Climate Change Is Upending the Ecology of Lakes in the Andes

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.

Source: PSMag

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