Logan Finney, Idaho Reports:

Joining me this week is Colin Eagles-Smith with the U.S. Geological Survey to talk about a recent study involving fish and mercury levels in the Snake River. Colin, would you introduce yourself and the work that you do with the U.S. Geological Survey?

Colin Eagles-Smith, USGS:

Okay. Thank you, Logan. Yeah. So, I’m Colin Eagles-Smith with the U.S. Geological Survey and I’m a research ecologist in Corvallis, Oregon. Our research group works a lot on contaminants issues across the U.S., and especially we have a lot of expertise in mercury cycling and mercury by accumulation in aquatic ecosystems. So, this project and this paper that came out, led by Dr. James Willacker in my group, looks specifically at mercury levels in smallmouth bass throughout the extent of most of the Snake River, and focusing specifically on comparing mercury concentrations in reservoirs and the tail races, or the downstream extent below reservoirs, and then free flowing stretches of the Snake River to get a better understanding of how the mercury concentrations vary through that system.

IR:

What was the inspiration for this study and the questions that you wanted to answer? What about the Snake River made this the right place to look at this kind of information?

Eagles-Smith:

The motivation was a partnership that we had with Idaho Power Company, and we’ve been working on a research project with them in the Hells Canyon reservoir complex for several years. And as part of that research, we wanted to expand out and look at how Hells Canyon compared to the rest of the Snake River itself and other reservoirs within the Snake River.

IR:

Can you remind us what exactly the scope of the Snake River is? Because it’s a big river system. It’s the biggest tributary of the Columbia. It goes all the way from Washington to Oregon and spans east to west through Idaho and much of the north-south area as well. Can you give us just a little bit of perspective on how big of a watershed this is?

Eagles-Smith:

Yeah, it’s tremendous. I guess, I can talk more about the scope that that we studied, which was from about American Falls Reservoir upstream, all the way down to below Hells Canyon Dam, so into the Hells Canyon complex stretch of the Snake River to Pittsburg Landing. And so, we didn’t include that stretch below there that extends down to the intersection at the border with Washington and Oregon. We did not go as far downstream as that.

IR:

But still, from Pittsburg Landing – almost at Lewiston – all the way to American Falls. That’s a pretty big stretch there, I imagine that was a lot of work.

Eagles-Smith:

It was a lot of work, yeah. So, we did sampling in 2013, 2015 and 2020, so multiple years of sampling as well went into this.

IR:

How exactly do you collect this data? What exactly are we measuring when you guys are doing the study? Specifically, it’s measuring the presence of mercury in the river system?

Eagles-Smith:

Yeah. So, we’re again, working with Idaho Power Company and their environmental departments. They do annual fish surveys throughout the extent of much of the Snake River system. And so, we partnered with them and they did a lot of fish sampling for us, and then we take a segment of the fish. We’ll take a muscle sample and analyze that muscle for the content of mercury, the amount of mercury in that muscle relative to the amount of actual muscle tissue there, which gives us a concentration of mercury that’s in that tissue.

IR:

And so how does the mercury get into the fish in the first place? What sort of systems are you looking at here in the reservoirs versus the free-flowing sections of the river that can affect the mercury concentration in the fish?

Eagles-Smith:

So that’s a great question. And mercury is sort of uniquely complicated as a contaminant or an element in the ecosystem. So, mercury in its inorganic form is the most common form, and that can be deposited in watersheds and airways from the atmosphere. It can also come from mining. And most of the mercury that we see in the environment does come from atmospheric deposition, and it gets into the atmosphere from things like coal burning or using mercury in gold mining, and it distributes globally.

It’s when the mercury lands in aquatic systems, so in rivers, lakes, streams, that sort of thing. There’s a process by which the mercury – we call it methylation, but I like to refer to it as the mercury gets activated by microbes – it gets changed to a different form. And that form is called methylmercury. And that form methylmercury is more bioavailable. So, it can enter biological cells more easily than the more common inorganic form that deposits on waterways. And it takes specific environmental conditions for the microbial groups to be able to convert that mercury from inorganic to methylmercury. So, in other words, to activate that mercury, they require unique environmental characteristics for the microbes to function properly.

IR:

I think, in reading the abstract for the study, it spoke about anoxic conditions in lower parts of the water. Our audience may be familiar as we’ve done some coverage of Lake Coeur d’Alene and the mining waste up there, where their concern is not so much mercury, but the concern is lead in the sediment up there that’s kept in place by the oxygen, and anoxic conditions would cause some issues up there as well. Is that the same kind of kind of mechanism going on here?

Eagles-Smith:

It’s a different mechanism. But the microbial groups, the microbes that actually convert and activate the mercury and create methylmercury. Most of them only can exist in the anoxic conditions, so they require low or no oxygen for them to make a living and to exist. And so, what we’ve seen in other systems, across the world really, is when you have anoxia that tends to be one of the triggers for creating methylmercury in the environment. Many reservoirs and lakes, natural lakes, seasonally will stratify. And so, you’ll have a layer of warm water on top, and that sits on top of the layer of cold water, and they don’t mix over time. And you can have that, because of the lack of mixing the oxygen in, the lower portions of the reservoir can become anoxic. And when that happens, it may facilitate or trigger the formation of methylmercury and activate those microbial communities. And so that was one of the questions that we were asking, is do we see any sort of association between reservoir stratification and mercury concentrations in the fish?

IR:

What did you guys find? Did that correlate, did that pan out?

Eagles-Smith:

So, we did. We compared reservoirs with free-flowing stretches of the Snake River, and we found that concentrations in fish were about twice as high in all reservoirs on average than they were in the free-flowing sections of the Snake River. And then when we looked within individual reservoirs, there are a number of reservoirs in the Snake River system that don’t stratify, so, they remain mixed all year long, and there are a number of reservoirs that do stratify. And so, we compared those two and found that the fish in the reservoirs that do stratify had mercury concentrations that were about twice as high as the fish in reservoirs that don’t stratify.

IR:

If we break that out into three categories — so stratifying reservoirs, non-stratifying reservoirs, and then free-flowing river — how much of a difference is there between those three?

Eagles-Smith:

I think it’s about a threefold difference between the free-flowing and the stratified reservoir if you look at the two extremes.

IR:

There are a lot of dams on the Snake River. I was just looking at a map of it earlier, and it’s pretty impressive. Some of them are federal dams, some of them are private dams. Some of them are used for irrigation, some of them for hydroelectricity, some for both. Can you tell us how much of the river is dammed versus free flowing? How does that kind of break out?

Eagles-Smith:

Yeah, it’s a hard one to quantify, because the extent of what is and isn’t a reservoir is a little bit fuzzy. But at least in our study area, about 75% of the length of area that we studied could be classified as a reservoir. 20% we classified as a tail race, so the tail races being a section immediately below the reservoir, and then about 6% of the extent was we classified as free flowing. So, there are about 23 dams and reservoirs that we looked at in our study on the Snake River.

IR:

And so that tail race part specifically that you’re talking about, that’s the shorter stretch of the river where water is being released downstream of the dam? Is that right?

Eagles-Smith:

That’s correct, yeah.

IR:

Did you see any particular effects of mercury concentration in that part below these dams as well? Was there anything worth highlighting from that?

Eagles-Smith:

Yeah, we saw a pretty consistent pattern, similar to what we saw in the reservoirs, and that is that the fish in the tail race sections below stratified reservoirs tended to have higher concentrations than fish below reservoirs that didn’t stratify. And we could in stratified reservoirs, we could see that signal. It didn’t return to a free-flowing sort of concentration until about 25 or so miles below the dam. So, it continued down for a fairly large distance.

IR:

Are there any specific reservoirs worth mentioning that you guys studied, that stand out as examples in particular of stratifying or non-stratifying reservoirs?

Eagles-Smith:

I don’t know if there are any specific reservoirs. I think we have the most data from Brownlee Reservoir, Oxbow Reservoir and Hells Canyon, because that was part of another larger study. All of those have some form of stratification that occurs, and then CJ Strike was another reservoir that we studied fairly intensively.

IR:

And so, when we’re talking about this mercury that, in these conditions is more prevalent and in a form that is more readily taken up into these fish, what sort of fish were you guys studying? Was this a broad look? Was this one particular species? Why pick one species over a different one?

Eagles-Smith:

Right. That’s a great question. So, we focused exclusively on small smallmouth bass, and we did that for a number of reasons. One is that there are differences among species. And so, if you’re looking at mercury at one location in bluegill and in another location in small mouth bass, it might be hard to make comparisons between the two locations. So, we wanted a consistent species that was present throughout the entire system. Smallmouth bass is one such species that we could collect and we could find in all of these locations. So, that allowed us to provide an apples-to-apples comparison through the extent of the Snake River. It’s also an invasive species. So, from a conservation perspective, we weren’t collecting or taking any sort of native species as well. And then, it’s a really regularly harvested species and one that a lot of sport fishers target and like to fish for. So, there’s a linkage to human health and consumption because people do fish for smallmouth bass and eat them as well.

IR:

Yeah, that’s a perfect transition. Can you tell me a little bit about the health effects of mercury and why this is a concern that we’re looking out for and studying?

Eagles-Smith:

Yeah, so at elevated concentrations and with a lot of exposure to mercury, it’s a neurotoxin. So, it can affect your nervous system, it can affect your cognitive ability. It also has cardiac effects, so it can influence heart function as well. And it’s one of the most common contaminants that occur worldwide. And so, at elevated exposure it can have deleterious effects, and especially in children and fetuses. A lot of the consumption guidelines and human health guidance are centered around protection of women of childbearing age and children as they’re developing neurologically. It can impact those functions.

IR:

Even though this particular study in this particular area only looked at this one species, smallmouth bass, which is a popular sport fish, can you extrapolate these findings to the region more broadly? I guess a better way to phrase that is, even though you used one fish for consistent measurement, what sort of picture does that give us of the ecosystem overall?

Eagles-Smith:

Good question. It can be difficult to estimate mercury concentrations in another species from bass. But what it does allow us to do is identify locations and essentially say if mercury in smallmouth bass is low in location A in smallmouth bass, it’ll probably be low in other species in that location. In contrast, if it’s high in location B, we would expect that it would be high in other species that occur at location B. So, it provides an opportunity for us to gauge the potential exposure and health risks that we might see along different stretches of the river.

IR:

And so then how are the findings from this study, and ones like it, how are those results then used for policymakers when they’re deciding things like hunting and fishing regulations or things like fish consumption advisories? What happens now that this study has been published?

Eagles-Smith:

Right. So, we’ve released all the data, and the data are made available to decision makers and public health authorities, and they can take the data that we have, look at the report and the average concentrations of different locations and the proportion of fish, and compare them to benchmarks of health risk. And in different states and different federal agencies, there are varying degrees of benchmarks that are used. They can take that information and make some decisions on whether or not it’s valuable to communicate the potential for potential consumption advisories or communicate whether there’s a health risk to humans from consuming fish at different locations.

IR:

All right. Colin Eagles-Smith, research ecologist with the U.S. Geological Survey, thanks so much for your time this week.

Eagles-Smith:

All right, Logan, thank you very much. It was a pleasure to be here.