caused strong sediment resuspension, which remained trapped near the bed due to the intensified baroclinic forcing. These mechanisms potentially led to the intensification of landward sediment transport and accumulation of contaminated sediments in the inner regions of the bay.11Nsciescopu
Assessing the Reliability of ADCP-Derived Echo Intensity Under Variable Scattering Conditions: Roles of Sediment, Zooplankton, and Bubbles
No full textAn acoustic Doppler current profiler (ADCP) is widely used to measure current velocity and estimate suspended particulate matter (SPM) through echo intensity. However, acoustic signals are affected by diverse scatterers, including sediments, zooplankton, and vessel-induced bubbles, which can alter data reliability. This study evaluates the influence of these scatterer types on mean volume backscattering strength (MVBS) and Percent Good (PG) using moored observations in Onsan Bay, Korea. The analysis revealed that PG and data reliability followed the order: suspended sediments > vessel-induced bubbles > zooplankton. Sediment-dominated periods maintained high PG (> 89%) due to the homogeneous size and density of fine particles, ensuring stable backscatter even at high SPM. Zooplankton aggregations caused irregular scattering and marked PG reduction, especially when MVBS 70 mg l−1, increasing measurement uncertainty. Vessel-induced bubbles produced short-term PG decreases but minimal long-term degradation. PG threshold selection strongly influenced SPM flux estimates under zooplankton-rich conditions. Applying PG > 50% reduced overestimation to 70%, whereas unfiltered data overestimated flux by 128%. These findings highlight the need for adaptive PG thresholds tailored to environmental conditions to improve the accuracy of ADCP-based SPM monitoring in dynamic coastal environments.11Nsciescopuskc
Threshold-based analysis of eutrophication dynamics in a semi-enclosed bay: The dominant role of dissolved inorganic nitrogen in Masan Bay, South Korea (2010–2015)
No full textEutrophication in semi-enclosed coastal systems remains a persistent concern due to restricted water circulation and continuous nutrient inputs. To better characterize nutrient-driven water quality degradation, we applied a threshold-based analysis to seasonal monitoring data collected from Masan Bay, South Korea, between 2010 and 2015. Eutrophication status was assessed using a composite Eutrophication Index (EI) integrating chemical oxygen demand (COD), dissolved inorganic nitrogen (DIN), and dissolved inorganic phosphorus (DIP). Although COD remained stable, EI increased significantly over time (p 17.05) occurred most frequently during summer and autumn at inner bay stations with limited circulation. Simultaneously, total phytoplankton abundance declined significantly (p < 0.01), and the community composition shifted from Bacillariophyceae to Dinophyceae. This shift was associated with nutrient imbalance and oxygen stress, with phosphorus limitation and nitrate enrichment favoring Dinophyceae, and hypoxia further supporting their prevalence. Our findings emphasize the utility of DIN-based thresholds in capturing eutrophication risk and support the integration of nutrient and biological indicators into coastal water quality management frameworks.11Nsciescopu
Impacts of stratified water column on summer phytoplankton community structure and dynamics in the East Sea, Korea
No full textSummer stratification strongly regulates nutrient availability and phytoplankton productivity in the East Sea. We examined the combined influences of the East Korea Warm Current (EKWC) and stratification intensity on phytoplankton communities in the Ulleung Basin during four consecutive summers (2021–2024). Years of weak EKWC transport (2021, 2023; 0.1–0.3 m s−1) coincided with restricted offshore dispersal of coastal production and lower surface chlorophyll a (Chl. a; mean 0.34 μg L−1). In contrast, strong EKWC years (2022, 2024; 0.5–0.8 m s−1) exhibited enhanced offshore dispersion and higher Chl. a (mean 0.79 μg L−1). Intensified stratification produced sharp vertical gradients in temperature (24–29 °C at 0–30 m vs. 6–13 °C at 50–100 m), salinity (31.8–32.6 vs. 33.9–34.2), and nitrate (≤5 vs. 6–12 μM), and supported the formation of subsurface chlorophyll maxima (SCM) at 13–47 m, where light and residual nutrients intersected. Community composition displayed strong vertical partitioning: pico-phytoplankton dominated nutrient-depleted surface layers (mean 61 % of biomass), while diatoms prevailed in SCM layers (38–70 %). Dinoflagellates, including Katodinium glaucum and Gyrodinium spp., increased under stratified conditions, and cryptophytes became more abundant at depth. Overall, these results demonstrate that EKWC variability controls horizontal transport of phytoplankton biomass, while stratification governs vertical zonation and taxonomic composition. As sea surface warming intensifies summer stratification, these findings provide critical baseline data for ecosystem models predicting future shifts in nutrient cycling, productivity, and food web dynamics in the East Sea.11Nsciescopu
Factors constraining the morphodynamics of tidal meanders in non-vegetated tidal flats under a monsoon climate
No full textTidal meanders, comprising large-scale channels, medium-sized creeks, and small-sized gullies, serve as critical lifelines supporting tidal flat ecosystems. While extensive research has been conducted on vegetated meanders in terrestrial and coastal environments, the morphodynamics of tidal meanders in non-vegetated tidal flats, particularly those influenced by monsoonal climates, remain poorly explored. This study investigates the migration dynamics of tidal meanders across three distinct non-vegetated tidal flats along the west coast of Korea, each differing in tidal range, embayment geometry, and surrounding topography. Based on over a decade of Google Earth imagery, migration rates were analyzed according to meander size. The results reveal that smaller meanders exhibit faster migration rates when normalized by channel width. Furthermore, the migration rates of tidal meanders in non-vegetated flats were found to be approximately an order of magnitude higher than those reported in the literature for vegetated environments such as salt marshes. The results also highlight significant differences in migration rates among the analyzed tidal flats, driven primarily by variations in tidal range and exposure to the northwesterly East Asian Winter Monsoon. These findings highlight the complex interactions between hydrodynamic, climatic and geomorphological factors in the dynamic evolution of tidal flat meanders.11Nsciescopu
Environmental factors on microalgal resuspension and dynamics in tidal flats on the west coast of Korea
No full textBenthic microalgal resuspension is driven by environmental factors such as wind, rainfall, and tidal currents, exerting substantial influence on coastal ecosystem dynamics. This study examined resuspension processes and microalgal fluxes on tidal flats along the west coast of Korea. Temporal variations in chlorophyll-a concentrations and turbidity were monitored at short intervals over two spring-neap tidal cycles. Tychopelagic diatoms were the dominant microalgal group resuspended into the water column. Strong winds (> 4 m s−1) and heavy rainfall further enhanced resuspension, while site-specific sedimentary settings and diel cycles affected microalgal flux. The near-equilibrium between inflow and outflow over the tidal cycles highlights a dynamic balance of microalgal biomass exchange between tidal flats and nearshore waters. These findings highlight the importance of environmental factors in shaping microalgal dynamics and their implications for coastal carbon cycling.11Nsciescopu
Spatiotemporal distributions and mass budgets of artificial radionuclides (137Cs and 239,240Pu) in the seas surrounding Korea
No full textIn order to quantitatively evaluate and predict the behavior of the anthropogenic radionuclides, this study examined the spatiotemporal distributions and mass budgets of 137Cs and 239,240Pu in the seas surrounding Korean Peninsula (i.e., the East/Japan Sea, the Yellow Sea, and the southern sea of Korea) from 2018 to 2024. Surface activities of 137Cs ranged from 0.56 to 2.43 mBq kg−1, while those of 239,240Pu ranged from 1.28 to 5.70 μBq kg−1. 137Cs showed a gradual decline over time, with surface distributions exhibiting slight spatial and temporal variations. The vertical distribution of 137Cs showed surface or subsurface (< 100 m) peaks followed by a decrease with depth. In contrast, 239,240Pu activities were depleted near the surface and increased with depth, displaying a distinct maximum at mid-depth (750–1000 m). Mass balance calculations suggest the negative inventory change rates (
) across all regions, indicating net losses of 137Cs primarily due to radioactive decay and particle scavenging. The corresponding residence times of 137Cs were 70.7 ± 1.0 years in the East/Japan Sea, 40.1 ± 0.7 years in the Yellow Sea, and 53.8 ± 1.2 years in the southern sea of Korea—all exceeding the radiological half-life of 137Cs (30.17 years). These findings offer quantitative insights that can enhance future predictions of the variability in artificial radionuclide activities, such as 137Cs and 239,240Pu, in Korean seas, where external inputs from surrounding regions play significant roles.11Nsciescopu