The Influence of Various Restoration Techniques on the Content of Selected Ions in Water of an Urban Lake

Abstract

The research was carried out on Lake Długie, which, from the mid-1950s was transformed into a receiver for domestic and storm water sewage. Together with the sewage, 51 tons of phosphates, 51 tons of ammonia, 2.6 tons of nitrates, 243 tons of calcium, and 294 tons of chlorides were introduced into the lake. The lake was completely degraded (P > 4 mg/L, N > 30 mg/L, Cl > 70 mg/L). Cutting off the sewage inflow did not improve the environmental conditions in the water body, which indicated that it was necessary to carry out further protection and restoration treatments: artificial aeration with destratification (1987–2000), a phosphorus inactivation method with the use of PAX 18 liquid coagulant (2001, 2002, 2003), cutting off the inflow of storm water (2015), and biomanipulation via the removal of macrophytes (2020). Research has shown that the protective measures carried out in the lake’s catchment area, in combination with appropriately selected restoration methods, are an example of good practices that enable the improvement of water quality. The phosphate concentrations in the bottom layers of water do not exceed 0.2 mg P/L, and the ammoniacal nitrogen does not exceed 1.2 mg N/L. The chloride content in the lake water is kept at the level of 20 mg Cl/L, and the calcium in the range from 28 to 40 mg Ca/L.