Seasonal Variation of Water Quality and Cryptomonads Distribution in Oncheon River

Abstract

BACKGROUND: Recently, the inflow of nonpoint pol-lutants into rivers caused by rapid urban and industrializa-tion promotes the proliferation of algae, which causes eutrophication of rivers. This study was conducted to eval-uate the seasonal variation of water quality characteristics and cryptomonads growth in the Oncheon River. METHODS AND RESULTS: The water quality and distribution characteristics of cryptomonads in the Oncheon River were investigated monthly for 12 months from January 2021. The cell number of cryptomonads was in-tensively developed in January-April, and it decreased sharply in the summer with heavy rainfall. In particular, cryptomonads moved to the downstream side of the river depending on the time, and as a result, significant differ-ences were shown for each investigation point. The Korean trophic state index (Tsi KO ) in Oncheon River was classified as eutrophy all year round, indicating that cryptomonads can grow year-round. Distribution characteristics of cryptomonads in Oncheon River showed high correlations with DO ( r =0.678), BOD ( r =0.826) and chlorophyll-a ( r =0.613) in water. CONCLUSION(S): In order to reduce cryptomonads in the Oncheon River, it is judged that a complex counter-measure considering the residence time, insolation and precipitation along with water quality factors is required.