Impact of wildfires on sediment quality in estuaries in New South Wales, Australia.

Climate change is increasing wildfire intensity, introducing new risks to estuarine systems. However, the impacts of wildfires on estuaries and their recovery remain poorly understood. To address this, we conducted a large-scale longitudinal survey investigating sediment quality across river-to-estuary systems affected by fire. We measured concentrations of carbon, nutrients, chlorophyll-a, and silt content in sediment at 90 sites across six waterways with varying extents of burnt catchment area. Pyrogenic carbon (PyC), measured using mid-infrared spectroscopy, proved a reliable indicator of fire impacts, whereas nutrients levels varied more with seasonal changes. PyC concentrations declined significantly over 12 months post-fire, halving in most fire-affected estuaries. However, in one catchment with 92 % burnt area, there was no reduction in the concentration of PyC within 12 months, suggesting prolonged impact. Fire location and burnt area extent influenced temporal PyC trends. This study is the first to assess sediment quality over time in the upper, middle and lower estuarine sections following wildfires. Our findings are important for managing coastal areas amid increasing wildfire frequency and severity. Using PyC as a stable indicator of fire impact can improve monitoring and guide recovery efforts, helping safeguard estuarine health and function.