Primary productivity of phytoplankton in Kosi River at Bhagalpur and Katihar district of North Bihar

The primary productivity of phytoplankton in the river Kosi has been analysed both spatially and seasonally in year 2017 and 2018 at three sites. The maximum was noted during pre- monsoon season in all Gross Primary Productivity (GPP) the study sites. Net Primary Productivity (NPP) of phytoplankton varied from 11.25 g Cm⁻³ day⁻¹ to1.35 g Cm⁻³ day⁻¹ in the first year and 5.62 g Cm⁻³ day⁻¹ to2.7 g Cm⁻³ day⁻¹ in the second year of observation. The community respiration (CR) showed a systematic seasonal pattern where the maximum value was observed during pre-monsoon and minimum during winter. Respiration as per cent of GPP was higher in pre monsoon in 2018.The ratio between NPP and GPP was highest in winter and Production Respiration Ratio (P/R ratio) was observed higher in winter in both the years. Physico-chemical parameters of water were analysed concurrently. Production Respiration Ratio (P/R ratio) determination is a good measure of new organic matter created in the water body. This study provides base line information to find out influence of water quality on primary productivity.