새만금 방조제 건설에 따른 내ㆍ외측 수역의 식물플랑크톤 군집구조

Abstract

To investigate the patterns of environmental factors and phytoplankton abundance changing due to the construction of the Saemangeum sea dike, data were obtained and analyzed before and through the construction of the sea dike and after its completion in 2014. In the result of Pearson correlation analysis of discharging rates, precipitation and elevation level, discharging rates from the two sluices in the Saemangeum sea dike had no correlation with precipitation, but it was correlated with the water elevation level outside Sinsi Sluice Gate. Regarding water environmental factors inside the sea dike, salinity tended to decrease, gradually changing to fresh water level, whereas the nutrient concentration tended to increase as the construction progressed. In contrast, the water environmental factors inside the sea dike showed no significant change in salinity as the construction progressed, but the concentration of dissolved inorganic nitrogen and dissolved inorganic phosphate tended to decrease and dissolved silicate concentration remained constant due to supply from the outer sea. Chlorophyll-a, also expressed as the biomass of phytoplankton, tended to increase in concentration both inside and outside, as the construction progressed. Regarding species composition of phytoplankton, the proportion of cyanobacteria increased inside the sea dike after construction of the last tide embankment, whereas that of Chlorophyta and of cyanobacteria species increased outside before and after completion of the last tide embankment construction. Phytoplankton abundance showed highly significant changes depending on the construction stage and time of study. General phytoplankton blooming patterns were observed in spring and autumn, and phytoplankton abundance remained high in winter, 2014. Regarding dominant species, marine species became dominant inside as the construction progressed, whereas brackish water species became dominant outside the dike. Inside the dike, correlation analysis between phytoplankton abundance and water environmental factors showed a positive correlation with nutrients and a negative correlation with salinity. On the surface of the outer water, phytoplankton abundance showed a positive correlation with chlorophyll-a and a negative correlation with salinity. In the bottom layer, it had a positive correlation with chlorophyll-a. A stepwise regression analysis showed that the phytoplankton abundance had direct statical causal relationships with dissolved inorganic nitrogen inside the sea dike and chlorophyll–a outside. It appeared that the construction of the Saemangeum sea dike caused the accumulation of nutrients which flowed from the land to the inside of the sea dike, and which led the dominance of causative phytoplankton of red and green tides, causing degradation of water quality. Contrarily, outside the sea dike, nutrient concentrations decreased due to the sea dike construction, but harmful phytoplankton species from artificial lake were observed. Thus, a continuous and careful monitoring is required on these harmful phytoplankton species. Additionally, the correlation analysis revealed that phytoplankton abundance was affected by chemical factors inside the sea dike, and complex physical and biological factors were found to affect the phytoplankton abundance outside the dike. Therefore, thorough maintenance and continuous efforts should be implemented inside the sea dike to prevent the water from being further contaminated, whereas the physical and biological aspects should be closely examined on the outer side.