• Korean Journal of Ecology and Environment
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• v.40 no.2
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• pp.273-284
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• 2007

The spatial and temporal zooplankton dynamics were examined along ca. 100-km section of the middle to lower Seomjin River (without estuary dam in river mouth) and Youngsan River (with estuary dam in river mouth) systems during study periods (2004. Nov.${\sim}$2006. Aug.) based on a monthly sampling intervals. The spatial variation of zooplankton biomass at both river ecosystems was distinct. There was considerable longitudinal variation in total zooplankton abundance in Youngsan R. stretch. The increase in total zooplankton abundance were observed along the longitudinal stretch toward the estuary dam. In contrast, there were not statistically significant longitudinal differences in total zooplankton abundance in Seomjin R. stretch. In Youngsan R. stretch, average abundance of total zooplankton (average ranges: $199{\sim}817$ Ind. $L^{-1}$ at 3 sampling sites, n=20) were nearly $4{\sim}60$ fold higher than that of Seomjin R. stretch (average ranges: $12{\sim}43$ Ind. $L^{-1}$ at 4 sampling sites, n=20). Relative abundance of rotifers (over 80% of total zooplankton abundance) at the whole sampling sites in Youngsan R. stretch were Much higher than that of the Seomjin R. stretch. The most abundant rotifers were Polyarthra spp., Brachionus spp., Colurella spp., and Keratella spp. at the both river ecosystems. In Seomjin R. stretch, copepods carbon biomass sharply increased toward in river mouth (over 40% of total zooplankton carbon biomass). Average ranges of total zooplankton filtering rates for phytoplankton at both river ecosystems varied from 21.2 to 92.9 mL $L^{-1}\;D^{-1}$ in Youngsan R. stretch and from 2.1 to 2.6 mL $L^{-1}\;D^{-1}$ in Seomjin R. stretch. Considering the zooplankton filtering rates, zooplankton as grazers of phytoplankton in Youngsan R. stretch seemed to play the more important role in planktonic food web than that of the Seomjin R. stretch.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.37 no.4
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• pp.323-329
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• 2004

In situ particle size and volume concentration of suspended sediment was measured at the mouth of Seomjin River Estuary In February 2001, using an optical instrument, 'LISST-100'. Time variation of in situ particle size and concentration shows: (1) during ebb tide, Seomjin River supplies relatively fine-grained particles with less-fluctuated, compared to during flood tide, and well-behaved concentrations following the tidal cycle; and (2) during flood tide, relatively coarse-grained particles with highly variable in size distribution and concentration flow upstream from Kwangyang Bay. This explains a poor correlation $(r^{2}=0.10)$ between sediment concentration and beam attenuation coefficient during flood and a high degree of correlation $(r^{2}=0.80)$ during ebb tide. Relatively fine grained and well defined, monotonous size distribution may promote the correlation between concentration and beam attenuation coefficient due to optical homogeneity of particles during ebb tide. Abundance of large aggregates with time-varying size and shape distributions may be mainly responsible for variations in optical properties of the sediment during flood tide, and thus may confound the relationship between the two variables. The difference in particle sizes and shapes between flood and ebb tides can also be observed on SEM images.

• Journal of Korea Water Resources Association
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• v.53 no.1
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• pp.57-70
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• 2020

This study is to establish the situation of inter-basin transfer from Seomjin river basin to Yeongsan river basin using SWAT (Soil and Water Assessment Tool). Firstly, the SWAT modeling was conducted for each river basin. After, the inter-basin transfer was established using SWAT reservoir operating parameters WURESN (Water Use Reservoir Withdrawn) and inlet function from Juam dam of Seomjin river basin to Gwangju stream of Yeongsan river basin respectively. Each river basin was calibrated and validated using 13 years (2005~2017) data of Seomjin- Juam dam reservoir storage (JAD), release, transfer and Yeongsan-Mareuk (MR) stream gauge station. The results of root mean square error RMSE, Nash-Sutcliffe efficiency NSE, and determination coefficient R² of JAD were 2.22 mm/day, 0.62 and 0.86 respectively. The RMSE, NSE, and R² of MR were 1.38 mm/day, 0.69 and 0.84 respectively. To evaluate the downstream effects by the transferred water, the water levels of 2 multi-function weirs (SCW, JSW) in Yeongsan river basin and the Gokseong (GS) and Gurye (GR) stream gauge stations in Seomjin river basin were also calibrated. The RMSE, NSE, and R² of SCW, JSW, GS and GR were 1.49~2.49 mm/day, 0.45~0.76, 0.81~0.90 respectively.

• Korean Journal of Environmental Biology
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• v.37 no.4
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• pp.592-599
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• 2019

Ostrea denselamellosa and Eriocheir japonica samples were collected from the Seomjin River in 2019 as part of the "Research of Host-Associated Bacteria" research program. Almost 200 bacterial strains were isolated from the O. denselamellosa and E. japonica samples and subsequently identified by 16S rRNA gene sequencing. Among the bacterial isolates, ten strains possessed greater than 98.7% sequence similarity with published bacterial species that had not previously been recorded in Korea. These species were phylogenetically diverse, belonging to three phyla, four classes, seven orders, and eight genera. At the genus and class level, the previously unrecorded species belonged to Pseudoalteromonas, Aliivibrio, Rheinheimera, Leucothrix, and Shewanella of the class Gamma-proteobacteria, Olleya of the class Flavobacteriia, Algoriphagus of the class Cytophagia, and Lactococcus of the class Bacilli. The previously unrecorded species were further characterized by examining their Gram staining, colony and cell morphology, biochemical properties, and phylogenetic positions.

• Korean Journal of Ecology and Environment
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• v.55 no.2
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• pp.132-144
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• 2022

The fish community in the Seomjin River-Seomjin River Estuary-Gwangyang Bay coast continuum was investigated three times from March 2019 to October 2019. The collected species at the eight sites during the survey period were 49 species belonging to 31 families, including two endangered species. According to Bray-Curtis similarities, observations were divided into four groups based on the fish community composition; two groups (group 1, 2) and two uncategorized groups (group 3, 4). ANOSIM based on spatial and temporal groupings indicated that the spatial differences in fish communities (R=0.398, P=0.001) were relatively more important than the temporal differences (analysis of similarities, R=0.273, P=0.002). In particular, there were significant differences between groups 1 and 2 (analysis of similarities, R=0.556, P=0.001), and similarity percentage analysis revealed that Argyrosomus argentatus (9.4%), Favonigobius gymnauchen (6.9%) and Konosirus punctatus (5.9%) contributed to these differences of fish assemblages for each group. The fish fauna distributed in the Seomjin River-Gwangyang Bay ecosystem were spatially divided and the number of species and number of individuals showed seasonal differences. This study could be a basis for understanding changes in the fish community and implementing conservation and management strategies on major species within a continuous environment of the river-estuary-ocean continuum.

• Korean Journal of Ecology and Environment
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• v.54 no.1
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• pp.12-23
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• 2021

As fish communities are sensitive to natural environmental changes as well as anthropogenic pressures, their composition and characteristics help us to assess the aquatic ecosystem health. The fish fauna and the length-weight relationship of Zacco platypus in the Seomjin River system were investigated from July 2018 to May 2019. The collected species during the survey period were 49 species belong to 14 families including 19 Korean endemic and two endangered species. According to Bray-Curtis similarities, 14 sites were divided into four groups based on the fish community composition; two groups(group A, B) and two uncategorized sites(group C, D). There were significant differences between groups A and B(analysis of similarities, R=0.722, p=0.002). A similarity percentage analysis revealed that Z. koreanus(8.55%), Micropterus salmoides(6.90%), and Lepomis macrochirus (4.90%) contributed to these differences of fish assemblages between group A and B. Group A showed higher relative abundances of exotic species such as M. salmoides and L. macrochirus, while Z. platypus and Z. koreanus which are the common species in Korea, were the most dominant species in group B. Based on the length-weight relationship of Z. platypus, b values were varied from 2.82 to 3.80, indicating that growth patterns of the species were spatially different. This study could be served as baseline data for understanding fish fauna, assessing habitat characteristics based on the fauna, and identifying health conditions of Z. platypus in the Seomjin River system.

• Korean Journal of Ichthyology
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• v.35 no.4
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• pp.285-293
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• 2023

This study conducted to investigate the temporal and spatial variations in the fish community structure in the Seomjin River estuary (ES1~ES3) and Gwangyang Bay (ES4~ES8). Surveys were conducted at eight points between May and September from 2020 to 2021. A total of 5,111 fish were collected, representing 42 families, 68 genera, and 78 species. The dominant species collected during the survey period were Pennahia argentata, with 2,370 individuals and a relative abundance of 46.4%. Also, as a subdominant species, Nuchequula nuchalis, 1643 individuals were caught, accounting for 32.1% relative abundance. According to Bray-Curtis similarities, observations were divided into three groups based on the fish community composition, and they were further categorized into brackish water areas, coastal areas, inner areas, and outer areas. Group 1 mainly consisted of fish inhabiting freshwater and brackish water areas, while group 3 exclusively contained fish living in marine waters. ANOSIM (Analysis of Similarity) analysis revealed a significant difference (ANOSIM R=0.783, p=0.001) between Group 2 and Group 3, and the species contributing to these clusters were P. argentata and Muraenesox cinereus. The study demonstrated spatial changes in the fish community structure from the Seomjin River estuary to the outer coast. The findings highlight the importance of long-term monitoring of major species that exhibit spatial variations, serving as essential foundational data for the conservation and management of economically significant fish species.

• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.5
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• pp.513-523
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• 2017

We evaluated the viability of phytoplankton along the salinity gradient in the flood and ebb tides of spring tide of February and the ebb tide of neap tide of March 2017 in the Seomjin River Estuary. Additional laboratory experiments were also conducted to determine the reason of the pH changes along the salinity gradient using the field natural sample in February. In field, saltwater was well mixed at downstream vertically and the salinity gradient was horizontally appeared toward upstream of freshwater zone. There were strong negative correlations between salinity and nutrient (nitrate + nitrite R=0.99, p<0.001, and silicate R=0.98, p<0.001), implying that those two nutrients of freshwater origin were gradually diluted with mixing the saltwater. On the other hands, relatively high phosphate concentration was kept in the stations of saltwater over 15 psu, indicating that it was caused by resuspended sediments of Gwangyang Bay and downstream by tidal water mixing.Among phytoplankton community structure in winter, Eucampia zodiacus have occupied to be c.a. 70 % in the most stations. Based on the field survey results for survivability of phytoplankton by phytoPAM instrument, there was positive correlations between salinity and chlorophyll a (R=0.82, p<0.001) and, salinity and active chlorophyll a (R=0.80, p<0.001), implying that the dominant marine diatom species may have significantly damaged in low salinity conditions of upstream. Also, maximum mortality rate of phytoplankton caused by low salinity shock was appered to be 75% in the upstream station. In particular, the pH in spring tides of February had tended to increase with high phytoplankton accmulated stations, suggesting that it was related with absorption of $CO_2$ by the photosynthesis of dominant diatom. In laboratory experiments, phytoplankton mass-mortality caused by low salinity shock was also occurred, which is confirmed with reducing the photosynthetic electron transport activity. Following the phytoplankton mass-mortality, bacteria abundance was significantly increased in 24 hours. As a result, the mass-proliferating bacteria can produce the $CO_2$ in the process of biodegradation of diatoms, which can lead to pH decrease. Therefore, marine phytoplankton species was greatly damaged in freshwater mixing area, depending on along the salinity gradient that was considered to be an important role in elevating and reducing of pH in Seomjin River Estuary.

• Proceedings of The Korean Society of Agricultural and Forest Meteorology Conference
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• 2015.08a
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• pp.135-141
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• 2015

• Ecology and Resilient Infrastructure
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• v.9 no.2
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• pp.100-106
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• 2022

The relationships between river length and weir density versus fish species observed were analyzed for 210 local rivers in the Seomjin River system (SJR). A nonlinear exponential relationship between river length and number of fish species were observed. Model coefficient was 0.03 and coefficient of determinant (R²) was 0.59, meaning that about 59.0% of total variance was explained by river length variable. Predicted value by model and observed number of species showed a difference. About 110 local rivers (about 52.4%) showed lower value than predictive value. The average index of weir's density (IWD) in the SJR was about 2.7/km, which was significantly higher than that of other river basins. As a result of nonparametric 2-Kimensional Kolmogorov-Smirnov (2-DKS) analysis based on the IWD, the threshold value affecting fish diversity was about 2.5/km (D_max=0.048, p<0.05). Above the threshold value, it means that the number of fish species would be decreased. In fact, the ratio of the expected species to the observed species was lowered to less than 70%, when the IWD is higher than the threshold value. To maintain aquatic ecological connectivity in future, it is necessary to manage IWD below the threshold value.