Fig. 5: Transformation pathways of different DOM species in unidirectional tracer reactions and bidirectional tracer reactions of SRNOM.

Unidirectional tracer reactions: Fenton + δ¹³C/δD-monomers + SRNOM; Bidirectional tracer reactions: •OD + δ¹³C/δD-monomers + SRNOM. Transformation pathways were calculated based on the exact mass difference between Fenton-derived DOM molecules and corresponding δ¹³C/δD-monomers for different DOM species. The transformation pathway calculations took into account the case of •OD addition reactions and reactions involving ¹³C in the δ¹³C-monomers, where the exact mass of δD was 2.014102 and the exact mass of δ¹³C was 13.003355. a The distribution of transformation pathway subtypes in the unidirectional tracer reactions. b The statistical distribution of transformation pathway subtypes for different DOM species in the unidirectional tracer reactions. The bar + data overlap plot shows the median (bar), whiskers representing 1.5 × the interquartile range, outliers as points beyond the whiskers. c The distribution of transformation pathway subtypes in the bidirectional tracer reactions. d The statistical distribution of transformation pathway subtypes for different DOM species in the bidirectional tracer reactions. The bar + data overlap plot shows the median (bar), whiskers representing 1.5 × the interquartile range, outliers as points beyond the whiskers. The axis in all panels represents absolute number. The methods and p-values for statistical hypothesis tests in all panels were shown in the Source Data file.