• Korean Journal of Fisheries and Aquatic Sciences
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• v.37 no.6
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• pp.469-477
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• 2004

This study examined distributional patterns of Asterias amurensis in Tongyeong, the central South Sea of Korea. The density of the sea star was estimated at 10 chosen sites in the inner and the outer parts of the Tongyeong coast from December 2000. The mean density of the species in this area was $2.4ind./m^{2}$. The seasonal surveys conducted at 3 arbitrary chosen sites (i.e., sea cage, reef and soft sediment) also showed that the abundance of the species at the sea cage site $(density:\;3.6\;ind./m^{2};\;biomass:\;250.7\;gwwt/m^{2})$ was significantly higher than at the reef site $(density:\;1.7\;ind./m^{2};\;biomass:\;63.5\;gwwt/m^{2})$ and the soft sediment site $(density:\;0.4\;ind./m^{2};\;biomass:\;18.9\;gwwt/m^{2})$. Densities were higher at sea cages areas than at reefs and soft bottom sites. At sea cage site, A. amurensis population exhibited a strong aggregated distributional pattern. In contrast, at reef and soft bottom sites, A. amurensis population showed a random distributional pattern. The spatial difference in prey species and its abundance was the primary factor determining the spatial heterogeneity of the sea star in its behavior characteristics. Experiments on the feeding preference indicated that A. amurensis had a strong selectivity on its prey, but this selectivity varied between populations living in different sites. In particular, A. amurensis populations at the reef site showed a strong selectivity on various sessile and mobile animals living in reef areas, suggesting that these animal groups may play a role as "windows for the survival of A. amurensis". These results suggest that the distribution of A. amurensis in Tongyeong is closely associated with abundance of prey species and the bottom composition.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.23 no.3
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• pp.185-191
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• 1990

A study on the characteristics of phosphorus sedimentation in Nakdong Estuary Barrage was conducted in June and July, 1989. Cylindric type sediment trap was designed for collecting of downward material. Downward flux and settling velocity of downward material were $296g/m^2/d$, 1.25m/hr in mid-layer and $955g/m^2/d$, 3.31m/hr in bottom-layer, respectively Downward flux and settling velocity of phosphorus were $0.64g/m^2/d$, 0.85m/hr in mid-layer and $1.97g/m^2/d$, 1.89m/hr in bottom-layer, respectively. Fractional composition of organic phophorus in downward material was $51.9\%$ in mid-layer water and $48.3\%$ in bottom-layer water. According to the result of this study, sedimentation of phosphorus plays an important role as a sinking effect in Nakdong Estuary Barrage.

• Journal of the korean society of oceanography
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• v.33 no.4
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• pp.168-177
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• 1998

Five and a half months after the Keumdong oil spill accident on the 21$^{st}$ of September 1993, 34 seawater samples and 94 sediment samples were collected from Kwangyang Bay and Namhaedo area to assess its environmental impacts. Hydrocarbon concentration in the seawater ranged from 0.8 to 9.2 ${\mu}$g/1 with an average of 3.3 ${\mu}$g/1. This average value was nearly the same as the value(3.7 ${\mu}$g/1) before the oil spill accident. This suggests that by the early March of 1994 majority of the coastal water in the study area restored to its background hydrocarbon concentration before the oil spill accident. Nutrients, heavy metals and other general environmental parameters of the seawater did not show any aggravated seawater quality compared with the previous records. From the regression analysis of time-course observation of hydrocarbon in the seawater, except the sediment environment, the effect of oil spill on the water column was estimated to last at least 4 months in the study area after the oil spill accident. In the shoreline sediments, oil deposits were, however, still found at the high water marks at several stations, and very high values were found in the west of Namhaedo, ranging from 3.7 to 40.1 mg/g of wet sediment. Gas chromatography of these samples showed a very distinct Bunker C chromatogram identical to the Keumdong oil spill. Hydrocarbons in the subtidal bottom sediments in the study area and the reference stations (YB and CB) ranged from 0.45 to 18.08 ${\mu}$g/g of wet sediment with an average of 3.09 ${\mu}$g/g. West of Namhaedo (Stations Bl2-B33) generally showed much higher values than inner Kwangyang Bay and in Chinju Bay. Chinju Bay generally showed the lowest value among the study area. Subtidal bottom sediments in inner Kwangyang Bay and Chinju Bay seemed to be less affected than west of Namhaedo. Heavy metal concentrations in the sediment were relatively higher in the Kwangyang Bay than in the Chinju Bay. However, metal concentrations in the study area were in general comparable to the reference areas.

• Journal of Aquaculture
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• v.13 no.1
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• pp.39-46
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• 2000

Successive management of prawn farm is strongly dependent upon monitoring of pond seawater quality which is generally influenced by an excessive food supplied sediment type and phytoplankton composition in the pond. For good condition of seawater quality it must need exchangning of fresh seawater by tidal current. Two distinct shrimp ponds Galha and Yunho which were different in seawater exchanging system and sediment type were selected to understand how some factors affected to seawater and sediment qualities in the pond. Prawn growth was also determined. Galha pond characterized by sand bottom with water exchanging by turn of the tidal current accumulated 1.8 mgS/g-dry as sulfide in sediment while Yunho pond mud- bottomed with seawater exchanging of pumping system showed 4.7mgS/g-dry when it was highest, Ammonia-N and hydrogen sulfide measured in the seawater were 0.31mg/${\ell}$ and 21.2 ${\mu}$${\ell}$/${\ell}$in Yunho and 0.10mg/${\ell}$and 10.8${\mu}$${\ell}$/${\ell}$in Galha pond respectively. Dissolved oxygen remained below 6.0mg/${\ell}$ in Galha and 5.0mg/${\ell}$in Yunho pond from June through August. Less growth of prawn was found in Yunho pond than in Galha pond. Prawn growth expressed as body length and weight were 138.3mm 22.9g in Yunho pond while they were length 158.2mm and 28.9g in Galha pond respectively when they were harvested in October. These results indicate that higher levels of ammonia-N and hydrogen sulfide and lower dissolved oxygen in bottom seawater of Yunho pond might affect the growth of cultured prawn.

• The Journal of the Acoustical Society of Korea
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• v.28 no.5
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• pp.424-431
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• 2009

This study investigates the difference of sound velocity (compressional wave velocity) between gas hydrate-bearing sediments and nongas hydrate-bearing sediments in the Ulleung Basin, East Sea. We use a dataset measured from one site in the central part of the Ulleung Basin. Sound velocity for gas hydrate-bearing sediment shows the range from 1600 m/s to 2200 m/s. However, the value for nongas hydrate-bearing sediment is mostly around 1500 m/s, being less than 1400 m/s below 140 m subbottom depth. This trend is probably due to the presence of free gas below BSR (Bottom Simulating Reflector). Gas hydrate-bearing sediments show high value (maximum 150 Ohm-m) of resistivity. The physical properties between gas hydrate-bearing sediment and nongas hydrate-bearing sediment are characterized by the different patterns due to the presence of gas hydrate in comparison with those of marine unconsolidated sediments. Therefore, in order to investigate acoustic and physical properties for gas hydrate-bearing sediments, the study for the occurrence type and the amount of gas hydrates should be conducted simultaneously.

• Ocean Science Journal
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• v.40 no.1
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• pp.1-10
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• 2005

Variations in species diversity and abundance of polychaete taxocenes that occurred in 1980-1989 under different contamination levels of bottom sediments were studied in three areas of Peter the Great Bay. The most polluted area was shown to be the Golden Horn Inlet where contaminant contents in the bottom sediments exceed the threshold values of negative biota alterations. Amursky Bay is characterized by a moderate level of contamination, while Ussuriysky Bay has the lowest level of contamination. Pollutant contents vary considerably within the same areas and their separate patches are polluted differently. An integral index characterizing the contamination of bottom sediments is proposed. This index is an average grade of the rank value of contaminant contents in sediments. The index was used to compare the contamination level and data on polychaete species diversity and abundance. The highest species diversity of polychaetes is found in the least affected zones. Monotonous decrease of the species number, as well as decrease in the indices of diversity and evenness, is correlated with pollution level increases. Significant growth of the average polychaete biomass and polychaete density is observed in the case of an increase of contamination from low to moderate levels. Conversely, the biomass and abundance of polychaetes decline following an increase in contamination.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.17 no.3
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• pp.129-137
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• 2005

In this study, we developed a model to simulate the interaction between sediment and the overlying water. The model deals with water-sediment interaction in terms of the sedimentation of organic detritus from the pelagic zone into the benthic zone and the release of nutrients occurring in the reverse direction. The model was tested and verified by comparing the predicted release rates of phosphorus from the sediment in Osaka Bay with actual observed values. The results accurately reproduced the seasonal change in release rates. The results well represented seasonal change of the release rates. A long-term prediction of water and sediment quality was performed for the period from 1950 to 1999. Nutrient loads from land and the boundary conditions of 3-D baroclinic flows were season-adjusted. The model accurately reproduced the changing trends in phosphorus, nitrogen, and COD concentrations in Osaka Bay over a long period of time.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.20 no.6
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• pp.611-620
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• 2008

The process of sediment transport has a very complex mechanism due to waves, currents and bottom topography changes. Usually, beach erosion occurs from various causes such as non-equilibrium sediment transport condition, construction of seawall and rip currents. Therefore, when we try to reduce and develop countermeasures for beach erosion, we have to know the main mode and direction of sediment transport that causes beach erosion. In this study, the process of sediment transport on Jeonchon-Najung beach and main causes of beach erosion have been studied. Field investigation data, aerial photos and the results of numerical model test were used in the analysis. As a result, it was realized that the main causes of beach erosion at Jeonchon-Najung beach was due to the construction of fishery harbors and a seawall.

• Journal of The Geomorphological Association of Korea
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• v.26 no.1
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• pp.41-57
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• 2019

The grain size characteristics of river sediments and the characteristics of bedrock were investigated for the 24km section of the Dong River upstream of the Han River. The bedrock of the study area is various limestone belonging to the Paleozoic Choseon limestone group, and Mesozoic sandstone and conglomerate occur in some areas. Most of the river channel is made of limestone, and most of the river bottom is covered with fluvial sediments. More than 70% of these sediments are sandstone and conglomerate, rather than limestone which forms the basis of the valley. Sediment particles seem to have been supplied upstream of the study area rather supplied from the slope near of the channel. It is difficult to find the statistically significant difference in the shape of the sediment particles of limestones and non-limestones. However, limestones has platy forms rather than block forms, it can be assumed that the limestone was supplied from the surrounding valley wall and transported over a short distance. The particle sizes of DG1~DG2(the upstream section) are decreasing in the downstream direction. However, at DG3, which is a tributary, Jijangcheon, confluence particle size increases and at DG4 particle size increases more. In the case of DG4, it may be influenced by the influx of tributaries, but it also can be supposed as the impact of the large flood in 2002. In the downstream parts(DG5~DG7), the particle size decreases exponentially with distance. The rebound strength of stream sediments and bedrock was measured by using Schmidt hammer. Limestone showed lower rebound strength than non-limestone. According to the results of the sediment and bedrock, it can be seen that the sandstone and conglomerate with high rebound values pass through valley with the relatively low strength limestone. The sediments of limestone were decreased in grain size more rapidly than those of limestone sediments.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.29 no.3
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• pp.154-161
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• 2017

The purpose of this study was to investigate the change of length, opening width, and number of openings effecting on topography change around artificial reefs under erosive wave condition. Hydraulic model test was conducted to see sediment transport around the structures and the relation among the installation condition of the artificial reefs, generated velocity, wave deformation, and topographic change was reviewed. Experimental results show that the sediment transport rate was reduced; however, the scour around the structures was increased under the condition of having a single opening compared to the structures having a plurality of openings which shows inversely proportional to the size of Lr/W.