The kingdom of Bhutan, characterized by mountainous terrain with an intricate network of drainage system and rich watershed, is endowed with diversity of lentic ecosystems including glacial lakes, ponds, wetlands and paddy-fields scattered throughout different climatic regimes of the country. However, there is no single limnological work in Bhutan that deals with biological diversity in water bodies or temporal variations in abiotic attributes in any particular aquatic biotope. In light of the above lacunae, present pioneering study carried out between February 2000-January 2002 brings into limelight the water quality, species richness of net plankton, zooplankton, phytoplankton, percentage similarities, richness, abundance, diversity, dominance, evenness and other related ecological attributes in three selected ecosystems in eastern Bhutan with emphasis on biodiversity of zooplankton in east Bhutan in general and Rotifera diversity in all sampled biotopes in different parts of the country in particular.

The sampled lentic ecosystems of Bhutan depicted acidic to slightly alkaline soft waters of low to moderate ionic concentration and comprised considerable plankton diversity with sixty species of rotifers consisting mainly of semi-planktonic and littoral fauna with few taxa of biogeographical and ecological importance including a new Keratella sp. Three regularly monitored ecosystems in eastern part of the country, on the other hand, differed in their basic ecological attributes with the pond (Site 1) exhibiting its circum-neutral waters of relatively high silica content, which exhibited a bloom of copepods with significant annual variations indicating its unstable condition owing to the influence from its catchments. Poorly oxygenated, the acidic peat bog (Site 2) with low nutrients in general showed high abundance of filamentous algae, high diversity and dominance as well as evenness of phytoplankton. On the other hand, the ephemeral paddy-field (Site 3) exhibited comparatively higher ionic concentration, total alkalinity, hardness as well as calcium, potassium and sodium, due to regular ploughing and puddling hence discharging ions and minerals into the surface water and also recorded highest qualitative as well as quantitative abundance of net plankton, phytoplankton and zooplankton among three sampled biotopes.