• Development and Reproduction
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• v.12 no.2
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• pp.195-202
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• 2008

The gonadosomatic index, germ cell differentiation, and the ovarian cycle in female jicon scallop, Chlamys farreri were studied by histologic and cytologic observations. In the early vitellogenic oocyte, the Golgi complex, mitochondria and rough endoplasmic reticulum were involved in the formation of lipid droplets. In the late vitellogenic oocyte, exogenous substances, namely, glycogen particles and lipid granular substances appeared in the germinal epithelium passed into the ooplasm through the microvilli of the envelope. Yolk granules and multivesicular bodies were involved in the formation of proteinecious yolk granules in the late vitellogenic oocyte. Vitellogenesis occurrs by endogenous autosynthesis and exogenous heterosynthesis. The auxiliary cells function as nutritive cells in the formation and development of the previtellogenic and early vitellogenic oocytes in their earlr stages. Monthly changes in the gonadosomatic index were closely associated with ovarian developmental phases. The reproductive cycle of this species can be classified into five stages: early active stage (January to March), late active stage (March to April), ripe stage (April to August), partially spawned stage (June to August), and spent/inactive stage (August to December). Spawning occurred from June to August, and the major spawning season was from July to August when the sea water was at high temperature.

• Korean Journal of Soil Science and Fertilizer
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• v.45 no.6
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• pp.1222-1229
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• 2012

The total area of a reclaimed tidal soil distributed on the south-west coast is approximately 156,600 ha, and the soil contains high contents of sand and silt as well as highly saline. Most of the reclaimed tidal soils are used as a paddy due to bad permeability and high groundwater table, resulting in easy accumulation of salts on the soil surface by capillary rise. Therefore, resalinization may occur because of rise of groundwater table after desalinization. The researches related to the reclaimed tidal soil mainly focused on desalinazation while most of the researches completed were limited to yields of crop based on desalinazation. pH of old reclaimed tidal soil is neutral or less than 7 while that of newly developed reclaimed tidal soils is greater than 7, that cause N-fertilizer to be volatile as ammonia. Thus, the physical and chemical properties should be investigated to be used as an arable upland instead of a paddy soil due to change in government policy. We need to develop measures to make soils grow crops normally by identifying problems related to reclaimed tidal soils.

• Korean Journal of Weed Science
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• v.12 no.1
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• pp.46-51
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• 1992

The survey of weed population in paddy field was carried out to invegstigate the weed group on 340 fields in Kyonggi Area in 1991. The weed species observed include 4 species of grasses, 7 species of sedges, and 14 species of broadleaf weeds, and the ratio of annual weed vs perennial weed was 25 : 75. Major dominant weed species were Eleocharis kuroguwai, Sagitaria trifolia, Echinochloa crusgalli and Cyperus serotinus. The dominant weed species in South Plain Region were Echinochloa crusgalli, Eleocharis kuroguwai, Sagitariu trifolia, Cyperus strotinus, in West Coast Region were Eleocharis kuroguwai, Sagitaria trifolia, Echinochloa crusgalli, Cyperus serotinus, in East Interior Region were Eleocharis kuroguwai, Sagitaria trifolia, Echinochloa crusgalli, Cyperus difformis and were Sagitaria trifolia, Eleocharis kuroguwai, Echinochloa crusgalli and Monochoria vaginalis in North Region. The dominant weed species in Normal and Poorly drained soil were Eleocharis kuroguwdi, Sagitaria trifolia, Echinochloa crusgalli and Cyperus serotinus and were Scirpus maritinus, Cyperus serotinus, Echinochlod crusgalli and Myriophyllum verticillatum in Saline Soil. More and many weeds were growing in single cropped field than double cropped field.

• Korean Journal of Soil Science and Fertilizer
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• v.40 no.4
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• pp.330-348
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• 2007

Soil problems and agricultural water management of the reclaimed land in Korea were reviewed through research results conducted in RDA and ADC. According to the Korean Soil Classification and Soil Survey(NIAST, 2002), the 5 soil orders with the 45 soil series were distributed on the fluvio-marine or marine deposit of the west and south coastal plains. Yeompo, Munpo, Hasa, Gwangwhal, and Poseung soil series were most commonly distributed soil on the fluvio-marine deposits, associated with tideland of the sea coast. Former 4 soils were Entisols, and the latest one was the Inceptisols. Buyong soil associated with Poseung series was an Alfisols. Extent of Myeongji soil, a Molisols, and Yongho soil, a Histosol, were minor. Salinity control and management problems were closely related with high water table and low percolation rate due to plow-pan layer developed during the leaching process in the silty textured soil. For evaluation of field salinity, use of an electromagnetic inductance, EM38, with GPS was helpful to understand salinity status and field variability. Deep plowing, subsoiling and drainage improvement by tile drainage might be effective in paddy with plow-pan. New technology such as variable rate fertilization might save fertilizers and thus reduce environmental impact of agriculture on water quality. Water quality of agricultural water resources in reclaimed land was less adequate than that of inland water resources. Proper crop management is necessary depended upon quality for crop growth as well as to match with water quality target.

• The Korean Journal of Malacology
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• v.29 no.2
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• pp.113-120
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• 2013

The reproductive cycle, gonad index, condition index, and the sex ratio in female and male Coecella chinensis, which were collected from the coastal waters of Namhae, the South Coast of Korea, were investigated by histological analysis and morphometric data. Monthly variations of the gonad index and condition index of this species showed similar patterns to that of the reproductive cycle. The reproductive cycle in female and male C. chinensis can be classified into six successive stages: early active stage (April), late active stage (May), ripe stage (June), partially spawned/spent stage (June to August), degeneration stage (August) and inactive stage (September to March). According to monthly changes in relative frequency distributions of ovarian egg diameters of this species, in particular, a number of ripe eggs ranging about 70 ${\mu}m$ appear in June, however, in July and August, although the mode of egg diameters ranging about 50 ${\mu}m$ appear about 80%, these ripe eggs ranging from 60 ${\mu}m$ to 70 ${\mu}m$ are gradually decreased during the period from June to August. Therefore, the spawning period of this species is continued from June to August with a peak between July and August when the seawater temperature exceeds about $24.5^{\circ}C$. The sex ratio of female and male individuals was not significantly different from 1:1 (${\chi}^2$=1.20, p>0.05). No hermaphrodites were found.

• Journal of Navigation and Port Research
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• v.38 no.2
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• pp.105-110
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• 2014

Korean government sets up a goal that jumps up to the third ranked powerful nation of offshore wind in the world until 2020 and announced "The plan for 2.5-gigawatt wind farm off the south-west coast by 2019". Such above, according to green energy policy, offshore wind farms(OWF) will be increased continuously. The development of OWF should be taken account of wind volume as well as marine traffic environment. Specially aids to navigation of OWF play a significant role in preventing collision between vessels navigating near waters and structures. For purpose of distinguishing OWF, IALA recommendations define installation of lights on SPS and IPS. However, there is no mention of light character that plays important role in identification of lights as marking offshore wind farm. Also the research on selection of proper light character has been insufficient state. Therefore in this paper, we analyzed internal and external regulations concerned marking with light on SPS and IPS in OWF. And suggested patterns and rhythms of light having not only easily recognized feature but also no confusion with other light of aids to navigation. The proposed light characters were verified by simulation, and the results were analysed that synchronism flickering of "Fl Y(4) 12s(SPS)" and "Fl Y 6s(IPS)" would be useful in combination of both lights.

• Journal of Korea Water Resources Association
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• v.33 no.3
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• pp.299-306
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• 2000

Korea IS one of countries to be predicted short of water in the 21st century. The government has been investigating various alternatives to resolve the problems including construction of reservoirs. Freshwater retention techniques using boom and skirt system is one of them. It is very difficult to intake water in the estuaries of south and west coast of Korea because a big tide penetrates into an upstream river. Thus, means or retaining and keeping separate freshwater from seawater could potentially be helpful in solving the water supply problems. In this study, the proposed means to achieve freshwater retention is by use of floating boom and skirt systems. The hydraulic viability of these systems in taking advantage of natural stratification tendencies between the fresh and seawaters has been investigated through hydraulic experiments. It is found that freshwater retention capacity depends on skirt length and the opening beneath the skirt. The choice of skirt length IS very important to optimize freshwater storage because longer skirt lengths cause faster mixing and shorter lengths retain less volume. Results show that the freshwater retention volume generally increases as the length of the skirt increases. However, they show that water storage might be insufficient if skirts were either too long or too short.

• Journal of the Mineralogical Society of Korea
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• v.24 no.3
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• pp.205-216
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• 2011

Mineral compositions of 69 southeastern Yellow Sea surface sediments collected at the Korea Ocean Research and Development Institute (KORDI) cruise in 2010, were determined using the quantitative X-ray diffraction analysis. Southeastern Yellow Sea surface sediments are composed of major minerals (quartz 49.1%, plagioclase 13.0% and alkali feldspar 9.3%), clay minerals, calcite, and aragonite. Illite (9.4%) is the most abundant clay mineral, chlorite (4.6%) is the second, and kaolinite (0.8%) is few. Quartz and alkali feldspar contents are high in coarse-grained sediments, whereas amphibole and clay mineral contents are high in fine-grained sediments. Quartz, plagioclase, alkali feldspar, chlorite, and kaolinite contents are higher, and illite content is lower in mud zone 1 corresponding to south margin of Central Yellow Sea Mud than in mud zone 2, a part of Southeastern Yellow Sea Mud. Difference of mineral composition between two mud zone suggests that source of fine sediment may be different in two mud zone and Southeastern Yellow Sea Mud might be largely supplied from the Keum and Youngsan rivers in southern part of the west coast in the Korean Peninsula.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.55 no.4
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• pp.294-302
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• 2019

As a series of fundamental researches on the development of an automatic identification monitoring system for fishing gear. Firstly, the study on the installation method of automated identification buoy for the coastal improvement net fishing net with many loss problems on the west coast was carried out. Secondly, the study was conducted find out how to install an automatic identification buoy for coastal gill net which has the highest loss rate among the fisheries. GPS for fishing was used six times in the coastal waters around Seogwipo city in Jeju Island to determine the developmental status and underwater behavior to conduct a field survey. Next, a questionnaire was administered in parallel on the type of loss and the quantity and location of fishing gear to be developed and the water transmitter. In the field experiment, the data collection was possible from a minimum of 13 hours, ten minutes to a maximum of 20 hours and ten minutes using GPS, identifying the development status and underwater behavior of the coastal gillnet fishing gear. The result of the survey showed that the loss of coastal net fishing gear was in the following order: net (27.3%), full fishing gear (24.2%), buoys, and anchors (18.2%). The causes were active algae (50.0%), fish catches (33.3%) and natural disasters (12.5%). To solve this problem, the installation method is to attach one and two electronic buoys to top of each end of the fishing gear, and one underwater transmitter at both ends of the float line connected to the anchor. By identifying and managing abnormal conditions such as damage or loss of fishing gear due to external factors such as potent algae and cutting of fishing gear, loss of fishing gear can be reduced. If the lost fishing gear is found, it will be efficiently collected.

• 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.