March 20, 2015

Wisconsin lakes need stronger management to tolerate climate change

“We in Wisconsin can do a lot to build our resilience to climate change,” says Stephen Carpenter, director of UW-Madison’s Center for Limnology and a principal investigator on the Water Sustainability and Climate project.

Carpenter is part of an international research team that just published a paper in the journal Science, which warns better management is necessary if we want wetlands, forests and other valued ecosystems to survive climate change.

Many of the world’s ecosystems are under a double whammy of threats: global climate change and local pressures, varying 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.

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 in a brief interview how their study is relevant to Wisconsin.

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.

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.

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.

Read the full press release for the study here; view an open-access reprint of the study here.