COMPOSITION AND DISTRIBUTION OF AQUATIC INSECT COMMUNITIES IN RELATION TO WATER QUALITY IN TWO FRESHWATER STREAMS OF HULU TERENGGANU, TERENGGANU.

The impact of human disturbance and agricultural activity on aquatic insect communities in two freshwater streams (Sungai Peres and Sungai Bubu) in Hulu Terengganu, Terengganu were studied. A total of 3409 individuals of aquatic insects representing 42 families from 9 orders were successfully collected from August until November 2006. No significant difference was detected for the total abundance of aquatic insects between Sungai Peres and Sungai Bubu (Mann-Whitney Test = -1.550, P = 0.121). However, total abundance of aquatic insects was significantly higher at the upstream stations than downstream stations in both streams (Kruskal-Wallis Test = 2.519, P = 0.012). Heptageniidae (Ephemeroptera), Perlidae (Plecoptera) and Hydropsychidae (Trichoptera) were the most abundant groups collected in both streams. The Ephemeroptera, Plecoptera, Trichoptera (EPT) Index and EPT to Chironomidae ratio (EPT:C) showed that the pollution-sensitive group (EPT) were highly abundant and more diverse at the upstream stations, but higher numbers of pollution-tolerant taxa (Chironomidae) were found at the downstream stations in both streams. Unexpectedly, the Family Biotic Index (FBI), Biological Monitoring Work Party (BMWP) and Average Score Per Taxon (ASPT) indicated that the water quality of both streams varied from clean-to-excellent categories, even though both streams received pollutants from various anthropogenic activities. Width and pH of the streams were positively correlated with the total abundance of aquatic insects (R width = 0.360, P = 0.014; R pH = 0.509, P = 0.003), whereas lower abundance of aquatic insects was found in more turbid water with high total suspended solids (TSS) in both streams (R TSS = -0.291, P = 0.050). This study shows that distribution of aquatic insect communities could provide useful bioindicators of the biomonitoring approach in relation to water physico-chemical parameters to assess, classify and compare the water quality of freshwater streams in Malaysia.