Impacts of a small dam on macroinvertebrates: A case study in the Tinau River, Nepal

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.

Keywords:

• NEPBIOS
• Substrates

Acknowledgements

We would like to extend our sincere thanks to Noragric, Agricultural University of Norway, for providing financial support for the study. We appreciate the thorough review and valuable comments of our manuscript by Assoc. Professor Svein Dale, Norwegian University of Life Sciences. We also appreciate the constructive comments of Dr. Jeppe Kolding, University of Bergen, and Dr. Odd T. Sandlund, NINA, Norway, to improve the quality of the manuscript. Bharat Shrestha, Rinjan Shrestha and Deepak Rijal, PhD students, Norwegian University of Life Sciences, also deserve our thanks for commenting on the manuscript. We would like to extend our heartfelt acknowledgements to the students of Kathmandu University, Bibhuti R. Jha, Anil Shrestha, Bibhuti Bista and Shekhar Koirala for their painstaking assistance during the fieldwork.

Notes

^a Classification of functional groups like scrapers and filter collectors is done after Dudgeon (1999).

^b Biological condition categories are based on the % comparison to Reference score (> 83% = non-impaired, 54–79% = slightly impaired, 21–50% = moderately impaired, and < 17% = severely impaired) Plafkin et al. (1989).