As glaciers across South America gradually vanish from existence, another key, but often underlooked, source of water—lakes—are also under threat. Climate change is fundamentally re-shaping lake ecology in the Tropical Andes, a development that could undermine biodiversity and jeopardize critical water resources in a region stretching from Venezuela to Bolivia, according to a study published this past February in PLoS One.
The study was carried out in southern Ecuador’s Cajas National Park by a team of five scientists led by John Smol and Neal Michelutti of Queen’s University. The implications help us understand the future of water resources in tropical, high elevation zones throughout the world, most notably in South America and East Africa.
While there’s been significant research around the issue of glacial retreat in the Andes, researchers have paid less attention to the region’s lakes, which also serve as a significant source of drinking water for local populations, particularly in Ecuador, Colombia, and northern Peru. Lakes in Ecuador’s Cajas National Park, for example, provide Cuenca, a nearby city of 400,000 residents, with 60 percent of its drinking water. Larger metropolitan areas such as Quito, Ecuador, and Bogotá, Colombia, also derive a significant percentage of their drinking water from lakes located in páramos—tropical wetlands set at high elevation.
“Not a lot was known about these lakes, despite their importance, and despite the major environmental changes that were going on there,” Michelutti says. “And no one knows how they’re going to respond to future warming. They’re just really understudied systems.”
Climate-driven changes to ecology in the lakes of the Tropical Andes take on greater significance when we consider that the Andes in general have warmed at roughly twice the global average. Higher elevations are likely to remain more vulnerable to climate change in the coming years, according to Mathias Vuille, a professor of atmospheric and environmental sciences at the University of Albany, and a co-author of the Cajas lake study; a 2013 report for the Inter-American Development Bank on “Climate Change and Water Resources in the Tropical Andes” echoes these concerns.
In warmer areas, Vuille notes, the air holds higher quantities of water vapor—a greenhouse gas. At higher elevations, where the air is colder, this increase in moisture has a much stronger greenhouse effect, following a logarithmic relationship. A warmer world will also generate a more vigorous hydrologic cycle, as the increase in water vapor generates condensation and, ultimately, precipitation. This process also releases energy in the form of heat, an effect that takes place only at high elevations where the condensation occurs.
“If you look at climate models out for next 100 years, they all have much larger warming in the mid and upper troposphere in the tropics than at the surface,” he says.
In Cajas National Park, the scientists took sediment cores from three pristine lakes at varying altitudes. By dating the cores and examining microscopic algae known as diatoms, the research team was able to piece together a history of the lakes’ ecology. As a result, Smol says, the scientists were able to overcome one of the biggest challenges to ecological and environmental science: the lack of long-term monitoring data.
“Every lake is a passive sampler, slowly recording what’s happening in the world around us by the sediments,” Smol says. “It’s like a history book or a time machine.”
The cores showed a significant increase in planktonic diatoms beginning in the early 1960s, a finding consistent with the observed increase in air temperatures and reduction in wind speed in recent decades. The increase in planktonic diatoms is significant as a harbinger of weaker nutrient flow throughout the lake.
“One of the things that we inferred from the changes is these lakes, as they warm, are starting to stratify more,” Michelutti says. “The surface of the lake is becoming warmer, so it becomes less dense, and you get this stable body of water on top. What this does is it prevents nutrients in the deeper waters from circulating up.”
As nutrients remain stuck at the bottom of the lake, organisms ranging from microscopic algae to fish can be threatened.
“With this thermal stratification, you’re making a barrier or nutrient trap,” Smol says. “Of course that will cascade through the whole ecosystem.
As the ecology of high alpine lakes changes, Vuille is also concerned about the effects of soil degradation in the surrounding wetlands.
“The páramos are important because they hold a lot of carbon,” Vuille says. “So if those wetlands degrade, the fear is a lot of carbon could come out of those soils.”
Since the study at Cajas National Park was published earlier this year, Smol and Michelutti have expanded their research on tropical Andean lakes, publishing a study in the Journal of Paleolimnology showing similar results in lakes in the Peruvian Andes. A forthcoming study in the Journal of Limnology measures changes in lakes in an ecological reserve near Quito. Moreover, Michelutti returned to Cajas over the summer to install additional equipment with park officials and faculty members from the University of Cuenca. Contact with local policymakers has been minimal to this stage, although future collaborations remain possible. Juan Carlos Quezada, an official with ETAPA EC, Cuenca’s Water Authority, told me that his organization is still reviewing the study. Commenting generally, Vuille sees a disconnect between scientists and water authorities in how they think about ecological changes.
“A lot of the things we as scientists do—the language that we use, the metrics by which we measure things—don’t really match-up with the types of things a water manager or a minister of environment would like to know or understand,” he says. “We measure in uncertainties. For a water manager that’s very frustrating because they can’t really plan based on that. They don’t want the range of outcomes, they want one specific number. As scientists, we have to try to explain that that’s not possible.”
As water run-off from Andean glaciers decreases, Michelutti believes that more people will look to lakes as their main source of drinking water, especially during the dry season. This includes not just Andean populations, but cities and towns on the Pacific coasts of Peru and Ecuador, which depend on rivers sourced from páramo lakes. It is therefore important, Michelutti says, to determine whether those resources will be there when people they need them. Lower water quality could also affect future agricultural production by contaminating crops.
Despite the change in lake ecology, the scientists were clear that water from Cajas National Park remains potable for now, as shown by a chemistry analysis of the three lakes. But as these lakes enter into what Vuille refers to as a “zero-analog” future, further changes to the balance of nutrients could have widespread consequences.
“Although there’s been this fundamental change in the way these lakes operate, the water quality’s still high,”Smol says. “But it is changing ecologically very quickly.”
While it is possible that páramos will survive by migrating upslope as temperatures rise, Vuille says the rate of temperature increase forecast over the coming decades could overwhelm the ability of these ecosystems to adapt.
“We don’t really know how these ecosystems will respond to warmer temperatures,” Vuille says. “Generally we think of ecosystems or plants moving upslope with warmer temperatures, but any ecosystem can do this only with a certain rate, at a certain speed. And the concern is that the rate of change we’re seeing in temperature is much too fast for these ecosystems to adapt.”
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