Phytoplankton photosynthesis parameters in central Canadian lakes

Abstract

Values for two biological parameters — (i) PBm, the light saturated rate of photosynthesis per unit of chlorophyll and (ii) α, the slope of the light limited part of the photosynthesis versus light curve per unit of chlorophyll — must be known in order to be able to estimate rates of phytoplankton primary production from chlorophyll data. These parameters were measured for periods of up to 9 years in central Canadian lakes located in temperate, subarctic and arctic climatic zones. Regardless of their geographic locations, lakes where integral photosynthesis was nutrient limited had lower values of these parameters than did lakes where integral photosynthesis was light limited. Temperature set an upper limit to the variability of PBm but was not a good predictor of its actual value. Year-to-year variability of photosynthesis parameters in the most intensively studied group of lakes was large: annual means varied by a factor of three over a 9-year period. Until the sources and extent of this variability are known, accurate production estimates can be obtained from chlorophyll data only if PBm and α are measured in each water body and in every year. Implications for estimating primary production from remotely-sensed chlorophyll data are discussed.