Diversity and Seasonal Variations of Plankton Communities After Major Flash Flood in the River Mandakini of Garhwal Himalaya

摘要

Plankton diversity acts as an ecological indicator of aquatic ecosystems due to their rapid response to environmental changes. Plankton samples were collected monthly for a period of 24 months. A total of 35 genera of phytoplankton belonging to three classes, Bacillariophyceae (21 genera), Chlorophyceae (9 genera) and Cyanophyceae (5 genera) were found. The abundance of phytoplankton was in the order, Bacillariophyceae (83%) followed by Chlorophyceae (9%) and Cyanophyceae (8%). Maximum phytoplankton density in winter season was attributed to the low water temperature, gentle water velocity, high transparency, availability of sufficient nutrients and most stable substratum. Eight genera of zooplankton belonging to three major groups, Protozoa (2 genera), Rotifera (5 genera) and Copepoda (1 genus) was recorded. Shannon-Wiener diversity index of phytoplankton and zooplankton was computed maximum to be 2.61 and 1.56 respectively in the winter season. PCA indicates Cymbella, Navicula, Synedra, Cocconeis, Achnanthidium, Amphora, Nitzschia, Tabellaria, Fragilaria, Ulothrix, Spirogyra and Phormidium to be most dominant genera in the Mandakini river. Total alkalinity, water temperature, transparency, velocity, dissolved oxygen, free carbon dioxide, turbidity, phosphate and nitrate were found to be the most important factors affecting plankton diversity in the Mandakini river.