• Ocean and Polar Research
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• v.29 no.2
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• pp.135-153
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• 2007

Temporal (seasonal) and spatial distributions and variations of various physico-chemical factors (salinity, temperature, pH, DO, COD, SPM, POC, silicate, DIP, DIN) in surface and bottom waters were studied in the coastal environment with typical macro-tidal range and monsoonal weather condition, Gyeonggi Bay, west coast of Korea. Spacial distribution patterns of these factors were generally similar to each other, and appeared to be inversely related to the distribution pattern of salinity, suggesting that water quality of the study area was primarily controlled by the physical mixing process of Han-River freshwater with nearby coastal seawater. During flooding season, silicate- and nitrogen-rich Han River water directly flowed into offshore as far as $20\sim30\;km$ from the river mouth, probably causing serious environmental problems such as eutrophication and unusual and/or noxious algal bloom, etc. Except the surface water during summer flooding season, high concentrations of nutrients appeared generally in dry season, whereas low values in spring, possibly because of the occurrence of spring phytoplankton bloom. On the other hand, nutrient flux through the estuary seems to be primarily depending on river discharge, sewage discharge and agricultural activities, especially during the rainy season. Also, nutrients in this coastal waters are considered to be supplied from the sediments of tidal-flats, which developed extensively around the Han-River mouth, especially during fall and winter of dry and low discharge seasons, possibly due to the stirring of tidal flat sediments with highly enriched pore-water nutrients by storm. And also, COD and DIN concentrations in the study area consistently increased during the last 20 years, probably because of agricultural activities and increasing discharge of industrial and domestic wastes.

• Journal of fish pathology
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• v.34 no.2
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• pp.255-259
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• 2021

This is the first report describing acute mass mortality occurred in juvenile olive flounder (Paralichthys olivaceus) caused by gas bubble disease (GBD). A total of 610 fish (average weight = 35 g), which were more than half of the fish acclimated at 17℃ in an aquarium, were killed within two days of acclimation. The dead and moribund fish showed excessively opened opercula and mouths, and occasionally, severe exophthalmia. Through microscopic observation, numerous gas emboli were found in the gills of the dead and live fish, while the fish were not infected with any microbial pathogens. The dissolved oxygen (DO) saturation level of the rearing water and seawater nearby the facility reached 145% and 286%, respectively, whereas other water quality parameters (such as salinity, pH, and chemical oxygen demand) were normal. The extreme saturation rate of seawater in the shore nearby seemed to be due to an enormous algal bloom that occurred there. Through molecular identification based on 18S rDNA sequences, the most dominant algal species was most closely related to Ulva californica (99.87% sequence identity) followed by U. prolifera, U. linza, and U. curvata (99.81%). Therefore, it can be concluded that supersaturated seawater due to mass algal bloom caused gas bubble disease in the olive flounder, leading to mass mortality. After technical adjustment, such as increased aeration, lowered water circulation rate, and inlet water filtration using micro-pore carbon filters, the DO level became normal, no further mortality occurred and the status of the fish was stabilized.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.25 no.4
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• pp.106-116
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• 2020

To examine distribution of the Zostera species growing naturally in Ulleungdo, scuba diving surveys using ships were conducted along the coast and inside the harbors of the island at the end of September 2019. In areas of seagrass occurrence, environmental factors such as nutrient concentrations in water column and sediment pore water, salinity, and sediment organic content were also analyzed. Zostera caulescens meadows appeared in the relatively deep waters (14-24 m MSL) of Cheonbu-ri, Jeodong-ri, Sadong-ri, and Namyang-ri in Ulleungdo, and the total seagrass coverage was approximately 4.9 ha. Approximately 0.9 ha of Zostera marina meadow was found at the depths of 3-5 m MSL within Hyeonpo-hang in Hyeonpo-ri. The average shoot density and biomass of Z. caulescens were 121.9±9.7 shoot m^-2 and 99.0±13.2 gDW m^-2, respectively, with no significant differences by location. The average shoot density and biomass of Z. marina were 193.8±18.8 shoot m^-2 and 102.6±6.8 gDW m^-2, respectively. The nutrient concentrations in the sediment pore water and sediment organic content in the seagrass meadows in Ulleungdo were lower than those in eelgrass meadows on the southern and eastern coasts of Korea. These results will provide useful basic information for the marine protected species, Z. caulescens and Z. marina, and for the conservation of the waters of Ulleungdo, which has been designated as a marine protected area.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.413-416
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• 2008

Reinforcement corrosion is generally prohibited under normal condition by the alkalinity of the pore water in the concrete. However, concrete structures in marine environment are subjected to chloride attack due to the high salinity of the sea water. Thus the probability of steel corrosion becomes higher when the chloride ions are introduced into the concrete. Steel corrosion is a decisive factor for the determination of service life of the marine concrete structure because chloride ions are abundant in the sea, and piers are the typical construction elements in concrete structures in marine environment. Hence, it is of great importance to evaluate the service life of the piers. In this paper, chloride penetration analysis for the rectangular pier in the marine environment is performed considering the diffusion and convection movement of chlorides. Result reveals that the service life of the reinforcement with drying-wetting cycles is much shorter than that of the reinforcement with saturated condition. This may be due to the fact that moisture movement is much faster that chloride diffusion.

• Journal of the Korea Organic Resources Recycling Association
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• v.13 no.1
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• pp.61-70
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• 2005

In order to reduce salt(as NaCl) contents in food waste and to improve the quality of discharged wastewater produced during the recycling process of food waste for the purpose of compost and feed stuff, a salt reduction process by added water into food waste was developed. The pilot plant with a rotary type salt reduction equipment to manage continuously 0.5 ton food waste per hour was constructed and the efficiency was tested. The amount of added water was calculated by the water content and the efficiency of dewatering process of food waste. Approximately 0.8 liter water per a kilogram of food waste was injected into the reactor in which food waste was pouring simultaneously, then diluted/mixed in a rotary reactor. About 1.1 liter of leachate including added water was generated, but the leachate contained a very high content of organic particles, so most particles were recovered by two step solid-liquid separation process. The first step was a gravitational filtering process using screens with a pore diameter of 1mm, and the second separation process was centrifugal process. Organic quality of food waste which had been desalted was maintained by inputting the entirely recovered organic particles. The efficiency of salt reduction of food waste was estimated by measuring a chloride anion by titration and salinity by a probe. The results by the two different measuring methods were always over 50%, and the quality of final wastewater was improved up to $200mg/{\ell}$ as TS(total solid) by an additional settling process after the two step solid-liquid separation process.

• ALGAE
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• v.34 no.1
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• pp.7-21
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• 2019

The genus Heterocapsa is one of the major dinoflagellate groups, with some of its species having worldwide distributions. However, prior to the present study, the phototrophic species Heterocapsa minima has been reported only from the northeast Atlantic Ocean. Recently, H. minima was found in the Korean waters, and a clonal culture was established. This culture was used to examine the morphology of the Korean strain H. minima HMMJ1604 through light and scanning electron microscopy, as well as for its genetic characterization. Furthermore, to determine the nationwide distribution of H. minima in Korea, its abundance was quantified in the waters of 28 stations in all four seasons in 2016-2018 using the quantitative real-time polymerase chain reaction method. The overall morphology of H. minima HMMJ1604 was very similar to that of the Irish strain H. minima JK2. However, the Korean strain had five pores around the pore plate, whereas the Irish strain had six pores. When properly aligned, the sequences of the large subunit and internal transcribed spacer regions of the ribosomal DNA of the Korean strain were identical to those of the Irish strain. This species was detected in the waters of 26 out of 28 stations, but its abundance was greater than $1.0cells\;mL^{-1}$ at 8 stations. The highest abundance of H. minima was $44.4cells\;mL^{-1}$. Although this species was found in all seasons, its abundance was greater than $1.0cells\;mL^{-1}$ when the water temperature and salinity were $10.9-25.0^{\circ}C$ and 17.5-34.1, respectively. To the best knowledge, the present study reported for the first time that H. minima lives in the Pacific Ocean and is widely distributed in the Korean waters.

• Korean Journal of Environmental Biology
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• v.23 no.3 s.59
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• pp.293-303
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• 2005

Japanese medaka, Oryzias latipes is widely distributed in the North East Asia including Korea, Japan and east China, and commonly used for freshwater toxicity tests and cytotoxicological studies worldwide. In this study, a series of experiments were conducted to identify the potential of the fish as a standard test species for saltwater toxicity evaluation such as marine receiving waters, ocean-dumped materials and sediment pore waters etc. Hatching, growth and mortality rates of the fish were estimated with the wide ranges of salinity from freshwater to seawater (35 psu). Direct exposure of the fertilized eggs in freshwater to the wide ranges of salinity (from 0 to 35 psu) without pre- acclimation to the saltwater revealed no significant differences in hatching rates by salinities (p =0.24). On the other hand, medaka larvae hatched in freshwater and exposed to saltwater directly showed high mortality at > 25 psu treatment groups (p < 0.0001). However, there was no significant difference in mortality of medaka larvae hatched in 13.8 and 14.2 psu at the wide ranges of salinities ($0\~35$ psu). Growth rates of medaka larvae hatched in the above two salinities showed no differences in body length either from 0 to 35 psu treatment groups (p =0.64 for 13.8 psu group and p=0.32 for 14.2 psu group). The number of gill chloride cell in medaka larvae sharply increased when the larvae were exposed to high salinity. Reference tests with zinc chloride revealed 96h $LC_{50}=8.84(7.19\~10.87)mg\;L^{-1}$ using 7~10 day old medaka larvae. These were comparable or better sensitivity in comparison with the other standard test species such as North American sheepshead minnow Cyprinodon variegatus. Based on the results of these experiments, hatching rates and larvalmortality of medaka must be good toxicity parameters for seawater bioassay and the species seems to be a good standard species for both the freshwater and seawater toxicity test.

• The Korean Journal of Malacology
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• v.23 no.1
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• pp.1-8
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• 2007

The influence of individual size, sediment, gain size, water temperature, salinity and air exposure on burrowing rate was investigated in order to obtain the basic biological data on applying shellfish farm for a sustainable production of ark shell, Scapharca broughtonii (Schrenk). The burrowing rate on individual size 300 minutes after starting the experiment was the highest in the shell length $16.3\;{\pm}\;1.2\;mm$, 97.7%. The highest burrowing rates were 97.0% in $12.8\;{\pm}\;0.8\;mm$, 96.7% in $9.2\;{\pm}\;1.0\;mm$, and 96.3% in $5.9\;{\pm}\;0.7\;mm$. The clams over 6 mm of shell length had burrowing ability and the burrowing rate was not related to the shell size. The burrowing rate depending on the kind of grain at the bottom after 300 minutes was the highest, 98.3%, in the mixture of sand and silt with a ratio of 75:25. The rates were 98% in silt (100%), 97.3% in mixture sand and silt with a ratio of 50:50, 97.3% in sand and silt ratio of 25:75, and 86.3% in sand (100%) in this specific order. On grain size of the soil in the seafloor, the burrowing rates after 300 minutes was at its highest in the group of sand in pore size 1 mm with 85.0%, and the $12\;{\mu}m$ to 1 mm in the grain size was fitted to burrowing of artificial seed. In the case of water temperature, the burrowing rates were at its highest after 300 minutes. In $30^{\circ}C$ group, the rate was 96.7% and in $25^{\circ}C$ and $20^{\circ}C$, 90.0%. The rates decreased as the water temperature decreased below $15^{\circ}C$. The burrowing rates on salinity were the highest in 30 psu with 93.3% and at 15 psu and below, there was no noticeable change in the burrowing rate. On air exposure, the burrowing rates after 300 minutes were the highest in 1 hour with 93.3%, and remarkably decreased as air exposure time is longer after 12 hours of air exposure.

• Journal of Korean Society of Forest Science
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• v.105 no.3
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• pp.303-308
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• 2016

To investigate the effect of calcium chloride ($CaCl_2$) using for deicing salts in winter on gas exchange and stomatal responses of 3-year-old Prunus serrulata, we treated twice (1 L) $CaCl_2$ solution (0.5%, 1.0% and 3.0%) in the root zone before leaf unfolding. Stomatal conductance ($g_s$), photosynthetic rate ($P_n$), transpiration rate ($T_r$) and water use efficiency (WUE) in the leaves of P. serrulata were decreased with increasing of $CaCl_2$ concentration. Even though stomatal conductance and photosynthetic rate were reduced by $CaCl_2$, intercellular $CO_2$ concentration ($C_i$) in $CaCl_2$ treatments has similar or higher values compared with control. These results suggest that non-stomatal limitation as well as stomatal limitation induced the reduction of photosynthetic rate together. On the other hands, treatment of $CaCl_2$ before leaf unfolding also affected leaf morphology traits. We proposed that reductions of stomatal length and leaf size and high pore density with increasing salinity is adaptative mechanism to reduce the water loss in plant.

• Korean Journal of Soil Science and Fertilizer
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• v.30 no.3
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• pp.226-233
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• 1997

To investigate the salt accumulation in the plastic film house soils, bulk density, electrical conductivity(EC), exchangeable canons and water soluble anions were determined at different depths(0~60cm) in the salt-accumulated plastic film house soils in Yesan, Chungnam, Korea. Bulk density were increased from $1.2Mg/m^3$ to $1.5Mg/m^3$ as the depth changed from 0cm(top soil) to 30cm(subsoil) below the soil surface, whereas the bulk densities between 30cm to 60cm slightly decreased to $1.42Mg/m^3$. These changes of soil bulk densities might influence the porosity and pore size distribution, resulting in affecting the water flow throughout, soil layers. Electrical conductivity and Exchangeable sodium percentage(ESP) for 0 to 10cm soil layer were 5.08 dS/m and 6.4, respectively, while the EC was decreased to less than 1.63 dS/m in 20~30cm depth and about 0.7 dS/m. Salt accumulation patterns in the plastic film house soils might be influenced by the changes of the bulk densities in soil.