Impact of water quality parameters on aquatic insect fauna of Majuli river island, Assam, India

Aim: To study the diversity of aquatic insects and establish correlation between key water quality parameters and aquatic insect diversity in selected aquatic systems of Majuli island. Methodology: Fixed plot surveys covering 25 sampling sites under 5 aquatic systems viz., water bodies with dense, floating and submerged vegetation S1), seasonal natural streams (S2), periodically managed streams (S3), open water areas completely devoid of vegetation (S4) and water areas near brick industry (S5) were carried out seasonally. Species diversity indices were calculated. Standard protocols were followed to estimate the key physico-chemical water quality parameters. Correlation coefficient was computed to establish significant correlations. Results: Study revealed the presence of 7692 numbers of aquatic insect belonging to 6 orders and 19 families. Highest and lowest mean population was observed in S4 during monsoon and S5 during winter. Ranatra sp. was found to be the dominant species during pre-monsoon and winter from S2. The highest value of diversity indices was recorded during monsoon from S4 whereas the lowest value was observed in S5 during winter. Significant positive correlation (p<0.05) was observed between nitrate and bicarbonate with that of diversity and evenness of aquatic insects in S1, S2 and S4. Correlation study also showed a non-significant positive correlation between dissolved oxygen, carbonate and pH with that of diversity and evenness of aquatic insects. Interpretation: The present study indicated the diversity of aquatic insects', their population and relationship with key water quality parameters. Aquatic insects are considered as potential bioindicators so extensive exploration should be undertaken to assess their actual role in ecosystem as bioindicators.