Phosphorus Dynamics in Riverine Lakes

Abstract

Abstract Simple models based on conservation of mass capture the essential dynamics of total phosphorus in lakes. The concentration of total phosphorus in shallow riverine lakes on the Prairies was simulated as a forced response to the inflow concentration. The lake dynamics were characterized by three independent time scales based on water inflow, water outflow and sedimentation. Both inflow and outflow time scales were necessary to model lakes with non-stationary hydrographe and varying lake levels. Flood periods had a pronounced effect on lake phosphorus because high concentrations in the inflow occurred when the lake was dynamically able to respond. In the Fishing Lakes, the 1974 flood appears to have established the lake conditions for the next decade. Most other large peaks in the concentration of total phosphorus in the inflow occurred when the outflow time scale was large and the lakes were dynamically unable to respond. Net sedimentation of total phosphorus appeared to be zero in these lakes over the two decades for which data were available. Verification of the lack of net sedimentation in shallow lakes means that no model calibration is needed to apply these simple models to other shallow lakes. Presently, however, even the simplest models are restricted by the lack of appropriate data required for verification.