• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.21 no.1
• /
• pp.62-66
• /
• 1985

The periodic variations of the surface water temperature and the relationships between the surface water and air temperature are found in Youngil bay as follows: It is considered that the average surface water temperature is the lowest in February and the highest in August in the Youngil bay (Pohang bay and Janggi cape) from January, 1962 to December, 1981. It is only in October and November that the average surface water temperature was higher in pohang bay than in the Janggi cape from January, 1962 to December, 1981. Since the periodic secular variation in the vincity of Youngil bay and the variation of the Tsushima Current seem to have similar tendencies, we may conclude that the changes of the surface water temperature in Youngil bay are primarily influenced by the Taushima Current. The average temperature of surface water is 14.5$^{\circ}C$ in Pohang bay and 15.$0^{\circ}C$ in Janggi cape in the secular variation.

• Journal of the Korean Society for Marine Environment & Energy
• /
• v.4 no.1
• /
• pp.14-23
• /
• 2001

The characteristics of tidal circulation with Hyungsan River discharges in Youngil Bay by the numerical experiments is elucidated. For the simulation of tidal residual currents related to inflow by the river discharges in Youngil Bay located in the southeastern part of Korean Peninsula, the two-dimensional numerical experiment is peformed. The tidal elevation boundary conditions of the 4 main tidal harmonic constituents (M₂, S₂, K₁ and O₁) on the open boundary and river discharges at the river boundary are considered. The computed results obtained from numerical experiment showed good agreements with the field observation ones. The residual currents generally flow toward the inner bay through the western (Dalman-Gap) and central areas of the bay, and then the currents go toward the outer bay along the eastern shore (Changgi-Gap) of the bay with anti-clockwise circulation. Especially, in the numerical experiment without Hyungsan River discharges, these flow patterns are disappeared. Based on the results, it showed that the Hyungsan River discharges play the dominant role in the patterns of tidal residual currents. This flow pattern of tidal residual currents are important mechanism of water quality, material transport in Youngil Bay.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.19 no.6
• /
• pp.511-520
• /
• 2007

WAM(WAve Model), deep water wave model has been extended to the region of shallow water, incorporating wave breaking, and triad wave interaction. To verify the model, numerical simulation of waves in Youngil bay, Pohang is performed and the simulated results show good agreements with measured wave data sets, one station at the mouth of bay and two stations inside the bay. As waves propagate toward the shore, wave height gradually diminishes by bottom friction and wave breaking, and wave direction, initially NE changes normal to the shore due to depth refraction.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.42 no.6
• /
• pp.664-673
• /
• 2009

An intertidal marine benthic algal vegetation and vertical distribution at Youngil Bay, the eastern coast of Korea was investigated to clarify the community structure and vertical distribution by quadrat method from February 2003 to January 2009. Marine algae identified from the area were 152 species; 25 green, 38 brown and 89 red algae. The dominant species were Ulva spp., Ulva pertusa, Chaetomorpha moniligera, Undaria pinnatifida, Sargassum horneri, S. miyabei, S. thunbergii, Gelidium amansii, Corallina pilulifera, Grateloupia elliptica, G. filicina, Prionitis cornea, Chondrus ocellatus, Chondracanthus intermedia, Acrosorium polyneurum, Chondria crassicaulis, Polysiphonia morrowii and Symphyocladia latiuscula at study sites. The vertical distribution of intertidal marine algae was divided into three distinct zones. They were characterized by Porphyra spp. and Ulva spp. at the upper, Ulva spp. and Ulva pertusa at the middle, and Sargassum spp., Gelidium amansii, Grateloupia spp., Chondrus ocellatus and Chondria crassicaulis at the lower zones, respectively. Functional form group analysis showed that coarsely branched forms comprised 44.7% of the algal community, whereas thick leathery forms, sheet forms and filamentous forms comprised 6.6-25.7%. R/P, C/P and (R+C)/P values were 2.34, 0.66 and 3.00, respectively.

• Journal of Environmental Science International
• /
• v.22 no.12
• /
• pp.1683-1690
• /
• 2013

We investigated the spatial and temporal variations of phytoplankton in Youngil Bay as well as the effect of water physico-chemical parameters. Water samples at three stations were collected and measured monthly from May to November in 2010. The taxa of phytoplankton observed in this study were classified as 33 Bacillariophyceae, 23 Dinophyceae, 1 Euglenophyceae, 2 Crysophyceae and 1 Cryptophyceae. The highest biomass of phytoplankton was observed at inner station in September, which was characterized high concentration of dissolved inorganic phosphate(DIP) in surface water after rainfall. Nutrient concentrations, chlorophyll-a and phytoplankton biomass values showed the marked trend to decrease from the inner bay to the outer bay. Pearson's correlation co-efficient between salinity and other water parameters including chlorophyll-a, pH and DIP showed the strong negative relationship r=-0.82, r=-0.78 and r=-0.75 (p<0.01), respectively. These results indicate that the water quality of Youngil Bay could be stimulated by nutrient enriched input from Hyeogsan River discharge, and the spatial and temporal distribution of phytoplankton biomass principally limited to DIP concentration from Hyeogsan river.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.16 no.3
• /
• pp.197-201
• /
• 1983

Underwater ambient noise level was measured at two points near the Youngil Bay. The environmental characteristics depend upon oceanographic conditions of sound propagation ana its implication on the source of ambient noise. Some noise sources were estimated, and the effect of the oceanographic conditions on the noise level variation had been considered. The results were as follows : 1) At the nearshore station of Youngil Bay, the ambient noise level in the near bottom(45m) was lower than that of the near surface(10m) by 15dB. This difference was due to spherical spreading from the upper to the lower layer. 2) At the open sea station which is located outside of the thermal front existing near the Youngil Bay, the ambient noise level of the upper layer(20m) was higher than that of the lower layer (100m) by $8{\sim}12dB$ below 50Hz and $15{\sim}23dB$ above 50Hz. 3) Above 60Hz the ambient noise level at the nearshore station was higher than that of the open sea station, while below 60Hz, the result was reverse. It appears that a boundary layer existed between the two stations.

• Journal of the korean society of oceanography
• /
• v.35 no.2
• /
• pp.124-127
• /
• 2000

The analysis of stable carbon isotope ratios for benthic fauna was applied to identify the source of carbon in benthic food webs in Youngil Bay, Korea. The ${\delta}^{13}$C values of 9 invertebrate species collected in this area showed a narrow range between -20.5 and -16.3%$_o$ with a mean of-18.1 (${\pm}$1.1)"%$_o$. The results suggest that the major source of organic carbon for the benthic fauna of the lower estuarine reaches and the oceanic sites is autochthonous marine particulate organic matter. The contribution of organic matter from terrestrial and riverine sources to the diet of the benthic fauna in this area appears to be minor, despite the considerable inflow of riverine waters.

• Journal of the Korean Institute of Navigation
• /
• v.13 no.1
• /
• pp.77-106
• /
• 1989

Two numerical models of the shoreline change and sediment transport rates, explicit and implicit, are simulated with shore structures such as breakwaters, a jetty, groins and a seawall. The applied study area is songdo Beach, Youngil bay, Korea since it has all the shore structures mentinoed above. The two models investigate the beach line changes and sedimen transport rates for the beach before design of three groins with and without an offshore breakwater. In order to estimate the shoreline changes after three groins were built, the beach response inside the three groin compartiments and the offshore barrier are also investigated. The simulation based on the initial shoreline conditions surveyed by the Hydrographic office, Koreai 1979 and 1984. The breaking wave characteristics are introduced into the models by calculation from the empirical equations and modification from the numerical and hydraulic model test results developed for waves behind an offshore breakwater. The numerical simulation describes well the tendencies of the sand transport and shoreline changes affected by wave diffraction behind a detached breakwater and by interruption of sand transport at three groins.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
• /
• v.4 no.1
• /
• pp.63-70
• /
• 1999

The optimum sampling area which can be applied to the benthic community study is estimated from large survey data in the Songdo tidal flat and subtidal zone of Youngil Bay, Korea. A total of 250 samples by 0.02 $m^2$ box corer for the benthic fauna in Songdo tidal flat and 50 samples by 0.1 $m^2$ van Veen grab in Youngil Bay were taken from the total sampling area of 5 $m^2$. It was assumed that the sampling area could contain sufficient information on sediment fauna, if cumulative number of species, ecological indices, and similarity index by cluster analysis reflect the similarity level of 75% to those found at total sampling area (5 $m^2$). A total of 56 and 60 species occurred from Songdo tidal flat and Youngil Bay, respectively. The cumulative curve of the species number ($N_{sp}$) as a function of the sampling area (A in $m^2$ ) was fitted as $N_{sp}=37.379A^{0.257}$ ($r^2=0.99$) for intertidal fauna and $N_{sp}=40.895A^{0.257}$ ($r^2=0.98$) for subtidal fauna. Based on these curves and 75% of similarity to the total sampling area (5 $m^2$), the optimum sampling area was proposed as 1.6 $m^2$ for the intertidal and 1.5 $m^2$ for the subtidal fauna. Ecological indices (species diversity, richness, evenness and dominance indices) were again calculated on the basis of species composition in differently simulated sample sizes. Changes in ecological indices with these sample sizes indicated that samplings could be done by collecting fauna from < 0.5 $m^2$-1.5 $m^2$ on the Songdo tidal flat and from < 0.5 $m^2$-1.2 $m^2$ in Youngil Bay. Changes in similarity level of all units of each simulated sample size showed that sampling area of 0.3 $m^2$ (Songdo tidal flat) and 0.6 $m^2$ (Youngil Bay) should be taken to obtain a similarity level of 75%. In conclusion, sampling area which was determined by cumulative number of species, ecological indices and similarity index by cluster analysis could be determined as 1.5 $m^2$ (0.02 $m^2$ box corer, n=75) for Songdo tidal flat and 1.2 $m^2$ (0.1 $m^2$ van Veen grab, n=12) for Youngil Bay. If these sampling areas could be covered in the field survey, population densities of seven dominant species comprising 68% of the total faunal abundance occurring on Songdo tidal flat and six species comprising 90% in Youngil Bay can be estimated at the precision level of P=0.2.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.41 no.5
• /
• pp.353-362
• /
• 2008

The fish species composition and variation in the Youngil Bay, East Sea of Korea, were investigated every month from January, 2001, to December, 2002, using gill nets for sample collection. A total of 63 fish species belonging to 31 families under 10 orders, and a total of 40 species belonging to 26 families under 8 orders, were identified in 2001 and 2002, respectively. Of these, the families Pleuronectidae (9 species), Scorpaenidae (8 species) and Cottidae (5 species) were dominant in 2001, whereas Pleuronectidae (4 species), Cottidae (3 species) and Hexagrammidae (3 species) were dominant in 2002. The number of species recovered was the highest in August, 2001 (34 species) and January and September, 2002 (14 species each), and lowest in May, 2001 (6 species) and December, 2002 (5 species). The principal component analysis for each year showed that fish species composition differed over time even within the same sample area. In addition, the relationship between PC scores and temperature showed a positive relationship in 2001, but a negative relationship in 2002.