Linking diatom community structure to pesticide input as evaluated through a spatial contamination potential (Phytopixal): A case study in the Neste river system (South-West France)

Abstract

A large-scale field survey was undertaken in the Neste system (South-West France) to investigate the impact of pesticide inputs on the structure of riverine benthic diatom communities. A total of 18 sites in the "Coteaux de Gascogne" study area were sampled during periods of pesticide use over two consecutive years (2005-2006). The typology of the diatoms collected was determined using artificial neural networks generating patterns in diatom community composition that indicated the species influenced by pesticide inputs, combined with organic pollution. Small, pioneer species of the Achnanthales group were more frequent in the pesticide-contaminated assemblages, whereas slower colonizers were more often found in the sites where disturbance was lower. The Phytopixal approach, a means to assess the spatial contamination potential, provided valuable information about pesticide exposure and was a successful means of discriminating diatom assemblages, suggesting that a global estimate of pesticide pollution risk, although rough, would be more appropriate and more representative than sporadic pesticide analyses.

Impact of the herbicide metolachlor on river periphytic diatoms: Experimental comparison of descriptors at different biological organization levels

“…Nevertheless Si limitation occurred similarly in each channel only at the end of the experiment and may not have differentially influenced the effect of the herbicide on diatom community composition. These results obtained under controlled conditions confirm that the diatom community alterations observed in the field can be the consequence of chronic river contamination by herbicides (Morin et al, 2009;Roubeix et al, 2010). Here, the demonstration of the toxic effect of metolachlor on river diatom community composition at environmental contamination levels is clearly evidenced.…”

“…However, as the relative abundance of deformities is generally just a few ‰ (Fig. 7) (Morin et al, 2009), this would require a higher counting effort than bioindication on a taxonomic basis (AFNOR, 2004). The example of S. angusta shows that it would be easier to focus on widespread sensitive species that could be used as sentinels.…”

“…As diatoms are useful bioindicators of river eutrophication and saproby (Prygiel et al, 1999), there have been many attempts to find specific indicators of toxic pollution in diatom communities. Some field studies have tried to relate periphytic diatom community variations to herbicide concentrations; however, the variations in the field of many interfering factors (e.g., trophic level, shading and current velocity) make the isolation and clear demonstration of the toxic effect difficult (Morin et al, 2009;Roubeix et al, 2010). The experimental exposure of diatom communities to a chosen toxicant in enclosed controlled systems is then a suitable complementary approach.…”

Variations of periphytic diatom sensitivity to the herbicide diuron and relation to species distribution in a contamination gradient: implications for biomonitoring

“…It was suggested that diatom community variations may also reflect the presence of toxic stressors such as pesticides. [2][3][4][5] As plants, diatoms may be particularly sensitive to herbicides which are commonly found in rivers draining agricultural areas with peak concentrations in spring after field application and rain events. 6 Diuron (3,4-dichlorophenyl)-1,1-dimethylurea is a herbicide which belongs to the phenylurea class.…”

Evaluation of river model biofilm for assessing pesticide effects: a case study with atrazine

“…[2][3][4] Because the epilithic microbial communities in the river biofilm are the first organisms in the river to be exposed to pesticide runoff from agricultural fields, 5,6) it is important to evaluate the adverse effects and to assess the ecological risk of pesticides on the biofilms. There have been reports on the pesticide effects on a river biofilm formed on stones or artificial substances set in a river or in a laboratory experimental system [7][8][9] ; however, it would be difficult to evaluate the effects of pesticides on natural biofilms due to the poor reproducibility of biofilm settlement in which biological parameters such as biomass, activity and community structure vary among season and sites, 10,11) and are affected by environmental conditions. 12) Additionally, it has been reported that environmental conditions influence the effects of pesticides on river biofilm [13][14][15][16][17] ; therefore, a test system with high reproducibility and reliable endpoints should be established to determine the toxicity of pesticides on natural river biofilms.…”