• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.19 no.2
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• pp.147-154
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• 2014

Bacteria play an important role in biogeochemical cycles in marine environments and their functional attributes in ecosystems depend primarily on species composition. In this study, seasonal variation of bacterial diversity was investigated by pyrosequencing of 16S rDNA in surface sediment and overlying seawater collected in the south East Sea, planned for the site of $CO_2$ sequestration by the carbon capture and storage (CCS) project. Gammaproteobacteria was dominant in the sediment in most seasons, whereas Alphaproteobacteria was a most dominant group in the overlying water. Thus, the bacterial diversity greatly differ between sediment and seawater samples. On the genus level, bacterial diversity between two habitats was also different. However, the number of genera found over 5% were less than 10 in both habitats and the bacterial community was composed of a number of diverse minor or rare genera. Elevation of $CO_2$ concentration during a $CO_2$ storage process, could result in change of bacterial diversity. Thus, this study will be very useful to access the effect of $CO_2$ on bacterial diversity and to predict functional change of the ecosystem during the process of CCS project.

• Journal of the Korean Society for Marine Environment & Energy
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• v.7 no.1
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• pp.13-21
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• 2004

Temporal changes of Chl-α, physical and chemical factors were investigated by diurnal observation at 2-hour interval at three fixed stations in the western Chinhae Bay from 12 Aug. to 13 Aug. 1999. Difference of dissolved oxygen between surface and bottom layer was maximum when the thermocline were strong. Organic distribution such as COD was affected by the growth of phytoplankton. Limitting factor was nitrogen, that is, inorganic nitrogen plays a significant role on regulating the algal growth. Surface distribution of dissolved inorganic nitrogen was very low compared to bottom layer by uptake of organisms. Maximum value of Chl-α at station C2 and C11 were observed from subsurface layer, ranges of which exceeded possibility concentration of red tide outbreak, 10 mg/㎥. On the other hand, that of C15 exist at surface layer. In this area, DIN and DIP concentrations increased by input sources such as rainfall and benthic flux before the bloom of phytoplankton. Accumulation of phytoplankton occurred at subsurface layer by the rapid uptake of DIN, especially nitrate ion, when strong thermocline existed as approach to the afternoon, which led to the increase of organics in water column and oxygen deficiency water mass at bottom layer until late at evening. Since then, DIN increases gradually as water temperature decrease to minimum. The quantitative understanding of nitrogen of fluxed to and from the various sources is necessary for environmental management.

• Korean Journal of Ecology and Environment
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• v.36 no.3 s.104
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• pp.311-321
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• 2003

We surveyed physico-chemical properties of bottom water and sediment to evaluate the influence of sediment on the eutrophication in the downstream of Nagdong River from 1998 to 2000. From May to August, DO concentration of bottom waters dropped below 5 mg $O_2/l$ and $NH_4\;^+$ and $PO_4\;^{3-}$ concentrations significantly increased in the bottom waters, resulting in the great differences between surface and bottom waters. Fluxes across water-sediment interface would be substantially active in this period. The serial orders of the water fertility or eutrophication were Joman River > Sonagdong River > Nagdong River. The organic nutrient contents of sediment increased toward the lower parts of the river system. Organic contents of the sediment would be under the influence of water pollution and exhibited a negative correlation with sediment bulk-density or particle size. The concentrations of exchangeable inorganic nutrients of sediment were greater than those of pore waters, and $PO_4\;^{3-}$, $NH_4\;^+$ and $SiO_2$ increased along the sediment depth. $PO_4\;^{3-}$ and $NO_3\;^-$ concentrations of the pore water were less than the overlying waters, while NH4+ and $SiO_2$ concentrations showed opposite trends. Exchangeable nutrients of sediment could be the repository for t]me nutrient exchange in the water-sediment interface.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.10
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• pp.490-498
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• 2020

In this study, the seismic performance of low-rise piloti buildings with eccentric core (shear wall) positions was analyzed and reviewed. A prototype was selected among constructed low-rise piloti buildings with eccentric cores designed based on KBC2005. The seismic performance of the building showed plastic behavior in the X-direction and elastic behavior in the Y-direction. The inter-story drift is larger than that of a concentric core case and has the maximum allowed drift ratio. The displacement ratio of the first story is much larger than that of upper stories, and the frame structure in the first story is vulnerable to lateral force. Therefore, low-rise piloti buildings with eccentric cores need to have less lateral displacement, as well as reinforcement of the lateral resistance capacity in seismic design and seismic retrofit.

• Journal of the Korean Society of Marine Environment & Safety
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• v.13 no.1 s.28
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• pp.93-102
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• 2007

Particle materials sink in bottom and dissolved inorganic substances release from sediment and many kinds of materials continuously exchange in sediment and water column as well as transfer and transformation in sediment. The study of sediment quality means the state of sediment pollution relation of the water quality, sediment biota, materials fluxes between sediment and water column, transformation of materials in sediment is being important in recent. The state of sediment quality imply that the history of water pollution for long time, because the sediment quality does not change temporally. The sediment quality of bottom water can be used as a good indicator of pollution at present and in future. The major index of sediment qualities are the content of nutrients and hazard materials such as metals, Ignition Loss (IL), Total Sulfur (TS), Oxidation Reduction Potential (ORP), sediment COD, color, odor and the release of nutrients from sediment. However, there are some arguments between researchers about compare to estimation of sediment quality and sampling and analysis of sediment. In this study, I will introduce the method of sediment sampling, analyzing and estimating of the sediment pollution.

• Journal of the Korean Society of Marine Environment & Safety
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• v.22 no.7
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• pp.854-862
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• 2016

In summer 2010, we measured the concentration of dissolved oxygen (DO) and nutrients in the water collected at the bottom of Cheonsu Bay, off the west coast of Korea. We also measured nutrient fluxes across the sediment-water interface by deploying a fully-automated benthic lander, which collected time-series water samples inside a benthic chamber. We confirmed on-going hypoxia in the northern parts of the bay where polluted lake water was discharged. DO content in the water at the bottom was 2 mg/l, compared to 5 mg/l at the mouth of the bay in the south. Nutrient concentrations showed a trend that was opposite to that of DO. The variation of N/P ratios implies phosphate desorption and a release of nutrients caused by hypoxia. The organic carbon oxidation rate and oxygen consumption rate in the northern parts of the bay were about twice as fast as those at the mouth of the bay. Benthic fluxes of nutrients in the northern part of the bay were 4 to 6 times higher than those at the mouth. Our results imply that it is important to understand the role of hypoxia events to make an accurate estimation of material fluxes across the sediment-water interface.

• Journal of the Earthquake Engineering Society of Korea
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• v.11 no.5
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• pp.61-69
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• 2007

The main purpose of this study is to provide a basic information for the seismic capacity evaluation and the seismic design of low-rise reinforced concrete (RC) shear wall buildings, which are comprised of a pilotis in the first story. In this study, relationships between strengths and ductilities of each story of RC buildings with pilotis are investigated based on the nonlinear seismic response analysis. The characteristics of low-rise RC buildings with pilotis are assumed as the double degree of freedom structural systems. In order to simulate these systems, the pilotis is idealized as a degrading trilinear hysteretic model that fails in flexure and the upper story of shear wall system is idealized as a origin-oriented hysteretic model that fails in shear, respectively. Stiffness properties of both models are varied in terms of story shear coefficients and structures are subjected to various ground motion components. By analyzing these systems, interaction curves of required strengths for various levels of ductility factors are finally derived for practical purposes. The result indicates that the required strength levels derived can be used as a basic information for seismic evaluation and design criteria of low-rise reinforced concrete shear wall buildings having pilotis structure.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.8 no.2
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• pp.177-186
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• 2003

The influences of horizontal and vertical flow components including the stratification of water column and the wind field on the formation of oxygen-deficient water in summer in Jindong Bay, northern part of Chinhae Bay, were examined. Temperature, salinity and dissolved oxygen in seawater, and direction and velocity of wind were observed in Jindong Bay from March 1998 to February 1999. Low concentration of 5 mg/L in dissolved oxygen (DO) appeared at the bottom layer from May to September. Extremely low DO concentration less than 3 mg/L was investigated in summer (July to August) when stratification was strongest due to abrupt vertical gradients of temperature and salinity in water column. Bottom waters with the extremely low DO concentration were observed even in spring (May to June) at the inner part of the bay. In summer (August to September), the bottom waters with the low DO concentration (less than 5 mg/L) existed at the water depth from 4 to 6 m, being moved upward to the surface layer compared to other seasons. Vertical components of residual flow, calculated by the direction and velocity of wind, in Jindong Bay in summer showed that locally prevailed northerly and westerly wind resulted in downwelling flow at the outer part of the bay and conversely, upwelling at the inner part of the bay. In addition, bottom current at the outer part corresponding to the downwelling area directed to the inner part, probably resulting in a transport of the particulate organic matter settled at the bottom waters to the inner part of the bay. The oxygen-deficient watermass, which was formed at the bottom layer of the inner part, was likely to transported to the surface layer by the upwelling flow.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.spc
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• pp.18-22
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• 2022

Because it is difficult to apply direct and optical detection techniques to sunken hazardous and noxious substances (HNS), effective acoustic detection techniques are required to detect sunken HNS in water. In this study, the possibility of acoustic detection of sunken HNS was investigated through backscattering signal measurement experiments using chloroform, a sunken HNS. After establishing a pool in an acrylic tank, backscattering signals were measured according to the presences or absence of chloroform by varying the grazing angle from 90° to 50° in 0.5° intervals using a pan&tilt system. A directional transducer transmitted and received sinusoidal signals with a frequency of 200 kHz and a pulse length of 25 ㎲ in a monostatic state. When chloroform was deposited, the received level of the backscattering signal at the interface between water and chloroform became low at a grazing angle of approximately 80° or smaller. Based on the backscattering signal results obtained at the interface between water and chloroform, the possibility of acoustic detection of sunken HNS was demonstrated.

• Journal of the Korean Society of Marine Environment & Safety
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• v.29 no.6
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• pp.562-575
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• 2023

In an effort to improve water quality, the South Korean government has implemented measures to increase seawater circulation in Saemangeum Lake. We analyzed the effect of increasing the frequency of seawater circulation based on salinity levels and bottom water exchange in the lake, using an environmental fluid dynamics code model. When the sluice gate opening and shutting frequency increased from once to twice per day, the internal water level of Saemangeum Lake increased by up to ~0.7 m. The salinity increased by 2.12 psu near the western breakwater and decreased by 1.18 psu near the freshwater inlet. We analyzed the extent of bottom water exchange using a particle tracing method and observed that the residual rate of particles shallower than 5 m in water depth decreased by 2.52% in Case 2 (opening and shutting twice per day) compared to Case 1 (opening and shutting once per day). This indicates that increasing the frequency of sluice gate opening and shutting would promote enhanced bottom water exchange. Consequently, the increased salinity and bottom water exchange associated with increased seawater circulation are expected to improve water quality in Saemangeum Lake.