Modelling faecal indicator concentrations in large rural catchments using land use and topographic data

Area of Science:

• Environmental microbiology
• Water quality assessment
• Hydrology

Background:

• Faecal indicator organisms (FIOs) are crucial for assessing water quality, especially in rural catchments during bathing seasons.
• Understanding spatial variations in FIOs is essential for managing coastal water quality.

Purpose of the Study:

• To characterize and model spatial variations in faecal-indicator organism concentrations in watercourses draining a large rural catchment.
• To investigate the relationship between FIOs and land use/topographic variables.

Main Methods:

• Monitoring of presumptive coliform (PC), presumptive Escherichia coli (PE), and presumptive enterococci (PEnt) at 24 points in the Rheidol/Ystwyth catchment.
• Analysis of FIO concentrations under base- and high-flow conditions.
• Correlation of FIO data with land use and topographic variables within subcatchments using distributed modeling.

Main Results:

• FIO concentrations increased over 10-fold during high-flow conditions.
• The proportion of improved pasture explained over 80% of the variance in high-flow FIO concentrations (PC, PE, PEnt).
• Organism loss due to die-off/sedimentation occurred at base flow but not high flow; reservoir impoundments also reduced concentrations.

Conclusions:

• Large rural catchments are significant contributors to coastal faecal indicator loadings.
• Land use and topographic data provide a successful modeling approach for FIO concentrations.
• The developed model offers insights into FIO sources, transport, and survival within catchments.