Pesticide peak concentration reduction in a small vegetated treatment system controlled by chemograph shape

Abstract. Pesticides may impact aquatic organisms when entering water bodies. Measures for mitigation against pesticide inputs include vegetated treatment systems (VTS). Some of these systems have very short hydraulic retention time (< 1 h) but nevertheless manage to effectively reduce peak concentrations of contaminants. We hypothesize that this is not solely the result of contaminant and VTS properties but also related to the shape of the contaminants input chemograph, i.e. its sensitivity to dispersion. In order to test this hypothesis we performed a cluster analysis on the chemographs of contaminants mobilized in response to rainfall events in a viticultural catchment and derived a measure for dispersion sensitivity which we included into multiple linear regression analysis. The resulting measure was then incorporated into multiple linear regression models for description of contaminant mitigation in a VTS located at the catchment outlet. We found that the mobilization clusters reflected the source areas of the contaminants and that dispersion sensitivity was the dominant explanatory variable for the reduction of contaminant peak concentration. These findings imply that mitigation of the toxicological risk in VTS may be stronger for compounds with pronounced peaks than for those abundantly available in a catchment.