• Korean Journal of Fisheries and Aquatic Sciences
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• v.26 no.1
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• pp.76-90
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• 1993

To clarify the relations between photoperiodism and x-organ of eyestalks to the control of gonadal maturation in a freshwater prawn, Macrobrachium nipponense, the present investigation was performed with following examinations: 1) the influence of water temperature and daylength on the control of gonadal maturation, 2) the effect of eyestalk ablation on the gonadal maturation, 3) the seasonal variation of histology of MEX-organ (medulla externa X-organ) in the eyestalk. In previtellogenesis period (December${\sim}$March) and vitellogenesis period (April${\sim}$May), gonadal maturation was considerablely influnced by water temperature. In these periods, GSI increased and gonads were matured with water temperature rising without regard to photoperiod conditions (12L/12D and 15L/9D). In spawning period (June${\sim}$August), however, gonadal maturation was influenced by photoperiod condition. While high value of GSI was kept at long photoperiod regime (15L/9D), GSI was decreased at short photoperiod regime (12L/12D). In resting period (September${\sim}$November), no rematuration was occurred at all the experimental regimes combinated with water temperatures ($16^{\circ}C,\;22^{\circ}C,\;28^{\circ}C$) and photoperiod (12L/12D, 15L/9D). Effect of X-organ which inhibite the gonadal maturation was stronger in resting period than that in previtellogenesis and ealy spawning periods by observations on the effectiveness of eyestalk ablation on the gonadal maturation. In MEX-organ of eyestalk, the number of neurosecretory cells of which size was over $20{\mu}m$ in diameter varied according to the reproductive cycle. The number of cells increased $77{\pm}12$ in resting period, and decreased $55{\pm}7$ in vitellogenesis period. Volume of Bellonci's organ, however, increased in vitellogenesis period in comparison with that in resting period.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.18 no.2
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• pp.124-130
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• 1985

In the previous papers (Kim and Park, 1984 a, b; 1985 a), we have reported on alginic acid from Ecklonia cava and Sargassum ringgoldianum. The seasonal variation in the composition of uronic acids and their block structures of alginic acid from Myagropsis myagroides Fensholt and Sargassum horneri C. Agardh (collected from Iee Chun village on the coast of Ilgwang-myon, Yansan-gun, Kyungnam, Korea, in the period of January to December in 1982) are investigated, and their relationship between the chemical composition and some related properties are discussed in this study. One year average contents of alginic acid were $25.2\%$ in the M. myagroides and $26.5\%$ in the S. horneri, and one year average values of M/G ratios were 1.97 in the M. myagroides and 1.38 in the S. horneri. The value of M. myagroides was largest in the period of December to April, and smallest in May to June and October to November. The value of S. horneri was largest in January and smallest in March to April. The proportion of alternating, M and G block in M. myagroides were $18.4\%,\;40.4\%$, and $41.2\%$, and those in S. horneri $9.8\%,\;33.3\%$ and $56.9\%$, respectively. The higher viscosity showed the value of 45.3 cP in M. myagroides (in November), and 26.0 cP in S. horneri(in January), respectively. Furthermore, the dependence on temperature of M. myagroides alginic acid was also larger in November, that of S. horneri alginic acid in June. Ion exchange ability of M. myagroides alginic acid was highest in November and the exchange amounts were $Pb^{2+}\;4.4,\;Cu^{2+}\;1.8,\;Zn^{2+}\;2.5$ and $Co^{2+}\;2.0\;meq/g$. Na-Alg., and the ability of S. horneri alginic acid was highest in June and the amounts were $Pb^{2+}\;4.5,\;Cu^{2+}\;2.2,\;Zn^{2+}\;2.4$ and $Co^{2+}\;2.1\;meq/g.$ Na-Alg. The affinity with metallic ions appeared higher in order of $Pb^{2+}>Cu^{2+}>Zn^{2+}>Co^{2+}$, and the exchange ability assumed to relate with the block ratio of uronic acid.

• Journal of the Korean Society for Marine Environment & Energy
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• v.15 no.2
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• pp.76-88
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• 2012

In order to investigate the distribution of water masses and spatio-temporal variation of nutrients in the coastal areas of Gangwon province of the Korean East Sea, a survey of the physico-chemical parameters (temperature and salinity) and nutrients ($NO_2$-N, $NO_3$-N, $NH_4$-N, $PO_4$-P, and $SiO_2$-Si) was carried out at 5 locations (Goseong, Sokcho, Yangyang, Gangneung, and Donghae) in February, May, August, and November 2009. The water masses included in the study area were divided into 4 groups; 1) Tsushima Surface Water (TSW), 2) Tsushima Middle Water (TMW), 3) North Korean Cold Water (NKCW), and 4) East Sea Proper Water (ESPW). The distribution of water masses was affected by the change of season. In February, surface water was derived from the TMW. The TSW was not observed in May, but only observed in August. In November, as the influence of the TSW weakened, that of the NKCW strengthened. Considering the vertical profiles of nutrients, the concentrations in all the seasons were very low within the surface water, but increased rapidly near the thermocline. Most of nutrient concentrations, except for dissolved silicate, remained constant below the depth of 200 m. However, the dissolved silicate concentration increased with depth, suggesting that silicate has a delayed regenerative pattern. The ESPW had the highest nutrient concentration, followed by the NKCW, TMW, and TSW. In February, May, and November, the N/P ratio in most of the water masses was similar to or larger than the Redfield ratio, indicating that nitrogenous nutrients did not act as a limiting factor for phytoplankton growth. However, in August, the N/P ratio in the TSW was less than the Redfield ratio, and the concentration of $NO_2$-N+$NO_3$-N was 0.86 ${\mu}m$, indicating that nitrogenous nutrients did act as a limiting factor for phytoplankton growth in the study area.

• Weed & Turfgrass Science
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• v.6 no.4
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• pp.333-344
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• 2017

This study was conducted to examine the effect of cool-season grass overseeding on the green period, turf quality and density in zoysiagrass lawn. Treatments were perennial ryegrass (PR) overseeding ($60g\;m^{-2}$) on medium-leaf type zoysiagrass, Kentucky bluegrass (KB) overseeding ($20g\;m^{-2}$) on medium-leaf type zoysiagrass and narrow-leaf type zoysiagrass, and no overseeding on medium-leaf type zoysiagrass. Overseeding of KB or PR effectively provided quality improvement of zoysiagrass lawn by extending green-period about one month in spring and two months in fall season. PR overseeding showed quick green cover within 2-3 weeks but decreased the quality of overseeded zoysiagrass lawn during the summer season. Whereas, KB overseeding showed slow green cover taking two to three month after seeding but provided stable and good turf quality throughout the years. KB or PR overseeding significantly increased the turf density of zoysiagrass lawn except the period of summer depression of PR. The ground coverage of cool-season grasses ranged from 30 to 80% with considerable seasonal variation. As a result, KB and PR have their strengths and weaknesses as an overseeding material. Thus, the use of KB and PR as a mixture would provide better overseeding performance in zoysiagrass lawn.

• Korean Journal of Soil Science and Fertilizer
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• v.42 no.3
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• pp.222-229
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• 2009

This study was performed to evaluate effect of different fertilization management practices on soil microbial activities and community structure using soil enzyme activities and PLFA contents in volcanic ash citrus orchard soil. Six experiment plots have differently managed based on the recommended application rate(NPK) of chemical fertilizer and compost for 13 years. Experiment plots were composed of no-fertilization(control), compost only, half amount of NPK with compost (1/2NPK+COM), NPK, NPK with compost(NPK+COM), and 3 times amount of NPK(3NPK). Soil samples collected in early March, May, July, and September 2007. Urease activity was high at NPK+COM in March, May, and September. It was higher in NPK+COM than in NPK. Urease activity decreased according to the order NPK>compost>control in March and May; compost>NPK>control in July and September. Dehydrogenase activity was significantly higher in 1/2NPK+COM($4.3ug\;TPF\;g^{-1}\;24h^{-1}$) than in control($2.4ug\;TPF\;g^{-1}\;24h^{-1}$), May. $\beta$-glucosidase activity was significantly higher in NPK and 1/2NPK+COM than in control, May. In March, Total PLFA contents were higher in NPK+COM($349.2n\;mol\;g^{-1}$) than in 3NPK($228.5n\;mol\;g^{-1}$). And that were higher in 1/2NPK+COM($237.8n\;mol\;g^{-1}$) than in 3NPK($133.1n\;mol\;g^{-1}$), May. Distribution ratio of soil microbial groups by PLFA biomaker were not significantly difference in between seasonal and treatments. Principal component analysis by PLFA profiles showed that microbial community in compost and 3NPK plot were different compared with other treatments in March. But Differences in compost and 3NPK plot were not found in May. Our result showed that the change of microbial community structure affected by fertilization effect and seasonable variation.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.34 no.4
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• pp.291-298
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• 2001

Seawater, sediment and biota in the Kwangyang Bay were analyzed by gas chromatography/quartz furnace atomic absorption spectroscopy (GC-QFAAS) to investigate concentrations and distribution pattern of butyltin compounds (TBT, DBT, MBT) during February, April and July, 1996, Marine biota analyzed were Tapes japcnicus and Crassostrea gigas. The concentrations of tributyltin (TBT) in seawater were in the range of ND-15.7 ng/L for the surface and ND-68.5 ng/L for the bottom. The highest concentration of TBT in seawater was detected in April for the both, surface and bottom water. The maximum value of $TBT_{(bottom)}/TBT_{(surface)}$, 3.6 in April showed the increased input of TBT from the surface water in April compared to February (2.1) and July (0.9). The concentrations of TBT in the sediment were in the range of ND-8.5 ng/g dry wt. The highest concentration of TBT in the sediment was measured in July, This result seems to attributed to the removal of TBT from water column via sorption onto particulate matters to the relatively undisturbed underlying sediment and increased input of TBT by increased fluxes of detritus of marine plankton after spring bloom, in July. The mean values of partitioning coefficient ($K_d$) of TBT between seawater and sediment were $3.0\times10^3$(February), $7.4\times10^3$(April) and $9.4\times10^3$(July). The concentrations of TBT in biosamples were in the range of ND-93.30 ng/g dru wt. (T. japonicus) and ND-138.53 ng/g dry wt. (C. gigas). The seasonal variation of TBT contents in biota was remarkable. The $K_d$ (biological concentration factor) was $7-41\times10^3$ for T. japonicus. and $5-34\times10^3$ for C. gigas. The measured TBT concentrations in seawater in the study area was sufficient to cause the imposex of shellfish and to retard the growth of aquatic organisms including oyster upon chronic exposure.

• Journal of Korea Water Resources Association
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• v.51 no.3
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• pp.247-261
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• 2018

The purpose of this study is to evaluate the groundwater level behavior of Geum river basin ($9,645.5km^2$) under future climate change scenario projection periods (2020s: 2010~2039, 2050s: 2040~2069, 2080s: 2070~2099) using SWAT (Soil and Water Assessment Tool). Before future evaluation, the SWAT was calibrated and validated using 11 years (2005~2015) daily multi-purpose dam inflow at 2 locations (DCD, YDD), ground water level data at 5 locations (JSJS, OCCS, BEMR, CASS, BYBY), and three years (2012~2015) daily multi-function weir inflow at 3 locations (SJW, GJW, BJW). For the two dam inflow and dam storage, the Nash-Sutcliffe efficiency (NSE) was 0.57~0.67 and 0.87~0.94, and the coefficient of determination ($R^2$) was 0.69~0.73 and 0.63~0.73 respectively. For the three weir inflow and storage, the NSE was 0.68~0.70 and 0.94~0.99, and the $R^2$ was 0.83~0.86 and 0.48~0.61 respectively. The average $R^2$ for groundwater level was from 0.53 to 0.61. Under the future temperature increase of $4.3^{\circ}C$ and precipitation increase of 6.9% in 2080s (2070~2099) based on the historical periods (1976~2005) from HadGEM3-RA RCP 8.5 scenario, the future groundwater level shows decrease of -13.0 cm, -5.0 cm, -9.0 cm at 3 upstream locations (JSJS, OCCS, BEMR) and increase of +3.0 cm, +1.0 cm at 2 downstream locations (CASS, BYBY) respectively. The future groundwater level was directly affected by the groundwater recharge by the future seasonal spatial variation of rainfall in the watershed.

• Korean Journal of Microbiology
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• v.39 no.2
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• pp.95-101
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• 2003

The total bacterial numbers, Eubacterial community structures and environmental factors which affect bacterial community were estimated monthly using DAPI and fluorescent in situ hybridization monthly, from June to November 2000 to evaluate the correlation between the bacterial community and environmental factors in eutrophic agricultural Masan reservoir in Asan. Average water temperatures varied from 12.3 to $27.5^{\circ}C$, pH 7.5 to 9.0, DO 7. I~12.8 mg/L, COD 6.4~13.0 mg/L, chlorophyll a 30.5~99.0 mg/㎥, SS 7.S~25.7 mg/L, TN 1.748~3.543 mg/L., and TP 0.104~0.581 mg/L, respectively. Total bacterial numbers showed high ranges from 0.4 to 9.6$\times$ $10^{6}$ cells/ml, and these indicated the mesotrophic or eutrophic state. The ratio of Eubacteria to total bacteria was 67.6-88.0%, which was higher than that in other reservoir. The relationships of total bacteria and Eubacteria community were more significant with organic nitrogen (Org-N), and organic phosphorus (Org-P) than with water temperature. Proteobacteria groups showed strongly significant relationships with Org-P and Org-N and significant relationships with water temperature, conductivity, COD, and inorganic nitrogen. C-F group was the most significant with Org-N, and HGC group with water temperature. However, relationships of Chl-a, pH, DO and SS showed no significance with any bacterial community. These results were different from other studies, because of the specific characteristics of Masan reservoir such as old, shallow and eutrophic states. The seasonal variation of bacterial community in Masan reservoir does not seem to depend on phytoplankton dynamics but on storm event and organic materials from watershed and the sediment of reservoir.

• The Korean Journal of Malacology
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• v.28 no.3
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• pp.197-213
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• 2012

This study was performed to know the community structure of macrobenthos and environmental factors at each 16 stations in the subtidal sandy bottoms of the southern coastal water of Jeju Island from July to November, 2011. Mean temperature and mean salinity were $20.2-22.7^{\circ}C$, 33.7-34.9 psu which shows stable water messes. Chlorophyll a concentrations of phytoplankton ranged from 0.71 to 1.71 mg/L (1.11 mg/L), showing higher July than September and November with a blooming in summer. The mean concentration values (the ranges in parentheses) of nitrate, phosphate, and silicate are 0.029-0.206 mg/L (0.101 mg/L), 0.001-0.027 mg/L (0.007 mg/L), 0.024-0.682 mg/L (0.454 mg/L), respectively. However, the values higher coastal zone due to influxes from the land. A total of 37 species was identified. of these mollusca comprised 29 secies (78.4%); Echinodermata 5 (13.5%); Arthropoda 3 (8.1%). density and biomass were estimated to be 550 ind./$m^2$ and 20,951.8 gwwt/$m^2$, respectively. Mollusca were the most dominant faunal group in terms of abundance (481 ind./$m^2$) and number of species as well, whereas bivalves were predominant in biomass (16,647.6 gwwt/$m^2$). The dominant species were Vasticardium burchardi, Oblimopa japonica, Mactar achatina, Bornatemishistrioiw akawai, Paphia vernicosa, Amusium japonicum, Glycymeris albolineata, Astriclypeus manni in 15-30 m. The seasonal variation appeared as distinct, Mollusca of individual and biomass. When summer was make a slow increase, after the highest decrease in autumn. The abundance of macrobenthic invertebrates showed significant correlation with environmental factors (Chlorophyll a, DIN, $SiO_2$, Fine sand, Very fine sand) in almost all sampling depths. The biodiversity, evenness richness index were appeared 1.56-2.50 (H'), 0.49-0.80 (E'), 4.12-4.67 (R) in each stations. The dominace index were appeared Highest in November and lowest in September.

• Korean Journal of Agricultural Science
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• v.2 no.2
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• pp.331-339
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• 1975

This experiment was carried out to obtain some imformations about the ecological variations of the heading time of the newly breeded Indica x Japonica varieties/pedigrees according to the seasonal changes of the seeding date. day length and temperature. The results obtained are summarized as follows; 1) At all varieties. days to heading showed a straight reduction according as the seeding time was delayed. 2) At the group of Japonica varieties. the days to heading of early maturing varieties were much shortened and that of medium or late maturing varieties were little or not shortened under high temperature condition but at the group of Indica ${\times}$ Japonica va rieties/pedigrees. days to heading were significantly elongated under high temerature condition. 3) At the group of Japonica varieties. the effect of the short day condition on the days to heading was significantly high at the medium and the late maturing varieties than at the early maturing varieties. however. the short day effect on the reduction of days to heading was not related with the earlyness of each varieties at the group of Indica ${\times}$ Japonica varieties/pedigrees. 4) Days to heading of all varieties under the high temperature condition were longer than that under the ordinary culture. On the other hand, the days to heading of Japonica varieties under the short day treatment were shorter than the days to heading of ordinary culture but at the group of Indica x Japonica varieties/pedigrees. the days to heading under the short day treatment were longer than ordinary culture. 5) At both varieties groups. the days to heading at each seeding time were significantly correlated with days to heading at ordinary cultivation. fl) At the group of Japonica varieties. relatively high correlation(p=0.1) was recognized between the days to heading by delay of seeding time, but at the group of Indica ${\times}$ Japonicava rieties/pedigrees, correlation between the ordinary heading date and the shortening rate of days to heading was very low.