Drift and Benthic Densities of Aquatic Insects and The Evaluation of Water Quality in Selected Streams in Sarawak

The presence and composition of aquatic insects are important bioindicators of the level of pollution and quality of freshwater systems such as rivers and streams. In this regard, the abundance and diversity of drift and benthic aquatic insects in streams can provide important indicators on the health of the streams. The results obtained from this study can be used as a baseline data to monitor the level of pollution and health of the streams in Sarawak. The objective of this study aims to (i) document the diversity and abundance of aquatic insects in the drift and composition of benthic aquatic insects during sunrise and sunset at five selected streams in Sarawak, (ii) identify the relationship between the compositions of aquatic insects in the drift and composition of benthic aquatic insects during sunrise and sunset with its physicochemical parameters of the streams, (iii) evaluate the status of the water quality and organic pollution of the streams. The five streams involved in the study were the Sabong Stream, Duyoh Stream, Cina Stream, Serin Stream and Bak Muan Sadir Stream. Drift samplings of aquatic insects in the streams were carried out using the Surber Sampler while benthic samplings were conducted using Kick net between March - June 2016. The aquatic insects in the drift were collected every three hours for 24 hours while the benthic aquatic insects were collected during sunrise and sunset. A total of 15 samplings were conducted. The samplings data were then subjected to Pearson’s correlation analysis to analyse the relationships among diversity of the streams and water quality while Analysis of Variance (ANOVA) was used to compare the variations in water quality between sampling locations and sampling periods and Canonical Correspondence Analysis (CCA) was conducted to examine the relationship between the aquatic insect community structure and stream physicochemical parameters. A total of 462.29 aquatic insect individuals per 100m3 belonging to 39 taxa, 25 families and 7 orders were recorded in the drift in five streams. The Baetis sp. from the family Baetidae was the common taxa which dominated the drift in the Duyoh Stream, Cina Stream, Serin Stream and Bak Muan Sadir Stream, while the drift in Sabong Stream was dominated by Simulium sp. The drift density of the aquatic insects increases just after sunset in every sampling in the streams. Irregular patterns of aquatic insects drifting throughout night time were observed in the streams and the drift density of aquatic insects fluctuated just after sunrise in the streams. The community structure of the aquatic insects in the drift in the Sabong Stream was significantly influenced by pH and dissolved oxygen. On the other hand, the drift of aquatic insects in the Cina Stream was significantly influenced by temperature and water discharge. The aquatic insect density in the Serin Stream was influenced by pH, temperature, turbidity and water current. Whereas, drift in the Bak Muan Sadir Stream was affected by water discharge and total suspended solid (TSS). In terms of diversity of the benthic aquatic insects, the results of the study showed that a total of 36 taxa belonging to 19 families and 5 orders of aquatic insects were recorded during sunrise while 30 taxa, 18 families and 5 orders of aquatic insects were recorded in the five streams during sunset. The order Ephemeroptera was most diverse in terms of number of individuals followed by Dipterans and Trichopterans, while other orders of aquatic insects were less abundant in the streams. The richness of the EPT (Ephemeroptera, Plecoptera and Trichoptera) taxa indicated that the streams have good water quality. Based on the analysis of the biotic indices (BMWP, ASPT, BMWPTHAI and ASPTTHAI), it is indicate that the water quality of each stream in this study was clean and experiences low level of pollution