Assessment of the Microbiological Quality of the River Tisa in Serbia - page 03



Physical and chemical characteristics of the River Tisa

During the sampling seasons the water reaction was mildly alkaline. As expected, the quantity of dissolved oxygen was higher during spring, when a lower water temperature was recorded. Concentrations of ammonia and nitrates indicated a satisfactory water quality (EC, 1991b - EU Nitrates Directive 91/676/EEC) during both sampling seasons. An increase of phosphate concentration was recorded during spring. The highest values were recorded at the Ada site, where unsatisfactory levels of water quality were detected (EC 1991a - EU Directive 91/271/EEC) (Table 2).


Microbiological analysis of the River Tisa

The sanitary analyses indicated a critical to strong faecal contamination at the majority of the sampling sites (EC, 2006 - EU Bathing Water Directive 2006/7/EEC, 2006). Faecal coliform numbers ranged from 103 to 1.7 x 104 CFU/100 ml. Strong faecal pollution (>10000 CFU/100 ml) was found at the Novi Bečej locality in autumn and at the Titel locality in spring. At all sampling locations, the number of faecal coliforms was more than 4 times higher than the number of Enterococci, showing the great impact of human urban pollution (Figure 1).

The presence of sulphite reducing clostridia as well as Bacillus sp. was noticed in all water samples while Pseudomonas aeruginosa was isolated from the samples in autumn (Table 3). Mercury resistant bacteria were detected in all water samples, indicating a potential pollution of these localities with mercury (Viti and Giobannetti, 2001).

The index of phosphatase activity was applied to evaluate the extent of organic water pollution of the River Tisa. Analyses of the results indicated a satisfactory purity (class IIA) at the Novi Bečej site and light pollution (class III) at a majority of sampling sites (Figure 2).

The organic load assessment was also performed by using the oligotrophs to heterotrophs ratio.  The domination of oligotrophs in almost all water samples indicated a satisfactory level of self purification (Figure 3).

Microbiological parameters of the sanitary quality of sediment varied in correlation with the sampling location. Total coliform numbers ranged from 1.2 x 103 to 1.3 x 105 CFU per gram of sediment. The highest pollution values were recorded at the Ada location during autumn. The isolation of mercury resistant bacteria was performed only during autumn, and during that season mercury resistant bacteria were isolated from all sediment samples (Figure 4).