Wind induced dispersion and algal growth in shallow lakes

The objectives of this paper are (1) to present experimental measurements of wind induced, vertical dispersion in Lake Brielle, The Netherlands, and (2) to examine the utility of a euphotic—dark zone model for investigation of the effects of dispersion and sedimentation on algal growth and phosphate cycling in shallow lakes. A tracer technique was used to measure dispersion (D) caused by a moderate wind of 4 m/s. The resulting values ranged between 4 and 6 cm2/s and compared well with that predicted from theory. The latter objective was accomplished by comparing the results of a simple, two compartment model with those using a more complex, but more descriptive, finite difference model which accounts for the algal concentration gradient induced by growth, dispersion and sedimentation. Simulations showed good agreement in computation of the average euphotic and dark zone algal concentrations between the two models for D ranging from 0 to 6 cm2/s and for a sedimentation rate constant, Ks, of 0.002 and 0.02 m/h. The results of simulations suggest that rapid algal growth occurs most readily in calm weather when wind induced dispersion in negligible. Dispersion may also influence the rate of particulate phosphate accumulation in the sediment (due to the settling out of algal cells) and the soluble phosphate profile in the overlying water column. Field data is needed to verify the relationship between algal growth and wind induced dispersion.