Researchers at the University of Colorado Boulder revealed Monday that the surface waters of Lake Dillon have warmed at twice the average rate for global lakes over the last 35 years.
The reservoir, which supplies Denver with water, has risen nearly 5 degrees Fahrenheit during the last 35 years, according to the study from CU’s Cooperative Institute for Research in Environmental Sciences. Unsurprisingly, researchers attributed the rising temperatures to climate change. More surprising is the same study found there has been no adverse environmental impacts due to the warming.
The researchers say Lake Dillon remains in “excellent condition,” as its high elevation — just over 9,000 feet — and thus colder temperatures, have helped the reservoir avoid the ecological responses tied to warming that have harmed other bodies of water at lower altitudes, especially in the tropics.
“The warming of Lake Dillon is a result of climate change but, in contrast with warm lakes, which respond in undesirable ways to warming, Lake Dillon shows no environmental response to warming,” said William Lewis, director of the institute’s Center for Limnology and lead author of the research paper.
“The explanation for the lake’s ecological stability lies in its low temperature, which serves as a buffer against ecological effects of warming,” he noted.
Researchers published the findings from their multi-decadal study of Lake Dillon in the American Geophysical Union’s “Water Resources Research” on Monday.
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According to the researchers, Dillon is the highest lake that’s ever been studied for full water column warming, and this is the first study to analyze the effects of warming on a reservoir, opposed to a natural lake.
“Reservoirs can differ fundamentally from other lakes in their response to warming because they often release water from the bottom as well as the top of the water column,” Lewis said. “They can warm not only from the top, in response to solar radiation reaching the surface, but also from the bottom, as tributaries subject to climatic warming replace cold bottom water with progressively warmer tributary water.”
Full vertical profiles of water temperature document changes in vertical distribution of heat over time. The record shows that warming of tributary water contributes to warming of the lake’s deepest waters, as well.
Natural events like droughts and floods can obscure the effects of climate change over short intervals of time, but data sets spanning decades show more clearly the effects of climatic warming, the researchers explained.
“The 35-year data set allows us to see the complete warming pattern of the lake,” said James McCutchan, associate director of the Center for Limnology.
The Lake Dillon study program is funded by Denver Water and by the Summit Water Quality Committee, which is comprised of individuals from Summit County’s towns, the county and other stakeholders with an interest in preserving Lake Dillon’s water quality.
Lewis and his colleagues have collected detailed information, not only on Lake Dillon’s temperature, but also on its water quality and aquatic life since 1981, as the research for the study paper published Monday actually began as an effort to monitor Lake Dillon’s nutrient levels.
“Right now, it’s kind of an aha thing for everybody,” Wyatt said of the researcher’s findings, adding that the committee was relieved to hear there hasn’t been the environmental impacts on Lake Dillon with nutrients remaining at acceptable levels, no major algae blooms and no depletion of oxygen levels tied to the warming temperatures.
Even though Wyatt said the committee hasn’t made any decisions about where they might go from here, researchers believe the study could have implications for future water management practices in Colorado and beyond.
While the study shows that lakes at the highest elevation have a natural buffer against climate change not present at lower elevations or the tropics, Lewis did not want to make any predictions about what might happen if Lake Dillon’s temperatures continue to rise at the rate they have been the last three decades.