The relationship between epilithic diatom communities and changes in water quality along the lower Han River, South Korea

Abstract

Epilithic diatom communities were sampled every two weeks from February 2001 to February 2002 at three sites in the lower Han River (LHR), South Korea, to investigate how epilithic diatom communities reflected longitudinal gradients in environmental quality measures. The water quality in the LHR differed between the rainy and dry seasons and also varied at different sites according to levels of pollution. The epilithic diatom communities responded to changes in the aquatic environment and hydrological characteristics. There were few predominant diatom species during the rainy season, and they were found at lower concentrations than in the dry season because of the high current velocities caused by heavy rainfall. The predominant species at the three study sites in the LHR were different because of the effects of eutrophication gradients. Cocconeis placentula, Diatoma vulgaris, and Nitzschia dissipata were dominant at site 1 (clean to nutrient-rich conditions). Fragilaria capucina var. gracilis and Gomphonema parvulum were dominant at site 2 and their growth was accelerated by the moderately-nutrient-rich conditions. Luticola goepperitnana, N. palea, small Nitzschia spp., and small Navicula spp. were dominant in the most polluted pools at site 3. We conclude that the LHR has a water quality gradient along its course, and that this causes marked changes in the epilithic diatom species compositions found along the river. The results confirm that epilithic diatoms are important bioindicators for assessing ecological quality in the LHR.