• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.24 no.4
• /
• pp.257-268
• /
• 2012

The EFDC model with find grid resolution system connecting the Gyeong-Gi bay and Han River estuary was constructed to study on spring-neap variability of net volume transport at each channel of the Han River estuary. The simulation time of numerical model is 124 days from May to August, 2009 with freshwater discharge at Han, Imjin and Yeseong River. The calibration and verification of model results was confirmed using harmonic components of water level and tidal current. The net volume transport was calculated during 30 days with normal freshwater conditions at Seokmo channel and Yeomha channel around Ganghwado. The ebbing net volume transport of 44% and 56% is drained into Gyeong-Gi bay through Yeomha and Seokmo channel, respectively. The ebbing net volume transport nearby Seodo at Yeomha channel convergence flooding net volume transport at Incheon harbor, and drain (westward direction) through channel of tidal flat between Ganghwado and Yeongjongdo to the Gyeong-Gi bay. The averaged net volume transport during 4 tidal cycles was compared to variation of spring-neap periods of the Yeomha channel. The convergence position is moved up- and down-ward according to spring-neap variability. The movement of the convergence zone is appeared because 1) increasing of discharged rate tidal flat channel between Ganghwado and Yeongjongdo at the spring period, 2) The growth of barotropic forcing with downward direction at the spring tide, and 3) The strength of the baroclinic pressure gradient is greater than spring with mixing processes.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
• /
• v.11 no.2
• /
• pp.49-67
• /
• 2006

A mesocosm, an artificial tidal flat ecosystem, was constructed outdoors to simulate in situ physical and biochemical environmental conditions of natural tidal flat as much as possible. During the experiment from February to August 2004, the study was focused on the biogeochemical variations of superficial water and porewater after introduction of freshwater into the mesocosm. The mesocosm has three experimental conditions; SW-M-T: maintaining the saline water of approximately 20 psu; FW-M-T: complete exchange of freshwater ul the mesocosm with continuous mixing of water column: FW-NM-T: complete exchange of saline water to freshwater in the mesocosm without mixing of water column. Mass extinction of benthic macrofauna appeared due to drastic decrease of porewater salinity from 20 psu to less than 10 psu between the 63th and 91st day of freshwater introduction in FW-M-T and FW-NM-T. Throughout the periods, 7/8 of bivalves and 2/3 of polychaete populations have been extinguished in the sediment. In FW-NM-T, as temperature rises, both evident decrease of DO in water column and active release of DIP from sediment were observed. ${NO_3}^-$ was removed from water column into sediment throughout the periods. Therefore extremely low ${NO_3}^-$ was found during late spring and summer. Whereas ${NH_4}^+$ exhibited only $1/2{\sim}1/8$ of ${NO_3}^-$ concentration. Unexpectedly even after mass extinction of benthic macrofauna, we were not able to find high ${NH_4}^+$. This mesocosm study suggests that when fresh water introduce to natural tidal flat, its sediment activity functions as a potential source of DIP, but a sink of ${NO_3}^-$.

• Korean Journal of Soil Science and Fertilizer
• /
• v.42 no.6
• /
• pp.415-422
• /
• 2009

Effect of soil salinity variation on the growth of barley, rye and oat was studied at the Hwaong, Iweon and Yeongsangang reclaimed lands in the western seaside of Korea. Soil salinity variation and soil EC were very high for crops to be killed or to be brought serious growth retardation during the growing season at the Iweon and Hwaong reclaimed lands, but fully low not to bring growth retardation at the Yeongsangang reclaimed land. Relation between soil salinity and crop growth and yield was well expressed as logarithmic function. Surface soil EC to reach at 50% of seed-emergence reduction was estimated $6.5dS\;m^{-1}$ for barley and $5.1dS\;m^{-1}$ for rye and oat by logarithmic function. In addition, surface soil EC to reach at 50% of grain yield reduction to the best growth in the experimental site was estimated $5.6dS\;m^{-1}$ for barley, $5.8dS\;m^{-1}$ for rye and $5.7dS\;m^{-1}$ for oat, while soil EC to reach at 50% of dry matter reduction was estimated $5.5dS\;m^{-1}$ for barley, $6.2dS\;m^{-1}$ for rye and $5.8dS\;m^{-1}$ for oat by logarithmic function. Grain yield of barley, rye and oat was 395, 164 and $325kg\;10a^{-1}$ in the Yeongsangang reclaimed lands naturally controlled below condition of $6dS\;m^{-1}$ of soil EC, but no harvest was obtained in the Hwaong and Iweon reclaimed land because of high salinity more than $15dS\;m^{-1}$ in maximum soil EC during growing period. Consequentially, it was concluded that soil salinity must be controlled below $6dS\;m^{-1}$ for good growth and high yield of winter barley, rye and oat in the reclaimed land in Korea.

• Korean Journal of Soil Science and Fertilizer
• /
• v.42 no.6
• /
• pp.492-499
• /
• 2009

Effect of drip irrigation on soil salinity control and growth of vegetable crops was studied in the three reclaimed lands of Korea in 2007. Drip irrigation was done one or two times per month for reduction of salt stress by using vinyl hose with tiny holes laid on ridge surface under black plastic film mulch during growing season of cabbage and chinese cabbage. It was observed that drip irrigation was generally effective to soil salinity control, but soil salinity variation of some place was not fully solved to lower down under level of free salt stress. It is also considered that high salinity of runoff water spilled out from cultivation ridge plays another key role for soil salinity management. Consequentially, this soil salinity variation might be one of factors brought low average yield and low commercial ratio of agricultural products. Relation between soil salinity and head growth of cabbage and chinese cabbage was well expressed as logarithmic function. Surface soil EC to reach at 50% of growth reduction to the heaviest head can be estimated was $6.1dS^{\circ}{\S}m^{-1}$ for cabbage and $5.7dS\;m^{-1}$ for chinese cabbage transplanted at optimum season.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.28 no.1
• /
• pp.67-79
• /
• 1995

Temporal variation of demersal fish in Asan Bay was determined by analyzing seasonal samples collected by an otter tyawl from November 1990 to August 1993. Of 49 species identified, Cynogiossus joyneri, Thrissa koreans and Johnius belengerii predominated in abundance, consisting of $84.7\%$ in fish numbers and $70.5\%$ in biomass. The number of species did not show any significant seasonal variation. Fish numbers and biomass were comparatively high 3n spring, summer and tall, and low in winter. Community structure, analyzed by principal component analysis using rank correlation, showed a clear seasonal trend, which seems to be related to the seasonal effects such as temperature. The number of species and their abundance in the study area were lower than those in other embayments of Korean peninsula. It seems that unstability of the sediments by tidal mixing caused this phenomenon. The total number of species decreased annually. The species of which the frequency of occurrence tends to diminish as time were mainly composed of the species which rarely occurred with low abundance.

• Journal of the Korean Geographical Society
• /
• v.49 no.3
• /
• pp.321-338
• /
• 2014

This study aims to identify spatial distribution of estuarine wetlands in Korea, and to assess temporal variation of the wetlands in the last few decades. Widely known in environmental and coastal management, watershed-based regions which composed with Han-river(western and eastern parts), Keum-river, Yeoungsan-river, Seomjin-river, Nakdong-river, and Jeju, are analyzed to evaluate temporal change of estuarine wetlands in the 1980s, 1990s, and 2000s, through the land-cover map. Results show that estuarine wetlands dramatically decreased in Han-river(western part), Keum-river, Yeoungsan-river that estuarine circulation have been interrupted with man-made structures such as dyke and drainage. But, estuarine wetlands surrounded by forests and grasslands has been relatively less damaged. Habitat diversity providing healthy estuary ecosystem is lower in interrupted estuaries than circulated estuaries, which are composed of tidal-flat, open water, salt marsh, rocky coasts and sandy shoreline. This study indicates that spatial distribution and temporal variation of estuarine wetlands are different with estuary type and region, so estuary type with seven regions can be applied to provides a framework for estuary management strategies and to establish estuary restoration plans.

• Journal of the Korean earth science society
• /
• v.21 no.2
• /
• pp.188-200
• /
• 2000

On the basis of the Landsat TM scenes with 15 year's time differences, the topographic maps with 50 years differences, and the air photos with 25 years differences, we carried out the field survey for geology and forestry and analyzed the topographical change and the variation of the forest resource in Anmyundo. In terms of the discrimination of forest trees in Anmyumdo, the NDVI with larger than 0.5 in the winter season is the indicator of the surface of the pine tree land-cover. The peak values of NDVI appear on the surface of the pine aging 30 through 50 years and decrease a little and grossly stabilized over the more aging trees. The distinction of the deciduous forest and grass land from the pine tree was capable with the correlation with the abrupt seasonal variation of NDVI and the surface aspect. The great change of topography is detected in the region Changgiri due to the continuous tidal erosion since the canal construction about 370 years ago and along the all around coast of Anmyundo due to the reclamation for the paddy field. The surface area of the pine tree land-cover in Anmyundo was estimated 35.91 km$^2$ in 1986 and 33.15 km$^2$ in 1993, which is originated from the grassland development in the southeastern part of Anmyundo where the pine tree dominated by 1986. In the northen part of Anmyundo the surface area of the pine land-cover increased a little in 1993 comparing to 1986.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.31 no.5
• /
• pp.727-738
• /
• 1998

Seasonal species composition of fishery resources was determined using samples collected by a stow net from April 1995 through January 1996 at 9 stations off Youngkwang. Catch data obtained from a set net using strong tidal current could be used for a quantitative analysis of dominant species. Of the 98 species identified, assemblages were consisted of $52.0\%$ in fishes, $44.6\%$ in shrimps, $2.0\%$ in cephalopods, $1.4\%$ in crabs and <$0.1\%$ in gastropods. Thryssa kammalensis, Crangon hakodatei, Metapenaeus joynezi and Johnius grypotus predominated in abundance, consisting of $68\%$ in the number of individuals, The abundance and species composition fluctuated seasonally, and species could be distinguished by life history pattern with seasons. Seasonal variation in species composition was greater than the spatial variation in a sampling period, As the fine sediment was predominated in the study area, the species composition were significantly different from those of other coastal waters of West Sea, Korea.

• Journal of Environmental Science International
• /
• v.11 no.7
• /
• pp.627-636
• /
• 2002

While typhoons were passing by the coastal and offshore waters around the Korean peninsula, the variations of the sea surface temperature (SST) were studied. To study on the variation, the data related to the 22 typhoons among 346 typhoons which occurred in the western Pacific during 1990∼1999, daily measured field SSTs at coastal and offshore, and imageries from advanced very high resolution radiometer on NOAA satellite during 1990∼1999 were used. The average variations of the SSTs were -0.9℃ at coastal waters and -2℃ at offshore around the Korean peninsula while the typhoons were passing by. In very near coastal waters from the land, the SST was not changed because the bottom depth of the coastal waters was shallower than the depth of thermalcline, while the typhoon was passing. The temporal and spatial variation of SSTs at coastal waters in summer were depended on the various types of the typhoons＇paths which were passing through the Korean peninsula. When a typhoon passed by the western parts including the Yellow Sea of the Korean peninsula upwelling cold water occurred along the eastern coastal waters of the peninsula. The reason was estimated with the typhoon that was as very strong wind which blew from south toward north direction along the eastern shore of the peninsula, led to the Ekman transport from near the eastern coastal area toward the offshore. While cold water was occurring in the eastern coast, a typhoon passed over the coastal area, the cold water disappeared. The reason was estimated that the cold water was mixed up with the surrounding warm water by the effect of the typhoon. While a cold water was occurring in the eastern coast, a typhoon passed by the offshore of the eastern coast, there were the increasing of the SST as well as the disappearing of the cold water. While a typhoon was passing by the offshore of the eastern coast, the cold water which resulted from the strong tidal current in the western coast of the peninsula was horizontally spread from the onshore to the offshore. We think that the typhoon played the role of the very strong wind which was blowing from north toward south. Therefore, the Ekman transport occurred from the onshore toward the offshore of the western coast in the Korean peninsula.

• Journal of Marine Life Science
• /
• v.5 no.2
• /
• pp.72-80
• /
• 2020

A sea dike in the Yeongsan River estuary was constructed in 1981 to supply water and reclaim tidal flats for agriculture, separating the estuary into the freshwater and seawater zones. However, the sluice gates are frequently opened and freshwater is discharged in summer when more rainfall is recorded than other seasons, then converting the estuary to brackish water system. In this study, the direct effect of freshwater discharge was investigated by monitoring daily variation in water properties and phytoplankton size structure before and after the freshwater discharge events from 2013 to 2015. Freshwater discharge resulted in a sharp decrease in salinity and dissolved oxygen (DO) at surface water whereas it increased the turbidity of water column. However, salinity did not decrease sharply in 2014 when freshwater was discharged one day before the monitoring and salinity remained low prior to the monitoring. Levels of nutrients especially dissolved inorganic nitrogen (DIN) increased after the discharge and this contributed to potential limitation of nutrients such as P or Si rather than N in the estuary. Freshwater discharge also caused the changes in phytoplankton biomass (chlorophyll a) and size structure although their responses were different between years. The changes may affect growth of grazers and thus structure of marine food web by alternating food availability in the Yeongsan River estuary.