Soonmo An

Background level and composition of polybrominated diphenyl ethers (PBDEs) in creek and subtidal sediments in a rural area of Korea

To study background levels of polybrominated diphenyl ethers (PBDEs) in Korea, concentrations of PBDEs were measured for creek and subtidal sediments around Goseong Bay. Total concentrations of PBDEs (Σ19PBDE) in creek sediments ranged from 0.18 to 13.95 ng/g dry weight and were about twice those in subtidal sediments. PBDE concentrations were about two orders of magnitude lower than those reported in industrially active regions of Korea and other countries. BDE 209 was a major congener, accounting for 79.0% and 78.5% of total PBDEs in creek and subtidal sediments, respectively. This is consistent with the high consumption of deca-BDE in Korea and the very high octanol-water partition coefficient of deca-BDE. The relative compositions of PBDEs in creek and subtidal sediments were similar. BDE 209 and Σ19PBDE had statistically significant correlations with total organic carbon, the lower brominated congeners had a poor correlation with total organic carbon.

Effect of dikes on the distribution and characteristics of Phragmites australis in temperate intertidal wetlands located in the South Sea of Korea

We investigated the Korean Phragmites australis (haplotype P) distribution patterns and their association with environmental factors in estuaries with (Goseong) and without (Guman) a dike. The intertidal wetland of the Guman River Estuary has a flooding duration of 25% to 68% (average 40%), a range common to Phragmites habitats around the world. Porewater salinity in the Phragmites habitat of the Guman varied with the tides. Salinity of the overlying water influenced the salinity of pore-water only if flooding was above a certain height (overlying water depth of about 30 cm). High salinity was frequently observed in overlying water and pore-water of the Guman but the Phragmites may be able to survive with periodic exposure to freshwater, which relieves high salinity stresses. However, Phragmites experienced limited growth in some regions where flooding frequency was high but freshwater influence was low. Continuous measurement (two weeks) of pore-water salinity suggests that the salinity near the Phragmites rhizosphere is determined by the balance between the tidal and freshwater influences. Phragmites in the Goseong River Estuary was found at elevations about 100 cm lower than in the Guman and Phragmites growth was larger in the Goseong than in the Guman. We hypothesized that lower flooding duration and pore-water salinity, resulting from dike construction, allowed Phragmites to expand into lower elevation areas in the Goseong. The current study demonstrates the effects of coastal developments involving salinity structure and flooding duration changes on Phragmites distribution.

Dissolved Oxygen and Nutrients

Changing global temperatures may alter oceanic concentrations of both dissolved oxygen (DO), which reflects water quality, and nutrients, which are an essential factor for the growth and distribution of phytoplankton. The East Sea (Japan Sea) is often considered a “miniature ocean” and an ideal natural laboratory to estimate the impact of global climate change on the oceanic biogeochemical cycles, because of the East Sea’s physical dynamics. Thus, the monitoring of nutrients and DO concentrations in the East Sea may help predict the response of biogeochemical cycles in the global ocean to changing climate. We describe and discuss the history of studies on DO in the East Sea, the change in vertical structure of DO profiles, the trend of DO inventory in the bottom layer, and the controversy regarding future projections of DO in the bottom water mass. We also summarize the history of nutrient measurements in the region, the general structure of vertical nutrient profiles, the horizontal nutrient distribution pattern on isobaric surfaces, the seasonal nutrient flux through the Korea Strait, and the recent debate on nutrient dynamics in the East Sea. The results of the studies we examine suggest that the processes controlling the structures and inventories of DO and nutrients in the East Sea are very sensitive to global climate changes.