The research was conducted in a relatively small (26.8 ha) but quite deep (17.3 m) Lake Długie in Olsztyn, Poland. For over 20 years the lake was collecting sewage which eventually caused its complete degradation. In 1987-2000 the lake was restored using the artificial aeration method with destratification of water. The results showed that the artificial aeration effectively limited the internal loading. Application of this restoration method resulted in reduction of phosphorus compounds concentrations in the analyzed water strata. The decrease of TP in bottom sediments (to the level of 3-4 mg P g·' DW) was probably associated with the fact that a new layer of sediments was created, reflecting a change in the aquatic conditions caused by the restoration. The investigations conducted in the reference years showed that the changes were not permanent. A high concentration of phosphorus compounds in bottom sediments, low sorptivc capacity and a tendency to oxygen deficiency, indicate that further possibility to decrease the amount of phosphorus compounds in the lake by this restoration method is limited.

Seasonal changes in the numbers of sulphate-reducing bacteria in water, soil, the surface of sedge (Carex acutiformis Ehrb.) immersed in waler and roots (dead and live) were studied. The study on one of larger wetland near Olsztyn (Masurian Lake District) was carried out in two annual cycles. Sulphate-reducing bacteria in the studied ecosystems occurred sporadically and generally in inappreciable count. Their count did not exceed 20 cells in I cm3 ofwaler; in the soil and in di ffercnt parts of sedge the number of bacteria ranged from several lo over dozen thousands cells in I g of dry weight. In the first year of studies these bacteria were the most numerous in June, July and during first days of December, bul in the second - in April (in soil and sedge immersed in water), in August (in soil and dead and live roots), in November (in waler, soil, sedge immersed in water and dead roots) and exceptionally in other months.