Impact of low-severity wildfire on large water bodies: water quality and disinfection by-product precursors

Abstract

Most studies have focused on evaluating the impact of moderate-to-high-severity wildfires on various water quality (WQ) parameters in riverine systems. In contrast, this study investigates the effects of low-severity wildfires on selected WQ parameters and the formation potentials of selected disinfection by-products (DBPs) in a reservoir characterized by relatively low dissolved organic carbon (DOC) content in its water located downstream of a fire-impacted watershed. The results showed that post-fire initial flushes had a detrimental effect (i.e., increased turbidity [up to 150%], aromatic DOC [up to 98%], ammonia [up to 10 times] and reactive phosphorus [up to 113%], concentrations) in the headwater collecting the post-fire runoff across the burned watershed. The concentrations of DBP FPs (Trihalomethanes [THMs], haloacetic acids [HAAs] and Halonitromethanes [HANs]) were governed mainly by the DOC content of the water samples, except for N-nitrosodimethylamine (NDMA), regardless of the sample collection point. However, the impact of the fire was limited or had no effect on the water quality parameters at the drainage point of the reservoir, which was located on the opposite side of the headwaters. Moreover, the deterioration in the WQ of the headwaters significantly improved over 2-3 months, eventually reaching levels like those observed at the reservoir drainage point. Consequently, the findings of this study demonstrate that watersheds subjected to low-severity burns do not present significant or long-term water quality degradation in large downstream water bodies adjacent to the affected areas.