Modelling phytoplankton dynamics in the River Swale, an upland river in NE England

A mathematical model has been developed to examine the behaviour of the algal community in a fast-flowing river. The model has been applied to data for the River Swale, NE England, over a 1-year period (September 1993–August 1994). The data include environmental variables, chlorophyll a concentration and relative proportions (based on cell counts) of the major algal groups. A resuspension mechanism is proposed for benthic algae entering the overlying water column, which is related to suspended sediment concentration. During the winter period patterns in simulated chlorophyll a then match those in measured chlorophyll a although at a lower level. Results show that peaks in measured chlorophyll a during the summer are related to blooms in the phytoplankton and the benthic algae on the substrate. Further simulations indicate that the benthic community sustains phytoplankton populations during the winter period and enables their subsequent growth during the summer.