Seasonality in the photosynthetic productivity and biomass of phytoplankton in Lake Tinishu Abaya (Rift Valley, Ethiopia): The basis for fish production

The present study was undertaken to investigate the photosynthetic productivity and biomass of phytoplankton for Lake Tinishu Abaya to observe the potentiality of the lake water for fish production. The study was carried out from January to December 2016. For the analysis of various physicochemical parameters, water samples collection was taken from two predefined sampling stations (open-water and nearshore). Biomass of phytoplankton was measured as concentration of chlorophyll a. Primary productivity of phytoplankton was measured at the open station within the Euphotic depth using light-dark bottle technique. It was observed from the results that the light-saturated rate of photosynthesis (Amax), ranged from 0.62 g C m-3 h-1 to 2.02 g C m-3 h-1 and biomass-specific rate of photosynthetic productivity at light saturation (Pmax) ranged 0.02 g C (mg Chl a)-1 h-1) to 0.106 g C (mg Chl a)-1 h-1). The hourly integral photosynthetic production (∑A), varied between 0.247 g C m-2 h-1 and 1.022 g C m-2 h-1, whereas the calculated pattern of variation for the daily integral rates of photosynthesis (ΣΣA) was ranged 5.43 g C m-2 d-1 to 9.194 g C m-2 d-1. The concentration of phytoplankton biomass (chlorophyll-a) was varied from 18.97mg/L to 65.05 mg/L. Based on the results of the study on various physicochemical factors, photosynthetic productivity and biomass of phytoplankton, it was concluded that the water of Lake Tinishu Abaya was chemically and biologically productive which supports most aquatic lives, production of fish, and other related multidimensional uses. Key words: Biomass, photosynthetic productivity, physicochemical factors, phytoplankton, light-dark bottle technique.