• Korean Journal of Ecology and Environment
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• v.38 no.1 s.110
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• pp.18-29
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• 2005

This study was conducted to understand seasonal dynamics of phyto- and zooplankton communities in a shallow eutrophic reservoir (Shingu reservoir) from November 2002 to February 2004. Cyanophyceae dominated throughout the year, except for spring (March ${\sim}$ May) when Bacillariophyceae (Melosira varians) and Chlorophyceae (Dictyosphaerium puchellum) were dominant. The change of dominant species in Cyanophytes occurred in June and December 2003, and the increase of phytoplankton cell density in July and November was observed when the P loading through two inflows was high. In May, Oscillatoria spp. and Aphanizomenon sp. were dominant, but replaced by Microcystis spp. in the end of May. Dominant Microcystis spp. sustained until December and shifted to Oscillatoria spp. and Aphanizomenon sp. TN/TP ratio ranged from 13 to 46 (Avg. $27{\pm}6$) from June to December when cyanobacteria (Microcystis spp.) dominated. Rotifers such as Keratella cochlearis, Keratella valga, Polyarthra spp., Conochilus unicornis, Pompholyx complanata dominated in average 67.8% of the zooplankton community. Abundance of zooplankton was the highest in June 2003, when Pompholyx complanata (12,388 ind $L^{-1}$) was dominant. In May, the significant increase of Conochilus unicornis biomass ($1,048{\pm}28\;{\mu}g\;C\;L^{-1}$) was observed with distinct improvement of transparency ($Z_{eu}/\;Z_m=\;1.1$). These results suggest that the seasonal variation of phytoplankton communities in this reservoir are to be understood as results of multi-interactive factors such as temperature, light condition and nutrients, and small-sized rotifers as important predator.

• Korean Journal of Ecology and Environment
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• v.42 no.1
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• pp.19-25
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• 2009

The effects of artificial floating island on the changes in phytoplankton and zooplankton community structure were investigated monthly from September 2006 to May 2007 in Shingu reservoir. The total cell number of phytoplankton under the artificial floating island was three times less than those of control (without artificial floating island). The dominant species of phytoplankton were Lyngbya sp. on September, Cryptomonas sp. from October to January, Aulacoseira granulata on February and Oscillatoria sp. from March to May at lake water. Cyanophyta was dominated from February to March at lake water but it was dominated from March at artificial floating island area. The total individual number, species number of zooplankton and species diversity of phytoplankton and zooplankton under the artificial floating island were higher than those of lake water.

• Journal of the Korean Association of Geographic Information Studies
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• v.19 no.1
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• pp.64-79
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• 2016

The purpose of this study is to find the relationship between precipitation deficit, SPI(standardized precipitation index)-12 month, agricultural reservoir water storage deficit and agricultural drought-related big data, and to evaluate the usefulness of agricultural risk management through big data. For the long term drought (from January 2014 to September 2015), each data was collected and analysed with monthly and Provincial base. The minimum SPI-12 and maximum reservoir water storage deficit compared to normal year were occurred at the same time of July 2014, and August and September 2015. The maximum frequency of big data was occurred at June and July of 2014, and March and June to September of 2015. The maximum big data was occurred 1 month advanced in 2014 and 2 months advanced in 2015 than the maximum reservoir water storage deficit. The occurrence of big data was sensitive to spring drought from March, late Jangma of June, dry Jangma of July and the rainfall deficit of September 2015. The big data was closely related with the meteorological drought and agricultural drought. Because the big data is the in situ feeling drought, it is proved as a useful indicator for agricultural risk management.

• The Korean Journal of Malacology
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• v.17 no.1
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• pp.19-26
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• 2001

To study the growth of transplanted Pacific oysters, Crassostrea gigas, we sampled Korean and Japanese oysters attached in Chinhae Bay near Gaduk Island and in Seto inland sea in Japan, respectively, suspended in Pukman Bay. Water Temperature ranged from 11.2 to 27.8$^{\circ}C$ (mean 19.84 ${\pm}$ 5.47$^{\circ}C$) on the surface, and 11.1 to 23.6$^{\circ}C$ (mean 18.31 ${\pm}$ 4.18$^{\circ}C$) on the bottom. Salinity ranged from 31.45 to 34.57 (mean 33.10 ${\pm}$ 1.16) on the surface, and from 31.69 to 34.35 (mean 33.24 ${\pm}$ 1.06) on the bottom. salinity was the lowest in September and October, and the highest in December. Growth of oysters in shell height showed a significant difference after being suspended at the farm, reaching 70.3 ${\pm}$ 12.5 mm in the Korean oysters and 96.2 ${\pm}$ 14.6 mm in the Japanese oysters in December. While the Korean oysters showed relatively low growth rate and cessation of growth after sudden growth between June and July, the Japanese oysters showed continuous growth during the whole farming period, although stepwise growth was observed. It was not until September that meat weight showed a significant difference between the two. After September, there was a sudden increase in the Japanese oysters, reaching 7.5 ${\pm}$ 2.9 g in December, but growth of the Korean oysters showed slow growth rate during whole farming period, reaching 4.6 ${\pm}$ 1.9 g in December. here was an obvious decrease in the meat weight of Japanese oysters in December, which might be attributed to restriction of food. Condition factors rebounded in October in the Korean oysters and in September in the Japanese oysters, respectively, attaining 12.8 in the Korean oysters and 15.3 in the Japanese oysters at the end of investigation on December. Shell length-height regression equations were as follows: Korean oysters: S$\sub$h/=2.922S$\sub$t/,-4.8024 (r$^2$= 0.8541) Japanese oysters: S$\sub$t/=3.623S$\sub$h/,-5.1239 (r$^2$=0.7782) This showed the possibility of morphological transformation in the shell of the Korean oysters since shell height was longer than those reported by Bae et al. (1976) and Lee et al. (1992).

• Korean Journal of Weed Science
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• v.3 no.2
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• pp.129-136
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• 1983

To study ecological characteristics of Sagitiaria pygmaea and Sagittaria trifolia occurring in Korea their propagules were collected from 3 locations (Sagittaria pygmaea: Chuncheon, Suweon, Milyang; Sagittaria trifolia: Suweon, Iri, Jeonju) in 1981, cultured and replanted 4 times (May 20, June 5, June 20, July 5) in 1982. Sagitraria pygmaea from Suweon flowered earlier than those from Chuncheon and Milyang in the plants planted on May 20, but this was reversed in another planting dates. Three storied inflorescence was observed newly in Sagittaria pygmaea. Sagittaria pygmaea from Iri and Jeonju had more number of tillers, but less number of tubers per tiller than those from Suweon. Sagittaria rrifolia from Chuncheon flowered earlier than those from Suweon and Milyang. Sagirtaria trifolia from Milyang was narrower in the upper leaf width and less in the number of tubers per plant than those from Chuncheon and Suweon. Each of local collections may be regarded as different ecotype based on the above differences.

• Korean journal of applied entomology
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• v.20 no.2 s.47
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• pp.71-75
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• 1981

The percentage of lesion height vs. plant height was higher in Yushin than Jinheung within the same nitrogen level. The infection occurred at the same level of waterline and the symptoms developed with the same speed for two varieties, but the damage was greater in Yushin as the symptoms reached faster to the top due to the short length of the 1st and 2nd internodes from the top.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.18 no.1
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• pp.37-43
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• 1985

The present investigations were carried out for the purpose of making clear the fundamental features of the compositional difference of agarose and agaropectin in agar prepared from Gellidium amansii collected in different places and seasons, and its effect on properties of agar. The samples, Gellidium amansii, was collected every month from the same locality on the coast of the Ilgwang-myon, Yangsan-gun, Kyongnam, from March 1982 to February 1983. In addition, agarose and agaropectin in agar were isolated by dimethyl sulfoxide. The results obtained were summarized as follows : 1. In seasonal variation, the maximum yield of agar noted from spring through summer, and the minimum in February. 2. The experiment showed that the agarose and agaropectin composition in agar was changed, even if the seaweed collected from the same season was used as raw material. Seasonal variation of agarose and agaropectin contents in agar, the highest content occurred in August, $76.2\%$, and the lowest in January, $50.1%$. 3. Jelly strength, gelation ability of agar tended to increase as the agarose content was risen, but sulfate content was decreased.

• Korean Journal of Plant Resources
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• v.22 no.2
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• pp.123-127
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• 2009

This study was carried out to investigate the classification and the growing characteristics of biennial weed species in a newly formed transplanting lawn grass land. Measuring size in the experimental plot was $1{\times}1m$ in the 9 different locations, and experimental design was randomized complete plot with 3 replications. The results obtained are summarized as follows. 1) Weed species in a newly formed lawn field are consisted of 29.4% of Cruciferae, 29.4% of Compositae, 23.5% of Caryophyllaceae, 11.8% of Gramineae, and 5.9% of Labiatae family 2) Emerging percentage of weed species are consisted of 47.1% on October, 41.2% on November, 5.9% on both September and December, respectively. 3) Distribution rate about flowering time of weed species was in order of 58.5% on May, 23.5% on April, 11.8% on March, and 5.9% on June. 4) Weed species were grouped according to the plant height. It was observed that below 20cm, 20-40cm, 40-60cm and above 60cm of plant height were 23.5%, 47.1%, 17.6% and 11.8%, respectively.

• Korean Journal of Environmental Biology
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• v.24 no.3
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• pp.258-267
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• 2006

Distribution of population densities of heterotrophic bacteria, E. coli, and Salmonella and Shigella in seawater and sediments at 40 stations near Samcheonpo Bay were measured for 3 times from July to December, 2003. Population densities of heterotrophic bacteria in seawater during survey periods were in the range of $1.7{\pm}0.9{\times}10^3{\sim}2.4{\pm}0.9{\times}10^5$ CFU $mL^{-1}$ and the highest density was shown at St. 34 during the sampling period of September, 2003. Population densities of heterotrophic bacteria were shown higher values on September than those of July and December at all sampling stations. Population densities of anaerobic heterotrophic bacteria in sediments during survey periods were in the range of $2.2{\pm}0.2{\times}10^3{\sim}2.0{\pm}0.2{\times}10^5$ CFU $mL^{-1}$ and their population densities at sampling stations far from Samcheonpo Bay measured lower values than those near Samcheonpo Bay. Population densities of anaerobic heterotrophic bacteria in the sediments were not affected by physico-chemical factors of upper water environment. E. coli were detected only at 8 stations in seawater and 4 stations in the sediments among 40 sampling stations on July and were not detected during September and December. Salmonella and Shigella were detected only a few stations on July and September during sampling periods.

• Journal of Aquaculture
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• v.11 no.4
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• pp.475-485
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• 1998

To clarify annual reproductive cycle of Koran dark sleeper, odontobutis platycephala, we examined the seasonal changes of gonadosomatic index(GSI), testicular development stages and sex steroid hormones in blood from December 1995 to November 1997. Testis was podlike shape from July to October, and tadpole-like shape from November because of its expanded posterior part. GSI was 0.14~0.18 from July to September and increased to $0.43{\pm}0.04$ in October and then was not changed significantly until February. GSI was reincreased to $0.52{\pm}0.09$ from March and then was kept at similer levels until May, but fell down to $0.28{\pm}0.05$ in June. As results of histological observation, testis was divided into 3 parts(anterior, boundary, posterior) in the development progress of germ cells. In July, the testis was composed of only spermatogonia without seminiferous tubules in most fishes. In the anterior part of testis, the ferquency of spermatogenesis stage seminiferous tubules appearing in August was more than 80% from September to December. decreased gradually from January to March and drastically in April, and then disappeared in June. The frequency of spermiogenesis stage seminiferous tubules appearing in December, increased gradually from January to March and drastically to 80% in April, and reached to 90% the highest levels of the year in June. Post-spawning stage seminiferous tubules did not appear throughout the year. The frequency of spermatogonia was 100% and 65% in July and August, and less than 20% in the rest period of the year. In the boundary part, the frequency of spermatogenesis stage seminiferous tubules appearing in August increased from September and reached to 82% in November, decreased from December, adn disappeared in March. The frequency of spermiogenesis stage seminiferous tubules appearing in November was less than 18% until February, and increased to 29%~57% from March to June. The frequency of post-spawning stage seminiferous tubules appeared 12%~25% only from March to June. The frequency of spermatogonia was 100% in July, decreased to 85% in August and 10% in November, and increased gradually from December to 50% in April, and decreased again from May to June. In the posterior part, seminiferous tubules with some seminiferous tubules increased drastically 80%~85% in August and September, decreased drastically from October to November and remained below 10% until February, and disappeared after March. The frequency of spermiogenesis stage seminiferous tubules appearing in August increased sharply from October and reached to 75% in November. decreased to 15% in December and no significant changes until March, and disappeared after April. The frequency of post-spawning stage seminiferous tubules appearing very early in November increased to 82% in December and 85%~95% until June. The frequency of spermatogonia was 100% in July, decreased drastically to 15% in August, disappeared from October to Mrch, but reappeared from April and kept at less than 10% until June. The blood level of testosterone (T) increrased gradually from August was $0.61{\pm}0.09 ng/m\ell$ in November, increrased drastically to $3.99{\pm}1.22 ng/m\ell$ in December and maintained at in similar level until March, and decreased to $0.25{\pm}0.14 ng/m{\ell} ~ 0.17{\pm}0.13ng/m{\ell}$ in April and May and no significant changes until July (P<0.05). The blood level of 17, 20 -dihydroxy-4-pregnen-3-one $ng/m{\ell}$in the rest of year without significant changes(P<0.05). Taken together these results, the germ cell development of testis progressed in the order of posterior, boundary, anterior part during annual reproductive cycle in Korean dark sleeper. The testicular cycle of Korean dark sleeper was as follows. The anterior part of testis : i.e. spermatogonial proliferation period (July), early maturation period (from August to November), mid maturation period (from December to March), late maturation period (from April to May) and functional maturation period (June) were elucidated. The boundary of testis, i.e. spermatogonial proliferation period (July), early maturation period (from August to October), mid maturation period (from November to February) and the coexistence period of late maturation, functional maturation and post-spawn (from March to June) were elucidated. The posterior of testis, i.e. spermatogonial proliferation period (July), mid maturation period (from August ot September), late maturation period (October), functional maturation period (November) and post-spawn period (from December to June) were elucidated. It was showed that the changes of sex steroid hormone in blood played a important roles in the annual reproductive cycle of Korean dark sleeper.