Of the interest of monitoring complementary parameters to better understand nutrient and pesticides variability in groundwater

Pesticides and nutrients (as NO 3 , NO 2 , NH4) are the parameters degrading most of the groundwater bodies in France. The surveillance-monitoring network described under the Water Framework Directive (2000/60/EC) has for main goal the evaluation of the groundwater chemical status and the assessment of long-term trends in natural conditions and in pollutant concentrations resulting from human activity. The operational monitoring network allows to better assessing the groundwater bodies " at risk ". For management purposes, and particularly to identify the programme of measures needed to reduce the impact of diffuse contaminant on groundwater, the monitoring mentioned under WFD is not sufficient. A better comprehension of water and solute transfer is therefore necessary. Since 2008, high resolution monitoring of nutrient and pesticides in groundwater were performed for a limited period at five sites of various lithological contexts in France. Based on the geological and hydrogeological understanding complementary parameters were selected to be analysed in addition to the main contaminants. In volcanic and mountainous context, Martinique and La Reunion Islands, stable isotopes ( 18O, 2H) and age dating were analysed as in lowland context, alterites of granite formations in Brittany and sedimentary glacial-fluvial deposits in Rhone-Alpes region, age dating was complementing the analyses of major ions including NO 2 , NH4 and NO 3 and selected pesticides and metabolites. At all studied sites, the pattern of monthly variation of nutrients and dissolved ions is quite different from pesticides time evolution. In the described case studies, apparent age (or CFC and SF6 concentrations) and 18O and 2H (and calculated d-excess) are quite stable from one month to another even during intensive rainfall episodes and pesticide concentrations may vary at the same time to a large extend. A seasonal trend is observed for chemical data when water level is significantly changes within the year for all aquifers under investigation. However, isotope and age data signal is not always showing a similar seasonal trend, giving then additional information to the hydrogeological functioning of the system