• Korean Journal of Ecology and Environment
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• v.46 no.4
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• pp.524-540
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• 2013

After the construction of the Geum River estuary dam, we investigated the ecological property of phytoplankton community with physicochemical property in 9 stations of Geum River estuary 4 times seasonally in 2010 about the environmental changes through the change of phytoplankton. Physicochemical property seems to show eutrophication which developed from the tendency of accruing of the nutrients (those involved in intermittency of freshwater which flows from the dike and the surrounding cities), caused by the changing of tidal flow, the decreasing of the inflow of seawater after the construction of the Geum River estuary dam (dike). A total of 233 species of species composition of phytoplankton emerged, showing a highly increased result compared to that of the former research. The reason for the increase in number is considered as a phenomenon resulting from the mix of blackish and freshwater marine species in the flow of intermittency of freshwater discharge. Also, the standing crops of phytoplankton considerably increased compared to when the dike had not yet been built. Highly affected by the discharge of occasional freshwater, the diatoms of blackish water zone dominated in spring and winter, while freshwater species appeared to dominate in summer and autumn. The species diversity showed over 2.0 except in winter season. After a cluster analysis, the result showed that the Geum River estuary was influenced by runoff from cities like Gunsan, the sewage which flows from Gyeongpo River, and the intermittency of freshwater discharge from the Geum River estuary dam.

• Journal of the Korean Society for Marine Environment & Energy
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• v.12 no.4
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• pp.227-234
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• 2009

Using a finite volume ocean circulation model based on an unstructured grid (FVCOM), we studied the structure of a fresh water bulge that influences on the Region Of Freshwater Influence. Fresh water discharged a river forms a coastal boundary current to the righthand side and a cyclonically circulation freshwater bulge that grows with time. In the middle of the bulge, vertical motions bring fresh water to the bottom. When tidal motions are included, the bulge disappears while the boundary currents becomes wider. Through a simple comparison of areas occupied low salinity water we quantified vertical and horizontal mixing due to the tide and showed that the tidal motion enhances the vertical mixing. During the first few tidal cycles right after the onset of the river discharge, due to tidal excursion the horizontal mixing becomes stronger. The vertical mixing by the tide mixes the fresh water After a certain time the water around the river mouth is well mixed and the horizontal excursion of the fresh water near the river mouth does not have much effect on the horizontal mixing. When there is no tidal motion horizontal mixing is mainly by the inertial instability at the surface and the horizontal mixing becomes stronger over time.

• Journal of Bio-Environment Control
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• v.9 no.3
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• pp.141-145
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• 2000

This experiment was carried out to investigate the influence of flooding on the quality and yield of an oriental melon. Waterlogging for four periods, 0(not flooded), 5, 10 or 15h, were applied to 30cm depth from the soil surface. The soluble solids content of fruit flesh measured at 7 days after waterlogging was 12.6 Brix in not-flooded plot, but it decreased by 4.7-5.6 Brix in plots flooded 5, 10 or 15h, respectively. Difference in fruit hardness between the no-flooded and 5h-flooded plots was not observed, while a significant decrease in fruit hardness was observed in 10 or 15 h-flooded plots at 7 days after waterlogging. Decrease in fruit hardness in all plots except control plot was observed at 13 days after waterlogging. The percent decayed fruits at 7 days after waterlogging was not observed, but at 13 days after waterlogging it gradually increased as duration of flooding increased. The incidence of downy or powdery mildews increased is significantly in plots flooded for 5, 10 or 15h as compared to the not-flooded control. However, population of cotton caterpillar decreased in the flooded plots. Marketable fruits yield per 10a was 616.2kg in no-flooded plot, but it decreased by 33%, 45% and 66%, respectively, in plots flooded for 5, 10 or 15h. The waterlogging during fruit enlargement stage significantly deteriorated fruit quality and decreased marketable fruit yield.

• Research in Plant Disease
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• v.7 no.1
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• pp.25-30
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• 2001

Influence of soil flooding with organic matters amendment at various temperatures on population changes of fungi, including Fusarium, and bacteria in ginseng-replanting field soils was examined to evaluate the effective flooding conditions for reducing the progress of ginseng root rot. Populations of Fusarium spp. and total fungi in flooded soils declined with days after flooding. The higher was the temperature in range of 20$\^{C}$ to 35$\^{C}$, the greater was the effect of flooding on the decrease of the fungal population. Flooding of soils with organic matters amendment had synergistic effect on the decrease of the fungal population at the same temperature; Fungal populations in flooded soils with and without organic matters amendment were reduced to 1/100 and 1/10, respectively, relative to those in non-flooded soils after 60 days of treatment at 30$\^{C}$. rice straw seemed to be more effective than greens. Population changes of total bacteria in flooded soils were similar to the trend of total fungi. However, the flooding seemed to influence less effect on the bacterial population than on the fungal population. Based on these experiments, we suggest than the progress of ginseng root rot in ginseng-replanting field soils may be significantly reduced by flooding them for longer than 3 months near at 30$\^{C}$ after amendment of organic matters.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.33 no.3
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• pp.225-229
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• 2000

This study was performed to investigate production and hatching rate of the resting egg of freshwater rotifer, Brachionus calyciflorus fed the 5 different diets (ESP, freshwater Chlorella, baker's yeast, the mixture off$70{\%}\;ESP\;and\;30{\%}$freshwater Chlorelia, and the mixture of $30{\%}$ baker's yeast and $70{\%}$ freshwater Chlorella). The highest productions of resting eggs were 123.3 egg/ml and 126.7 egg/ml in the mixture of $70{\%}$ ESP and $30{\%}$ freshwater Chlorella, and the mixture of $30{\%}$ baker's yeast and $30{\%}$ and $70{\%}$ freshwater Chlorella, respectively, which were significantly better than ESP, freshwater Chlorella or baker's yeast alone (P<0.05). Hatching rate of the resting eggs from rotifer fed the mixture of $70{\%} ESP\;and\;30{\%}$ freshwater Chlorella was the highest, $71.9{\%}$ although this value was not significantly different compared with the mixture of $30{\%}$ baker's yeast and $70{\%}$ freshwater Chlorella, and freshwater Chlorella (P^lt;9.05). The results showed that the mixture of baker's yeast or ESP with the freshwater Chlorella seemed to be the best feeding regime for the production and hatching rate of resting egg of freshwater rotifer.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.37 no.6
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• pp.550-556
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• 1992

Performance of a rice breeding line, Milyang 95 was evaluated at four cultural methods, direct seeding on dry soil covered by making ridges (DS ridged), direct seeding on dry soil covered by rotortilling (DS rotary), direct seeding on flooded soil (FS), and machine transplanting (MT). Days from seeding to emergence in both DS ridged and DS rotary was 15 days. The number of seedlings at DS ridged and DS rotary was lower than that at FS. Heading was earliest at MT, latest at DS rotary and DS ridged, and that at FS was between them. Days from seeding to heading was 115 days at MT, 94-95 days at DS ridged and DS rotary, and 87 days at FS. Lodging index was similar among the cultural methods and lodging was not occurred in the field although fresh weight of tillers and breaking strength at MT were higher than those of direct seedings. Yield and most of yield components were similar among the cultural methods although the number of spikelets per panicle at MT was higher and 1,000 grain weight at FS was lower compared to other cultural methods. Grain appearance (rusty, chalky abortive rice), protein and amylose contents and alkali digestibility were observed.

• Korean Journal of Weed Science
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• v.8 no.1
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• pp.28-32
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• 1988

The effects of standing water and cultivation frequency on emergence of Echinochloa glabrescens Munro ex. Hook were determined at varied seeding methods under simulated field conditions for 4 months. In soil-incorporated seeding method total emergence for 4 months was highest in saturated condition followed by 4, 2, and 8cm standing water, whereas total emergence of seeds sown at the soil surface was highest at 2cm standing water followed by 4cm, saturated soil, and 8cm standing water. Within 2 weeks the emergence was highest at 4cm and lowest at 2cm standing water with the soil-incorporated seeding, but the seeds sown at the soil surface with 2cm standing water resulted in the highest emergence. Ratio of emergence within 2 weeks over total emergence during 4 months was lowest at 2cm standing water in the soil incorporation, indication that 2cm standing water would be the critical water level for E. glabrescens. Since most of the seedling was emerged within 2 weeks just before cultivation, the emergence pattern was little affected by cultivation at each standing water level.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.33 no.4
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• pp.148-159
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• 2021

This study estimates the region of freshwater influence (ROFI) by Han River discharge in the Yeomha channel, Gyeonggi Bay. A 3-D numerical model, which is validated for reproducibility of variation in current velocity and salinity, is applied in Gyeonggi Bay. Distance of freshwater influence (DOFI) is defined as the distance from the entrance of Yeomha channel to the point where surface salinity is 28 psu. Model scenarios were constructed by dividing the Han River discharge into 10 categories (200~10,000 m³/s). The relation equation between freshwater discharge and DOFI was calculated based on performing a non-linear regression analysis. ROFI in Yeomha channel expands from the southern sea area of Ganghwa-do to the northern sea area of Yeongheung-do as the intensity of Han River discharge increases. The discharge and DOFI are a proportional relationship, and the increase rate of DOFI gradually decreases as discharge increases. Based on the relation equation calculated in this study, DOFI in the Yeomha channel can be estimated through the monthly mean Han River discharge. Accordingly, it will be possible to respond and predict problems related to damage to water quality and ecology due to rapid freshwater runoff.

• Korean Journal of Ecology and Environment
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• v.56 no.3
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• pp.250-258
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• 2023

Freshwater jellyfish, a type of jellyfish exclusively found in freshwater, has a limited number of species but is found globally. However, their ecology and causes of occurrence are largely unknown. Therefore, understanding the distribution of polyps, which produce the larvae of freshwater jellyfish, can provide important data for comprehending their ecology. This study aims to explore the COI gene of freshwater jellyfish using environmental DNA from the microbial film in the Miho River system. Among the 12 survey points in the Miho River watershed, genetic material of freshwater jellyfish was detected in 8 points, mainly located upstream near reservoirs. These genetic materials were identified as genes of the well-known freshwater jellyfish species, Craspedacusta sowerbii. Notably, the C. sowerbii genes found in the Miho River watershed survey points were closely related to a species previously discovered in Italy. Consequently, utilizing environmental DNA to explore the genetic traces of freshwater jellyfish enables rapid screening of areas with a high likelihood of freshwater jellyfish occurrence. This approach is deemed to provide crucial information for understanding the distribution and ecology of freshwater jellyfish in Korea.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.82-82
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• 2015

해안 대수층은 해수와 담수가 공존하는 지역으로 상대적으로 밀도가 큰 해수가 대수층의 담수 아래에 쐐기형태로 존재하게 된다. 이러한 쐐기형태의 해수와 담수의 경계면은 압력경도의 평형에 의해 경계면이 유지되며, 해수면 또는 지하수위가 변동할 경우 해수-담수 경계면의 균형이 무너짐과 더불어 압력경도의 평행이 이루어질 때 까지 해수-담수 경계면의 이동이 계속 진행된다. 수위 변화의 주요 원인으로는 지구온난화 및 기후변화로 인한 지속적인 해수면 상승과 도서지역의 인구증가 및 산업화로 인한 무분별한 지하수의 사용 등에 의한 지하수위 저하 등을 꼽을 수 있다. 이와 같은 원인으로 해안 및 도서지역에서는 해안 대수층의 해수침투거리가 증가하여 지하수 이용에 큰 어려움을 겪고 있다. 이에 해안 대수층의 해수침투 범위 및 거리를 추정하기 위한 많은 연구들이 다양한 분야에서 지속해서 이루어지고 있지만, 서로 밀도가 다른 해수와 담수가 공존하는 해안 대수층 내의 수리특성을 명확히 파악하기에는 아직까지 미흡한 점들이 많다. 과거에는 Darcy의 법칙 및 Ghyben-Herzberg 식에 근거한 이론적인 연구들이 주로 이루어졌고, 근래에 현장관측이나 수리모형실험이 국내 외적으로 수행되고 있으나, 모든 영역의 지하수의 특성을 조사하는 것이 사실상 불가능하다. 이에 최근에는 컴퓨터 성능의 비약적인 발전과 더불어 다양한 수치해석방법에 의한 수치모델들이 개발되어 시뮬레이션에 적용되고 있다. 하지만 거의 대부분의 수치모델은 해안 대수층 수리특성을 투수계수에 의존하고 있을 뿐, 대수층 내부의 해수-담수에 의한 밀도류의 유동특성을 전혀 고려하지 못한 채 정수압에 근거한 해수-담수 경계면에 대해 모의하고 있는 정도이다. 따라서 본 연구에서는 해안 대수층 내부의 유동현상을 투수계수에 의존하는 방법에서 탈피하여 대수층 매체의 입경, 공극, 형상 등을 고려할 수 있을 뿐만 아니라, 염분 및 온도차에 의한 밀도류를 해석할 수 있는 강비선형 수치모델을 개발하여 해수침투 현상을 직접 모의한다. 나아가 대부분의 이전 연구들에서 간과하고 있는 해안지역의 대표적 물리력인 파랑과 조석의 영향이 해안 대수층의 해수침투에 미치는 영향, 해안 대수층의 지하수위 및 해수면의 수위차에 의한 해수침투 특성 그리고 이를 제어 할 수 있는 새로운 대응기술을 제안하는 것을 목적으로 한다.