Contribution of different molecular categories, H/Cwa and O/Cwa elemental ratios, aromaticity index (Aimodwa) and double bond equivalents (DBEwa) and indices of degradation (Ideg) and lability (MLBwl; Ibioprod). The contribution of each molecular category is expressed as a percentage of the total formulas in each sample obtained after normalization. Molecular formulas were additionally associated with different molecular categories because less than 6% of the DOM has been identified on a molecular level. Molecular categories are defined as follow: 1) condensed aromatics, with an AImod ≥ 0.67 (Koch and Dittmar, 2006, doi:10.1002/rcm.2386) was separated in 3 different subgroups, either <15 (condensed aromatics 0.5 but <0.67; 3) highly unsaturated formulas, with an AImod <0.5, H/C <1.5; 4) formulas of unsaturated aliphatics, with an 1.5< H/C <2, O/C 2, O/C 0.9 and with either no (sugars) or with heteroatoms (sugars-CHOx) and 7)unsaturated with N (unsaturated-N) molecular formulas, with 1.5 < H/C <2, O/C 0. Additionally, polyphenols, highly unsaturated and unsaturated aliphatics were further separated in oxygen rich (-O-rich) and oxygen poor (-O-poor) if the element ratio O/C was > 0.5 or < 0.5 respectively.