Compositional changes of dissolved organic matter during high flow events in headwater catchments along a gradient of climate and land use

High flow events in headwater catchments are associated with changes in the dissolved organic matter (DOM) composition. The aim of this work was to determine whether these changes are characteristic of headwater catchments and similar to what has been observed in other catchments. The evolution of the DOM composition during flood events was studied for five catchments covering a range of climatic, soil and land use contexts. The DOM composition was analyzed by thermochemolysis coupled with gas chromatography and mass spectrometry, making it possible to perform a joint analysis of several biomolecule families, monitor the proportion of compounds derived from plant inputs (%VEG) and study the lignin composition through the C/V ratio. The %VEG increased for all flood events studied. As this parameter is linked to the aromaticity of DOM, these increases are in line with worldwide observations. However, observations of increases in DOM aromaticity during floods in tropical and arctic zones are few and contradictory. This observation seems to be a general feature of temperate climates. This increase in aromaticity was accompanied by an increase in the C/V ratio for all rainfall-related flood events, indicating the mobilization of less biodegraded dissolved lignins than during base flows. These observations are in line with those made in the United States of America and could be characteristic of headwater catchments.