Sources of variability in the factors used for modelling primary productivity in eutrophic waters

Abstract

The accumulation of phytoplankton biomass, which oftenoccurs when water bodies receive enhanced inputs ofinorganic nutrients, causes large changes in theavailability and spectral composition of underwaterlight. Quantitative descriptions of the variations inlight available to phytoplankton are a prerequisitefor modelling of aquatic primary productivity. As anexample of the range of natural variation inirradiance, the main spectral, spatial and temporalchanges in underwater light, which occur in a shalloweutrophic estuary in response both to increasingchlorophyll concentration and to wind-induced verticalmixing, are described. Additionally, phytoplanktonwere shown to exhibit changes in photosyntheticphysiology which were triggered by changes in thequantity and spectra of light. The characteristics andkinetics of these responses are presented anddiscussed in relation to their impact on modelling ofprimary productivity.