RESPONSE OF PHOTOSYNTHESIS MODELS TO LIGHT LIMITATION

An investigation into the effect of rime step on a common photosynthes is algorithm reveals that the predicted phytoplankton production and b iomass depend strongly on the length of the time step. This time step dependence is due to the assumption that a light limitation factor der ived From integrating the irradiance over the time step is equivalent to the integrated light limitation factor over the time step. This sub tle inaccuracy in defining the factor For light limited phytoplankton production produces a substantial difference in the biomass estimates derived from the two models. To illustrate the difference, the light l imitation factor integrated over the time step is implemented in the o ne dimensional water quality model DYRESM-WQ. The new version of DYRES M-WQ is used to simulate chlorophyll a concentrations in Prospect Rese rvoir, New South Wales. These results are compared to concentrations p redicted using the original algorithm. The comparison shows that the n ew algorithm for phytoplankton production is relatively insensitive to time step, which decreases the difficulty of calibrating the model fo r chlorophyll a.