River systems are the diverse ecosystems in the globe. Despite their very low share in total area of Earth’s surface they support highly diverse habitat and wildlife. Fresh water habitats are home to more than 10% of known animals. Diverse communities of plants and animals depend on rivers, owing to the wide variety of shelter, breeding and feeding opportunities that river habitat provides. Over 140,000 described species – including 55% of all fishes rely on freshwater habitats for their survival. Habitats intimately connected to rivers include associated wetland areas, swamps and fens, bogs and marshes, flood plains and wet woodland. Waterfalls, rapids and cascades, riffles, glides and pools are micro-habitats that river system have to support diverse range of species.
The knowledge of total diversity of freshwater ecosystems are incomplete – particularly among invertebrates and microbes. Freshwater ecosystem supports almost as much of invertebrates (decapod crustaceans, molluscs, and aquatic insects) diversity described to date. Nearly 50% of the fish presently described are freshwater fishes.
Nepal is important in terms of freshwater biodiversity. In Nepal, there are 230 fresh water fish species among with 16 species are endemic to Nepal. Nepal’s fish species vary from small, short-lived species (e.g., Danio rerio that reaches 26 mm) to some of the world’s largest freshwater fishes (e.g., Gonch that can attain 80 kg ) (Sharma 2008).Reptiles and amphibians are also abundant in Nepal with 10 endemic among them. Turtles, Gharials, crocodile, and numerous snakes, frog and toad species. Besides fishes, 1001 species of phyto-plankton, 121 species of zooplankton, 192 species of mollusks, and 117 species of amphibians associated with fresh water systems. Much more remains to be explored about the lower animals like freshwater invertebrates.
Of the freshwater mammals, the Ganges River Dolphin is the only found in river systems of Nepal. The species is supposed to be found in Koshi, Gandaki and Karnali river systems but only viable population occurs in Karnali river. Besides the Ganges River Dolphin, other predominantly aquatic mammals are: Fishing Cat, several species of deer and otter, shrews, and the Indian water buffalo. Along with these, river systems are home to 307 birds species in Nepal. Also, an estimate of 25% of Nepal’s vascular plant species are at least partially dependent on wetlands. According to IUCN assessment, 284 freshwater plants are recorded in Nepal. The Ganges-Brahmaputra river system holds 612 freshwater species with 9% of endemic. The Kali Gandaki gorge is supposed to contain over 1,375 species of water beetles.
Freshwater ecosystems are in crisis. Freshwater species have lost over 83% of their populations since 1970 as reported by Living planet Report. Almost a third of freshwater species are threatened with extinction and over 200 are already extinct. River ecosystems are under threat due to over exploitation for construction of large dams, water diversions and pollution; resulting in loss of characteristic habitat and biodiversity. Climate change is likely to become a leading threat for freshwater systems in future.
Another 3,700 hydro-power dams are currently under construction or in pipeline over the globe. In context of Nepal there are 223 dams in operation, under construction and proposed across major rivers. Habitat destruction, obstruction of migration and breeding and change in limnological parameters are major impacts brought about by establishment of dams and diversion projects. Among freshwater animal species in Nepal, 11% (9 mammals, 14 amphibians/reptiles, 39 birds, 18 fish, 4 odonates, 1 mollusks) were found to be of conservation concern; including charismatic mega-fauna like Rhinoceros, Gharial, Crocodile, and Dolphin.
References
Sharma, C. M. (2008). Freshwater fishes, fisheries, and habitat prospects of Nepal. Aquatic Ecosystem Health & Management, 11:289-297