The bicarbonate compensation concentration (BCC) measmed in Scenedesmus quadricauda increased significantly with increasing total alkalínity (TA): ířom 2-5 inmol(HC03') m'^ at an alkalinity of 0.5 mol m'^ to 416-444 mmol(HC03") m"^ at an alkalinity of 10 mol m'^. This should be taken into account when evaluating a species ability to use HC03’. The increase of BCC at higher alkalinities could be caused by carbonate inhibition of HC03‘ uptake and/or by extremely high assimilatory pH reached.