Phytoplankton Spatio-temporal dynamics and its relation to nutrients and water retention time in multi-trophic system of Soan River, Pakistan

The present study aims at the spatial-temporal interactions of phytoplankton community with water physico-chemistry and hydrological features using chlorophyll-a as an indicator of phytoplankton biomass in Soan River at the pre- and post-monsoon seasons. Our results predicted that significant inter-catchment variations (p<0.01) at zone level were evident for all variables except nitrates. Along the seasonal scale, power of hydrogen ion concentration (pH), temperature, and total phosphorus (TP) showed significant (p<0.05) variations. Regression analysis revealed that drainage area and temperature are considered as the best predictors of phytoplankton biomass in the pre- and post-monsoon seasons (R2=0.44 & 0.45 and R2=0.33 & 0.49, respectively). Soan river was classified as eutrophic, super trophic and hypertrophic at upstream, midstream and downstream, respectively. Our results further highlighted that the hydrodynamics of Soan River are responsible for controlling the hydro-ecology of phytoplankton in nutrient enriched conditions. In order to cope with unchecked phytoplankton growth in Soan River, it is ultimately needed to lower the nutrient concentrations level to limit the phytoplankton growth. There is a dire need in future to control the gigantic untreated domestic and industrial loads to the surface water prior to its discharge and further to implement rules and regulations or levy heavy charges in case of violators.