Riverine connectivity influences the phytoplankton ecology in the open floodplain wetland of the lower river Ganga

The river Ganga has several floodplain wetlands that support its ecology and ecosystem. Phytoplankton is an important component of the aquatic ecosystem, which plays an important role as a bioindicator for the assessment of aquatic health. The present study was conducted between 2018 and 2019 to understand the seasonal variation in the phytoplankton diversity of the Charaganga wetland and, parallelly, in the river Ganga in Nabadweep, India. The study explains how riverine connectivity affects the structure of the algal community in the wetland ecosystem. In the study, it has been observed that in the wetland, maximum mean phytoplankton density was noticed during pre-monsoon, i.e., 4079 unit l−1 followed by post-monsoon 3812 unit l−1 and monsoon 550 unit l−1, respectively. In the river system, the phytoplankton density varied from 78 unit l−1 to 653 unit l−1 seasonally, i.e., highest during monsoon and lowest during pre-monsoon. In both the ecosystems, i.e., wetland and river, the supreme influential group was Cyanophyceae followed by diatoms. One-way ANOVA showed a significant variation (p > 0.05) of three algal groups of phytoplankton (Bacillariophyceae, Coscinodiscophyceae, Chlorophyceae) in the river, while in the wetland, no significant variation (p > 0.05) was found among the other algal groups. The observed higher Shannon and Margalef’s species richness value in the wetland was observed than in the river defines the significance and importance of the wetland ecosystem, which may support the growth and conservation of various aquatic organisms as well. The study highlighted that the influencing abiotic factors like water temperature, dissolved oxygen, pH, and nutrients have affected the phytoplankton community in both the water bodies, i.e., wetland and river. We concluded that river connectivity is required to restore the biotic flora of the wetland ecosystem.