After a hazy August caused by hundreds of wildfires burning across the province, the smoky skies have us wondering what impacts it might have on our waterways here in the Columbia Valley.
The combined impacts of wildfires can have negative consequences for water quality in a watershed.
Not only does the burning of vegetation and charring of soils cause high amounts of runoff and nutrient leaching, it also increases the risk of floods and mudslides in future years. The smoke and ash produced as a result of wildfires can have even more far-reaching impacts, going so far as to cross watershed boundaries and disperse smoke hundreds of kilometres from its source. Additionally, wildfire can consume riparian vegetation that shades cold-water streams. Removing the shade source can negatively impact the temperature of these streams, which is especially concerning in streams that are trout- or salmon-bearing.
“Soil burn severity” describes how intensely the soil has been burned in a fire. Mixed- to High-intensity soil burn, which can occur during large wildfires, produces white ash and burnt organic matter. These materials are highly susceptible to erosion, overland flow, and leaching into waterways, meaning they get carried by rain and wind into streams, rivers and lakes. In addition, high intensity burns remove much of the vegetation cover and root stability in the soil, further enhancing risks of erosion and runoff.
Runoff can carry contaminants, such as heavy metals or high amounts of dissolved solids, into surface waters. Loss of tree canopies due to wildfires can result in future mudslides and floods by reducing the amount of snow that gets intercepted by needles and branches over winter. More snow on the ground (not in the canopy) leads to higher peak runoff during the spring melt, which can cause debris flows or floods.
What about smoke?
The smoke from a wildfire is made up of many different types of gases and particles. The chemical composition of a plume of smoke changes, depending on what’s being burned and the temperature at which it is burning. When trees or other vegetation are consumed by fire, the combustion process releases nutrients contained in the plants, including nitrate, ammonia and phosphate. These molecules contribute to the cocktail of gases and particles within the smoke column. This mixture of gases gets easily transported by wind and can blanket the skies, like it did here last month.
When rain falls through this type of thick smoke, water droplets can accumulate ammonium from the smoke particles and deposit nitrates into surface waters – similar to the way in which precipitation falling through thick air pollution can produce acid rain. This is why areas with intense wildfire smoke sometimes see increases of nitrate concentrations in surface waters.
Additionally, ash produced by wildfires can travel through the air and settle onto surface waters far from the source of the flames, depositing phosphorous and ammonium molecules which can elevate nutrient levels in the water.
Although the Ambassadors did not monitor for nitrate this summer, we did monitor monthly for phosphorous. But we found no significant increase in Total or Dissolved Phosphorous concentrations in Lake Windermere in August; in fact, Total Phosphorous concentrations went down.
What this tells us is there would have been very little ash deposition from wildfires onto the surface of the lake, and because there was an absence of precipitation, there was very little runoff into surface waters as well.
All in all, this summer’s wildfires didn’t appear to impact our surface waters too much from a chemistry point of view. But from a water quality point of view, the ambient air temperature, which breached 37 degrees one day in August, did contribute to some of the warmest water temperatures we have recorded since 2011.
Although it’s a big relief when rain clears the smoky skies, we can’t forget that the smoke molecules the rain is washing away can end up in our soils and surface waters, where it has the potential to disrupt the nutrient balance and increase the turbidity (cloudiness) of our lakes and streams. Increased turbidity can lead to increased water temperatures, which stresses aquatic life and reduces water quality for swimming and drinking. With frequent summer wildfires becoming more of a concern, naturally oligotrophic (low-nutrient) lakes, such as Windermere and Columbia, will be sensitive to increases in nutrient inputs from several sources, including large-scale wildfires and runoff from burnt landscapes in the local watershed.
Is it all bad news?
Although it may seem like wildfires bring nothing but damage to a watershed, over enough time, a burnt area of land allows abundant new growth to take root. In this way, wildfires are an important contributor to natural regrowth and habitat change, which improves the overall diversity of vegetation and wildlife within a watershed. So, there are pros and cons to wildfires, but one thing is for certain: I am sure glad that smoke has now cleared and we can finally breathe again!