Bacterial source tracking from diverse land use catchments by sterol ratios

Area of Science:

• Environmental Science
• Water Quality Analysis
• Microbiology

Background:

• Assessing water contamination from various sources like septic tanks, cattle, and sewage treatment plants (STPs) is crucial for public health and ecosystem integrity.
• Faecal sterols offer a promising method for source tracking of fecal pollution, complementing traditional microbial indicators.

Purpose of the Study:

• To differentiate and quantify human and herbivore fecal contamination in water bodies using faecal sterol analysis.
• To correlate land use patterns with specific contamination profiles in water samples.

Main Methods:

• Collection of 296 water samples from diverse sites (septic tanks, cattle, STP, forests) over 21 months, including post-rainfall events.
• Analysis of faecal coliforms and a suite of faecal sterols (coprostanol, epicoprostanol, cholestanol, cholesterol, 24-ethylcoprostanol).
• Application of faecal sterol ratios to determine contamination sources and their relative contributions.

Main Results:

• Significant differences in contamination profiles were observed across catchments, aligning with land use (p<0.05).
• STP-impacted sites exhibited the highest human contamination indicators and mean coprostanol levels.
• Forested sites showed the highest proportion of uncontaminated samples and the lowest mean coprostanol concentrations.
• Faecal coliform counts did not consistently correlate with coprostanol concentrations.

Conclusions:

• Faecal sterol analysis effectively distinguishes human and herbivore fecal pollution sources in aquatic environments.
• Land use significantly influences water quality, with STP discharges being a major contributor to human fecal contamination.
• Coprostanol serves as a reliable indicator of human fecal pollution, though its correlation with faecal coliforms can be variable.