• Journal of the Korean Society of Marine Environment & Safety
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• v.20 no.6
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• pp.601-608
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• 2014

The purpose of this study was to explore the long-term variability of sea surface temperature (SST) and cluster analysis derived from in-situ data in the coastal oceanographic observation 8 stations (Sokcho, Jumunjin, Donghae, Jukbyeon, Pohang, Janggigab, Ulgi, Gampo) of the East Sea during 1971-2013. As a result of cluster analysis, SST variations in each area could be divided into two groups, which was a group A of Sokcho, Jumunjin, Donghae, and group B of Jukbyeon, Pohang, Janggigab, Ulgi, Gampo. The SST and SST anomalies at Sokcho, Jukbyeon, Pohang and Gampo during 1971-2013 showed the increase-trend with the variations of decadal-scale. Annual SST values also increased remarkably after 1988. The increases of SST for 43 years showed $2.26^{\circ}C$ at Sokcho, $1.99^{\circ}C$ at Jukbyeon, $1.11^{\circ}C$ at Pohang and $0.89^{\circ}C$ at Gampo. In particular, the SST variations of the northern areas were higher than those of southern areas. The seasonal SSTs increased the order of Sokcho-Jukbyeon-Pohang-Gampo in fall and winter and that of Jukbyeon-Sokcho-Pohang-Gampo in spring and summer.

• Journal of Korean Society of Water and Wastewater
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• v.35 no.5
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• pp.323-334
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• 2021

Pilot-scale coagulation and sedimentation processes were operated to investigate the T-P (Total phosphorus) removal efficiency. A multiple regression model was also derived to predict the water quality improvement effect with river water characteristics. The inflow rates for the pilot-scale facility were 157-576 m³/day, and the coagulant doses were in the range of 13.7-58.5 mg/L (average 38.9 mg/L) for PAC (Poly alum chloride) and 16.5-62.1 mg/L (average 36.0 mg/L) for alum. The results found that the influent BOD (Biochemical oxygen demand) and T-P concentrations were 4.9 mg/L and 0.115 mg/L, and the removal efficiencies were 52.7% and 59.4%, respectively. T-P removal efficiencies on wet weather days were higher by 10% than dry weather days because influent solids influenced T-P's coagulation process. The pH of river water was 6.9-7.8, and the average pH was 7.3. Although the pH variation was not significant, the trend showed that the treatment efficiency of T-P and PO₄-P removal increased. Thus, the pH range considered in this study seems to be appropriate for the coagulation process, which is essential for phosphorous removal. The T-P removal efficiencies were 19.6-93.3% (average 59.2%) for PAC and 16.4-98.5%(average 55.9%) for alum; thus, both coagulants showed similar results. Furthermore, the average coagulant doses were similar at 42.4 mg/L for PAC and 41.3 mg/L for alum. When the T-P concentration of the effluent was compared by the [Al]/[P] ratio, the phosphorus concentration of the treated water decreased with an increasing [Al]/[P] ratio, and the lowest T-P concentration range appeared at the [Al]/[P] ratio of 10-30. A seasonal multiple regression analysis equations were derived from the relationships between 10 independent and dependent variables (T-P concentration of effluent). This study could help lake water quality maintenance, reduce eutrophication, and improve direction settings for urban planning, especially plans related to developing waterfront cities.

• Journal of Wetlands Research
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• v.23 no.4
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• pp.364-371
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• 2021

Public awareness of alien species can vary by generation, period, or specific events associated with these species. An understanding of public awareness is important for the management of alien species because differences in public awareness can affect the establishment and implementation of management plans. We analyzed digital texts on social media platforms, news articles, and internet search volumes used in conservation culturomics to understand public interest and sentiment regarding alien freshwater species. The number of tweets, number of news articles, and relative search volume to 11 freshwater alien species were extracted to determine public interest. Additionally, the trend over time, seasonal variability, and repetition period of these data were confirmed. We also calculated the sentiment score and analyzed public sentiment in the collected data using sentiment analysis based on text mining techniques. The American bullfrog, nutria, bluegill, and largemouth bass drew relatively more public interest than other species. Some species showed repeated patterns in the number of Twitter posts, media coverage, and internet searches found according to the specified periods. The text mining analysis results showed negative sentiments from most people regarding alien freshwater species. Particularly, negative sentiments increased over the years after alien species were designated as ecologically disturbing species.

• Korean Journal of Remote Sensing
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• v.37 no.6_1
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• pp.1589-1597
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• 2021

Submarine groundwater discharge (SGD) in coastal areas is gaining importance as a major transport route that bring nutrients and trace metals into the ocean. This paper describes the analysis of the seasonal changes and spatiotemporal characteristicsthrough the modeling monthly SGD for 35 years from 1986 to 2020 for the Nakdong river basin. In this study, we extracted 210 watersheds and SGD estimation points using the SRTM (Shuttle Radar Topography Mission) DEM (Digital Elevation Model). The average annual SGD of the Nakdong River basin was estimated to be 466.7 m²/yr from the FLDAS (Famine Early Warning Systems Network Land Data Assimilation System) recharge data of 10 km which is the highest resolution global model applicable to Korea. There was no significant time-series variation of SGD in the Nakdong river basin, but the concentrated period of SGD was expanded from summer to autumn. In addition, it was confirmed that there is a large amount of SGD regardless of the season in coastal area nearby large rivers, and the trend has slightly increased since the 1980s. The characteristics are considered to be related to the change in the major precipitation period in the study area, and spatially it is due to the high baseflow-groundwater in the vicinity of large rivers. This study is a precedentstudy that presents a modeling technique to explore the characteristics of SGD in Korea, and is expected to be useful as foundational information for coastal management and evaluating the impact of SGD to the ocean.

• Journal of Digital Convergence
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• v.17 no.9
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• pp.135-145
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• 2019

Prolonged recession has caused the youth unemployment rate in Korea to remain at a high level of approximately 10% for years. Recently, the number of unemployed Koreans in their 30s and 40s has shown an upward trend. To expand the government's employment promotion and unemployment benefits from youth-centered policies to diverse age groups, including people in their 30s and 40s, prediction models for different age groups are required. Thus, we aimed to develop unemployment prediction models for specific age groups (30s and 40s) using available unemployment rates provided by Statistics Korea and Google search queries related to them. We first estimated multiple linear regressions (Model 1) using seasonal autoregressive integrated moving average approach with relevant unemployment rates. Then, we introduced Google search queries to obtain improved models (Model 2). For both groups, consequently, Model 2 additionally using web queries outperformed Model 1 during training and predictive periods. This result indicates that a web search query is still significant to improve the unemployment predictive models for Koreans. For practical application, this study needs to be furthered but will contribute to obtaining age-wise unemployment predictions.

• Pediatric Infection and Vaccine
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• v.27 no.3
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• pp.171-179
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• 2020

Purpose: In Korea, seasonal influenza is an important respiratory illness afflicting children every year. We aimed to investigate the childhood epidemiology in Jeju during the 2017-2018 and 2018-2019 seasons. Methods: Children aged <13 years, who were tested for influenza at the Jeju National University Hospital during the 2017-2018 and 2018-2019 influenza seasons, were included. Demographics and the influenza test results were retrospectively reviewed from their medical records. Results: This study included 5,219 cases of influenza-like illness (ILI) (2017-2018: n=2,279; 2018-2019: n=2,940). The mean age of the eligible children was 2.85±2.79 years, and the most common age among ILI patients in each season was 1 year group. There were 902 (17.3%, 902/5,219) confirmed influenza cases during the 2 seasons. The rate of influenza confirmed by rapid influenza diagnostic test or polymerase chain reaction among ILI patients in the 2017-2018 and 2018-2019 seasons was 10.4% (236/2,279) and 10.3% (303/2,940) for influenza A, and 9.1% (208/2,279) and 5.3% (155/2,940) for influenza B, respectively. The mean age of influenza-confirmed cases was 4.09 years and 5.05 years in the 2017-2018 and 2018-2019 seasons, respectively (P<0.05). Weekly distribution of influenza was similar to that of ILI in the clinical sentinel surveillance system in both seasons. Conclusion: The difference in the influenza epidemic trend and age-group distribution between the 2017-2018 and 2018-2019 seasons was distinct in Jeju. Steady epidemiological studies on influenza in Jeju are needed for comparison with other regions of Korea.

• Journal of Soil and Groundwater Environment
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• v.26 no.4
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• pp.27-43
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• 2021

Since climate factors, such as precipitation, temperature, etc., show repeated patterns every year, it can be said that future changes can be predicted by analyzing past climate data. As with groundwater, seasonal variations predominate. Therefore, when a drought occurs, the groundwater level is also lowered. Thus, a change in the groundwater level can represent a drought. Like precipitation, groundwater level changes also have a high correlation with drought, so many researchers use Standard Groundwater Level Index (SGI) to which the Standard Precipitation Index (SPI) method is applied to evaluate the severity of droughts and predict drought trends. However, due to the strong interferences caused by the recent increase in groundwater use, it is difficult to represent the droughts of regions or entire watersheds by only using groundwater level change data using the SPI or SGI methods, which analyze data from one representative observation station. Therefore, if the long-term groundwater level changes of all the provinces of a watershed are analyzed, the overall trend can be shown even if there is use interference. Thus, future groundwater level changes and droughts can be more accurately predicted. Therefore, in this study, it was confirmed that the groundwater level changes in the last 5 years compared with the monthly average groundwater level changes of the monitoring wells installed before 2015 appeared similar to the drought occurrence pattern. As a result of analyzing the correlation with the water storage yields of 3,423 agricultural reservoirs that do not immediately open their sluice gates in the cases of droughts or floods, it was confirmed that the correlation was higher than 56% in the natural state. Therefore, it was concluded that it is possible to re-evaluate agricultural droughts through long-term groundwater level change analyses.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.1B
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• pp.41-53
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• 2008

Unprecedented weather phenomena are occurring because of climate change: extreme heavy rains, heat waves, and severe rain storms after the rainy season. Recently, the frequency of these abnormal phenomena has increased. However, regular pattern or cycles cannot be found. Analysis of annual data or annual average data, which has been established a research method of climate change, should be applied to find frequency and tendencies of extreme climate events. In this paper, extreme indicators of precipitation and temperature marked by objectivity and consistency were established to analyze data collected by 66 observatories throughout Korea operated by the Meteorological Administration. To assess the statistical significance of the data, linear regression and Kendall-Tau method were applied for statistical diagnosis. The indicators were analyzed to find tendencies. The analysis revealed that an increase of precipitation along with a decrease of the number of rainy days. A seasonal trend was also found: precipitation rate and the heavy rainfall threshold increased to a greater extent in the summer(June-August) than in the winter (September-November). In the meanwhile, a tendency of temperature increase was more prominent in the winter (December-February) than in the summer (June-August). In general, this phenomenon was more widespread in inland areas than in coastal areas. Furthermore, the number of winter frost days diminished throughout Korea. As was mentioned in the literature, the progression of climate change has influenced the increase of temperature in the winter.

• Journal of the Korean Society of Marine Environment & Safety
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• v.29 no.6
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• pp.525-535
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• 2023

In thi study, we unveil the intricate interplay among picophytoplankton (0.2-2 ㎛) communities, warming surface water temperatures, and major inorganic nutrients within the southwestern East Sea from 2003-2022. The observed surface temperature rise, reflecting global climate trends, defies conventional seasonal patterns in temperate seas, with highest temperatures in summer and lowest in spring. Concurrently, concentrations of major dissolved inorganic nutrient display distinct seasonality, with peaks in winter and gradually declining thereafter during spring. The time course of chlorophyll-a concentrations, a proxy for phytoplankton biomass, reveals a typical bimodal pattern for temperate seas. Notably, contributions from picophytoplankton exhibited a steady annual increase of approximately 0.5% over the study period, although the total chlorophyll-a concentrations declined slightly. The strong correlations between picophytoplankton contributions and inorganic nutrient concentrations is noteworthy, highlighting their competitively advantageous responsiveness to the shifting nutrient regime. These findings reflect significant ecological implications for the scientific insights into the marine ecosystem responses to changing climate conditions.

• Korean Journal of Ecology and Environment
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• v.57 no.2
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• pp.61-74
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• 2024

Daemadeung, located in the estuary of the Nakdong River, is formed by sand dunes and possesses well-developed intertidal flats. This study aimed to investigate the habitat of benthic microalgae, photosynthetic pigments, and photosynthetic efficiency in the intertidal flats of Daemadeung from January to December 2011. The inorganic nitrogen content in the sediment pore water was primarily composed of ammonium, while nitrate + nitrite was dominant in the upper layer water. The concentration of chlorophyll a and fucoxanthin in the sediment surface was significantly higher than the mean of all the sediment layer. The average Fv/Fm of benthic microalgae during the entire survey period was 0.52±0.03, with the highest value (0.61±0.08) observed in February. The rETR_max showed a seasonal trend, being high from spring to early autumn (April to October) and low from winter to early spring (January to March, November, December), with the highest value (153.05±2.30 µmol electrons m^-2 s^-1) in July and the lowest (38.49±5.17 µmol electrons m^-2 s^-1) in January. The average Fv/Fm of diurnal microalgae was 0.48±0.03, with the highest value (0.61±0.08) observed at noon. The rETR_max showed a highest peak at noon (54.24±11.35 µmol electrons m^-2 s^-1) and reached its lowest point at 16:00 (26.17±4.75 µmol electrons m^-2 s^-1). These findings suggest that the productivity of benthic microalgae varies significantly depending on the survey time and sediment depth. Therefore, to quantify the productivity of benthic microalgae using Diving-PAM, surveys should be conducted based on tidal conditions, and simultaneous pigment analysis of sediment layers should also be performed.