Phytoplankton diversity in relation to physicochemical attributes and water quality of Mandakini River, Garhwal Himalaya.

Phytoplankton are important biological indicators of water quality. This current study assessed the physicochemical parameters and phytoplankton diversity of Mandakini River, an important tributary of the River Ganga. Water and phytoplankton samples were collected from three sampling sites located at three different altitudes for a period of twelve months (July 2018-June 2019). Water samples were analyzed for fourteen important physicochemical parameters along with the identification of phytoplankton by following the standard methodology. A total of 21 species of phytoplankton under three major groups Bacillariophyceae (Cymbella aequalis, Diatoma vulgaris, Fragilaria arcus, Frustulia rhomboids, Gomphonema geminatum, Navicula confervacea, Nitzchia diversa, and Synedra ulna); Chlorophyceae (Volvox sp., Cladophora glomerata, Closterium longissima, Hydrodictyon sp., Microspora amoena, Spirogyra sp., Oedogonium sp., Ulothrix zonata, and Zygnema cylindrospermum); and Cyanophyceae (Anabaena ambigua, Chlorococcum humicola, Nodularia sp., and Oscillatoria sancta) were observed and recorded during the study period. Site S (Rudraprayag) had the highest species diversity. From this study, the effect of physicochemical parameters on the diversity and density of phytoplankton was observed. It also includes the overall significance of phytoplankton and physicochemical parameters to the water quality of the Mandakini River along with the key factors that were responsible for the degradation of water quality. The current study also provides baseline information to future researchers working in a similar discipline.