Fecal bacteria in surface water may
indicate threats to human health.
Our hypothesis is that village settlements in tropical rural areas
are major hotspots of fecal contamination because of the number of
domestic animals usually roaming in the alleys and the lack of fecal
matter treatment before entering the river network. By jointly monitoring
the dynamics of Escherichia coli and
of seven stanol compounds during four flood events (July–August
2016) at the outlet of a ditch draining sewage and surface runoff
out of a village of Northern Lao PDR, our objectives were (1) to assess
the range of E. coli concentration
in the surface runoff washing off from a village settlement and (2)
to identify the major contributory sources of fecal contamination
using stanol compounds during flood events. E. coli pulses ranged from 4.7 × 104 to 3.2 × 106 most probable number (MPN) 100 mL–1, with
particle-attached E. coli ranging from
83 to 100%. Major contributory feces sources were chickens and humans
(about 66 and 29%, respectively), with the highest percentage switching
from the human pole to the chicken pole during flood events. Concentrations
indicate a severe fecal contamination of surface water during flood
events and suggest that villages may be considered as major hotspots
of fecal contamination pulses into the river network and thus as point
sources in hydrological models.