This study has been conducted to assess blackish-water phenomena in Dam reservoir. Tosearching for the reason, we survey physical changes in reservoir and analyze metal andorganic content in particulate materials and water.The blackish-water phenomena in lake A are occurred with turbidity increases in turnoverseason irregularly. It was reported on 6 Jan. 2005 weakly and the water column mixed with35~40m depth and water temperature shows 7˚C. The turbidity of AD and AM site increasedup to 20NTU. Especially, AN site shows 27NTU, such a result makes that Dam managerconclude it to blackish-water phenomena. The results of sequential extraction analysis showthat over 80% of Al, Cr and Fe is existed in residual form in sediment. On the other hand, themost part of Mn shows exchangeable and carbonates form, which have a good possibility ofrelease to water column. Mn contents in pore waters of the sediment samples are also found tobe ~4 times higher than Fe contents. The metal contents in pore water of different dam sites arein order of AN (Fe: 9.98, Mn: 40.6) > AD(8.33, 37.5) > DD(1.91, 2.55).According to the results of extracted organic materials from sediment, humic substances isoccupied with over 85% in total organic carbon including 23~45% of humic acid (HA) and0.9~8.5% of fulvic acid (FA). However, HA content in pore water is not detectable while FAcontents, acid-soluble humic fractions is higher than that of sediment(10~15%). whichindicating that FA is a main humic components affecting water color. The color unit per DOC ofFA in pore waters of different dam sites are found to be higher in lake A than lake D.
From the results, it could be suggested that blackish-water phenomena of lake A are mainly
arise from higher concentration of Mn and water soluble organic fractions (e.g., FA) released
from sediments as well as the strength of turnover in Dam reservoir.