TRACKING SOURCES AND DYNAMICS OF DISSOLVED ORGANIC MATTER (DOM) IN AN ALLUVIAL PLAIN IN CONTRASTED HYDROLOGICAL SITUATIONS

Summary UV/visible absorbance and excitation-emission matrix (EEM) fluorescence spectroscopy coupled to parallel factor analysis (PARAFAC) have been used to characterize dissolved organic matter (DOM) in surface and groundwater of a natural alluvial plain of the Seine River which is one of the most important regional and national wetlands in France. This work showed contrasting DOM optical properties between the three studied compartments of the system (river, alluvial aquifer, chalk regional aquifer) and between two hydrological periods (flood and low waters). During flood, DOM exhibited low molecular weights while groundwater was characterized by higher molecular sizes and biological activity. DOM optical characteristics for flood samples pointed out dominant terrestrial sources for river waters, a high biological activity and low terrestrial inputs in the chalk regional aquifer and mixed sources in alluvial aquifer. Whereas in low water, DOM molecular weights were generally lower with DOM characteristics for surface and groundwater still distinct, but with lower terrestrial inputs and higher autochthonous sources in rivers. Tracking DOM optical properties finally helped to understand the functioning of each of the three compartments and to identify possible connections and exchanges between the river, the alluvial aquifer and the underlying chalk regional aquifer depending on hydrological situations.