Dynamics of aquatic insects in the Mandakini river of Uttarakhand, India

摘要

Aquatic insects are very important for aquatic ecosystem contributing mostly as secondary producers and also bioindicators determining the health of the ecosystem. River ecosystems of Himalaya experience flash floods every year destroying the aquaticbiodiversity. Biodiversity lost due to flash floods in monsoon recovers soon. Keeping in view the importance of diversity and paucity of information on benthic insects diversity of Mandakini river, the present work was conducted. River Mandakini is a perennial and glacier fed tributary of river Alaknanda which originates from Chaurabari glacier above the Kedarnath peakes (6940m. a.s.l.). Three sampling sites, Kund (998m. a.s.l.), Agastmuni (760m. a.s.l.) and Rudraprayag (620m. a.s.l.) were selected forthe study. Sampling for benthic insects and physico-chemical parameters were done every month from January 2014 to December 2014. Aquatic insects belonging to 7 orders and 28 families were found in Mandakini river. Trichoptera was found to be the most abundant order (36) followed by Ephemeroptera (32) and Diptera (26). Aquatic insect diversity was found to be maximum (3.462±0.400) in winter reflecting good quality of river water and minimum (1.269±0.855) in rainy season due to high water velocity,high amount of silt, low transparency and disturbed substratum due to frequent flash floods in monsoon. The high density and diversity of aquatic insects in winter was attributed to low water velocity, high transparency, optimum water temperature, high dissolved oxygen, low turbidity and suitable composition of bottom substrates. The Shannon-Wiener diversity index reaching above 3.0 in winter indicated a good recovery of the benthic insect population. Canonical Correspondence Analysis (CCA) revealed that a myriad of physico-chemical factors like dissolved oxygen, total alkalinity, free C02 pH, water transparency, water velocity, water temperature, total hardness and dissolved phosphates affect the benthic insects abundance.