Fig. 3: Dissolved oxygen (DO) and its percent saturation (DO_%sat) variability between the flood and non-flood periods and the occurrence of hypoxia and anoxia.

A, B Ratios of DO and DO_%sat between the flood period (discharge ranked above the 95th percentile threshold) and the non-flood period, i.e., DO_flood:DO_non-flood and DO_{%sat flood}:DO_{%sat non-flood} calculated from nationwide 1156 rivers monitored daily from November 8, 2020, to December 31, 2023. C, D Boxplots showing different categories of DO_flood:DO_non-flood and DO_{%sat flood}:DO_{%sat non-flood} in rivers with different Strahler orders. E–G Locations of sites with at least one occurrence of hypoxia (DO ≤2 mg L⁻¹) or anoxia (DO ≤0.5 mg L⁻¹) during flood events, and these sites were categorized into different rivers with different Strahler orders. Each box shown in panels C, D and F, G represents the interquartile range, the horizontal line is the median and the whiskers are 1.5× the interquartile range. H–K Relationships between DO_flood:DO_non-flood and NH₄⁺-N_flood: NH₄⁺-N_non-flood, and between DO_flood:DO_non-flood and agricultural and urban land use (within 30 km radius of each site); Relationships between DO_{%sat flood}:DO_{%sat non-flood} and NH₄⁺-N_flood: NH₄⁺-N_non-flood, and between DO_{%sat flood}:DO_{%sat non-flood} and agricultural and urban land use. These relationships were categorized for rivers with different Strahler orders.