Quantification of fecal coliform inputs to aquatic systems through soil leaching

Area of Science:

• Environmental microbiology
• Water quality assessment
• River watershed studies

Background:

• Fecal contamination poses risks to aquatic ecosystems and human health.
• Understanding sources of fecal pollution is crucial for effective water management.
• Soil leaching is a potential pathway for fecal bacteria entering waterways.

Purpose of the Study:

• To assess fecal contamination in Seine watershed streams via soil leaching.
• To investigate the correlation between fecal coliforms and E. coli indicators.
• To evaluate the impact of land use and rainfall on fecal contamination.

Main Methods:

• Sampling of 78 rural streams in the Seine watershed, upstream of wastewater outfalls.
• Measurement of culturable fecal coliforms (FC) and beta-D-glucuronidase activity (Escherichia coli indicator).
• Statistical analysis to correlate contamination levels with land use and rainfall data.

Main Results:

• Significant correlation found between fecal coliform counts and E. coli activity.
• Most streams exhibited significant fecal bacterial contamination.
• Pasture land use and rainfall were associated with higher contamination levels.
• Fecal coliforms adsorbed onto suspended solids, increasing with rainfall.
• Soil leaching contributed minimally to overall watershed fecal contamination compared to wastewater discharge, but could be significant locally.

Conclusions:

• Soil leaching is a notable source of fecal contamination in Seine watershed streams, particularly in rural and pasture areas.
• Land management practices and rainfall patterns significantly influence fecal bacteria transport.
• While overall contribution is low, local-scale impacts of soil leaching warrant consideration in water quality management.