Modelling Potamogeton pectinatus : for better or for worse

The SAGA plant growth model is introduced in connection with integrated weed management. SAGA describes the seasonal development of Potamogeton pectinatus L. The model is mainly driven by light climate characteristics (water layer extinction, periphyton shading) and their effects on plant photosynthesis and tuber production. It could be a tool for evaluating several weed control methods (mowing, shading, grazing) as it was calibrated and validated quite well for a vegetation growing in Lake Veluwe (The Netherlands). The SAGA model was used to provide management advice for a P. pectinatus vegetation growing profusively in two Argentine irrigation schemes. The model's re-calibration to local conditions was hampered by some unexplained variation in seasonal biomass cycle data. Nevertheless, the results obtained were considered quite acceptable for comparative scenario analysis. The simulated vegetation dynamics suggest that the mowing regime currently applied in the channels is not an optimal solution. Neither is an artifically increased turbidity, created by the introduction of benthivorous common carp (Cyprinus carpio L.). Their combination, however, may lead to quite satisfactory results, allowing a repetition of the mowing operation to be postponed by two years. Direct grazing of the vegetation by grass carp (Ctenopharyngodon idella Val.) also proved a potential management tool with substantial effect.