Multivariate approach to link phytoplankton dynamics to environmental variations in a large tropical reservoir

The diversity and dynamics of phytoplankton are dependent on many environmental variables in an ecosystem. Their distribution, sudden surge in population, and the mere disappearance provide an indication of the ecology. Hence, the seasonal and spatial variations in phytoplankton diversity and abundance were investigated and correlated with abiotic variables for 2 years (2017–2018 and 2018–2019) in a large tropical reservoir in India, the Mettur reservoir. Plankton abundance was spatially similar with Cyanophyceae as the dominant class. The plankton density showed a 10-fold change ranging from 2.2 × 105 cells/liter during premonsoon to 2.3 × 106 cells/liter during post-monsoon season. The diversity index ranged from 1.202 (post-monsoon) to 2.057 (monsoon season). The reservoir recorded high organic pollution as evidenced by the estimated algal genus pollution index (AGPI). This may be attributed to anthropogenic activities, especially agricultural runoff from catchment areas or inflow of wastewater from the small-scale industries situated in the vicinity of the reservoir. Possible relationships of environmental variables in the ecosystem functioning with phytoplankton community composition were also derived. The outcomes of the present investigation can be extrapolated to other tropical aquatic ecosystems for assessing the ecological quality and the health status of water bodies for implementing efficient management practices for enhanced fish production, especially from underutilized reservoirs.