The objective of this work is to study the influence of different chemical properties of DOM and inorganic nutrients on the heterotrophic basis of the planktonic food web in order to provide evidence for the hierarchy of the main factors controlling the fate of DOM in environments. coastal sailors. DOM from two contrasting environments, with similar dissolved organic carbon (DOC) concentrations, but different DOM chemical composition and nutrient availability, were incubated with two microbial communities exhibiting short-term life histories and contrasting taxonomic structures. In order to compare the influences of the chemical properties of DOM, we measured various parameters for 22 days, including (i) the concentrations and availability of inorganic and organic nutrients and carbon, (ii) changes in the elemental and molecular composition of DOM, (iii) fluorescence. properties of DOM, (iv) growth of heterotrophic prokaryotes and (v) taxonomic diversity of prokaryotes.We report our data on the molecular composition of DOM at the initial and final time points of the incubation experiments. These data were acquired by high resolution mass spectrometry (HRMS) using an Orbitrap Q Exactive mass spectrometer (Thermo Fisher Scientific) in infusion mode at the Water Quality Center (Trent University, Canada). Negative [M - H] ions were examined with a resolving power of 140,000, using a full MS scan ranging from 100 to 1000. The capillary temperature was set at 320°C and the spray voltage was maintained at 3 kV. The sheath gas pressure was 12 (arbitrary unit). The injected solution (at 10 µL.min-1) was diluted to a concentration of 10 mgC.L-1 in a mixture of MilliQ 18 MΩ water and methanol (50/50, v/v). Prior to analysis, routine mass calibration was performed with Pierce™ LTQ ESI Positive/Negative Ion Calibration Solution (88322/88324, ThermoFisher Scientific). Samples were spiked with sodium dodecyl-d25 sulfate (m/z 290.3048) and dioctylsodium sulfosuccinate (m/z 421.2265) as locking masses to ensure mass tolerance at the ppm level. Samples were taken in 1 m water depths.

File descriptions: The T0-... and Tf-... files correspond to the raw data obtained by Orbitrap analysis.The other files are obtained after processing the raw data with the UltraMassExplorer (UME) software allowing the data to be filtered and the molecular formulas to be assigned.