Post-fire effects on dissolved organic carbon concentrations in freshwater streams: a meta-analysis
Wildfires are often discussed through smoke, trees, and erosion, but one of their quieter legacies can travel downstream. Dissolved organic carbon (DOC), the dark, tea-coloured fraction of organic matter in water, tends to rise after fire events, especially during storms. That matters because DOC is not only a carbon-export signal, it also shapes water treatment difficulty and can increase the formation potential of disinfection by-products when drinking-water is chlorinated.
In a recent meta-analysis, Polack and colleagues synthesised evidence on how forest fires affect peak-flow DOC concentrations in freshwater streams, focusing on the moments that often drive the largest exports: high-discharge events. Across 52 effect sizes from 14 peer-reviewed publications, their multi-level modelling estimated an average 26% increase in peak-flow DOC after fire, with the strongest signal occurring early in recovery.
The pattern was not uniform. The largest increases were reported for small catchments (≤10 km²), consistent with short flow paths and stronger hillslope–channel connectivity after canopy loss and altered infiltration. Climate and landscape context also mattered: humid continental sites showed clear increases, while subarctic sites tended towards declines, suggesting that post-fire DOC trajectories can differ substantially where permafrost and cold-region hydrology dominate. The analysis further indicated stronger responses in conifer-dominated systems, and soil texture appeared informative, with loam and clay loam showing particularly pronounced increases.
Mechanistically, the synthesis aligned two ideas that are intuitive yet easy to under-sample in practice: (i) post-fire hydrology can increase near-surface runoff and strengthen the connection between burnt hillslopes and channels, and (ii) fire can generate a pool of more labile residues that leach during storm events. The authors also highlighted a practical gap for both science and management: discharge-resolved chemistry remains scarce in the literature, and geographic coverage is still skewed, which limits transferability. The implication is straightforward: if the goal is to anticipate water-quality risk after fire, monitoring needs to follow the hydrograph, not only the calendar.
Find the study: Journal of Hydrology | ResearchGate
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