• Journal of Soil and Groundwater Environment
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• v.26 no.6
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• pp.95-105
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• 2021

Extensive groundwater abstraction has been recognized as one of the major challenges in management of coastal groundwater. The purpose of this study was to assess potential changes of groundwater distribution of northeastern Jeju Island over 10-year duration, where brackish water have been actively developed. To quantitatively estimate the coastal groundwater resources, numerical simulations using three-dimensional finite-difference density-dependent flow models were performed to describe spatial distribution of the groundwater in the aquifer under various pumping and recharge scenarios. The simulation results showed different spatial distribution of freshwater, brackish, and saline groundwater at varying seawater concentration from 10 to 90%. Volumetric analysis was also performed using three-dimensional concentration distribution of groundwater to calculate the volume of fresh, brackish, and saline groundwater below sea level. Based on the volumetric analysis, a quantitative analysis of future seawater intrusion vulnerability was performed using the volume-based vulnerability index adopted from the existing analytical approaches. The result showed that decrease in recharge can exacerbate vulnerability of coastal groundwater resources by inducing broader saline area as well as increasing brackish water volume of unconfined aquifers.

• Journal of Environmental Science International
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• v.13 no.4
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• pp.377-387
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• 2004

This study has been performed to clarify the characteristics of temporal and spatial distribution of surface ozone concentration over Jeju Island, one of the cleanest areas in Korea with low emissions of air pollutants. Ozone data are monitored at four sites in Jeju Island. These monitoring sites are located at two urban area(referred to Ido and Donghong), coastal area(Gosan site) and forest site(Chuna site). Ozone data has been routinely collected at these sites for the late four years. The patterns of seasonal cycle of ozone concentrations at all stations show the bimodal with the peaks on spring and autumn and a significant summer minimum. However, the patterns of diurnal variations at rural station, i.e., Gosan and Chuna sites are considerably different to those at urban stations such as Ido and Donghong sites. The patterns of $\DeltaO_3$ variations are very similar with those of monthly mean ozone concentrations and $\DeltaO_3$ values are exceeded 30 ppb, at urban stations. This may be that urban stations are more influenced by local photochemical reactions rather than rural stations. In order to assess the potential roles of meteorological parameters on ozone formation, the meteorological parameters, such as radiation, temperature, and wind are monitored together with ozone concentrations at all stations. The relationships of meteorological parameters to the corresponding ozone concentration are found to be insignificant in Jeju Island. However, at Gosan and Donghong stations, when the sea breeze blew toward the station, the ozone concentration is considerably increased.

• Atmosphere
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• v.21 no.4
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• pp.361-371
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• 2011

In this study, characteristics and trends of tropical night (TN) are investigated by using the KMA 14 observation data for the recent 50 years (1958-2007) over South Korea. The TN is defined as a day with a daily minimum temperature exceeds the absolute threshold temperature ($25^{\circ}C$), and the relative deviation from normal temperature, 95th percentile of all observed daily minimum temperature. Although the spatial distribution of TN occurrence depends on the choice of the definitions, the frequency of TN shows strong spatial and interannual variations with the minimum at high land area (Chupungnyeong and wet years) and maximum at southern coastal area and large city area (Jeju, Busan, Seoul, Daegu). Most of TN occurs in August (56%) and July (41%), and the duration date of TN is proportional to the frequency of TN without regard to the definition method. In general, increasing trends are found in the TN time series without regard to the analysis method, but the trends are clearly depending on the analysis period and geographic locations. Decreasing trends are prominent during the most of analysis period, especially until the mid of 1990, whereas strong increasing trends are found during recent 30 years (1988-2007), especially at Jeju, Ulsan, Daegu and Pohang. Also the severity of TN is significantly increased in recent years.

• The Korean Journal of Malacology
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• v.23 no.2
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• pp.235-243
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• 2007

Macrobenthos were collected in each season by SCUBA diving to investigate the benthic faunal assemblages in the coastal water of Chagwido from September 2004 to August 2005. A total of 201 macrobenthos identified, 74 species (37.2%) of Mollusca were found; 43 species of Arthropoda (19.2%); 34 species of Cnidaria (16.7%) and others including 18 species of Porifera (9.8%). Mean density and biomass were estimated to be 455 individual/$m^2$ and 15,565.0 $g/m^2$, respectively. Whereas annelids was predominant in biomass (1,558.8 g), gastropods were the most dominant faunal group in terms of abundance (5,391 individuals) and the number of species. The dominant species were Trochus sacellus, Batillus cornutus, Pagurus gracilipes, and Cantharus cecillei. The seasonal variation of the number of species and individual Mollusca and Arthropoda was observed. There was a slow increase in spring, the peak in summer, and a slow decrease in autumn and winter. The dominance index was the highest in Gosan and lowest in Yongdang. The biodiversity indice (H') were 1.760-3.497 in each station. Mean biodiversity index was 2.858 (H'). The diversity index, the eveness index (E'), and the dominance index (R) were 3.218-3.743, 0.648-0.720, 17.690-22.826, respectively, in each station.

• 한국해양학회지
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• v.19 no.1
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• pp.68-81
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• 1984

To characterize community structure and distribution of phytoplankton, cluster analyses are performed on quantitative data of phytoplankton collected from the southwestern sea of Korea in early summer, 1980. The cluster analysis shows that the phytoplankton of the study area consists of three distinct characteristic communities, representing different water masses. The species of the first community, predominant in the southwestern coastal were of the main land, are mostly neritic and cold water diatoms. The second community consists of neritic and oceanic diatoms, a few flagellates and an euglenoid. These species are predominant in the vicinity of Jeju Island with warm and high saline waters which seems to be a branch of the Kuroshio Current. The species of the last community, consisting primarily of small-sized dinoflagellates, are predominant in the rest part of the study area with warm and low saline water. Addition, the vertical distributions of phytoplankton and environmental factors show that high concentration of phytoplankton cells, chlorophyll-a and dissolved oxygen are observed near the seasonal pycnocline in the off-coastal area. Fraction of nanoplankton take the above 90% of the total cell concentration in the surface mixed layer of off-coastal area where the seasonal pycnocline develops in summer.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.50 no.1
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• pp.12-20
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• 2014

The objective of this paper is to aid in basic directions for the countermeasure against marine accidents by using the statistical data of Jeju Coast Guard from 1983 to 2012. Marine accidents of about 600~1,000 vessels was reported in all the waters around South Korea from 2000 to 2008. From 2009, these accidents increased rapidly and reached 1,600~2,000 vessels. Although marine accidents of longline fishing vessels did not show a big change prior to 1993, the number have increased steadily until 2007. This is considered a tendency that appears when longline vessels, using the Port of Sungsanpo as a base and operating in fishing grounds in the East China Sea, are converted to long-term fishing from short-term fishing for reasons such as cost reduction due to the sudden rise of oil prices and the performance improvement of the fishing vessels. The number of vessels in marine accidents decreased gradually from 1999 to 2002 and for nearly 7 years from 2002 to 2008, the annual average of marine accidents stayed at 97 vessels. This is seemed to be the result of a change in the policy of either the central or local government and largely associated with changes in the way of statistical processing. This tendency is resulted in lower number of the accidents due to careless navigation which can be viewed as a human error than the number of marine accidents due to poor maintenance as a cause of mechanical failure in the same period. The increase rate in the marine accidents of Jeju Island-based fishing vessels is greater than that of other area-based fishing vessels among the fishing vessels operating in coastal and near sea around Jeju Island each year.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.51 no.5
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• pp.600-605
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• 2018

The Indo-Pacific bottlenose dolphins Tursiops aduncus are the only cetacean species that can be observed visually on coastal areas of Jeju Island and regarded as one of valuable tour resources. We attempted to figure out location and timing information of the dolphin sightings collected from two major social media, Naver $Caf{\acute{e}}$ and Instagram. 142 of dolphin sighting information were derived from 2,501 dolphin related postings on Naver $Caf{\acute{e}}$ between 2004 to 2017. 292 informative postings also were found on Instagram through hashtag searching. The number of posts about dolphin sighting was not frequent until 2014. Since 13 posts were found in 2014, dramatic increase of the sighting numbers was accelerated as 38 in 2015, 93 in 2016 and 269 in 2017. 195 (45.7%) from coastal area of Daejeong-eup, south-western part of the Island, were posted. The number of dolphin sightings also high from Gujwa-eup(n=50, 11.7%), Hangyeong-myeon (n=49, 11.5%), Seongsan-eup (n=38, 8.9%) and Seogwipo-si (n=34, 8.0%). Our results show that social media data has a high potential to be used as a data source for study of distribution pattern of the dolphins.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.34 no.3
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• pp.72-81
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• 2022

Positions of five drifting buoys deployed on August 2020 near southwestern area of Jeju Island and numerically predicted velocities were used to develop five Artificial Intelligence-based models (AI models) for the prediction of particle tracks. Five AI models consisted of three machine learning models (Extra Trees, LightGBM, and Support Vector Machine) and two deep learning models (DNN and RBFN). To evaluate the prediction accuracy for six models, the predicted positions from five AI models and one numerical model were compared with the observed positions from five drifting buoys. Three skills (MAE, RMSE, and NCLS) for the five buoys and their averaged values were calculated. DNN model showed the best prediction accuracy in MAE, RMSE, and NCLS.

• Korean Journal of Agricultural and Forest Meteorology
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• v.14 no.4
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• pp.179-188
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• 2012

A kiwifruit cultivar 'Hayward' has been grown in Jeju Island where the current climate is suitable for growth and development of this crop. Prediction of the geographical shift in the phenology can help the kiwifruits growers to adapt to the local climate change in the future. Two phenology models (i.e., chill-day and DVS) were parameterized to estimate flowering date of kiwifruits 'Hayward' based on the data collected from field plots and chamber experiments in the southern coastal and island locations in South Korea. Spatio-temporally independent datasets were used to evaluate performance of the two models in predicting flowering date of 'Hayward'. Chill-day model showed better performance than DVS model (2.5 vs. 4.0 days in RMSE). Daily temperature data interpolated at a higher spatial resolution over Jeju Island were used to predict flowering dates of 'Hayward' in 2021-2100 under the A1B scenario. According to the model calculation under the future climate condition, the flowering of kiwifruits shall accelerate and the area with poor flowering might increase due to the warmer winter induced insufficient chilling. Optimal land area for growing 'Hayward' could increase for a while in the near future (2021-2030), whereas such areas could decrease to one half of the current areas by 2100. The geographic locations suitable for 'Hayward' cultivation would migrate from the current coastal area to the elevated mountain area by 250 m.

• Journal of the Korean earth science society
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• v.28 no.7
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• pp.925-935
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• 2007

Water sources in volcanic Jeju Island are almost entirely dependent on groundwater because there are actually no perennial streams or rivers due to the permeable nature of surface soils derived from basaltic or trachytic rocks. Uncontrolled development of groundwater resulted in substantial water-level decline, groundwater pollution, and seawater intrusion in several places of the island. To maintain its sustainable groundwater, the provincial government has declared some parts of the island as the Special Groundwater Conservation/Management Area since 1994. Hence, all the activities for the groundwater development in the area should obtain official permit from relevant authorities. Furthermore, to acquire information on groundwater status, a network of groundwater monitoring was established to cover most of the low land and coastal areas with the installation of automatic monitoring systems since 2001. The analysis of the groundwater monitoring data indicated that the water levels had decreased at coastal area, especially in northern part of the island. Moreover, very high electrical conductivity (EC) levels and their increasing trends were observed in the eastern part, which was ascribable to seawater intrusion by intensive pumping in recent years. Water level decline and EC rise in the coastal area are expected to continue despite the present strict control on additional groundwater development.