| Abstract [eng] |
Investigations were carried out in water layers and bottom sediments of Suderve (Salote, Giluzis, Gineitiskes) and Riese (Paezeriai, Raudondvaris, Riese) rivers lakes, which undergo anthropogenic impact, in different seasons (spring, summer, autumn) of 2006-2007. It was established that the whole complex of abiotic factors formed favorable conditions for the growth of SRB, heterotrophic and E. coli bacteria. The differences in the abundance of sulphate reducing bacteria in bottom sediments did not reflect the intensity of the process. Generally, their amount varied from 0 to 106 colony forming units (CFU) per ml on media with lactate. The highest abundance of SRB in the lakes of Suderve river basin was recorded in July and reached 104 CFU per ml. Meanwhile, the highest abundance of SRB in the lakes of Riese river basin was recorded in September and reached 106 CFU per ml. The highest amount of heterotrophic bacteria was registered in bottom sediments while in water layer it was estimated 1000 times lower amount. In comparison with other investigated lakes the highest abundance of heterotrophic bacteria in water layer and bottom sediments was determined in Lake Riese. The highest amount of E. coli bacteria was determined in water layer by a high water temperature in July (18, 4 - 21, 8 °C) in basins of Suderve and Riese rivers lakes. The highest abundance of these bacteria was recorded in Giluzis Lake. The intensity of sulphate reducing process mainly depends on sulphate concentration. The highest amount of sulphate ions in bottom sediments was determined in summer. The highest rate of sulphate reducing process was observed in summer as well. The intensity of this process was about 2 times lower in basin of Riese river lakes in comparison with the lakes of Suderve river basin. The highest concentration of hydrogen sulphide (the end product of sulphate reduction) in bottom sediments of basins Suderve and Riese rivers lakes was accumulated in summer stratification period. It was established that amount of hydrogen sulphide and acid soluble sulphides in bottom sediments was 3 times higher in the Riese river basin lakes in comparison with the Suderve river basin lakes. |
