Development of indicators of risk of surface water contamination by pesticides at the little catchment scale. Taking into account spatial and temporal scales
Développement d'indicateurs de risque de contamination des eaux de surface à l'échelle d'un petit bassin versant. Prise en compte des dimensions spatiales et temporelles
Résumé
There is a need of tools to assess risk of fresh water contamination induced by the use of pesticides. Moreover, in the French context, where pesticides uses are supposed to be reduced by half in the following years, it is necessary to be able to evaluate the impact of these changes on water quality and aquatic organisms. Yet, although models of pesticides fate in the environment have been developed at the plot scale there is not, at the time being, satisfactory tool enough to predict pesticide fate at the catchment scale. However, such a model would need many input data and variables and would be time consuming, which is not reasonable in an operational context. Indicators are an interesting alternative in this way but currently, their relevance at the catchment scale is quite limited, because the static way they are designed prevent them to properly take into account the spatial connections, the possible presence of buffer zones, or the temporal interaction between transfers coming from different plots. As a consequence, the study presented here aims at developing indicators able to take into account these aspects. The idea consists in using a plot scale model, for a range of scenarios, representative of different meaningful climate conditions, for each filed plot of the considered catchment. Then a method will be developed in order to aggregate the resulting simulated flow and pesticides transfers at the catchment scale, in a statistic way. Moreover, it is intended to modulate these transfers considering wether flow is going through buffer zones or not. Thus the indicator will be defined at the catchment scale, after this aggregation, and will not result, as is usual at he time being of aggregation of plot scale indicators.