Major stressors influencing the river ecosystems of Far and Mid Western Development Regions of Nepal

Abstract

Maintaining healthy river ecosystem is essential both from aquatic biodiversity conservation perspective as well as for the socio-cultural and economic development of nations all over the world. Many rivers in Nepal have largely been modified with the purpose of supplying drinking water, irrigating agricultural lands, producing hydro-electricity, and operating water mills. During the process, rivers are channelized and the river bed materials are removed. Such activities of river bed excavation have changed both the natural flow regimes and morphological characteristics of rivers. Studies on the impacts caused by such stressors on river ecosystems are lacking in the context of Nepalese river systems. Therefore we have assessed how these stressors might change the faunal composition of benthic macroinvertebrates in headwaters of the Western region of Nepal. The study was conducted in the headwaters of rivers of Mahakali and Karnali rivers. Habitat specific benthic macroinvertebrates were sampled from 33 sites seasonally in the year 2016 and 2017. Physical characteristics of rivers including river bed composition, water abstractions and other local stressors including waste dumping and washing-bathing were noted in the field. The study showed that macroinvertebrates community structures were significantly different in the habitat modified sites compared to reference sites. In general, abstracted sites coupled with river bed removals were found to be colonized by fewer taxa with high dominance of pool preference biota such as genera of Mayflies (Torleya spp., Caenis spp., Choroterpes spp.) and families of true flies (Chironomidae and Ceratopogoniidae). Macroinvertebrates’ abundance was significantly lower in the habitat modified sites. This study envisages that maintaining river’s habitats with minimal flows all round year could preserve ecological integrity of river systems.