Coulometric measurement of primary production, with comparison against dissolved oxygen and 14C methods in a seasonal study

Consumption of carbon dioxide, as measured by direct coulometry in light and dark bottles, was used to estimate the rate of natural assemblages of phytoplankton incubated in situ.A total of 30 experiments were made during a 12 mo period in Bedford as&, Nova Scotia.For comparison, simultaneous estimates of primary production were made on each occasion using both the Light-and-darkbottle oxygen method and the I4C method.Primary production values fell in the range < 1 to 50 mm01 C m-3 d-l.Throughout this range, excellent agreement was found between primary production as estimated by the 14C method and gross primary production estimated by change in dissolved carbon dioxide.Release of labelled carbon into solution accounted for 2 to 19 % of total pnmary production as measured by the I4C method, with the lower values occurring in the spring bloom period.When the carbon-based results were compared w t h the oxygen-based ones, they agreed to within a mean apparent photosynthetic quotient of 1.6.High apparent PQ's in ulnter are attnbuted to an overestimation of oxygen primary production and an undereshmation of I4C primary production.Direct coulometry offers considerable promise as a technique for measuring photosynthesis by phytoplankton.