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As winters warm and lake ice duration shortens, algal blooms are interfering with water quality in lakes

Lakes represent some of the most vital natural resources on Earth. While they only hold a small percentage of the �鶹ӰԺ overall water supply, they provide most of the fresh water people depend on daily. Supported by a new five-year, $2.5 million grant from the National Science Foundation, a group of researchers at five universities will examine how rapidly warming temperatures and shorter winters can influence the growth and toxicity of lake algae. Isabella Oleksy, who studies aquatic ecosystems and recently joined INSTAAR, is leading the Colorado contingent at CU �鶹ӰԺ.

The researchers will use predictive modeling to forecast future outcomes on samples taken from more than 30 lakes across the country to measure the impact of climate change. They will study how year-round algal growth and increasingly warmer winter temperatures could negatively affect lake ecosystems and water quality.

“We're looking to make future projections of what to expect out of water quality, specifically levels of phytoplankton and the cyanobacteria that are harmful algal blooms, and then potential increases or decreases in toxin concentrations,” said University of Missouri researcher Rebecca North. “To do that, we’ll collect data from a whole suite of lakes all the way from alpine lakes in the Rocky Mountains in Colorado and ice-covered lakes up in Vermont and New York State, down to lakes in Missouri and some in Florida. These are the endpoints in terms of what we can expect from a changing climate.”

Researchers will deploy several instruments in the lakes to collect data throughout the year, including during times when lakes are covered in ice. Wildlife cameras and remote sensing imagery will show when ice appears and disappears on the lakes.

“Ice duration and ice cover set the stage for all kinds of biological and ecological processes in lakes,” said Oleksy. “We’re seeing winter conditions—specifically ice cover duration—change very rapidly all over the world, including Colorado. But because we mostly take measurements from lakes in the summer, we have a pretty poor understanding of what this loss of winter means for ecosystem processes in lakes.”

Most of the data the researchers will collect is about lake productivity: broadly defined as a lake’s ability to support plant and animal life, or as how much carbon the lake is cycling. More is productivity is not necessarily better—just different. Different levels of productivity determine the types of insects, fish, and other creatures that can live in the lake. Algae is the foundation layer of productivity.

“Algae are the base of the lake food web,” said Oleksy. “Most organisms rely on algae. But if the species and abundance of algae changes, that changes what insects can thrive there. And that changes what fish can live there. The changes cascade up.”

“We want a more holistic understanding of what’s happening,” added Oleksy.

Oleksy’s field sites include lakes in Rocky Mountain National Park and in the Green Lakes Valley, near the city of �鶹ӰԺ. Her Colorado-based research team documented dramatic changes to productivity of Rocky Mountain lakes. They have found increases in the abundance of filamentous green algae—basically big mats of algae—on the margins of lakes, which is unusual for these lakes.

Mountain lakes are usually thought of as having low productivity, with few nutrients. “But we know now that Rocky Mountain lakes have become much more productive since the 1850s, with an accelerating trend in the last few decades,” said Oleksy. Researchers aren’t sure exactly what is driving the change. Increased temperatures? Nitrogen deposition? Less ice cover? All of the above? Oleksy wants to find what she describes as the “dominant lever.”

“I’m motivated because we’re seeing, in these cold regions of the world, fast rates of change. We’re losing lake ice cover in Colorado at twice the rates of other temperate lakes in the U.S. There’s so much we don’t know about the ecological impacts. Getting a full, year-round picture of ecosystem processes with give us a better idea of what’s coming.”

Joining Oleksy and North on the project are Ana Morales at the University of Vermont, Meredith Holgerson at Cornell University, and Dave Richardson at State University of New York at New Paltz. .