| Abstract: | Recovery of polluted lakes is a complicated process involving many factors. Different lake rehabilitation techniques and former experiences with advanced wastewater treatment and sewage diversion are reviewed. The response in water quality after a nutrient reduction may vary significantly, despite a lowering of the phosphorus concentration in the lake. The different factors influencing the process, such as climatic fluctuations, the growth-limiting effect of nutrients and phosphorus release from the sediments, are discussed, based on examples from a lake recovery study in Sweden carried out in 30 lakes. Due to various interrelationships between physical characteristics and biological mechanisms involved, and to significant fluctuations in these factors from one year to the next, it is difficult to generalize and to forecast the actual response of a certain water body to a reduced nutrient input. Unfortunately, too many monitoring programmes aimed at elucidating the effects of remedial efforts are not designed in such a manner that relevant information can be obtained about the nutrient load — lake response relationships. Ways for optimizing and increasing the predictive power of inventory studies and monitoring programmes are discussed. |
