Fig. 1: van Krevelen Diagram (VKD) with marginal density plots of molecular formulae.

VKD shows formulae unique to only deep groundwater (yellow), shallow groundwater (blue) or stream water (green), and molecular formulae common to all samples (black) as presented in Supplementary Table 4. Black solid lines represent the direction of change in H/C and O/C for chemical reactions including hydrogenation, methylation (or alkyl chain elongation), reduction, and condensation¹¹². Marginal density plots are area-normalized and use a Gaussian kernel function for kernel density estimation. Individual VKDs for all samples are shown in Supplementary Figure 1. The approximate region where carboxylic-rich alicyclic molecules (CRAM) lie is represented by the red dashed polygon⁵⁷. It is noted that CRAM formulae may represent a highly complex mixture of isomers⁴⁰. As FT-ICR MS does not allow for discrimination between isomers, it is not possible to determine the chemical structure of these individual CRAM formulae.