In this paper the authors discuss the effects of cold fronts on the dynamics of freshwater ecosystems of southeast South America. Cold fronts originating from the Antarctic show a monthly frequency that promotes turbulence and vertical mixing in reservoirs with a consequence to homogenize nutrient distribution, dissolved oxygen and temperature. Weak thermoclines and the athelomixis process immediately before, during and after the passage of cold fronts interfere with phytoplankton succession in reservoirs. Cyanobacteria blooms in eutrophic reservoirs are frequently connected with periods of stratification and stability of the water column. Cold fronts in the Amazon and Pantanal lakes may produce fish killings during the process of "friagem" associated mixing events. Further studies will try to implement a model to predict the impact of cold fronts and prepare management procedures in order to cope with cyanobacteria blooms during warm and stable water column periods. Changes in water quality of reservoirs are expected during circulation periods caused by cold fronts.
cold fronts; ecological dynamics; reservoirs; stability; turbulence; cyanobacteria blooms; water quality
