CHANGES OF THE ORGANIC MATTER CONTENT IN THE WATER OF LAKES WITH LOW ALKALINITY OCCURRING UNDER THE INFLUENCE OF THE USE ALUMINUM SALTS.

Our paper presents the impact of the use of aluminum salts - as a tool for the rehabilitation of water bodies - on the changes of selected environmental conditions in lakes with low water alkalinity. The method for the lakes restoration with aluminum or iron coagulants called phosphorus inactivation is widely used for more than 30 years. The main objective of this method is precipitating excess phosphorus into insoluble compounds unavailable to algae. However, these coagulants are usually acidic in nature, which limit their use in lakes susceptible to pH changes. Therefore there is a need to look for ways to optimize restoration treatments in this type of lakes. Field examinations were conducted in five small (5-30 ha) lakes affected with moderate anthropopressure, characterized by a low alkalinity (0.5-2.5 meq/dm³) and varying reaction (pH 5,7-8.5), localized in the Masurian Lake District (Poland). In each lake four experimental mesocosms were placed, in which aluminum coagulant were introduced in varied dose (used as polyaluminum chloride - the most commonly phosphorus sorbent in the full-scale restoration projects). The duration of the experiments (2 years) allow determining the long-term response of ecosystems to the restoration treatments. The in situ fragmentary-technical scale results showed that the use of the tested coagulant strongly affects the level of pollution of lakes with organic matter and it is clearly correlated with the dose of used salt. The study discussed the impact of physicochemical conditions of water, including changes in pH on the effectiveness of the water purification process from an excess of organic impurities by coagulation. The results indicate that the application of aluminum coagulants with optimized dose can be an effective and safe method of water purification in the natural, soft-water reservoirs which are susceptible to acidification. [ABSTRACT FROM AUTHOR]