The evolution of the eutrophication of the Palić Lake (Serbia)

Eutrophication is a world-wide environmental issue. The Palic Lake is a shallow lake typical for the Pannonian plain. The Lake itself was in a very bad condition during the late sixties of the last century; polluted and hypertrophic. Due to inadequate water quality, it was dried out in 1971 and re-established in 1977 and since then its trophicity has been worsening. The lake has recreational purposes but it is also a collector for treated municipal waste waters coming from the lagoons for active sludge water treatment. The sewage discharges from rapidly developing towns in the watershed and the growing use of fertilizers in agriculture increased the nutrient load to the Lake in the last decades. A steady increase of phosphorus loading is the most important factor of the lake  eutrophication. The result of the accelerated eutrophication is the enormous amount of sediment at the bottom of the Palic Lake. Therefore, in the lake that covers an area of 565 ha and volume of 10 million m3, there was 1.900.160 m3 of sediment. The sediment thickness varied from 0.3 to 1.2 m. In summer 2010, the recreational part of the lake (sector IV) was 1.311.356 m3 of sediment, characterized with concentrations of total phosphorus (TP) of 2885 mg/kg, 4300 mg/kg total nitrogen (TN) and 39000 mg/kg total organic carbon TOC. The sediment of the Palic Lake was not loaded with high concentrations of heavy metals. Everything mentioned supports the fact that the restoration of this aquatic system is necessary and applied measures have to be grounded on the principles of ecoremediation technologies.Key words: Eutrophication, Palic Lake, sediment, total N, total P

Isolation of chromium resistant bacteria from a former bauxite mine area and their capacity for Cr (VI) reduction

The Cr (VI) reducing capacity of bacteria has been investigated in many different soils and waters but little or no information is available from soils originating from bauxite mine areas. From soil, mud and rhizospheres of the floating aquatic plant Potamogeton natans L. and the terrestrial plant Carduus acanthoides L., the Cr content was determined and the microbial populations were sampled. The highest total chromium concentration (204.6 mgkg-1) was found in the rhizosphere of C. acanthoides. To determine the numbers and percentages of chromate-resistant bacteria, the autochthonous microbial populations were subjected to different Cr (VI) concentrations (40, 100, 300 and 1000 mM as K2Cr2O7). At 1000 mM Cr (VI) in the medium, about 25% of bacteria from soil and 45% of bacteria from the rhizospheres were resistant. Of 34 bacterial isolates, within 24 h, only Bacillus stearothermophilus 12 ms, Pseudomonas sp. 12 bk3 and Serratia fonticola 7 be were able to reduce 50 μM Cr (VI). Using prolonged 72 h incubation, they were able to reduce 500 μM Cr (VI) concentrations added to the medium. These chromate-resistant bacteria isolated from rhizosphere of plants growing in bauxite mine soil have great potential for bioremediation of Cr (VI)-polluted wastes.Key words: Chromate-resistant bacteria, chromate reduction, bauxite mine, rhizosphere, plant