TEMPORAL VARIABILITY OF FAECAL INDICATORS IN THE SAVA RIVER NEAR ŠABAC, SERBIA: INSIGHTSFROM A FIVE-YEAR MONITORING STUDY

The assessment of surface water quality traditionally relies on faecal indicators, which signal the potential presence of pathogens. Understanding their temporal variation is crucial for evaluating water quality trends. This study analyzed monitoring data from the Sava River near Šabac, focusing on samples collected from June to August (2015–2019) and within daily intervals (7:30 a.m. – 1:15 p.m.). The examined bacterial groups included total coliforms, faecal coliforms, and faecal enterococci, detected via enzymatic substrate decomposition and quantified using the most probable number (MPN/100 ml). Statistical analyses (correlation, regression, and Eta-square test) revealed a significant positive correlation between total coliforms and sampling time, while all three groups showed a high dependence on this factor. Conversely, their abundance decreased slightly over the summer months, but this correlation was not statistically significant. A multi-year analysis showed an increasing trend in total and faecal coliforms, while faecal enterococci exhibited a statistically significant upward trend. These findings underscore the importance of tailored sampling strategies for capturing diurnal, seasonal, and annual dynamics, as standard monitoring programs—typically based on periodic grab sampling and physico-chemical indicators such as BOD (biochemical oxygen demand)—may fail to reflect short-term microbiological fluctuations critical to public health risk assessments.