Changes in agricultural practices related to environmental policies such as the European Water
Framework Directive should lead to a decrease in pesticide contamination levels in rivers draining
agricultural areas. However, there is still a need for biological tools to evaluate resulting ecological
changes, namely to evaluate ecological recovery following the improvement of surface water chemical
quality. Accordingly, the main purpose of this study was to assess the relevance of a pollution-induced
community tolerance (PICT) approach in natural phototrophic biofilms to estimate microbial community
recovery following a decrease in diuron contamination due to the ban of the use of this herbicide on
vineyards. To this end, we performed a 3-year field study (2009–2011) in the Morcille River (France),
located in the French Beaujolais wine region. This river was frequently contaminated by diuron (among
other organic and inorganic pesticides), with increasing concentrations downstream. Following the ban
on diuron, imposed in December 2008, a progressive decrease in diuron concentrations was observed in
the Morcille River. While the mean annual tolerance levels measured at the low contaminated station
remained relatively constant over years, a clear and significant decreasing trend was observed at the
medium and high contaminated stations during the survey. This temporal evolution revealed a directlink
between a change in agricultural practice due to the ban of diuron and an increase in the sensitivity of
phototrophic biofilms to this herbicide. This finding brings further new evidence that PICT has great
potential to detect microbial community recovery following chemical restoration due to changes in the
agricultural use of pesticides.