• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.41 no.1
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• pp.46-53
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• 2005

This paper describes the mean grain size and shear strength properties related to subsidence characteristics using sediment samples and acoustic images obtained from artificial reef areas in Tongyoung and Jangsungpo offshore. The acoustic images collected from chirp sonar and side scan sonar show well the attitude/orientation, the distribution pattern, and the degree of subsidence of artificial reefs, suggesting the possibility of suitable site investigation and the management of the reefs using acoustic sonar. The sediments were largely composed of clayey silt and silty clay. The mean grain sizes in Tongyoung and Jangsungpo offshore show the ranges of 5${\sim}$9${\Phi}$ and 8${\sim}$9${\Phi}$, respectively. The shear strength was significantly increased at the depths of 20cm in Tongyoung offshore and 80cm in Jangsungpo offshore, corresponding to the subsidence depth of artificial reefs. The relationship between mean grain size and shear strength did not show a correlation, suggesting the shear strength does not totally depend on mean grain size. Provided subsidence characteristics with respect to various artificial reefs and seabed condition are investigated in more details, the constructing area of the reef can be more extended.

• Journal of Korean Society of Forest Science
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• v.104 no.1
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• pp.43-49
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• 2015

The production of high quality seedlings is a very important phase in silvicultural systems for successful reforestation or restoration. The purpose of this study was to quantitatively measure both growth performances and nutrient responses of Fraxinus rhynchophylla, Pinus densiflora, and Pinus koraiensis seedlings, which are commercially planted in Korea, according to the different types of soil improvement treatments. We applied soil brought (hereafter 'brought'), subsoil inversion (hereafter 'subsoil'), and mixture of brought soil with soil on nursery bed (hereafter 'mixing') in a permanent national nursery. Silt and clay contents were the highest at the subsoil treatment and organic material, soil nitrogen and phosphorus concentrations were the lowest at the brought treatment. The growth of F. rhynchophylla was the lowest at the subsoil treatment, but there were no significant differences among treatments. There were significant differences in only root nutrient concentrations of F. rhynchophylla among treatments: nitrogen, phosphorus, and potassium concentrations were the lowest at the subsoil or brought treatment. Mixing treatment increased N contents with deduction of N concentrations ('dilution') because of more dry weight increase compared with the amount of N uptake. This study suggested mix of brought soil with soil on a nursery bed in a permanently used nursery can economically be an effective technique to improve soil quality.

• Korean journal of applied entomology
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• v.58 no.1
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• pp.37-47
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• 2019

A survey on the geographical distribution of two soybean cyst nematodes, Heterodera glycines and Heterodera sojae, was conducted in soybean cultivation areas in the Gangwon-do and Chungcheongbuk-do provinces. In 67 fields of 10 counties or cities in Gangwon-do province, H. glycines was detected in 13 fields, H. sojae was detected in five fields, and both species were found in two fields. In 84 fields of nine counties or cities in Chungcheongbuk-do province, H. glycines was detected in 27 fields, H. sojae was detected in four fields, and both species were found in five fields. The diversity and dominance of the plant parasitic nematodes in the Gangwon and Chungbuk provinces were not significantly different among the soybean cultivars. The diversity and dominance index of the plant parasitic nematodes according to the presence or absence of soybean cyst nematodes did not show any significant difference between the soybean cultivation areas of both provinces. The relationship between the soybean cyst nematodes and soil chemical properties showed a low coefficient of determination, and the density of soybean cyst nematodes tended to increase as the pH and available phosphate content in soil samples increased. The soil texture of cyst nematode-detected fields was mostly sandy soils, which amounted to about 60% of the total. As the clay and silt content increased, the density of soybean cyst nematodes tended to decrease, and as the sand content increased, the density of cyst nematodes tended to increase.

• Journal of Coastal Disaster Prevention
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• v.5 no.4
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• pp.173-182
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• 2018

As the research about increasing the efficiency of dredging soil transport, the technology, which reduce the friction between pipe wall and fluid in the pipe and disturbed generating pipe blockage, has been developed. So for the purpose of applying this technology to real construction site, main test has been tried at the real scale test in field. As a test result, this paper will show 30% flow efficiency increasing by permitted electro magnetic force to the pipe. And test result was evaluated as a ultra sonic velocity profiler. To propose the design technique and the execution manual of the high efficiency dredging material transport technic, this research have confirmed flow status changing depending on a soil material kind under electro-magnetic field and analyze the effect of electro-magnetic field which affects to each dredged soil material transportation. For achieving this research, EMF(Electro-Magnetic Field) generator is installed on the dredger(20,000HP) and through monitored flow status, dredging soil flow rate and sampled material specification is confirmed. Also dredger operating condition is measured and dredger power for soil transportation, hydraulic gradient and flow rate are compared, as transportation efficiency is calculated by this parameter, it is possible to check transportation efficiency improvement depending on each dredged soil material under electro-magnetic field. To verify the technique of dredged soil transfer using electromagnetic field, which is the core technique of the high efficiency dredged soil transfer, and the technique of expert system for pipeline transfer and the flow state. This could lead to a verification of transfer efficiency according to the characteristics of the dredged soil (sand, clay, silt) and the transfer distance (5km, 10km, 15km), which is planned to be used for a technology development of pump power reduction and long-distance transfer applying the high efficiency dredged soil transfer technology.

• Korean Journal of Ecology and Environment
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• v.37 no.4 s.109
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• pp.462-468
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• 2004

Most of the surveys of periphyton carried out for environmental and ecosystem health assessment of streams have considered the impact made on their fixative substrates (stones, rocks, sand, silt, clay and other abiotic matters), but there has been virtually no research that considered moving substrates. This study attempted to make an analysis and assessment of the habitat environments of the microalgae attached to the skin surfaces of fish living in small streams, with a focus on their species composition and community structure. The dominant fish in the this survey were Zacco temmincki and Zacco platypus, which are usually found in the streams, and rivers, and they accounted for 62% and 19%, respectively, in relative abundance. Substrates of fish, a representative organism with the trait of moving a long distance, show a marked contrast with those of organisms fixed at a certain place. Characteristics of both the upstream and the downstream reach well reflected in the microalgae attached to the skin surface of fishes, of which diatoms took the major composition. The result of this observation is considered to be useful to provide basic data in assessment of stream health. Also it may be suggested as a biological tool for the assessment of aquatic environment in the future.

• Journal of Aquaculture
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• v.8 no.2
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• pp.85-98
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• 1995

In Kunsan coastal areas, there are some plans to construct industrial zone and, it will affect physical and chemical parameters of marine environment of the area. As one of many environmental surveys on the aquacultural farm in Korean west coast, the survey on the bottom sediment characteristics of intertidal farm was conducted from May 1992 to April 1993. Dominant grain size was fine sand $(69-98\%)$ and the pH of sediment was ranged of $7.2\~9.1$. Especially the pH increased after embank was constructed. The water holding capacity was $11.1-28.1\%$ and showed high value in silt and clay area. The COD was 1.27 mg/g dry mud and increased after embank was constructed. The total organic matter content ranged of $0.84-8.11\%$ and the DO absorption was $0\~6.56 mg/g$ dry mud. The value of DO absorption showed low in winter and spring, but high in summer and fall. The total nitrogen and the sulfide were rang of $0\~402{\mu}g/g$ dry mud and $0\~122{\mu}g/g$ dry mud respectively. These values were high in summer and winter season, and higher in upper layer than that of lower layer in general.

• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.2
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• pp.127-140
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• 2015

A fault is one of the critical factors that may lead to a possible ground collapse occurring in construction site. A fault core, however, possibly acting as a failure plane in whole fault zone, is composed of fractured rock and gouge nonuniformly distributed and thus can be characterized by its wide range of shear strength which is generally acquired by experimental method for stability analysis. In this study, we performed direct shear test and grain size distribution analysis for 62 fault core samples cropped from 12 different spots located in the vicinity of Kyongju and Ulsan, Korea. As a result, the range of shear strength representing the characteristics of fault cores in the study regions is determined with regard to vertical stress using a regression analysis for experiment data. The weight ratio of gravels in the samples is proportional to the shear strength and that of silt and clay is in inverse proportion to the shear strength. For most samples, the coefficient of determination is over 0.7 despite of inhomogeneity of them and consequently we determined the lower limit and upper limit of the shear strength with regard to the weight ratio by setting the confidence interval of 95%.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.38 no.6
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• pp.399-412
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• 2005

This study investigated the composition and the distribution of the benthic polychaeta community in the semi-enclosed Yoja Bay on the southern coast of Korea and was designed to deduce temporal changes in the community with the comparison of the previous studies. In YoJa Bay, benthic polychaetous community structure was investigated on the base of the samples from 87 stations. The surface sediment was mainly composed of fine-grained sediment, mixed clayey silt and silty clay. The total benthic macrofaunal density was $387 indiv./m^2$, and the density was higher in the middle bay, and in the mouth of bay than in the inner bay. scapharca subcrenata (Bivalvia) and amphipods (Crustacea) were important species in the inner and the middle of the bar, respectively. Benthic polychaetes were comprised of 72 species with a mean density of $149 indiv./m^2$. Their distributions showed higher densities in the mouth of bay than in the rest of bay. The dominant species over 1.0 percentages were composed of the 20 species, and they occupied $84.5\%$ of the total density. The most dominant species was Sternaspis scutata ($13.6\%$), fallowed fly Heteromastus filiformis ($9.8\%$), Polynoidae indet. ($8.3\%$), Sigambra tentacuzata ($7.1\%$) and others. The cluster analysis revealed that the study area was divided into three station groups. At the station group YI located in the inner bay, the most dominant species was Heteromastus filiformis . At the station group YII in the middle bay, the dominant species was Sternaspis scutata. And at the station group YIII in the mouth of bay, the dominant species was Paraiacydonia paradoxa. Whereas Sternaspis scutata and Mediomastus sp. were the dominant species in the past study, Heteromastus filiformis and Tharyx sp. appeared newly to be the dominant species, even if their low densities that in the past. These facts mean that Yoja Bay be maintained yet as little polluted area compared to other bays on the coast of Korea, but needed some caution of marine environmental management.

• Journal of Wetlands Research
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• v.14 no.1
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• pp.139-146
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• 2012

Stream ecosystems carry out significant functions such as water purification, especially denitrification. However, rapid landuse change since industrialization has altered ecological functions of streams. In this study, we aimed to investigate denitrification rates and their determinant factors in streams with different landuse patterns, and how denitrification rates vary with microtopology within streams. Ten fifth streams of each landuse were selected, and each stream was divided into four microtopological sites within streams - riparian zone, subsoil, and both head and tail parts of sand bars. In situ denitrification rates and physicochemical properties of soil were examined. Denitrification rates of agricultural, urban, and forest streams were $289.62{\pm}70.69$, $157.01{\pm}37.06$, $31.38{\pm}18.65mg$ $N_2O-N\;m^{-2}\;d^{-1}$ respectively. There were no significant differences in denitrification rates depending on microtopology, but the rates in riparian zone were the highest, and the rates in the head parts of sandbars were lower than those of tail parts. The determinant factors for denitrification rates included water temperature, silt and clay contents of soil, inorganic nitrogen, and organic carbon, and these factors all showed positive correlations with denitrification rates. Through this study, we find that landuse pattern in watershed region affects denitrification rates that is one of considerable functions of streams. In addition, estimation of denitrification rates taking into account for microtopology would contribute to developing ecological management and restoration strategy of streams.

• Korean Journal of Environment and Ecology
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• v.20 no.3
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• pp.299-310
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• 2006

The germination period, the germination under different saline concentration and temperature condition, the survival percent several halophytes in cross-transplanting experiment of marsh type and the soil environment factor of five dominant species were investigated on the halophytes population formation strategies on the salt marsh of Mankyeong river estuary from February to October 2005. In terms of germination, Suaeda japonica appeared first followed by Aster tyipolium Salicornia herbacda, Atriplex gmelini and Suaeda asparagoides. The germination percent on the humidify conditions and saline concentrations of halophytes were that Suaeda japonica germinated well under inundation conditions, high temperature and low salinity; Salicornia herbacda under high salinity; Aster tripolium and Atriplex gmelini under dry or inundation conditions, and Suaeda aspar agoides under dry conditions and high salinity. The survival percent in cross-transplanting experiment of five halophytes were high with Suaeda japonica in the low marsh; Salicornia herbacda, Aster tripolium and Atriplex gmelini in the mid marsh, Suaeda asparagoides in the high marsh. The soil properties were similar for the five halophytes, but soil texture appeared high in order of silt, sand and clay. These results suggested that population formation strategies of five halphytes. Suaeda iaponica was distributed in the low tidal marsh, Salicornia herbacda, Aster tripolium, Atriplex gmelini in the mid tidal marsh and Suaeda asparagoides in the high tidal marsh.