Keun-Hyung Choi

Enhancing the efficacy of electrolytic chlorination for ballast water treatment by adding carbon dioxide

We examined the synergistic effects of CO2 injection on electro-chlorination in disinfection of plankton and bacteria in simulated ballast water. Chlorination was performed at dosages of 4 and 6ppm with and without CO2 injection on electro-chlorination. Testing was performed in both seawater and brackish water quality as defined by IMO G8 guidelines. CO2 injection notably decreased from the control the number of Artemia franciscana, a brine shrimp, surviving during a 5-day post-treatment incubation (1.8 and 2.3 log10 reduction in seawater and brackish water, respectively at 6ppm TRO+CO2) compared with water electro-chlorinated only (1.2 and 1.3 log10 reduction in seawater and brackish water, respectively at 6ppm TRO). The phytoplankton Tetraselmis suecica, was completely disinfected with no live cell found at >4ppm TRO with and without CO2 addition. The effects of CO2 addition on heterotrophic bacterial growth was not different from electro-chlorination only. Total residual oxidant concentration (TRO) more rapidly declined in electro-chlorination of both marine and brackish waters compared to chlorine+CO2 treated waters, with significantly higher amount of TRO being left in waters treated with the CO2 addition. Total concentration of trihalomethanes (THMs) and haloacetic acids (HAAs) measured at day 0 in brackish water test were found to be 2- to 3-fold higher in 6ppm TRO+CO2-treated water than in 6ppm TRO treated water. The addition of CO2 to electro-chlorination may improve the efficiency of this sterilizing treatment of ballast water, yet the increased production of some disinfection byproducts needs further study.

In Situ Hatching Success of Calanoid Copepod Eggs in Hypoxic Sediments of a Coastal Bay

ABSTRACT Choi, K-H.; Jang, M-C.; Shin, H.H.; Lee, W-J., and Shin, K., 2016. In situ hatching success of calanoid copepod eggs in hypoxic sediments of a coastal bay. Hypoxia can have adverse effects on recruitment of marine copepods via its effects on egg hatching and survival of nauplii. This study investigated the effects of hypoxia on in situ hatching success of calanoid copepods in Gamak Bay, Korea, a shallow (9-m) microtidal coastal bay with long water residence times exceeding a month. Plankton emergence trap/chambers were placed into seafloor–surface sediments in July at a hypoxic site (mean = 0.6 mL L−1) in the inner part of the bay and at a normoxic site in the mid bay. Nauplii that hatched and left the sediment were collected daily for 12 days, and the top 1 cm of sediment was preserved at the end of incubation. The number of eggs in the sediment was >3 × 105 eggs m−2 at the hypoxic site, about six times that at the normoxic site. Most of the eggs appeared to be subitaneous. Egg-hatching rate in the hypoxic site, however, was only 4% of that at the normoxic site, where 57% of the eggs present hatched. Cumulative numbers of eggs hatching into the hypoxic chambers were about half the numbers hatching into the normoxic chambers. The pH level in the sediment was 7.1 to 7.3 at the hypoxic site, slightly lower than in the normoxic sediment (pH > 7.5). That difference seemed to have little effect on egg hatching. High sulfide concentration at the hypoxic site (>300 μM), combined with low dissolved oxygen in summer were likely responsible for the depressed egg hatching. However, the cumulative number of eggs that hatched in the hypoxic chambers was still about half of that in the normoxic chambers. Thus, it appears that the hypoxic site might still be a significant source of juveniles for the next generation of the copepods.

Effects of Increased CO 2 and Temperature on the Growth of Four Diatom Species (Chaetoceros debilis, Chaetoceros didymus, Skeletonema costatum and Thalassiosira nordenskioeldii) in Laboratory Experiments

We examined the combined impacts of future increases of CO2 and temperature on the growth of four marine diatoms (Skeletonema costatum, Chaetoceros debilis, Chaetoceros didymus, Thalassiosira nordenskioeldii). The four strains were incubated under four different conditions: present (pCO2: 400ppm, temperature: 20℃), acidification (pCO2: 1000ppm, temperature: 20℃), global warming (pCO2: 400ppm, temperature: 25℃), and greenhouse (pCO2: 1000ppm, temperature: 2 5℃) conditions. Under the condition of higher temperatures, growth of S. costatum was suppressed, while C. debilis showed enhanced growth. Both C. didymus and T. nodenskioldii showed similar growth rates under current and elevated temperature. None of the four species appeared affected in their cell growth by elevated CO2 concentrations. Chetoceros spp. showed increase of pH per unit fluorescence under elevated CO2 concentrations, but no difference in pH from that under current conditions was observed for either S. costatum or T. nodenskioeldii, implying that Chetoceros spp. can take up more CO2 per cell than the other two diatoms. Our results of cell growth and pH change per unit fluorescence suggest that both C. debilis and C. didymus are better adapted to future oceanic conditions of rising water temperature and CO2 than are S. costatum and T. nodenskioeldii.

Predicting the Invasion Pathway of Balanus perforatus in Korean Seawaters

The European Common Barnacle Balanus perforatus Brugiere (Crustacea, Cirripedia) has been introduced into the east coast of Korea, presumably via the ballast water of ships. The species has since been spreading along both the northern and southern coast to the east, most likely due to alongshore currents. We predicted the potential range expansion of Balanus perforatus in Korean waters using Genetic Algorithm for Rule-set Prediction (GARP), an environmental niche modeling technique. The results show that much of the southern coastal waters of Korea could be colonized by the spread of the nonindigenous species, but that the west coast is unlikely to be invaded. More sampling on the west coast would enhance the predictability of the model. To our knowledge, this is the first report of its kind for predicting marine nonindigenous species in Korean waters using GARP modeling.

Collapse of the Crustacean Mesozooplankton in the Northern East China Sea: Effects of the Three Gorges Dam?

ABSTRACT Hwang, S.-W.; Kang, H.-K.; Son, Y.-B.; Jang, M.-C., and Choi, K.-H., 2013. Collapse of the crustacean mesozooplankton in the northern East China Sea: effects of Three Gorges Dam? The damming of major rivers can have broad impacts on ecological processes in adjacent marine ecosystems. Thirty years of sampling data from the northern East China Sea show that the recent impounding of water by the Three Gorges Dam on the Changjiang River (Yangtze River) might have had dramatic impacts on the mesozooplankton community. The reduction in freshwater discharge and subsequent increases in phytoplankton biomass have resulted in a substantial increase in total mesozooplankton wet weight but sharp declines in the abundance of all of the crustacean components. The increase in mesozooplankton biomass is probably associated with an increase in small, gelatinous zooplankton. Together with an increase in sea surface temperature in the region, the reduced freshwater and sediment discharge might have led to the proliferation of gelatinous mesozooplankton in this historically overfished region, generating significantly increased grazing pressure on planktonic crustaceans.

The impact of adding organic carbon on the concentrations of total residual oxidants and disinfection by-products in approval tests for ballast water management systems

In the G8 and G9 approval tests for ballast water management systems, organic carbon additives are frequently supplemented into test water to satisfy the water quality requirements. Because organic additives can affect the approval test, the additive selected, and its use and validation should be included in the test report. This study assessed the effects of organic carbon additives on the concentration of total residual oxidants (TROs) and the formation of disinfection by-products (DBPs). The concentration of dissolved organic carbon (DOC) in test water containing additives varied depending on the type of additive, but all additives, except for methylcellulose, had concentrations similar to or higher than the theoretical values. There was a low concentration of particulate organic carbon (POC) compared to the amount of corn starch added. Over the course of the five-day holding time, TRO concentrations tended to decrease. In general, substances with a large molecular size had a higher DBP concentration than their counterparts with a smaller molecular size, some of which, however produced the highest DBP concentrations due to their molecular structure. The results suggest that the formation of DBPs is affected by the reaction with TROs, molecular size, and molecular structure in a complex manner.

Development Needs and Direction of an Ecological Grading System of Korean Tidal Flats

There is a host of habitat assessment systems available to evaluate and grade tidal flat ecosystems in Korea. Nevertheless, we recognize the need to develop a better ecological scheme to improve reliability and accuracy given the importance of using an empirical approach in assigning grades to indicators and the limitation of current systems which evaluate tidal flats on a regional basis. A preferable system would be one that enables habitat mapping within a tidal flat, provides a diagnosis of ecological stress/health, has a high level of ecological relevance, communicability, and statistical robustness, and enables evaluation of diverse habitats within a tidal flat. The following points should be considered in framing such a system. Indicators should discriminate habitat quality into five to seven grades accomodating diverse characteristics and conservation value of a habitat, and the grading should be made from frequency distribution of indicators based on nationwide data.We suggest the following tasks in crafting such a system: ⅰ) The decision on selection of indicators should be made based on accuracy of assessment and practical application; ⅱ) effects of physical habitat conditions on variability of indicators should be reflected; and, ⅲ) further works on stress/health indicators should be addressed for adopting a multiple-indicator approach which reduces misdiagnosis.

A rapid assessment survey of invasive species of macrobenthic invertebrates in Korean waters

Introduced species are a growing and imminent threat to living marine resources in parts of the world’s oceans. The present study is a rapid assessment survey of invasive macrobenthic invertebrate species in Korean ports. We surveyed over 40 ports around Korea during the period of May 2010~March 2013. Among the sampling sites were concrete walls, docks and associated floats, bumpers, tires, and ropes which might harbor non-native species. We found 15 invasive species as follows: one Sponge, two Bryozoans, three Mollusks, one Polychaete, four Cirripedes, and four Ascidians. Three morphologically similar species, namely X. atrata, M. galloprovincialis, and X. securis were further examined for distinctions in their morphology. Although they could be reasonably distinguished based on shell shapes, significant overlap was noted so that additional analysis may be required to correctly distinguish them. Although many of the introduced species have already spread to all three coastal areas, newly arrived invasive species showed a relatively restricted range, with a serpulid polychaete Ficopomatus enigmaticus and a mytilid bivalve Xenostrobus securis found only at a few sites on the East Coast. An exception is for Balanus perforatus, which has rapidly colonized the East coast of Korea following its introduction into the region. Successful management of invasive macrobenthic invertebrates should be established in order to contain the spread of these newly arrived species.

Potential invasions of phytoplankton in ship ballast water at South Korean ports

We studied the phytoplankton communities in ballast water in ships that arrived at two South Korean ports. We determined the potential for phytoplankton in the ballast water to invade the South Korean marine environment, given the specific growth rates of the phytoplankton, the delay before the phytoplankton started growing, and the rate at which the phytoplankton would initially disperse in ports and bays. Most of the phytoplankton in the ballast water samples originated in countries such as China and Japan that are adjacent to South Korea, and diatoms dominated these phytoplankton communities. The abundance of phytoplankton in a sample did not appear to be related to any particular environmental parameter, including the voyage duration. However, the number of phytoplankton taxa in a sample decreased as the voyage duration increased. The survival and growth of phytoplankton communities in the South Korean marine environment were assessed, and we found that most invasions failed at the initial dispersal phase, especially when a community was introduced to pier-side seawater. However, some members of phytoplankton communities, if they were dispersed and where conditions were highly eutrophic, could grow fast enough to overcome the initial dispersal phase in South Korean ports and bays.

Mesozooplankton community in a seasonally hypoxic and highly eutrophic bay

A 2-year survey of seawater chemistry and mesozooplankton abundance was carried out in Masan Bay, South Korea, one of the most eutrophic coastal ecosystems known. The study aimed to identify the major factors contributing to the seasonally persistent hypoxia in the bay, to characterise the Bay’s mesozooplankton community and to examine the effects of low oxygen on the distribution of mesozooplankton. Hypoxia ( 4000 individuals m–3) during summer. During hypoxic events, the abundance of Penilia avirostris was positively related to oxygen levels in the bottom water, suggesting that hypoxic conditions may cause mortality or have sublethal negative effects on population growth of this filter-feeding cladoceran.