From Ash to Algae: Wildfire-Driven Water-Quality Change and Emerging Cyanotoxin Risk in Aquatic Systems

Zhikun Chen; Xiaying Xin

Abstract

Wildfire can alter downstream water quality, aquatic productivity, and drinking-water treatability. Evidence for chemical and physical water-quality change is substantial, whereas evidence connecting those changes to harmful algal blooms (HABs) or cyanotoxins is less developed. This mini review examines evidence from freshwater receiving waters for post-fire water-quality change, algal or cyanobacterial responses, and cyanotoxin endpoints. Wildfire acts as a conditional amplifier of aquatic risk. Outcomes vary with fire severity, hydrologic connectivity, nutrient bioavailability, optical conditions, residence time, and receiving-water susceptibility. Evidence is strongest for changes in turbidity, sediment, nutrients, dissolved organic matter, and treatment-relevant chemistry; moderate for algal productivity and community responses; and limited for direct attribution of post-fire cyanotoxin occurrence. Event-coupled studies should link fire characteristics and hydrologic transport with water chemistry, cyanobacterial composition, cyanotoxins, and drinking-water outcomes in the same receiving water.

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