[Host]: New research reveals how a warming Arctic is affecting vast lakes in Canada's north, and has scientists raising the alarm. Kathleen Ruland is a senior scientist at the Paleoecological Environmental Assessment and Research Laboratory at Queen's University, and she joins me on the line. Great to have you, Kathleen. How are you doing?

[Kathleen Ruland]: Great. Thanks for having me.

[Host]: Help me understand. Why did you choose these northern lakes for research? We're talking about Great Slave Lake, Great Bear Lake and Hazen Lake on Ellesmere Island as the focus of your study.

[Kathleen Ruland]: Well, these are three of the largest and deepest lakes on earth, particularly Great Slave and Great Bear Lake. They're the largest lakes by area and volume that are entirely within Canada. And yet we know very little about these lakes. So the Lake David Schindler, back in 2001, wrote in a paper that the lack of knowledge on these lakes is a national disgrace. So I think most of your viewing audience would probably be more familiar with Laurentian Great Lakes, but Canada really has 3 or 2 of the largest lakes in the world that are north of 60. So, for example, Great Slave Lake and Great Bear Lake would fit the size of the country of Belgium in them. So it's huge and they're very deep. So Great slave Lake, for example, could fit the CN Tower with room to spare. And the Great Bear Lake could fit the Eiffel Tower with room to spare. So our past research that's led by Doctor John Smol, he heads our lab here at PEARL. Our past research on small and medium sized lakes have found really big biological responses to climate warming in the Arctic. But these large, huge lakes are extensively ice covered for most of the year, and we really find them to be quite resilient or protected from the full impacts of climate warming. So one of the things that we set out to do, because now the Arctic is heating up to 3 to 4 times more faster than the global average. So we wanted to see whether these huge, big sleeping monsters, they're not waking up. Are they going to respond similarly? Or have they responded to this new climate regime? And that's what we're hoping to find out. And that's what we found out.

[Host]: Well, we're talking about these giant, vast bodies of water, but we're really going into onto a microscope and looking at these small microorganisms in layman's terms, help us understand diatoms. There are different kinds of algae, but generally, and we'll get into the specifics a little later. But generally, why are they important to the ecosystems?

[Kathleen Ruland]: Well, they are the bottom of the food chain or food webs in. And they are the main algal or the main primary producers in oceans and in our lake systems. So they photosynthesize. So they're like, you know, the algae of the water bodies are like grass and terrestrial systems. So they feed the rest of the food chain and they provide energy to the smaller organisms all the way up to the, the fish species. So they are very essential to keep that ecosystem fueled. So and their cell walls are made out of glass and they're quite beautiful. But in terms of how we use them for our purposes, for our research. So we want to go back in time. We are paleo limnologists. So we want to look at lake systems and past lake systems, and we want to use that to establish what the environment was like before anthropogenic, you know, impacts. So these diatoms, because they're made out of cell, their cell walls are made out of glass. They preserve really well in sediments. So for example, you know, once they die, they sink to the bottom of the lake and they become part of the they get incorporated in the mud. So day after day, year after year, for hundreds to thousands of years, they accumulate at the bottom of the of these lakes, and they become part of the fossil record. So it's like, we could use that as a kind of a time machine for these lake ecosystems. So we can go to that lake and, and take a core or take a tube of that lake sediment. And we have a means to date them. So we know that at the bottom of the core, it's maybe 1850. And at the top of the core, it's 2000. And then we would spend a lot of time looking at the diatoms. So my colleague Neil McLeod, he looked at the Lake Hazen cores and we would spend time looking at these diatoms. And, you know, there's thousands of species. So a whole assemblage of species might prefer, you know, open water, light conditions, and a whole different assemblage would prefer lighter or darker conditions and maybe more ice cover in that kind of thing.

[Host]: Well, let's talk about. We actually have some images of that. So I want to pull that up.

[Kathleen Ruland]: Oh, sure.

[Host]: The first photo shows the type of long diatom usually found in these northern Great lakes. The measurement at the bottom of the photo is in micrometers or millionths of a metre. Now, the second photo shows the kind of pancake diatom that is appearing more frequently in those lakes as a result of climate change. Besides the shape, which is quite obvious here, what are the main differences, as you were just alluding to a little bit in terms of how they sort of sort of deal with sunlight, but the shapes themselves are quite important as well. When we talk about the ecosystems being at the bottom of the web.

[Kathleen Ruland]: Exactly. So that larger diatom that you first showed us, that's a kind of it's shaped like a tin can. And they're very heavy. And in terms of, you know, relative to other diatoms, they're very heavy diatoms. And in the water column, they would require turbulent conditions or the movement of the water to keep them afloat in the photic zone because they're photosynthetic organisms. So they need the sunlight to photosynthesize, whereas the smaller pancake sized diatoms, those small Cyclotella taxa are more nutrient poor. And so, you know, there's a big shift in the food source. So in the past, those large diatoms were what dominated, for example, in Great Slave Lake for hundreds of years, the environment was very stable for hundreds of years. And that was the dominant taxon throughout that lake. And then at around 2000, at the turn of the 21st century, we suddenly get a shift towards these very small, prolific, pancake shaped diatoms that are poor nutrient source for the next chain in the food link. And so we have an example of that in. So we can make a comparison, for example, to Lake Michigan. So our colleagues in Minnesota have looked at very similar changes. So they took a core much like we did, and they found very similar changes with these large diatoms shifting to these small taxa. And that had really big repercussions all the way up the food web, where that next link in the chain actually didn't fare well. It was completely collapsed. And that had real big repercussions for, you know, fish species up, up the food chain. Whether that will happen in these lakes is really hard to tell because it's a different system. We don't have invasive species like zebra mussels, as we do in the Laurentian Great Lakes. And, you know, the impact human impacts are minimal. But I think, you know, this is an early warning sign that things are going to change.

[Host]: I am curious in terms of the size themselves, what does that mean for zooplankton who are eating on diatoms? And then as we move up the food chain for fish.

[Kathleen Ruland]: That's an excellent question. Yeah. So those large pancakes, those large, you know, tubular diatoms, they're very calorie rich, lipid rich diatoms. And they're a very important or nutritious food source for these smaller kind of little organisms that feed on diatoms. Whereas the pancake shaped diatoms, these small Cyclotella taxa are more nutrient poor. And so, you know, there's a big shift in the food source. So in the past, those large diatoms were what dominated, for example, in Great Slave Lake for hundreds of years, the environment was very stable for hundreds of years. And that was the dominant taxon throughout that lake. And then at around 2000, at the turn of the 21st century, we suddenly get a shift towards these very small, prolific, pancake shaped diatoms that are poor nutrient source for the next chain in the food link. And so we have an example of that in. So we can make a comparison, for example, to Lake Michigan. So our colleagues in Minnesota have looked at very similar changes. So they took a core much like we did, and they found very similar changes with these large diatoms shifting to these small taxa. And that had really big repercussions all the way up the food web, where that next link in the chain actually didn't fare well. It was completely collapsed. And that had real big repercussions for, you know, fish species up, up the food chain. Whether that will happen in these lakes is really hard to tell because it's a different system. We don't have invasive species like zebra mussels, as we do in the Laurentian Great Lakes. And, you know, the impact human impacts are minimal. But I think, you know, this is an early warning sign that things are going to change.

[Host]: Well, let's talk a little bit about that. You know, as we mentioned, these are lakes that for the most part are quite isolated, very far from where I am here in southern Ontario. What does this all mean?

[Kathleen Ruland]: Right? So if you're living in Toronto, you might think, well, why should I care about these, these lakes? So if you're living in the north, of course, these are very important lakes for they're one of the most unpolluted systems or Great Lakes in the world. But they're important for things like transportation and food security as well as cultural identity, that kind of thing. But if you're living in the south, you think, well, why would I care about this? So I think maybe the best way to explain that is why my colleagues and I were so surprised to see these changes. And, you know, we're talking about Great Slave Lake that's in the south. It's around 61 degrees north all the way to Lake Hazen, which is about 81.4 degrees north. So many different degrees of latitude. They also have different degrees of remoteness. Great Slave Lake is home to 60% of the Northwest Territories. Lake Hazen has no community, permanent community there. Great Slave Lake has, you know, 35 fish species. Great Bear Lake has maybe 15. And Lake Hazen has only one fish species. So the food web dynamics are a little bit different. But what we found surprising was the pace and the magnitude, and actually the almost synchronous nature of the changes across all of these lakes. And that really highlights the widespread and powerful shift that climate, this new climate regime has on these lakes, that it kind of just, you know, overrides those differences among the lakes. So, you know, I think we've pushed climate warming to a point now where no lakes are protected. So, for example, Great Bear Lake has always been known as the most unpolluted great lake in the world. And that's certainly true when it comes to things like contaminants and so on. But when we start looking at the microscopic organisms and how things are changing, it's now no longer untouched by climate warming. So I think the take home message for anyone in the world, whether you're living in Toronto or up north, that no ecosystem is immune to anthropogenic change, and especially not accelerated warming. And that's what we're showing, I think, with our results.

[Host]: An important message. Kathleen, thank you so much for your time. I really appreciate it.

[Kathleen Ruland]: Thank you for having me.