Abstract
Eutrophication of drainage ditches by over-fertilization with nitrogen and phosphorus causes a shift from a mainly submerged
aquaticvegetation to a dominance of duckweed. This causes anoxic conditions, loss of biodiversity and hampering of the agricultural
functions of the ditches. Simulations with the modelPCDifch, previously calibrated on experimental ditches, indicate that this switch
may occur as soon as a certain threshold nutrient loading level is exceeded. This level tends to increase with the water depth. It is
recommended to validate the model predictions in field situations.