High field FT-ICR mass spectrometry data sets enlighten qualitative DOM alteration in lake sediment porewater profiles

This study investigates how changes in dissolved organic matter (DOM) quality can be evaluated considering all existing principal data pools from high field Fourier transform ion cyclotron mass spectrometry (FT-ICR-MS). We recommend five steps, including suggestions on underlying processes. Two different sediment profiles from a highly acidic mining lake in Germany with different mixis of the overlying lake water (dimictic vs. meromictic) were selected as a model for the analysis of sediment porewater sample to a depth of 30 cm. FT-ICR-MS datasets of elemental composition were evaluated for the presence of specific CHO molecular series. In six (seven) porewater depth groups of 63 (127) different data pools were identified. In the first step, the data pools were evaluated with components present in all six (seven) samples (total common presence). This group of components was analysed via a statistical rank analysis of the mass peak intensities (inter sample rankings analysis). The second step comprised the allocation of components which were not present in all samples to specific data pools (partial common presence and different presence pools). Of these pools the largest (containing most components) were selected in the third step for visualization of DOM quality change using van Krevelen diagrams. Underlying DOM transformations were discussed in the fourth step. The fifth step comprised the parallel allocation of changes in DOM quality and in concentrations of inorganic compounds. We identified the principal changes in both depth profiles and thereby demonstrated the potential of DOM data pool evaluation for elucidating biogeochemical processes.