Creating safe operating spaces for Wisconsin’s lakes could curb climate change impacts


A sign warns swimmers of the presence of toxic algae in Lake Mendota in Madison, WI, near the UW-Madison campus

On July 16, 2012, one of several signs posted along Lake Mendota near the Memorial Union Terrace at the University of Wisconsin-Madison warn against swimming during the presence of toxic blue-green algae in the water. Known as cyanobacteria, the algae are photosynthetic bacteria that live in colonies, typically in lakes with excess fertility//Photo by Jeff Miller/UW-Madison)

“We in Wisconsin can do a lot to build our resilience to climate change,” Stephen Carpenter, director of UW-Madison Center for Limnology (CFL) and a principal researcher on the Water Sustainability and Climate (WSC) project, recently told Jenny Seifert, science writer for CFL and outreach coordinator for WSC.

The two got together to discuss a paper Carpenter and a team of researchers across the globe published today in the journal Science, warning that better local management is necessary if we want wetlands, forests and other valued ecosystems to survive climate change.

Seifert writes about it here today, and at WSC’s insightful blog, Yahara in situ:


Many of the world’s ecosystems are under a double whammy of threats: global climate change and local pressures. These vary from deforestation to fertilizer pollution. Carpenter and his colleagues point out that we can help these natural places cope better with climate change if we do a good job of controlling local pressures.

Steve Carpenter in Lake Mendota near the UW-Madison campus shoreline on July 29, 2009. No stranger to being wet, Carpenter says, "What interests limnologists most in research is often found under the surface of the water."// Photo by Jeff Miller, UW-Madison

Steve Carpenter in Lake Mendota near the UW-Madison campus shoreline on July 29, 2009. No stranger to being wet, Carpenter says, “What interests limnologists most in research is often found under the surface of the water.”// Photo by Jeff Miller, UW-Madison

For example, numerous lakes in Wisconsin suffer from phosphorus pollution, which runs off agricultural and urban land and can cause toxic algal blooms. If climate change makes lake water warmer, algae can become more reactive to phosphorus, meaning lower concentrations of phosphorus in a lake could cause a bloom. Reducing phosphorus runoff will thus make our lakes less susceptible to toxic algal blooms and more resilient to climate change.

While the study highlighted three UNESCO World Heritage Sites—places of global importance for biodiversity such as the Amazon rainforest and Great Barrier Reef—its findings could be applied to any cherished ecosystem, especially Wisconsin’s beloved lakes.

Carpenter explains further how the study is relevant to Wisconsin.

JS: You and your co-authors talk about a “safe operating space” for ecosystems. What does this mean, and how can we think about this in a Wisconsin context?

SC: A safe operating space is like a curb on a busy street. It is smart to stay out of the street. Walking into the street is dangerous and maybe not very smart.

Wisconsin’s safe operating space for floods, droughts, diseases, algal blooms and other risks depends on things we control, such as land use, and things like the climate, which depend on global behavior. The curb will move as climate moves. We can adjust our local practices to reduce risk to our land, water, livestock and other natural resources as the climate changes.

JS: How are climate change and local pressures threatening the resilience of Wisconsin’s “iconic” ecosystems—specifically, the lakes?

SC: A main concern is how climate change will affect our lakes’ vulnerability to algal blooms. For algal blooms, there is a transition between a state of steady, low biomass [or the amount of algae] and an unstable state—meaning, highly fluctuating biomass that can grow quite large at the peaks. This transition from low and steady to unstable is considered a “tipping point” for blooms, and passing this threshold can make the blooms dangerous to people and animals who swim in the affected lake.

The tipping point for toxic algal blooms occurs at lower phosphorus levels as lake water gets warmer. Therefore, as warming occurs, we have to decrease phosphorus to a greater extent to remain below the tipping point and lessen the potential health risk.

JS: What local measures currently exist that could help to improve our lakes’ ability to tolerate climate change, and how could we be doing better?

SC: We can greatly decrease the use of phosphorus fertilizer in agriculture. We can process manure to remove phosphorus instead of spreading it on fields. We can use cover crops to prevent erosion when crop plants are not present. We can increase the area of natural vegetation that absorbs pollution and flood water.


If you want to read more about the study, hop over here.