The scores for Sts. 1–4 that were characterized by the low pH and high concentrations of metals were distributed into the third quadrant in all seasons except for St. 1 in (c) fall which distributed into the second quadrant due to the presence of just one individualof
Psychodidae. Community structure of benthic macroinvertebrates at the stations distributed into the third quadrant was very simple and consisted of mainly Capnidae and Nemouridae that are tolerant of acid. Dills et al. (1974) have reported that the number of species and individuals of benthic macroinvertebrates were extremely small and their community structure was very simple in strongly acidic conditions. Therefore, it is possible to say that the communities of benthic macroinvertebrates under acidic conditions are generally characterized by simple structure and small number of species and individual.