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Macroinvertebrate were collected from 31 sampling stations in the Han, Seomjin and Mankyung river system for an ecological study. The number of species and total individuals collected in the Seomjin were always relatively higher in all stations than in those in other rivers. In the upstream of the three rivers, Ephemeroptera, Trichoptera and Plecoptera were dominant. In the downstream of Han and Mankyong river, Oligochedeae such as Limnodrilus gotai was dominant. Average diversity values in the upper and middle stream of Han river were rather consistent, ranging from 2.4 to 3.7, however, in the downstream, it decreased below 1.0. The diversity values of seomjin river were generally higher than those in the Han river. In Mankyong river, only station 27 showed a high value(2.7) and the rest of stations showed much lower values. The equitability, similarity and Trent Biotic Index values showed similar tendancy. Twelve water quality parameters were compared with the diversity and equitability values by rank correlation analysis. Conductivity, the concentration of DO, BOD, SS, SO₄^(2-) and hardness had significant correlation with both diversity and equitability of the benthic community, while chloride concentration and alkalinity only had significant correlation with the equitability value.
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