A simple model to predict extinction coefficients and phytoplankton biomass in eutrophic waters1

Data from nutrient-saturated rivers, estuaries, and coastal upwelling zones imply a simple relationship between phytoplankton standing crop, depth of the mixed layer, and extinction due to nonliving material. Systems evolve to a steady state where the optical depth of the mixed layer is between 5 and 10. The observations are interpreted using a model for light-limited growth of phytoplankton. Model parameters can be evaluated using measurements of total extinction coefficient, mixed layer depth, chlorophyll concentration, and suspended sediment concentration. Simple equations are derived for the capacity of polluted rivers to assimilate anthropogenic nutrients. These relations may be used to assess the effects of water pollution control projects on water quality.