Tae-Woo Kang

Mining activities are not only sources of potentially toxic element (PTE) pollution, but are also closely associated with natural radioisotopes. This study combined uranium radioisotopes to better understand the behavior of mine-derived PTEs in lake sediments. We collected surface sediments near an abandoned mine in Lake Daecheong, South Korea, and determined the concentration distribution of PTEs (Pb, Zn, Cu, Cr, Ni, As, Cd, and Hg) and uranium radioisotopes (²³⁵U and ²³⁸U) using an inductively coupled plasma mass spectrometer and a gamma spectrometer, respectively. The mean Zn, Cu, Ni, and Cd concentrations in the tributary near the mine were significantly higher than those of other PTEs, and their distributions tended to decrease downstream. The mean concentrations and distributions of ²³⁵U and ²³⁸U showed a consistent trend similar to that of PTEs. PTE pollution was extremely high only in sites downstream of the tributary directly affected by the mine. Zn, Cu, Ni, Cd, ²³⁵U, and ²³⁸U were closely related and were the most important factors controlling PTE origin. Consequently, the surface sediments were dominated by mine-derived PTEs (Zn, Cu, Ni, and Cd), suggesting a close relationship between the locations and PTE concentrations, highlighting mines as sources. Moreover, uranium radioisotopes were highly correlated with mine-derived PTEs, which will help improve our understanding of PTE behavior. Therefore, uranium radioisotopes can be used as tracers to assess the origin of PTEs from mining activities.

The chemical fractions of heavy metals in sediments provides important information on their mobility, bioavailability, and toxicity. This study identified the chemical fractions of six heavy metals (Pb, Zn, Cu, Cd, Cr, and Ni) in the sediments of Yeongsan River Basin, South Korea. The heavy metals were bound to sediments in the order of Pb ≈ Cd > Zn > Cu > Ni > Cr in the labile fraction, and Pb, Cd, Zn, and Cu exhibited high mobility and bioavailability. The risk assessment code (RAC), individual contamination factor (ICF), and global contamination factor (GCF) assessment results confirmed that the mobility and bioavailability of the heavy metals were relatively higher in the mid–upstream compared to downstream. The sediments in the mid–upstream had a high proportion of heavy metals bound in the labile fraction, indicating a close relationship with pollutants discharged from densely populated regions and industrial complexes.

The assessment of potential radiation hazards in accumulated sediments in aquatic ecosystems is vital for the management and disposal of sediments. Furthermore, preemptive management of radionuclides in terrestrial ecosystems is critical for marine ecosystem conservation. We analyzed the activity concentrations of natural radionuclides (²²⁶Ra,²³²Th, ²³⁸U, and ⁴⁰K) in the surface sediments of major river watersheds in Korea and evaluated the radiation hazards stemming from these activity concentrations. The mean activity concentrations of ²²⁶Ra and ²³⁸U were lower than the global average, whereas those of ²³²Th and ⁴⁰K were higher. The mean values of radium equivalent activity, external hazard index, and internal hazard index calculated from these activity concentrations did not exceed the recommended maximum values. The mean values of absorbed gamma dose rate in air and annual outdoor effective dose rate (AEDR_out) were higher than the global average by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) but remarkably lower than the recommended and background values by the International Commission on Radiological Protection (ICRP) and the Korea Institute of Nuclear Safety (KINS). The contribution of ⁴⁰K and ²³²Th to the AEDR_out mean value was predominant. In conclusion, the surface sediments of major river watersheds in Korea are associated with negligible radiation hazards. These findings provide fundamental data for the management and treatment of sediments in terrestrial and marine ecosystems.

Effective management of nitrate loading in complex river systems requires quantitative estimation to trace different nitrogen sources. This study aims to validate an integrated framework using soluble nitrogen isotope ratios (δ¹⁵N–NH₄ and δ¹⁵N–NO₃) and hydrological modeling (hydrological simulation program SPARROW) of the main stream and tributaries in the Yeongsan River to determine anthropogenic nitrogen fluxes among different land-use types in the complex river watershed. The δ¹⁵N–NH₄ and δ¹⁵N–NO₃ isotopic compositions varied across different land-use types (4.9 to 15.5‰ for δ¹⁵N–NH₄ and −4.9 to 12.1‰ for δ¹⁵N–NO₃), reflecting the different sources of nitrogen in the watershed (soil N including synthetic fertilizer N, manure N, and sewage treatment plant effluent N). We compared the soluble nitrogen isotopic compositions (δ¹⁵N–NH₄ and δ¹⁵N–NO₃) of the river water with various nitrogen sources (soil N, manure N, and sewage N) to assess their contribution, revealing that N from sewage treatment plant effluent as a point source was dominant during the dry season and N from forest- and soil-derived non-point sources was dominant due to intensive rainfall during the wet season. The coefficient of determination (R²) between the measured pollution load and the predicted pollution load calculated by the SPARROW model was 0.95, indicating a high correlation. In addition, the EMMA-based nitrogen contributions compared to the SPARROW-based nitrogen fluxes were similar to each other, indicating that large amounts of forest- and soil-derived N may be transported to the Yeongsan River watershed as non-point sources, along with the effect of sewage treatment plant effluent N as a point source. This study provides valuable insights for the formulation of management policies to control nitrogen inputs from point and non-point sources across different land-use types for the restoration of water quality and aquatic ecosystems in complex river systems. Given the recent escalation in human activity near aquatic environments, this framework is effective in estimating the quantitative contribution of individual anthropogenic nitrogen sources transported along riverine systems.

This study utilized the Delft3D and HABITAT models to investigate the impact of environmental changes resulting from various weir operation scenarios on aquatic habitats and ecosystem health. The weirs were configured to operate with their sluice gates either fully or partially open. The Delft3D model effectively predicted the dominance of diatoms and green algae due to physicochemical changes in weir operation, replicating adaptive processes such as algal growth, competition, and succession. The model indicated a transition to diatom dominance when weirs were fully open and green algae became abundant. The analysis of aquatic ecosystem health in this study, focusing on habitat changes using the HABITAT model, revealed an improvement in aquatic ecosystem health by one level, even with a single weir sluice gate fully open. Furthermore, the utilization of all input variables in the prediction of algae, through the application of artificial intelligence technology, considerably improved prediction accuracy when compared with selectively employing variables with high correlations to changes in chlorophyll-a concentration. These findings underscore the significance of considering various weir operation scenarios and employing advanced modeling techniques to effectively manage and maintain the health of aquatic ecosystems in the face of environmental changes.

This study investigated the accumulation of total phosphorus (TP) and heavy metals (HMs; Pb, Zn, Cu, Cd, Cr, and Ni) in citrus orchard soils in Jeju Island, Korea, identifying potential soil pollution sources using statistical analysis. Anthropogenic HM pollution was evaluated using the geoaccumulation index and enrichment factors, whereas HM bioavailability was assessed via single extraction. TP, Zn, Cu, and Cr concentrations in citrus orchard topsoil were significantly higher than those in forestland soils, indicating their accumulation in the surface layer. Statistical analyses confirmed that elements with high concentrations were closely related to potential pollution sources accumulated on the surface layer of citrus orchards owing to agricultural activities. Particularly, Zn and Cu accumulation was confirmed to originate from intensive compost and pesticide use in citrus orchards. Cu showed the highest contamination and enrichment of all HMs. However, Zn and Cu fractions, determined via an availability assessment, were dominated by acid or complex compounds, indicating that labile Zn and Cu have potential bioavailability for plants. Nevertheless, their fractions accounted for a small proportion (mean < 15%). Therefore, despite the high pollution levels of Zn and Cu, their availabilities were extremely low, indicating a negligible bioavailability in crops and no impact on aquatic ecosystems.

This study verified pollution levels through evaluation of the Sediment Quality Guidelines (SQGs), pollution load index (PLI), and potential ecological risk index (PERI) by analyzing the concentrations of heavy metals in sediments of an urban‒agricultural watershed in the Yeongsan River basin, South Korea. Statistical analyses were performed to determine the relationships between pollution levels and land use, and potential sources of pollution were identified. For spatial distributions, Pb, Zn, Cu, Cd, and Hg concentrations were highest at mid-upstream, but As, Cr, and Ni concentrations were similar at most sites. The polluted sites, which showed the potential toxicity toward benthic organisms in comparison to SQGs, were most frequently observed at mid-upstream. Moreover, PLI and PERI evaluations also confirmed levels of high anthropogenic pollution and the potential ecological risk at mid-upstream. The mid-upstream sites with high heavy metal pollutions showed high correlations with urban land use, which showed the highest distribution, implying a close relationship with anthropogenic impacts such as high population density and industrial complexes. Statistical analyses also confirmed that high heavy metal concentrations in the mid-upstream were closely related to urban land use. These findings suggest that urban areas are highly likely to cause anthropogenic heavy metal pollution in sediments as point or non-point sources such as domestic sewage and industrial wastewater flow into rivers.

The Seungchon and Juksan Weirs were constructed in 2012 through four major river projects to control floods and secure water in the Yeongsan River. However, anthropogenic changes in the environment can lead to loss of biodiversity and longitudinal connectivity and the deterioration of ecosystem health. The objective of this study is to evaluate the effects of physical and chemical changes in the Yeongsan River on aquatic habitats through an integrated (water quality–aquatic habitat) model (i.e., Delft3D and HABITAT). The target species used to simulate habitat suitability included Squalidus chankaensis tsuchigae (an endemic fish), Cyprinus carpio, and Micropterus salmoides (an invasive species of fish). Based on the results, maintaining the lowest water level in one of the two weirs was predicted to improve the habitat of the target species. In particular, the habitat area was greatly improved, especially when the Juksan Weir was completely opened. Furthermore, resistance to environmental changes due to habitat area changes indicates that invasive species adapt more to environmental changes than endemic species. This study suggests that physical and chemical changes in the environment can predict the impact on the health of the aquatic ecosystems, which will be useful in establishing an integrated water management plan. These results can be used as basic data for supporting water management policy, to apply an aquatic ecology prediction model suitable for the Yeongsan River system, and to present a management plan for improving the health of an aquatic ecosystem.