Hoi-Soo Jung

Unvegetated tidal flats store sedimentary organic carbon (OC), but their contribution to blue-carbon inventories remains poorly constrained because sparse cores must represent heterogeneous intertidal environments. This study quantified OC stock within the upper 1 m of Hwangdo tidal flat, South Korea, by integrating ten 100-cm cores, 107 surface-sediment samples, and an unmanned-aerial-vehicle-derived digital elevation model covering 4.841 km². The surface survey characterized variations in elevation, sediment texture, and OC, while the cores provided profiles of grain size, dry bulk density, and OC content. Core stocks were integrated over 0–100 cm and evaluated using a spatially grouped, cross-validated adjustment based on surface elevation and uppermost-sediment OC to reduce bias from sparse core distribution. Measured core stocks ranged from 13.61 to 30.20 Mg C ha⁻¹, with an unadjusted mean of 23.04 Mg C ha⁻¹. Mean OC contents were low in surface sediments (0.18%) and core sediments (0.17%). Across the pooled surface and core dataset, TOC correlated positively with mud content (Spearman’s ρ = 0.47) and negatively with sand content (ρ = −0.51), indicating sediment-textural control over OC distribution. The adjustment increased the mean stock by 5.9% to 24.39 Mg C ha⁻¹. Applying this value to 484.108 ha yielded a regional OC storage of 11.81 Gg C, with a conditional bootstrap interval of 9.12–12.90 Gg C. However, the low cross-validated Q² (0.070) shows that the model adjusts the core mean rather than providing a spatially explicit prediction. Overall, Hwangdo’s comparatively low OC pool likely reflects the combined effects of limited inputs of terrestrial organic matter; the absence of vascular vegetation and the associated belowground biomass that would otherwise promote carbon retention; and the frequent reworking, oxygenation, and export of organic matter from its sand-dominated, hydrodynamically energetic sediments. By integrating depth-resolved cores with dense surface observations and UAV-derived topography while explicitly reporting conditional uncertainty, this study establishes a transferable framework for more defensible blue-carbon inventories and strategically targeted sampling in data-limited unvegetated tidal flats.

This study investigated the long-term changes in sediment grain size characteristics of tidal flats along the southwestern coast of Korea using datasets collected through the National Marine Ecosystem Survey from 2015 to 2025. The study area consisted of 129 survey lines and 387 monitoring stations distributed across the western and southwestern coastal regions of Korea, including the Gyeonggi-do, Incheon, Chungcheong, Jeonbuk-do, and Jeollanam-do regions. Spatial distributions and temporal variations of mean grain size were analyzed to identify regional sedimentary characteristics and long-term trends. The results showed that relatively coarse sediments were dominant in the Gyeonggi-do, Incheon, and Chungcheong regions, whereas finer sediments were generally distributed in the Jeonbuk-do and Jeollanam-do regions. These spatial differences were interpreted as the combined effects of tidal and wave energy, exposure to the open sea, terrestrial sediment supply, and geomorphological enclosure. Long-term time-series analysis revealed that although sediment grain size variations were observed in some regions and years, no clear nationwide trend of overall coarsening or fining was identified during the study period. In addition, grain-size class analysis indicated that coarse sediments showed relatively large interannual variability, whereas fine sediments exhibited comparatively stable distribution patterns. These findings suggest that tidal flats along the southwestern coast of Korea are characterized not by a simple one-way erosion system, but rather by a dynamic equilibrium environment where resuspension and redeposition continuously occur under tidal and wave influences. This study is meaningful in that it quantitatively evaluated long-term sedimentary environmental changes in Korean tidal flats based on a national-scale monitoring dataset, and the results are expected to provide fundamental information for future tidal flat conservation and coastal management policies.

This study investigated the spatial distribution of labile biogenic silica (lBSi) and its controls in terms of production, dilution, and preservation along a land–shelf continuum (LSC) from the area adjacent to the Nakdong River estuary to the distal Korea Strait shelf mud (KSSM). Surface sediments were uniformly fine-grained (mud 94.0 ± 1.6%; mean grain size 6.8 ± 0.2 Φ) with minimal variability. Excess 210Pb-derived sedimentation rates decreased offshore, from 6.5 mm yr⁻¹ near the estuary (BS01) to 0.9 mm yr⁻¹ at the outer shelf (BS05). Conversely, lBSi increased by ~46% (2.8 ± 0.2 to 4.1 ± 0.7 wt%) and inversely correlated with sedimentation rate (R² = 0.8), indicating dilution by terrigenous sediments near the estuary. Mean bulk total organic carbon (TOC) averaged 1.3 ± 0.1%, with no clear gradient, while δ¹³Corg (-21.9 to -20.8‰) and TOC/total nitrogen (TN) (7.2 to 9.8) varied offshore, reflecting a declining freshwater influence. TOCmarine, estimated via a TOC/TN end-member mixing model, accounted for 35–60% of bulk TOC, peaking near the estuary and declining offshore, consistent with river nutrient-driven autochthonous production. The increasing offshore lBSi/TOCmarine ratio likely reflected the combined effects of diminished detrital dilution, decreasing TOCmarine, and preferential degradation of marine organic matter under lower sedimentation rates. These findings show that lBSi distribution in muddy LSCs, such as the KSSM, reflects integrated estuarine nutrient-driven production, terrigenous dilution, and preservation dynamics. Future applications should adopt a multi-proxy approach combining TOCmarine, sedimentation rate, grain size, and preservation factors rather than relying on bulk lBSi alone.

Understanding suspended sediment transport in macrotidal embayments is crucial for assessing water quality, ecosystem function, and long-term morphological stability. This study provides a high-resolution, localized estimate of suspended sediment flux and examines the empirical relationship between turbidity (NTU, nephelometric turbidity unit) and total suspended matter (TSM, mg·L⁻¹) in the main tidal channel of Gomso Bay, a UNESCO-designated tidal flat on the west coast of Korea. A 13 h high-resolution fixed-point observation was conducted during a semi-diurnal tidal cycle using a multi-instrument platform, including an RCM, CTD profiler, tide gauge, and water sampling for gravimetric TSM analysis. Vertical measurements at the surface, mid, and bottom layers, taken every 15–30 min, revealed a strong linear correlation (R² = 0.94) between turbidity and TSM, empirically validating the use of optical sensors for real-time sediment monitoring under the highly dynamic conditions of Korean west-coast tidal channels. The net suspended sediment transport load was estimated at approximately 5503 kg·m⁻¹, with ebb-dominant residual currents indicating a net seaward sediment flux at the observation site. Residual flows over macrotidal channels are known to vary laterally, with landward fluxes often occurring over shoals. Importantly, the results from this single-station, short-duration observation indicate a predominantly seaward suspended sediment transport during the study period, which should be interpreted as a localized and time-specific estimate rather than a bay-wide characteristic. Nevertheless, these findings provide a baseline for assessing sediment flux and contribute to future applications in digital twin modeling and coastal management. Gomso Bay is part of the UNESCO-designated ‘Getbol, Korean Tidal Flats’, underscoring the global significance of preserving and monitoring this dynamic coastal system.

This study analyzes the geological and geochemical features of surface sediments in the Hwangdo Tidal Flat, located on Korea’s West Coast. The tidal flat experiences semi-diurnal tides, impacting organic matter decomposition and nutrient cycling. Ninety one sediment samples were collected and analyzed for physical and chemical properties including grain size, density, water content, organic carbon, and nitrogen. Sediments consist mainly of sand and silt, with coarser sediments near the main channel and finer sediments towards the west. Sediment grain size averages 4.12 Φ with a sorting coefficient of 1.96 Φ, indicating diverse energy environments. Total organic carbon and nitrogen correlate positively with grain size and density, reflecting sediment origin and environment. Kriging maps sediment grain size distribution, while correlation and linear regression analyses show relationships between variables. High correlations exist between various parameters, aligning with tidal flat characteristics and aiding understanding of sediment transport and deposition. The study provides baseline data for understanding the tidal flat’s geological, geochemical, and physical aspects, valuable for remote sensing validation and environmental monitoring. The dataset is freely available for research and management purposes.