Vipul Dev Beniwal and Sushma Jain
Abstract
Study was conducted at the Kot Dam (27R 39â2'âN latitude and 75R 25â10'âE longitude) in the Jhunjhunu district of Rajasthan to assess seasonal variations in species richness and diversity of phytoplankton from April 2021 to March 2023. A total of 28 phytoplankton species belonging to five families were observed at sampling stations I, II, and III of the Kot Dam. Out of these maximum numbers of species belongs to Chlorophyceae family (13) followed by Bacillariophyceae (7), Cyanophyceae (6) and lowest number of species were observed from families Xanthophyceae and Dinophyceae (single species from each). Simpson diversity index ranged between 0.9431 to 0.9558 for sampling station I, 0.9272 to 0.9559 for sampling station II, and 0.9477 to 0.9548 for sampling station III of Kot Dam. Seasonal variation in the Simpson diversity index was observed at all three sampling stations. Shannon diversity index values ranged from 2.996 to 3.201 for sampling station I, 2.828 to 3.21 for sampling station II, and 3.068 to 3.204 for sampling station III. Increased sunlight and warmer temperatures promote the growth of phytoplankton and decrease mixing in the water column, allowing nutrients to accumulate in the surface layer. In monsoon season, phytoplankton species are often reduced because of the dilution of water bodies, and high turbidity and excessive nutrient loads inhibit the growth of certain phytoplankton. Freshwater influx from rainfall and runoff disrupts water salinity and temperature, impacting phytoplankton communities, high turbidity caused by increased suspended solids, and reduced light penetration responsible for the decline rate of photosynthesis; therefore, the number of phytoplankton also declines.