What Do Wildfires Mean for My Water Quality?

When wildfires strike, our attention is drawn to the flames. But, what about the water? As anyone who has been through this themselves will tell you, the impact of a wildfire extends well beyond the smoke, fire, and ash.  

Wildfire impacts on the hydrologic cycle can last for years after the flames subside, with impacts reaching as far as 100 miles from the fire center.

2017 has been an historic year of wildfires, so we–at SimpleLab–dig in deeper to understand what wildfires mean for your environment, tap water, and health.

Impacts on the Water Cycle:

While the human and environmental threats posed by floods and debris flow are cause for serious concern, it is also critical that regulatory agencies and water utilities address the following impacts on the local water cycle:

While some of these impacts may generate ecosystem benefits, they are often challenges to keep up with for drinking water systems.

How long might these detrimental impacts last?

The worst of the effects occur within the first year or two following a fire, however water quality changes may linger for nearly a decade.

How the Impacts of Wildfire Affect Drinking Water:

Unfortunately, the unpredictable nature of wildfires makes it extremely challenging to predict their long-lasting impacts. The duration and intensity of the fire, post-fire precipitation, local ecology, and watershed topography are all key factors that impact drinking water quality and supply.

The following impacts, which vary in severity according to the aforementioned factors, all affect drinking water treatment processes. Here’s how and why:

Increased erosion and runoff:

Affected land becomes substantially less stable and may erode quickly following a wildfire.The loss of vegetation and plant roots means that less water is absorbed by plants and leads to increases in runoff.

Erosion and runoff impact drinking water in multiple ways. Erosion may result in more downstream sediment accumulation. Increased runoff may change turbidity, nutrient content, and dissolved organic carbon concentrations in drinking water supplies.

Changes in sediment load:

Due largely in part to changes erosion and runoff, sediment load may increase rapidly and stress the capacity of a water treatment system. Sediment often carries other pollutants–especially phosphorus–which easily bind to sediment particles. Elevated levels of phosphorus in water bodies can lead to overgrowth of aquatic vegetation and algal blooms.

Large yet unpredictable, spikes in sediment load in the water supply increase both water treatment processing needs, as well as treatment costs. Another risk of sediment accumulation is that reservoirs and treatment plants will be damaged or disrupted by sediment. Such drastic changes in water quality are often detrimental to water treatment plant functionality because they are 1) hard to plan for and 2) treatment processes are most effective when water quality is constant.

Elevated turbidity:

Turbidity is a measure of the cloudiness of water due to large numbers of particles that are generally invisible to the naked eye. This increase is often due to the the erosion that follows a wildfire. Increased turbidity generally limits productivity in aquatic habitats initially, but can contribute to algal blooms later on.

Typical water treatment plants are prepared to correct average turbidity levels, as well as spikes. However, the spikes that occur following a wildfire tend to be so large that they usually require additional treatment chemicals and increase the wear-and-tear of the treatment filters. Increased turbidity may also result in large amounts of sludge–which in turn raises plant operating costs.

Changes in dissolved organic carbon:

Dissolved organic carbon (DOC) results when plant or animal material decomposes and subsequently dissolves when in contact with water. Increased sediment loads post-fires result in increased dissolved organic carbon in water sources.

Along with affecting coagulant dosing and oxidant demand during treatment processes, the taste and odor of your water may worsen with increased DOC. Natural organic matter reacts with the disinfectants present in treatment processes (e.g. chlorine). This can lead to an increase in  harmful disinfection by-products (DBPs) such as trihalomethanes and haloacetic acids.

Increased nitrate concentrations:

Nitrogen, an organic compound, does not pose a threat to human health. However, nitrate, which is a byproduct of nitrogen decomposition, certainly does. Ingestion of high levels of nitrates can result in methemoglobinemia–decreasing the ability of blood to carry oxygen. Also known as “blue baby syndrome,” methemoglobinemia lead to: