Unraveling the phytoplankton altitudinal dynamics in relation to environmental variables in a Himalayan River, Teesta, India

An investigation was carried out to comprehend the altitudinal variation of phytoplankton and their distribution pattern in River Teesta. Phytoplankton were recorded at two different altitude levels of the river. A total of 35 genera of phytoplankton were recorded with dominated by diatoms. The altitudinal differences reflected comparatively high genus richness in the high-altitude region. Seasonal spectrum of phytoplankton was maximum during post-monsoon (7.67 ± 13.42 ul −1 ) and pre-monsoon (51.6 ± 24.52 ul −1 ) in the high-altitude and low-altitude region, respectively. On the whole, the major compositions of phytoplankton are represented as Bacillariophyceae > Cyanophyceae > Chlorophyceae across seasons. The k -dominance curve revealed that there was no remarkable difference in dominance pattern of phytoplankton among the sampling sites with 9 to 15 species accumulated 80% cumulative relative abundance across sites. Negative altitudinal gradient of diversity indices (Shannon and Simpson index) was recorded which implies lower diversity exists at higher altitude. Further, GAM model ( R 2 = 0.36) depicted statistically a nonlinear pattern of genus turnover against the altitudinal distance. The significant positive relationship was observed between phytoplankton genus turnover and altitudinal distance in the river. Canonical correspondence analysis reflected that water variables such as total alkalinity, total hardness, sp. conductivity, nitrate, total phosphate and silicate were the influential factors for the distribution of phytoplankton community in both the altitudes of the river Teesta.