Wildfires can still contaminate water 8 years later, researchers find

Wildfires can negatively impact water quality, even after they’re extinguished. And new research shows those negative impacts can last for up to eight years.

Carli Brucker led the study of 100,000 samples from 500 watersheds across the western U.S. Their findings: Contaminants like nitrogen, phosphorus and carbon were in that water and, in some cases, stayed in it for years.

Brucker recently got her Ph.D. from the University of Colorado Boulder and now works as a water resources engineer in Colorado. She says there’ve been a number of studies looking at the post-wildfire impacts on water quality but that this is one of the first showing those impacts can last as long as eight years after a fire — she says that longevity is one of the study’s more striking findings.

She joins The Show to talk more about this.

Carli Brucker

Full conversation

MARK BRODIE: Carli, am I right that this is a lot longer than scientists had thought water quality problems could last after a wildfire?

CARLI BRUCKER: Yes and no. I think we kind of just didn't know. I mean, it's really difficult to conduct a fieldwork study where you're going out into a field collecting samples after a wildfire happened. It's hard to do that for more than two or three years in terms of funding and resources. And so there's only really a handful of studies that had actually looked at these impacts past two to three years.

And so we didn't really know what happened after those first couple of years. And I think that this study helps us get more of a look into that.

BRODIE: Yeah. Were there variables that helped determine for how long the negative impacts would last in terms of maybe how many acres the fire burned or where it burned or where the watershed was relative to the fire or anything like that?

BRUCKER: Yeah. So we looked at a couple of different characteristics, both the watershed characteristics, such as vegetation and soil type, but then also we looked at the burn characteristics, like you mentioned, where the fire burned in the watershed, how long it burned, the severity. And, and one of the key things that came out of that was the amount of forest coverage.

So the watersheds that had a higher amount of the total area that was covered by forest, those ones had a slightly, slightly higher water quality response, which makes sense. You know, trees provide a lot of fuel that, that can result in greater amounts of sediment being pushed downstream. But that was, that was kind of the biggest thing that we saw.

BRODIE: Did you find that the water quality got better over time? Like, was it still as bad in year eight as it was in year one after a fire?

BRUCKER: Yeah. So for all of the different water quality constituents we looked at, we did see gradual improvement over time. Some of them were surprisingly slow. At year eight, the magnitude was only a little bit less than at year three, for example. But overall, they all trended downwards, kind of returning back to what they looked like before the fire.

BRODIE: Well, I guess that's decent news, right? That while maybe it takes a little bit longer to get there than we thought, it does eventually get there.

BRUCKER: Definitely. Yes. And definitely the worst impacts, I would say, did happen in those first couple of years. So in terms of preparing for these potential effects, I think that, you know, water managers can expect to really have the greatest challenges within those first couple of years.

BRODIE: Well, so let me ask you about preparation. I mean, as you know, we saw wildfires in and around Los Angeles. You know, Arizona, of course, is no stranger to pretty severe wildfires. Like, what should water managers be doing about this to try to protect the water quality for folks who maybe rely on the water that is in the areas of these fires?

BRUCKER: Yeah, so I think that's, that's the question of the hour. I think that is what all water managers are, especially those in the West, are trying to grapple with and figure out next steps. And the answer is there's a lot of different things on sort of the wildfire mitigation side. There's a lot of steps that could be taken to decrease the chances of wildfires happening, decrease the severity that the wildfires are burning at.

You know, decreasing the amount of like vegetation in a certain area can really help with that. But then, you know, in the event that the wildfire does happen, it, it really impacts water quality. Water managers are looking towards making sure that the distribution and treatment systems are resilient enough and have high enough capacity to be able to handle these really, these really large loads of sediments and these really poorly degraded waters.

BRODIE: Are the typical processes that maybe municipalities have to treat water that's going into people's taps, can that handle everything that is in the water after a wildfire? Or maybe do they need additional or special equipment to do that?

BRUCKER: So typically, water treatment plants are not set up to have the capacity to handle a big water quality degradation event like a wildfire. Water managers have backups in place. Often what will happen is that that really low quality water will be diverted and they'll be able to rely on an alternate source while the water is poorly degraded and then switch, switch back to using that source eventually.

But typically, yeah, water treatment plants wouldn't have the capacity to be able to treat that water and deliver the high quality water that they're used to delivering before the wildfire happened.

BRODIE: Yeah, one, I would imagine that if they were to get additional treatment options, I'm sure that comes at a cost, right?

BRUCKER: Exactly, exactly. Yeah. I mean, I think especially in smaller, more rural areas where resources might be a little bit more limited, an event like that could be completely devastating to a utility and just result in costs that are really hard to meet.

BRODIE: How concerning are these findings to you?

BRUCKER: I would say, you know, I've had so many different conversations with water managers and folks who work at utilities over the years, and almost every single one of them is concerned about wildfires. You know, it's on everyone's mind. Everyone has a story of a neighbor or a nearby utility that got completely shut down from a wildfire or just really struggled to handle the impacts.

And so I think that the concern is out there. I think that water managers are already concerned, and I think that this research just emphasizes that a little bit more and puts some more concrete numbers behind that concern.

BRODIE: And as you were saying, though, it sounds like, as in so many facets of life, prevention might be the best cure. Like if you can prevent these severe, massive wildfires from happening, you prevent some of the worst degradation to water quality, right?

BRUCKER: Yeah. And I think that's something that folks are increasingly turning towards, is forest management. There are more studies that are coming out that are showing that, you know, having a healthy forest that's not overgrown, that's not going to be a good source of fuel for a really high severity fire and is a really great preventative method to sort of stop some of these really bad water quality degradation events from happening.