Odonata as biological indicator of freshwater ecosystem

Odonates are bioindicators as they provide information regarding the ecological conditions of freshwater ecosystems. Freshwater resources are under great anthropogenic pressure due to pollution, sediments, drought, and climate change. To list out odonate species in different types of aquatic environments and to identify indicator species, a total of 12 sampling sites in the Karnali River basin were surveyed using an ocular observation method with the help of a sweeping net for the adults and handpicking to the exuviae. Different ecological indices were calculated for different habitat types and study sites. At the same time, linear relationships between different indices were also evaluated. A total of 88 odonata species belonging to 52 genera and 12 families were recorded. Among them, based on the Odonata Value Index (OVI), 29 species were identified as indicator species, where 16 were specialist species and 13 were habitat indicator species. The odonata species richness was high in the lower elevations and remains scarce in higher elevation levels as they have environmental influence. The biotope diversity of dragonflies is found to be low in all study sites. The dragonfly biodiversity indices, i.e., the Dragonfly Biotic Index (DBI) and Habitat Integrity Index (HII), have a significant influence on each other. The study emphasizes the need for conservation priorities in riparian ecosystems and diverse types of habitats for the odonate community and the probability to use odonates to assess ecosystem health. Key words: Dragonfly, damselfly, bioindicator, ecological indices