Forested watersheds supply over two-thirds of the world’s drinking water. Recent headlines across Canada have emphasized that the last decade has seen an increase in the frequency and intensity of wildfires that is threatening these source watersheds, and necessitating more expensive water treatment to address degrading water quality. Given the increasing wildfire frequency in a changing climate, it is important to understand the magnitude of water quality impacts following fire.
Researchers from the forWater Network published a recent research snapshot exploring post-fire changes in the concentrations of nitrogen (N) species, phosphorus (P) species, dissolved organic carbon and total suspended sediments in 121 sites around the world (of which 81 were burned), documented in 34 research studies. Changes were documented over each study’s duration, which for 90 per cent of sites was (5) five years or fewer. The study features research by Tyler Hampton, PhD Candidate in Earth and Environmental Sciences, Water Institute member, Nandita Basu and Research Associate, Simon Lin.
The study uses a meta-analysis approach to quantify the effect of fire on the changes in concentrations of suspended sediments, nitrogen, phosphorus and carbon species, quantify the degree of covariation between the concentrations of these elements in post-fire landscapes, and quantify the effect of fire on concentration distributions.
The most commonly sampled parameter was nitrate at 67 of 81 sites, followed by total phosphorus (41), total nitrogen (31), ammonium (30), total suspended solids (26), phosphate (20), dissolved organic carbon (17), and dissolved organic nitrogen (14).
Only 47 per cent of sites had more than one year of data post-fire, with the greatest data density for nitrate (NO3) − and only 9 per cent of sites were sampled beyond five years after the fire. Wildfire studies tend to focus on collecting samples over a short timeframe, making it challenging to evaluate recovery times.
The research provides valuable insights into frequent post-wildfire increases in the concentrations of nitrogen and phosphorus species in streams and the large variability in post-fire water quality responses. It also revealed shifts in nutrient ratios that increased bioavailable fractions of nitrogen and phosphorus; potentially causing greater eutrophication risk downstream.
Study recommendations include that future research focus on capturing high concentration events that often cooccur with high flow events. The meta-analysis also highlights the need for continued long-term monitoring of water quality in post-fire landscapes, along with the exploration of covariation between multiple elemental cycles and storm-driven responses in concentration extremes.
Click the link below to see detailed figures and results on the impacted concentrations of nutrients and sediments after fire and learn more about their implications with respect to water treatability for downgradient communities using the rivers as a water source.
Visit
the forWater Network
to
continue
reading
or download the
full
research
snapshot here.
Contact
Information
For
more
information
on
this
research
please
contact:
Nandita
Basu
–
nandita.basu@uwaterloo.ca
Tyler
Hampton
–
tyler.hampton@uwaterloo.ca
Reference: Hampton TB, Lin S, Basu NB. 2022. Forest fire effects on stream water quality at continental scales: A meta-analysis. Environmental Research Letters, 17(6):064003, DOI 10.1088/1748-9326/ac6a6c.
Image by Dennis Larsen from Pixabay