Willamette Slough restoration project enters final year

Since 2019, the Willamette Riverkeeper has been working with the City of Salem to remove Ludwigia, an invasive aquatic weed, from the Willamette Slough at Minto-Brown Island Park. The plant threatens native plants and wildlife, including habitat for federally protected spring Chinook salmon and winter steelhead. As described in The Salem Reporter, crews are traveling the length of the 87-acre slough this week to spray herbicide on dense mats of water weeds to open up channels to kayakers and wildlife. More than 12,500 native shrubs and trees were planted along the riparian banks this spring to improve habitat and slow the spread of Ludwigia. Vanessa Youngblood is the restoration manager for Willamette Riverkeeper. She joins us with more details on the project as it enters its final year, and future restoration work along the river.

Note: This transcript was computer generated and edited by a volunteer.

Dave Miller: From the Gert Boyle Studio at OPB, this is Think Out Loud. I’m Dave Miller. For four years now, Willamette Riverkeeper has been working with the city of Salem to remove an invasive aquatic weed from the Willamette Slough at Minto-Brown Island Park. Ludwigia threatens native plants and wildlife, including habitat for federally protected spring Chinook salmon, and winter steelhead. Crews have been traveling the length of the 87 acre slew this week to spray herbicide on some remaining patches of the weed. Vanessa Youngblood is the restoration manager for Willamette Riverkeeper and she joins us now. Welcome to the show.

Vanessa Youngblood: Hi, thank you. I’m excited to be here today.

Miller: Thanks for joining us. Can you describe the Willamette Slough?

Youngblood: It is an off-channel habitat, it’s an 87-acre slough, and over the last decade has been infested with an aquatic invasive species called Ludwigia. It’s a species from South America that was introduced most likely from the aquarium trade or a pond system or something, and it has just infested the slough to basically choking out most of the native vegetation or fish and wildlife habitat that kind of depends on that slough.

Miller: Can you give us a sense for the scale of it [in the slough]? Before this eradication work started four years ago, how widespread was it?

Youngblood: Basically, the full slough was covered with this aquatic invasive species. The way it works is it basically creates a monoculture that is choking out any other native vegetation, meaning it’s really the only plant that’s surviving within that area. It forms these dense mats, so the vegetation dies off, and then now that vegetation is in there, it traps the sediment. Our contractors can actually walk on it, it becomes so dense. So the flow of water is really restricted and limited, which of course also affects any sort of native fish or wildlife, and again, the native vegetation as well.

Miller: So what did it actually mean for salmon?

Youngblood: So the salmon depend on the slow water refugia for their migration and rearing habitat. Our hope is to be able to open back up the slough. The water quality is degraded, the water temperatures are raised a lot with Ludwigia, it depletes dissolved oxygen in the water. And so the fish really are dependent on this, and not just the fish, but species like the western pond turtle or other different species that are within that habitat. It really potentially just chokes out their habitat.

So our hope is to open that back up. This year is our fourth year, and you can actually see flowing water in there, now open water. It’s actually been a really successful treatment over the past three years.

Miller: What has the work actually entailed? How have you been getting rid of it?

Youngblood: We work with our contractors, Integrated Resource Management. They are using an aquatic rated herbicide as a contact spray technique. Basically it’s a full year spray where they’re contacting the vegetation specifically of the Ludwigia. There’s multiple methods, it depends on if you have land access. We call it the amphibious approach, where a lot of this is actually done by canoes and backpack sprayers, and they’re out on the water targeting this weed.

Ideally, we do two treatments a season. So we’re working this week, and then usually about a month later we come back and do a second treatment. The goal is really to have enough success where we can actually reach the hand pulling method. And we’ve actually worked on quite a few sites with treating Ludwigia. We do something called a paddle and pull. The hope is to get Minto-Brown, after this last year where we’re empowering volunteers to come out paddling on the river and hand pulling weeds from canoes or kayaks. So that’s kind of the goal with this next year.

Miller: The way people might go to Forest Park in Portland and rip out as much English ivy as they can. Although that seems sadly like a sisyphean task right now when you look at how much there is.

You could literally walk on the mat of this weed a couple of years ago, there was that much?

Youngblood: Yeah, because the sediment gets trapped in as well, years and years of the senescing of the plant, now there’s the vegetation that’s died off, and the sediment is building up underneath that. We have photos of our contractors that are walking out there. I would definitely not advise anyone to do that, but yeah, you can really tell how it just completely chokes out most of any native life that would live under there.

Miller: Well, speaking of native life, this year my understanding is you planted 12,000 native trees and shrubs. What did it mean to you to be adding native species as opposed to just taking out non-native ones?

Youngblood: It’s incredible. Even hearing from our contractors, they were so excited too because, especially with this project, this was a huge moment for them. They’ve been removing weeds, but now to be able to actually install these crucial native plants within this system. It was a really huge thing for us. With funding, we weren’t 100% sure if we were going to be able to include this. And we were super grateful to Bonneville Environmental Foundation for donating some of the plants to us, and being able to get out there. And especially in this area, the hope is we’ll be able to build up this native vegetation that could potentially shade out any new growth of Ludwgia, and then of course also provide habitat for any of the wildlife or fish that are within that area as well.

As far as the aquatic planting, it’s not something that we’ve done as much. But my hope is to work with that and work with a few other partners who have been on the forefront for that in the next couple of years.

Miller: The funding for this project, I understand, runs out after this year. In fact, you were able to eke out, stretch out over four years project funding, I think was supposed to initially be three years. But what about next year?

Youngblood: That’s a great question. We’re super grateful that we’ve been able to kind of stretch this out for a fourth year of treatment, I don’t think we initially thought we’d be able to do that. Our main goal is, if a grant project ends, then we can kind of get into that paddle and pull, utilizing volunteers, the public to come out with us. And so then we’re not needing to do some sort of treatment or spending funds in that way, but instead we could spend a day out there, two days out there, where we’re literally paddling and pulling weeds. And so I think that’s kind of the goal. We definitely try to focus when we do plantings on plant establishment. Because these plants were just installed this last year, we really want to focus on doing some sort of kind of ring spray or plant establishment just to make sure those little native plants can outcompete any other,  invasive weed that wants to grow in there so they get to that free to grow stage where then they’re able to outcompete any of that invasive plant material as well.

Miller: Vanessa Youngblood, thanks very much.

Youngblood: Yeah, thank you so much. Great to be here. Take care.

Miller: Vanessa Youngblood is the restoration manager for the Willamette Riverkeeper. She joined us to talk about the successful effort to get rid of most of the invasive water weed that had been spreading over most parts of the Willamette Slough near Salem.

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