How a little girl affects Boulder’s water

With the U.S. Winter Outlook released recently, the upcoming winter in Colorado is likely to be colder and snowier than normal, thanks to a climatic phenomenon known as La Nina – the little girl.

But if that forecast comes true, it will run counter to the long-term trend: Over the past 50 years, less late-winter precipitation falling as snow and earlier snowmelt had been observed in the Southwest regions, according to the National Climate Assessment. And thanks to the human-caused climate change, there is little hope of change, as reports point out.

Rain rather than snow in the winter poses significant challenges to the availability and quality of drinking water downstream – and it also leads to the loss of a unique ecosystem, according to the National Climate Assessment.

Actual and projected decrease in snow water equivalent for the Southwest region. [USGCRP]

Losing alpine lake ecosystems is a major concern for Kim Vincent, PhD candidate in the Microbial Observatory at the University of Colorado Boulder and her colleagues. The scientists study microbial life and processes that occur in the most species-poor areas around the world from high alpine settings to Antarctica.

Arctic and alpine ecosystems are more simple than other systems and therefore suitable “to most quickly observe [the effects of climate changes],” said Dorota Porazinska, researcher in the laboratory. For example, a shift in biodiversity.

At a height of approximately 13,261 feet, Green Lakes Valley in Colorado is one of the lab’s research areas – and a very important ecosystem for the City of Boulder.

According to Eli Gendron, PhD candidate in the Microbial Observatory and researcher in the Green Lakes area, this watershed accounts for about 40 percent of Boulder’s water supply.

The Green Lakes Valley lies immediately south of the western half of Niwot Ridge and stretches from the Arikaree Glacier at its head, southeast to the former mining camp of Albion.

Normally, when the snow melts in the spring, the water runs over frozen ground and feeds the lakes with no possibility to infiltrate into the subsurface. But with higher temperatures, more water can trickle into the soil that is no longer frozen.

“Then we see a decrease in available water,” said Gendron, because the water goes into the ground, rather than downstream.

Also, a thinner, earlier melting snowpack is a problem for the quality of Boulder’s drinking water. That’s because snow that falls on a frozen lake, insulates it and therefore keeps it frozen over a longer period. Rain instead of snow, melts the ice cover.

“So that means that the lake is basically open to its growing season,” explained Vincent.

Alpine lakes typically are nutrient poor and if they are not covered by ice, they are vulnerable to nitrogen and phosphorus pollution, by farms and cities down in the plains, falling out of the atmosphere.

Which then promotes the growth of algae, increases the nutrient concentration and the number of species occurring in the lakes, causing significant changes in the ecosystem.

Another impact is that earlier snowmelt will encourage the treeline to move higher. With plants now grow at higher altitudes, yet more nutrients accumulate in the ecosystem. Leafs falling, a more diverse soil community and more biodiversity in general, thinking of birds and insect, are food for the microbial communities in the lakes.

“That’s where you get stuff like cyanobacterial blooms, for example,” explained Gendron.

These are toxic and they pose other challenges as well. “These organisms grow really fast and take all those resources before other organisms,” explained Cliff Bueneo de Mesquito, also PhD candidate in the Microbial Observatory.

hey block the surface of the lake and absorb all the light.

“And then it becomes more than just light blockage,” added Gendron. If the growth continues, water flows get blocked off and species that need more stable conditions like cattails can establish. “Then the whole lake will start overgrowing. And then you’ll ultimately loose that lake,” summarized Gendron.

But according to the researchers, people in Boulder do not have to be concerned about their drinking water. Algae blooms are monitored and for the most parts, the concentration is currently small enough. “That is not an issue for us,” said Gendron.

At worst, the Green Lakes Valley might be affected by eutrophication and Boulder has to spent more money to clean the water – or will eventually lose this watershed.

Vincent added that excessive algae growth “is more extreme than what we would find around here.” As mentioned, she is more concerned about the loss of this unique ecosystem of alpine lakes which would occur way earlier before the lake finally dies.

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