Muddying the waters — Hydrocarbon pollution reduced, turbidity churns up new river threat

By Jenny Neyman
Redoubt Reporter

Just as the Kenai River celebrates a victory over pollution, there’s evidence of another threat to ecology lurking below the surface.

Score one for the Kenai River, at least as far as hydrocarbons go. But that isn’t the only threat the Kenai is facing, Robert Ruffner, executive director of the Kenai Watershed Forum, told the Kenai Area Fisherman’s Coalition in a meeting Thursday. There’s another challenge lurking in — or murking up — the water: turbidity.

Turbidity is muddy water — sediment suspended in the water column. It occurs naturally so it’s not pollution as it’s often thought of, like gasoline, oil or some other foreign substance dumped in the water. Turbidity can result from any number of natural circumstances, even a bear stirring up mud when it wades out to fish, or the fish flopping through shallow water if it happens to escape.

On the Kenai, there’s a certain amount of natural background turbidity, measured in NTUs (Nephelometric Turbidity Units). Five NTUs is about the level where turbidity becomes noticeable from clear water, Ruffner said. The Kenai’s normal background turbidity level can range from single digits up to the mid-20s, he said. The turbidity level can spike much higher — up to 50 or 60 NTUs — and still be a natural event, Ruffner said, when the Funny and Killey rivers pump runoff and meltwater into the Kenai.

But it can also occur from nonnatural events, as appears to be the case during July. The culprit, as it was with hydrocarbons, appears to be boats. As motorboat use increased during the summer, so did turbidity readings.

“Along the edge of the water where the boat wakes hit the bank there’s a pretty clearly defined zone of turbidity along the bank,” Ruffner said.

Mixing it up

The Kenai Watershed Forum studied turbidity this summer with instruments placed 15 to 30 feet from shore at Eagle Rock, river mile 11.5, and Swiftwater Park, river mile 23. The instruments took readings every 15 minutes from May 15 to Sept. 1 — except for a few hiccups.

“Somebody shot the buoy one day, which didn’t make us very happy. We lost a few day’s data,” Ruffner said. And at one point someone pulled the buoy at Swiftwater onshore. But, “we have a really good data set to take a look at this,” he said.

From mid-May to mid-June, turbidity levels were about the same at Swiftwater and Eagle Rock, ranging from single digits up to mid-20s NTUs. A little later in June, turbidity at both sites rose to a little above 50 NTUs for a few days, which is attributable to the Funny and Killey rivers discharging, Ruffner said.

In late June and July, things changed. The Swiftwater sensor, which is upriver from the busy motorboat section of the river, recorded turbidity levels similar to May and June, with a few increases in background turbidity from the Killey and Funny rivers. But Eagle Rock saw significant spikes in turbidity, up to just below 100 NTUs the first two weeks in July, and up to 140 and 150 NTUs the last two weeks of July. That’s 80 NTUs above even an elevated background level from the Funny and Killey rivers, and about 130 NTUs above a calm turbidity background.

The spikes at Eagle Rock occurred twice a day, once in early morning and once in the evening — which is typically when boats head out on the river and when they take out at the end of the day. The exception was Mondays, the drift boat-only day on the river, when there were no unnatural turbidity spikes.

“That’s a pretty repeatable pattern, and on Mondays we don’t see that,” Ruffner said. “There’s no other obvious explanation than boat traffic that causes those spikes.”

Even if the relationship between motorboat traffic and increased turbidity is clear, as Ruffner said, what isn’t clear is what might happen because of it.

One answer is nothing, at least for the time being. Ruffner said it takes two years of monitoring to establish baseline data, and the turbidity study will continue again this summer. And data can be interpreted in different ways. If DEC takes daily averages of turbidity levels, for example, that approach would obliterate the significance of the morning and evening spikes.

Coming up with clear turbidity data can be murky in and of itself, what with having to factor in the effects of tide changes, tributary stream drainage and river flow lag time between the two sensor locations.

“It’s a pretty monumental task, it’s not going to be simple,” Ruffner said. “If people want to question or consider how you get there, that’s one very obvious thing to criticize. I can see right away that I’m going to be faced with that challenge.”

Members of the Fishermen’s Coalition said they wanted to be proactive about the situation.

“Intuitively, it makes sense that there’s an impact there,” said Ken Tarbox. “… The burden of proof isn’t on biologists to show harm, the offending action has to show no harm, if you want to protect the resource.”

Jack Sinclair, area superintendent for the state Parks department, said that perhaps the Kenai River Special Management Area board will take up turbidity like it did hydrocarbon pollution and pursue regulatory changes to address the issue.

“We’ve gone through this once before and seen where it went, so maybe that will make a difference. I don’t know,” he said.

Dwight Kramer, chair of the coalition, said it may be up to concerned residents to drum up awareness of the topic if they want to see regulatory changes to address it, just as they did with hydrocarbons.

“I don’t think if we left it up to DEC we’d be where we are today,” Kramer said. “It might be incumbent on us, if we see this progressing in the next few years, to start pushing it from our level.”

So, what?

The Kenai’s turbidity can spike up to 50 or 60 NTUs naturally, and other rivers in the state, like the Yukon, can have higher turbidity levels than the Kenai and still support fish runs.

“When you look at the data you can tell that something different is going on. It’s pretty easy to see what is occurring naturally without going into any statistics or doing anything fancy from the data, and you can see these departures from what’s going on in the background,” Ruffner said. “The ultimate question is, so what? Is that a problem for the aquatic resources that are in the Kenai River and that make the Kenai River what it is? I don’t have a good answer for that.”

Turbidity can cause a variety of harms. For sight-feeding organisms, which can include juvenile fish, turbidity can mean they can’t see to find food. Certain sizes and shapes of particles can lodge in the gills of organisms that filter water. Turbidity can impact fish reproduction if sediment settles into the bottom of the river on spawning beds. And it’s a sign of bank erosion.

“That mud in the water is made up of the stuff that was on the bank,” Ruffner said.

Technically, the summer’s turbidity results put the Kenai out of compliance with water quality standards. For water bodies that don’t have a designated use — like recreation, transportation, etc. — by the state, the most stringent water quality standards under the Clean Water Act apply to it, Ruffner said. The state EPA hasn’t designated a use for the Kenai, or most water bodies in the state, so the standard for drinking water applies, which is no more than five NTUs above background levels. But Ruffner said he doubted this summer’s test results would land the river on the EPA’s impaired listing over turbidity anytime soon.

“The people who sit in the regulatory chair don’t really care what the people in the biology chair are saying. I doubt that we’re going to get an impaired status listing anytime soon,” he said.

There are a lot of questions still to sort out. Should turbidity be figured for the river as a whole, or in sections? Should turbidity results be looked at on an hourly, daily, weekly or some other basis? What effect do increases in turbidity have on the river?

People’s leaning on the politics of the river may affect their opinion of those questions.

“This is knowing full well that there will be people that will take this in and apply it to their interest, either for or against it, and that can’t be surprising to anybody. And it’s no different than what we saw with the hydrocarbon issue. People were able to spin that either way,” Ruffner said. “I don’t really know how people are going to take this and use it or not use it. From my perspective, if we’re documenting a problem with water quality, that ought to come first. We ought to protect water quality.”