LONG-TERM CHANGES IN PHYTOPLANKTON ASSEMBLAGES OF LAKE KHURPATAL, KUMAUN HIMALAYA, INDIAPragya Singh, Mamta Pant and P.K. GuptaAbstract This paper focuses on the long-term changes on phytoplankton community of a subtropical lake of Himalaya, Lake Khurpatal. The study was carried out during 2016-2018. The data obtained on phytoplankton assemblages were compared with the data of 1980s. The results showed that all attributes of phytoplankton assemblages were changed in last 35 years. The species richness declined by 27.2% while the community abundance increased by 21% in last 35 years. The most important changes occurred in the group composition of phytoplankton: the Cyanophyceae which was almost absent during 1980s appeared in good quantity during the present study; the concentration of Bacillariophycae increased by 8.5 % while the Cholorophyceae did not change significantly. The Shannon-Weiner diversity index during the present study oscillated from 0.8 to 1.07 while the concentration of dominance varied from 0.12 to 0.25. The high concentration of blue greens during current year suggested that the concentration of nitrogen will further increase in the lake as the blue greens are capable of fixing the atmospheric nitrogen. Thus, even if the entry of nitrogen into the lake from the catchment area is checked the concentration of nitrogen is likely to increase in the future. It will further increase the trophic status of the lake. |