THE INFLUENCE OF ARTIFICIAL MIXING AND OTHER FACTORS ON ALGAL BIOMASSIN THE BIESBOSCH RESERVOIRS

Experiences with the Biesbosch reservoirs confirm that artificial mixi ng of deep eutrophic reservoirs is an effective algal-control measure, because light is thus made a limiting factor of phytoplankton growth. The mixing characteristic of a reservoir depends on its morphology, h owever, and shallow littoral zones can promote algal growth. In additi on, the biomass and composition of the phytoplankton is dependent on b iotic and abiotic factors, such as zooplankton grazing (which in turn is influenced by fish and predatory invertebrates), availability of sp ecies-specific nutrients, (e.g. Si for diatoms), retention time and ac idity. Benthic cyanobacteria are not suppressed by the artificial mixi ng method. Cyanobacteria must be controlled, because they may have neg ative effects,on, drinking-water quality (e.g, taste, odour, toxins). Mechanical disturbance of the reservoir bottom has proven to be a succ essful control method for benthic cyanobacteria in one of the Biesbosc h reservoirs.