• Journal of Wetlands Research
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• v.21 no.1
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• pp.84-94
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• 2019

The Seocheon and Yubu Island mudflats in Geum Estuary are important stopover sites for migratory birds as energy supplementation area in the East Asia-Australasian Flyway. Benthic invertebrates in the tidal flats are important food resources for the migratory birds. In other words, benthic invertebrates in the tidal flats play an important ecological role in energy flow. This study was conducted to investigate the relationship between benthic invertebrate assemblages and environmental factors in Seocheon and Yubudo tidal flats in the Geum Estuary. As a result of the benthic invertebrate assemblage during the fall migration season, the total species number was 147, density and biomass were $1,772{\pm}1,342individuals/m^2$ and $445.1{\pm}807.6g/m^2$, respectively. Based on the appearance species and the density data, the result of analysis of mutual similarity among sampling sites was divided into two groups. Group A was the Macrophthalmus-Heteromastus community and Group B was the Spio-Urothoe-Mandibulophoxus community. Group B showed higher mean species number, density and biomass than Group A. The BIO-ENV analysis showed that the benthic invertebrate assemblages were most affected by the combination of sand content % and sediment sorting (${\rho}=0.500$). The variables of significant relationship with species number and biomass were sediment sorting (p=0.015) and the pore water DO(Dissolved Oxygen, p=0.003) in sediment, respectively.

• Korean Journal of Ecology and Environment
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• v.52 no.3
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• pp.274-283
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• 2019

Beta diversity is an efficient means of assessing the spatial variation in community composition among sites. To present fish community variation and LCBD (Local Contribution to Beta Diversity) among sites in stream, 6 sampling sites were selected in Cheonggye stream. Fish communities, environmental and habitat variables were collected at sites from April 2014 to October 2015. We used the total variance of the fish community data table (site-by-species community table) based on different forms, presence-absence, abundance, and Hellinger transformation, to estimate and compare beta diversity and LCBD. Fish community data table transformed by Hellinger distance showed the higher values of beta diversity than presence-absence and abundance data table. A similar patterns of LCBD were observed with presence-absence and Hellinger transformed data table. Low value of beta diversity calculated by community data table with abundance was due to the non-normality of fish assemblage data. Additionally, correlation coefficients were calculated to evaluate the relationships among LCBD, community indices and physicochemical variables. LCBD showed negative correlation coefficients with Shannon diversity. Overall, application of beta diversity analysis is an efficient method of addressing spatial variation of fish communities and ecological uniqueness of the sites in stream.

• Korean Journal of Ecology and Environment
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• v.52 no.3
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• pp.202-209
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• 2019

The primary productivity and production rate of photosynthetic pigment of periphyton and phytoplankton were estimated using a $^{13}C$ stable labeling technique in May 2011, in the waterfront of Lake Paldang. Primary productivity of periphyton ($28.15mgC\;m^{-2}\;d^{-1}$) was higher than phytoplankton production ($0.14mgC\;m^{-2}\;d^{-1}$). The net production rates of photosynthetic pigments(Chl a and Fucoxanthin) of periphyton were $2.53ngC\;m^{-2}\;d^{-1}$ and $0.12ngC\;m^{-2}\;d^{-1}$, respectively. On the other hand, the net production rate of pigments on phytoplankton (Chl a : $0.023ngC\;m^{-2}\;d^{-1}$, Fucoxanthin: $0.002ngC\;m^{-2}\;d^{-1}$) was lower than that of periphyton. Specific production rates of individual pigments of phytoplankton to the total primary productivity indicate the predominance of diatom (Fucoxanthin) species in phytoplankton assemblage in Lake Paldang. The net individual production rate of pigments by $^{13}C$ tracer was a useful tool to estimate the contribution of each phytoplankton class for total primary productivity, and it is possible to calculate the seasonal contribution of each phytoplankton class to the total primary productivity in the aquatic ecosystems. This study is the first report on photosynthetic pigment production rates of periphyton and phytoplankton.

• Journal of Environmental Impact Assessment
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• v.30 no.4
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• pp.203-214
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• 2021

Assessment of benthic quality status was implemented along the subtidal areas of Jindo and Jejudo to understand faunal structure of polychaete assemblages and ecological quality of the benthic environment. Sediment analysis was characterized by well sorted of both mud and sand in Jindo, and a little higher sand in Jejudo instead. A total of 68 polychaete species were found at 14 sampling stations with a mean density of 231 inds./m², and 61 species, 167 inds./m² and 62 species, 295 inds./m² in Jindo areas and Jejudo areas. Dominant species found in Jindo areas were Heteromastus filiformis, Ampharete arctica, Prionospio sp., Sigambra tentaculata, Thelepus sp. and Amphicteis gunneri, Ampharete arctica, Prionospio sp., Spiochaetopterus costarum, Heteromastus filiformis in Jejudo. With a help of cluster analysis, it was found that the sampling stations showed distinctive pattern of the distribution pattern and benthic quality status in Jindo and Jejudo except sampling station numbers 5 and 6, respectively. AMBI analysis the results were 1.2-3.4, grade V benthic polychaetes did not appear. It was evident that both Jindo and Jejudo had different sedimentary characteristics as well as distribution pattern of polychaete assemblages.

• Journal of the Korean earth science society
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• v.42 no.6
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• pp.677-687
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• 2021

In this study, we analyzed diatoms from core RS15-GC41 collected in Iselin Bank, Ross Sea. A total of 24 genera and 35 species of diatoms are identified, and the having valve abundance of diatoms varies from 0.2 to 28.6×10⁶/g. Four diatom assemblage zones are established by the vertical distribution of diatoms, and changed with a cycle of 100 kyrs. RS15-GC41 were deposited over the last 400 kyrs (corresponding to Marine Isotope Stages 1-11). The open-water species Fragilariopsis kerguelensis, Rhizosolenia styliformis, and Thalassionema nitzschioides abundantly occurred in interglacial periods. Whereas, Actinocyclus actinochilus abundantly dominant during the glacial periods. The distribution of these diatoms indicated, it can be seen that the sea-ice extent was larger and lasted longer during MIS 7, 9, and 11 than that of MIS 1, 3, and 5. Moreover, Paralia sulcata was abundantly predominant in MIS 7, 9, and 11; this finding suggests likely indicating that P. sulcata was transported from the coastal/inner shelf area to the study site, during accumulated in the sediments, reworked with the influx of ice-rafted debris by the currents

• Korean Journal of Ichthyology
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• v.33 no.1
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• pp.22-30
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• 2021

This study aimed to determine the monthly fish species composition in the eelgrass bed of Yeocha on Hansando Island, Korea, and to obtain fish species data by comparison with the nearby Bongam. The species composition was determined from monthly samples collected by a surf net from August 2009 to July 2010. During the survey, total 2,394 individuals of 29 species and 10,378 g of fish were collected. The dominant species were Gymnogobius heptacanthus, followed by Takifugu niphobles, Rudarius ercodes, Chaenogobius annularis, and Ditrema temminckii, accounting for 89% of the total individuals sampled and 83% of the fish biomass collected. The fish assemblages in the eelgrass bed varied seasonally; the number of individual fishes increased in May and was highest in July, whereas the biomass attained its highest level in April and subsequently decreased. This study confirms that the seagrass bed plays an important role as a fish nursery ground, and it is necessary to investigate changes in the coastal fishes of the southern coast via periodic surveys.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.12
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• pp.889-898
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• 2022

In this paper, parallel computing method on the three-dimensional electromagnetic field is proposed. The present electromagnetic scattering analysis is conducted based on the time-harmonic vector wave equation and the finite element method. The edge-based element and 2^nd -order absorbing boundary condition are used. Parallelization of the elemental numerical integration and the matrix assemblage is accomplished by allocating the partitioned finite element subdomain for each processor. The graph partitioning library, METIS, is employed for the subdomain generation. The large sparse matrix computation is conducted by MUMPS, which is the parallel computing library based on the multi-frontal method. The accuracy of the present program is validated by the comparison against the Mie-series analytical solution and the results by ANSYS HFSS. In addition, the scalability is verified by measuring the speed-up in terms of the number of processors used. The present electromagnetic scattering analysis is performed for a perfect electric conductor sphere, isotropic/anisotropic dielectric sphere, and the missile configuration. The algorithm of the present program will be applied to the finite element and tearing method, aiming for the further extended parallel computing performance.

• Korean Journal of Ecology and Environment
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• v.55 no.4
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• pp.285-293
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• 2022

Sampling gears for collecting fish are diverse, and the community of fish varies according to the selection and characteristics of the sampling gears. The present study compared the characteristics of fish communities in Yedang reservoir using four sampling gears (kick net, cast net, gill net, and fyke net). The kick net and cast net were inefficient in collecting the number of individuals. However, they increased the species diversity of fish inhabiting the waterfront. Although not many individuals were collected, the gill net mainly collected large fish. The largest number of individuals was collected in the fyke net, and the dominance was high due to the high species selectivity. Through Self-Organizing Map (SOM) analysis, large fish were collected in the gill net, whereas small fish were collected in the fyke net. The characteristics and efficiency of the fish differed depending on the sampling gears. It is expected that researchers will need to use it appropriately according to the characteristics of the sampling gears when investigating the fish community.

• Journal of the Korean earth science society
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• v.44 no.1
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• pp.36-46
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• 2023

In this study, small bird tracks from the Cretaceous Sanbukdong Formation in Gunsan City, South Korea, were briefly described. Detrital zircon SHRIMP U-Pb dating was conducted of the tuffaceous sandstone from the formation to determine the depositional age of the vertebrate track-bearing strata. Small bird tracks are not well-preserved but divided into two types: two consecutive tracks and three isolated tracks. They are small, asymmetric, slender, functionally-tridactyl tracks, which lack a web between digits. The consecutive and isolated tracks were identified as Koreanaornis dodsoni? and Koreanaornis ichnosp., respectively. This study adds avian tracks to the Sanbukdong tetrapod track assemblage composed of theropods, ornithopods, and pterosaur tracks. According to the U-Pb dating, the estimated age of the Sanbukdong Formation is 112.5±5.8 Ma, regard as the Aptian Stage, representing the maximum depositional age for the Sanbukdong Formation. The Sanbukdong Formation can be correlated with the lower part of the Jinju Formation in the Gyeongsang Basin. Thus, small avian tracks may represent the oldest Korean occurrence of Koreanaornis.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.6A
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• pp.495-502
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• 2010

A study for the nonlinear analysis method of flexural behavior of concrete girders strengthened with unbonded prestressed CFRP plates is presented. The concrete girders strengthened with unbonded prestressed CFRP plates exhibit more complex nonlinear behavior due to the slip between the concrete girder and the CFRP plates than the case of bonded CFRP plates. The unbonded CFRP plate is modeled as an assemblage of the curved elements both ends of which are rigidly linked to the nodes of fibered frame elements. The slip effect of the unbonded CFRP plate is taken into account using the force equilibrium relationship at each node. To evaluate the validity and the capability of the proposed analysis method, the ultimate analysis results of the concrete beams strengthened with unbonded prestressed CFRP plate are compared with the experimental results obtained from other investigators. The proposed analysis method is found to predict ultimate behaviors of these beams fairly well. Additionally the time-dependent deformations of the concrete beam seems to have little influence on the ultimate behaviors of concrete beams strengthened with unbonded prestressed CFRP plate, and the cracks of the concrete beam which occurred before strengthening it with CFRP plate are found to have almost no influence on the ultimate capacity of the beam.