ABSTRACT
Although the number of measurements regularly increase, mapping the pesticide concentrations and their evolution over time remains difficult. The Craie du Nord aquifer system was selected for a methodological study based on samples taken from 1997 to 2002 from three different networks: the information (good spatial coverage), the supply (preferential sampling) and the producer (few stations) networks. The atrazine annual mean concentrations are calculated either from few stations with long time series or on the whole data set; they are different but show similar evolutions with time. The connection between concentrations and land use is minor. Data on atrazine concentrations from the information network present a spatial structure, modelled through a space-time variogram. The sensitivity analysis shows that adding data from the supply network improves the accuracy of the estimation. The maps of interannual variations are discussed in relation to the accuracy of the estimations. Finally, recommendations are made on the systematic character and the regularity of the sampling.
