Phytoplankton biomass in relation to flow dynamics: the case of a tropical river Mahanadi, India

This present study was conducted to extend our understanding on the relationship between Chlorophyll a (Chl a) concentration and hydrological parameters typically flow velocity, environmental variables and trophic state conditions using lotic water as experimental system. River Mahanadi, India was selected as a model for the present study. Based on elevation from mean sea level, twelve sampling sites from Sambalpur to Naraj were grouped into three zones viz. upper zone (71 km), middle zone (142 km) and lower zone (103 km). Carlson Trophic State Index (CTSI) revealed eutrophic state in middle and lower zone and with mesotrophic condition in the upper zone. Along the river stretch, a negative correlation was observed between Chl a concentration and flow velocity at all three zones during post monsoon (r = - 0.15) and monsoon (r = - 0.31). Seasonal study revealed higher Chl a concentration (16.16-283.85 mu g l(-1)) in post-monsoon with recorded mean flow velocity (0.28 +/- 0.19 ms(-1)) as compared to monsoon season with lower Chl a (18.68-232.24 mu g l(-1)) and mean flow velocity (0.54 +/- 0.21 ms(-1)). Among environmental variables, water temperature and pH showed a positive correlation with Chl a. Overall, the findings of this study illustrated the occurrence of higher phytoplankton biomass (quantified as Chl a) during post-monsoon season coincides with low water velocity. The dataset of this work can be implicated for the hydrological and the ecological framework of the tropical river Mahanadi in the Indian Territory.