Measurement of primary production and community respiration in oligotrophic lakes using the Winkler method

The precision of the Winkler method can reach 2 µg ·L -1 if a potentiometric end-point detection method if used and if minor modifications to standard protocols are made. The major sources of variability encountered at this precision level are due to the gradual decrease (1-3 µg ·L -1 ·h -1 ) in apparent O 2 which occurs after reagent addition and to thermal expansion and contraction of the samples during storage. These sources of error can, however, be easily minimized or eliminated. The precision of the proposed protocols for Winkler determinations and metabolic rate measurements allows the detection of gross primary production and community respiration rates as low as 0.7 mg C ·m -3 ·h -1 after 4-h incubations. The methods are therefore adequate for metabolic studies in oligotrophic lakes, where epilimnetic production and respiration rates range between 5 and 50 mg C ·m -3 ·h -1 .