Fig. 2: Comparison of dissolved organic matter (DOM) formulae in stream water, shallow groundwater and deep confined groundwater.

van Krevelen Diagrams (VKD’s; H/C vs O/C ratios) are shown on the left of each panel, whilst regression lines (solid black lines) showing the correlation between intensity weighted average double bond equivalent (DBE) and number of oxygen atoms in each molecule for formulae: a higher in median relative intensity (intensity difference <0) in stream water compared to shallow groundwater, b higher in median relative intensity (intensity difference <0) in shallow groundwater compared to stream water, c higher in median relative intensity (intensity difference <0) in shallow groundwater compared to deep groundwater, and d higher in median relative intensity (intensity difference <0) in deep groundwater compared to shallow groundwater (see also Supplementary Table 5). Green and blue dashed lines represent the DBE/O regression lines for offshore coastal DOM and inland riverine DOM⁶³, respectively. Point colours in the VKD’s correspond to CHO (grey), CHON (black) and CHOS (red) formulae. “HUPs” refers to highly unsaturated and phenolic formulae. Note: the median differences in molecule intensities have been used in the VKDs to reduce the influence of outliers with very high or low compound intensity. Percentages of carboxylic-rich alicyclic molecules (CRAM) are weighted based on the total sum intensity of the CRAM molecules divided by the sum intensity of all molecules shown in the VKD. A comparison of intensity differences based on molecular mass is provided in Supplementary Figure 3. Separate VKDs are shown for each compound class (CHO, CHON and CHOS) in Supplementary Figure 4.