A new study led by Cornell University finds climate warming and lake browning are making lakes in the Adirondacks unlivable for cold water species such as trout, salmon and whitefish during the summer months. WAMC spoke with Cornell aquatic conservation specialist and professor Pete McIntyre about the findings and their implications.
McIntyre: From our perspective, the really startling facts that came out of this study, which was led by postdoc Steve Jane, is that a very large proportion of Adirondack lakes are really facing a bit of a crisis with deoxygenation of their bottom waters. And so what that means, we know within the lake science community that the world's lakes are warming, in the Adirondack lake community, we know that Adirondack lakes are warming faster than average for lakes at this latitude and the temperate zone. And other researchers have suggested that that was probably at least partly attributable to the lakes becoming more tea-stained or brown in color. So what Steve's work has added to that understanding is that that browning process, this increasing tea-staining of the lakes is leading to a loss of oxygen in the bottom waters in the late summer. And the reason that's so important is those bottom waters are the chilly places where in the heat of the summer, a brook trout or a lake trout or a whitefish can reliably go to seek shelter from the high temperatures up at the surface. And so we have always thought of that being a real virtue of Adirondack lakes is that they protected that cold water at the bottom, even in fairly shallow lakes. But what we discovered with this rapid browning process is that it is creating cold water, but that cold water doesn't have enough oxygen to keep the fish alive. And so in a majority of Adirondack lakes, there's a layer that's less than five feet thick that protects the fish in terms of meeting their oxygen requirements and meeting their cold-water requirements in the heat of the summer.
Levulis: And so as you mentioned, those conditions make it unlivable for the cold-water species such as trout, salmon, and whitefish. Those species are key to the Adirondacks’ fishing economy, and fishing tourism. What though environmental roles do trout, salmon and whitefish play for the aquatic ecosystems there?
Brook trout and lake trout are the native top predators in Adirondack lakes. And historically, brook trout were found in many, many lakes, not all but many, many lakes of the Adirondacks. Lake trout were found in fewer lakes. And so those two species both require that cold water. So from the fishery perspective, it's a really big deal for the cold bottom water to lose its oxygen. But that loss of oxygen causes all kinds of other environmental consequences that go way beyond the fish themselves. So our team is starting to investigate what the consequences are, for example, the mercury that accumulates in the fish. For the last 50 years, the Adirondacks have had a mercury problem. And that's kind of accompanied the acid rain problem, that hit its peak in the 1980s and early 90s, before the Clean Air Act started to remedy it. And so all this mercury that came into Adirondack lakes can only be transformed into an available form in the food web, that starts to accumulate in fish tissues, if there's low-oxygen conditions, and that's when bacteria can start to make it available. So historically, when there was much less low-oxygen habitat, the mercury even if it was there in the system couldn't find its way through the food web and end up in the fish tissues, where it can affect people who eat fish or loons that are eating fish, or otters or other wildlife. Now, today, with this extensive and often long-lasting, low-oxygen conditions, the transformation of the mercury and its entry into the food web becomes a much larger problem than it was before. The mercury is already there, but it now has the capacity to be converted into more available forms. So that's one example. But you can think of [it] as sort of a dead zone phenomenon where it's not just that the trout that are excluded from the bottom of these lakes. It's all life that requires oxygen. Everything is excluded. So you're sort of compressing the zone of biological activity for standard oxygen dependent biological activity into an ever-narrowing part of the lake up at the surface. And if you're a cold-water fish, that's a huge problem because you get squeezed between the hot water at the top and the deoxygenated water at the bottom. But even for species that aren't sensitive, don't have a sort of ceiling for their temperature tolerance, even those species are losing a substantial part of the habitat down in the bottom of the lake.
And now this study focused on lakes in the Adirondack Park, which is a protected 6-million-acre area with regulation set by agencies such as the Adirondack Park Agency. So if this browning is occurring in a protected park, what do the findings of this study indicate for areas without such protections?
So often we think of environmental problems as being sort of cut off at the pass when it comes to protected areas, and especially really large protected areas. So working in the Adirondacks, residents there, those of us that have the privilege of doing research there, we’re incredibly fortunate to work in such a large landscape where smart controls and regulations have been put in place to limit development, to limit the degree to which the environment is being altered. But for issues like browning, it's in part reflecting the legacy of acid rain throughout the whole Adirondack region. That acid rain stripped away some of the key elements that we call cations, positively charged elements that were part of the soil. Those are key elements for lots and lots of biological processes. So there's a whole host of problems that can arise there, aside from just the pH issue of the acid itself. But along with that, it reduced the capacity of the soils to hold onto all of this organic carbon, the stuff that leeches out of tree leaves or other decomposing vegetation. And that's what gives rise to this tea-staining phenomenon in the streams and lakes of the Adirondacks. This browning or tea-staining problem has been recognized for about a decade by a whole variety of different researchers working in the Adirondacks as a big challenge. A key difference between that and many of the other environmental challenges that we might think of, is that the landscape protection of the Adirondacks doesn't shelter the waters of the Adirondacks from this browning or tea-staining phenomenon because it's a legacy of the ecosystem, the terrestrial ecosystems, not being able to hold onto those colored organic molecules. So they just wash off at the landscape and into the lakes and rivers.
So when it comes to items like runoff that leads to the browning, are there any sort of remediation efforts that could be done?
Ordinarily we think of remediation as being a key strategy for addressing various kinds of environmental challenges or degradation caused by people. In this case, it's really a combination of the long-term change to the chemistry of Adirondack forests and soils, from acid rain combined with increasingly intense storms that are hitting the Adirondacks. They produce a kind of a pulse of runoff that's coming from the upper parts of the landscape down through the watershed into the rivers and lakes. That's what's delivering to the water bodies all of these colored organic substances that we refer to as browning. So, the browning is reflecting the delivery of more of these organic substances to the water and there's not really a lot we can do about it. That's going to happen whether you've got actively managed forests or old growth forests, they're still going to be producing a lot of this carbon and the storm pulses wash it efficiently into the water body. So we think that it's that intersection between climate change with greater pulses of runoff and the decreased stability of the soils to hold onto those organic acids that that lead to tea staining, the tannins in the water that is yielding this browning signature and there's not really any specific management method that we can take to intervene to reduce that.
