¹Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences, P.O. Box 5003, 1432 Aas, Norway
²Aquatic Ecology Centre (AEC), Department of Biological Sciences and Environmental Science, Kathmandu University, P.O. Box 6250, Dhulikhel, Kathmandu, Nepal, Voice: +977 11-661399, Fax: +977 11-661443, Email: sharmaku@yahoo.com
³Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences, P.O. Box 5003, 1432 Aas, Norway, Voice: +47 64948454, Fax:+4764948502, email: reidar.borgstrom@umb.no
⁴Department of International Environment and Development Studies (Noragric), Norwegian University of Life Sciences, P.O. Box 5003, 1432 Aas, Norway, Voice: +47 64948652, Fax: +47 64940670, Email:ian.bryceson@umb.no

^*Corresponding author: Tel: +47 64948477, Fax: +47 64948502, E-mail chhatra.sharma@umb.no

Abstract

  Macroinvertebrate composition, eco-morphological habitat descriptions and substrate composition were assessed above and below a small dam in the Tinau River, Nepal to explore the impact of the dam on biotic conditions. Four sites, one about 1.5 km above, one just above the dam site, one just below, and one about 2.5 km below the dam, were selected for qualitative and quantitative samplings of macroinvertebrates. The Nepalese Biotic Score method was used for the biological water quality assessment. The most abundant groups of macroinvertebrates among the total collection were of the family Chironomidae (53.5 percent) followed by Ephemeroptera (36 percent) and Trichoptera (5 percent). Only one of the dominant families, Baetidae, showed significant variability with substrate composition. The dam building had significant impacts on the macroinvertebrate composition just above the dam site, probably as a result of deposition of inorganic material within the small reservoir and changes in water speed. Damming of the Tinau River thus seems only to have a relatively minor impact on the river biota downstream of the dam site. The water quality of the river was assigned as Class II in all the stations, indicating its suitability for drinking after treatment.