• Korean Journal of Ecology and Environment
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• v.33 no.2 s.90
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• pp.152-161
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• 2000

Simocephalus mixtus Sars was redescribed and illustrated from Korea. It had been frequently confused with S. vetulus (O.F. M$\"{u}$ller) and S. vetuloides Sars in the Far East. Redescription was based on the materials collected from various freshwater habitats at 97 localities in South Korea during the period from May 1981 to June 1999. Previous records of Simocephalus species from Korea were examined. S. mixtus is well distinguishable from other related species by having short and wide dorso-posterior carapace angle prominence, distally protruding dorsal margin of carapace, deep depression of the ventral head margin near the rostrum, elongate ocellus, and postabdominal claw lacking the basal pecten of denticles.

• Korean Journal of Ecology and Environment
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• v.33 no.2 s.90
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• pp.119-127
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• 2000

Diurnal vertical distribution of phytoplankton and physico-chemical characteristics were studied in Kongsan reservoir during summer 1996, when a dense algal bloom, consisting mostly of Microcystis, developed. The maximum biomass was observed near the surface layer, where Microcystis aeruginosa dominated and declined gradually with depth. The dense population of blue-green alga M. aeruginosa acumulated near the surface layer during the early morning and evening, but abruptly decreased after sunrise. The most of biomass was distributed above 5 m of the water column and diurnal changes of biomass clearly appeared at the surface but was not showed upward and downward migration. The results of this study suggest that diurnal variation of biomass at the surface layer was affected by horizontal migration with wind.

• Korean Journal of Ecology and Environment
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• v.48 no.4
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• pp.280-286
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• 2015

Life cycles of Sweltsa illiesi and S. lepnevae were determined from a headwater stream in Mt. Jumbong. Identification of nymphs was done by using DNA barcoding. Nymphs begin to have species specific color pattern on their head several months prior to adult emergence and differ in the form of the third antennal segment. Two species appear to have similar semivoltine life cycles in this stream, beginning to hatch from June and finishing adult emergence about 701 days later. The combined annual mean biomass in ash free dry mass (AFDM) was estimated as $96mg\;AFDM\;m^{-2}$. The combined annual secondary production were 373 mg and $297mg\;AFDM\;m^{-2}\;yr^{-1}$, calculated by using size frequency method and increment summation method respectively.

• Korean Journal of Ecology and Environment
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• v.44 no.4
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• pp.337-346
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• 2011

We investigated nutrient loading and trophic states in a coastal estuarine system in the Asan estuary by assessing phytoplankton biomass and using the trophic index (TRIX). The monthly and yearly nutrient loading (TN, TP) from freshwater discharge from the Asan and Sapgyo reservoirs into the estuary were estimated and analyzed with related factors. Monitoring data (physio-chemical and biological variables) collected at five estuary stations were used to assess trophic states. Descriptive statistics of total phytoplankton cells, chl a concentrations and primary productivity were also used to assess seasonal trophic status. N loading from freshwater ranged $1.0{\sim}1.3{\times}10^4$ ton yearly. The yearly P loading ranged between 350 and 400 ton during 2004~2006, increasing to 570 ton in 2007. Regression results suggest that DIN and DSi were correlated with freshwater discharge at the upper region. Based on phytoplankton biomass and total cell abundance, the trophic state of the estuary was found to be eutrophic during spring due to phytoplankton bloom. Primary productivity level was remarkably high, especially in summer coinciding with high nutrient loading. Pheopigments increased during warm seasons, i.e. summer and fall. Trophic index results indicate that the trophic state varied between mesotrophic and eutrophic in the estuary water body, especially in the upper region. The results suggest that phytoplankton production was regulated by nutrient loading from freshwater whereas biomass was affected by other properties than nutrient loading in the Asan Estuary ecosystem.

• Korean Journal of Ecology and Environment
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• v.44 no.4
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• pp.317-326
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• 2011

With its recent advances, nanotechnology is now being applied to various areas. Despite the benefits of nanoparticles, their risk in the environment has caused controversy, which is now becoming an international issue. Nanoparticles can easily infiltrate into cells, accumulate in biota, and may cause adverse effects in the levels of molecules, cells and organisms, and in the community. If nanoparticles are released into the environment, they can be transferred to organisms in the ecosystem, and eventually to the human body through the food chain. In this study, the research trend of the trophic transfer of nanoparticles in the food chain was investigated. Although a few investigations have been conducted regarding this topic, the trophic transfer of nanoparticles is becoming a significant issue in the area of nanotoxicology due to the potential risk to humans via the biomagnification process. While previous studies have demonstrated evidence of the trophic transfer of nanoparticles intensive future studies are needed to provide further information on the properties of nanomaterials, the exposure media, and the in vivo mechanisms such as uptake, accumulation, and depuration.

• Korean Journal of Ecology and Environment
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• v.50 no.4
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• pp.374-380
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• 2017

Pine wilt disease (PWD) is one of the hazardous pine tree diseases in whole world. In Korea, PWD has been spreading since it was first observed in Busan in 1988. Dispersion of PWD is mainly mediated by its vectors such as Japanese pine sawyer. In this study, we characterized environmental condition including meteorological factors, geographical factors, and land use factors influencing on the occurrence of PWD. The occurrence data of PWD were collected at 153 sites where were the initial occurrence sites of PWD in local government regions such as city, Gun, or Gu scale. We used Akaike Information Criterion (AIC) to evaluate the relative importance of environmental variables on the discrimination of occurrence or absence of PWD. The results showed that altitude, slope, and distance to road were the most influential factors on the occurrence of PWD, followed by distance to building. Finally, our study presented that human activities highly influenced on the long term dispersal of PWD.

• Korean Journal of Ecology and Environment
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• v.53 no.1
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• pp.22-30
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• 2020

In this study, we investigated the relationships between benthic macroinvertebrate assemblages and various environmental factors in Iancheon (NIA) and Bukcheon (NBC) streams, Korea. We collected benthic macroinvertebrates and 33 environmental factors in April 2017 at 9 sites (5 sites in NIA and 4 sites in NBC). We identified 93 species(5 phyla, 9 classes, 16 orders, and 53 families) and 69 species(5 phyla, 9 classes, 17 orders, and 47 families) in NIA and NBC streams, respectively. Considering benthic macroinvertebrate index (BMI), NIA (88.2) and NBC (80.2) streams were in "very good" status. Upstream areas showed the highest scores, 95.5 (NIA1) and 94.2 (NBC1), whereas BMI score was the lowest in downstream areas of both streams, especially in NBC4 (51.0 "bad" status). Cluster analysis and non-metric multidimensional scaling analysis represented the differences of benthic macroinvertebrate assemblages according to spatial and anthropogenic gradients. Our findings provide reference data and highlight the need for the continued monitoring to maintain the good status and manage macroinvertebrate diversity in these two streams, in Sangju-si, Korea.

• Korean Journal of Ecology and Environment
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• v.53 no.1
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• pp.80-90
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• 2020

In order to understand the stress responses, we measured the concentration of stress hormones by using the fresh feces of wild otters in the Gwangju stream and Seomjin river during summer and winter in 2018. We compared seasonal and regional number of spraints (=otters' feces), temperature, altitude, water width, land cover, and water quality with stress hormones. The stress hormone levels were higher in summer than in winter, and significantly different to season and region. In addition, the number of feces were different according to the season and region, and showed a negative correlation with stress hormone. This study suggested assessing stress hormones as another promising method for the analysis of status of wild otters and it will contribute to establish the management and conservation policy, especially in urban area.

• Korean Journal of Ecology and Environment
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• v.33 no.1 s.89
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• pp.1-8
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• 2000

Four cyclopoids were tested for laboratory culture. Among these animals, only Eucyclops serrulatus was successfully cultured in the laboratory. Under the laboratory culture condition, nine kinds of diets were tested for the suitability of nauplius development. Development and reproduction of E. serrulatus were also investigated. Chlamydomonas reinhardii was the only one which could induce complete development from nauplii to adults. It was found that E. serrulatus had relatively short generation time, could produce lots of progenies, and could be handled easily, allowing to obtain many individuals during a short period. With these characteristics, this species may be a candidate for a good test organism for evaluating freshwater pollution.

• Korean Journal of Ecology and Environment
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• v.45 no.2
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• pp.200-209
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• 2012

The current of the water body is very important information for the water quality management on reservoirs. It is applied to hydraulics and water quality model for simulation. In this regard, the current characteristic of water body is the basic information that can be used to predict various conditions. However, it is very slow flowing and is affected by the reservoir operations and external factors. As such, an accurate measurement of the current is a difficult problem. In order to measure the water current, we constructed a drifter. According to the result of flow survey at Yongdam reservoir, 5m and 10 m depth layer flow was investigated from the upstream to the downstream, during a flood period. Maximum flow rate of 5 m depth is 13.8 cm $sec^{-1}$ and 10 m depth shows 4 cm $sec^{-1}$, respectively. But 2m depth shows a backward flow and maximum flow rate is 4 cm $sec^{-1}$. Density currents flow plays the role of back flow in reservoirs. Flow velocity in the reservoir was measured in the range of 1~2 cm $sec^{-1}$, at normal flow season, and the flow direction were different for each survey. This phenomenon occurs because the reservoir volume is very large, compared to the inflow and outflow volume.