Using diatom taxonomic diversity to assess herbicide contamination in rivers

The increasing contamination by micropollutants in freshwater systems has become a major problem in modern societies, giving rise to toxicological, sanitary and economical concerns. In 2010 the French government adopted a plan for a 50% reduction over 10 years in the use of pesticides which promotes research on contamination monitoring. Diatom bio-indication tools in rivers have been standardized and normalized (AFNOR NFT 90 354 ; CEN – EN 13946 & EN 14407) and are adapted to assess nutrient and organic matter levels. However these indicators do not assess micropollutants contamination despite diatoms being known to be sensitive to pesticide pollution. The objective of this study is to assess whether bio-indicators based on diatom communities could be developed to assess the impact of pesticide contamination, especially herbicides, on freshwater ecosystems quality. The hypothesis that increasing herbicide concentration reduces diatom diversity wastested on a diatom data set from the French Water Framework Directive monitoring network. The data set includes more than 2000 samples from 14 ecoregions from eastern France over the period 2000 - 2008. To each sample corresponds a list of diatom taxa and 531micropollutants (herbicides, insecticides, fungicides, heavy metals and organic micropollutants) concentration measurements. Diatom diversity was calculated by means of2 classic indices: Shannon’s H’ (Shannon, 1948) and Simpson’s D (Simpson, 1949) and 3taxonomic distinctness indices: ?, ?* and ?+ (Clarke and Warwick, 1998). This poster describes preliminary results which may lead to new bio-indication metrics adapted to pesticide contamination.