Ecology in the urban world

Stormwaters sweeping nutrient-laden runoff into lakes and streams. Trucks peppering streets with chunks of salt. Native trees dying.

At the University of Minnesota, these and other facets of city life drive a new breed of urban ecologists committed to making cities more livable, with the Twin Cities their focus of study. While human and environmental health concerns are primary, increased livability also brings tangible outcomes.

“There are clear economic benefits to unpolluted, functioning nature, including recreational and other health benefits," says Sarah Hobbie, an ecology professor in the University’s College of Biological Sciences. 

Since 2021, Hobbie and fellow ecology professor Emilie Snell-Rood have headed a team of more than 100 researchers and educators — including partners from the USDA Forest Service and the University of St. Thomas — in a National Science Foundation-funded study of urban ecology in the seven-county Twin Cities Metro Area. It is one of only two NSF-funded urban Long Term Ecological Research programs in the nation. 

Called the Minneapolis-St. Paul Metropolitan Area Long Term Ecological Research Program (MSP LTER), it is part of an extensive national network of research at “LTER sites” around the nation and the second long term ecological research program at the University. The first, at the University’s Cedar Creek Ecosystem Science Reserve in East Bethel, Minnesota, has been active since 1982. 

Tapping the talents of researchers from all walks of academia, public agencies, and communities, the MSP LTER contributes “science and knowledge for management of urban nature, and better understanding of how disparities in access to urban nature benefits came about,” Hobbie says. 

State and local agencies that collaborate with researchers include the Department of Natural Resources, the Metropolitan Council, counties, park districts, cities, and watershed management entities. Also, MSP LTER researchers work with local nonprofits like Urban Roots, which connects youth on St. Paul’s East Side to nature, healthy food and their community. 

Here is a glimpse of some MSP LTER projects.

Will trees bend to climate change?

An MSP LTER experiment in St. Paul’s Crosby Regional Park addresses the question of what tree species should be planted to preserve urban forests as the climate warms. Already, the park has been affected by the emerald ash borer beetle, and trees are dying.

“The trees aren’t regenerating. Their seedlings can’t compete with the understory growth,” says Hobbie, who works on the project with Rebecca Montgomery and Marcella Windmuller-Campione, both professors of forest resources in the College of Food, Agricultural and Natural Resource Sciences.

The experiment asks which would be better for this urban forest’s health: 1) keep the forest as is; or 2) plant slightly different genetic varieties of the current trees, plus species from more southern areas — such as southern pine and oak — which ought to better resist warming. 

So far, the southern species aren’t doing as well as the natives. 

“It seems to be more about locally adapted species doing the best,” Hobbie says. But this is a long-term experiment, so things could change.

The experimental area also features interpretive signs with artwork by Indigenous artist Willard Malebear, Jr., each showing a tree representing either resistance, resilience, or transition in response to environmental pressure. 

"The aim is to get park visitors thinking about climate change and how we might manage forests in the face of ash borer and other challenges," Hobbie says.

Easing the heavy burden of lead

Back when gasoline and paint were leaded, this heavy metal found its way into soil, especially near roads, and houses that used lead paint. 

"But lead is toxic, and while rates of lead poisoning in humans and urban wildlife have been in a steady decline, it can still be a health concern," Snell-Rood cautions. 

“Older parts of town have the biggest problem,” says ecology professor Jacques Finlay. “The cities can use data to identify areas of lead mobility for targeted testing and focused attention where there could be issues associated with lead poisoning.”

Work by Finlay’s and Snell-Rood’s teams has revealed the hidden life of lead. For example, lead from soil in high-lead areas moves into runoff to rain gardens, ponds, lakes, and streams. And pollinators in areas with high lead levels in soil or air have elevated lead in their bodies. 

“Lead ‘hitches a ride’ on small particles,” Finlay says. “Some good news is that it seems to get trapped in stormwater ponds.”  

These ponds are constructed or adapted from natural wetlands. A study led by postdoctoral researcher Lea Pollack, with other MSP LTER researchers, gathered data from 38 of the thousands in the Twin Cities. 

“They range from the size of my office to what we’d call a small lake,” Finlay says. The researchers have also been studying green spaces that have been planted for pollinators. Areas that have been urbanized the longest tend to have the highest soil lead levels. But, says Snell-Rood, its effects can be reduced by adding organic matter to the soil and planting vegetation to reduce erosion. 

Work by Snell-Rood and colleagues also shows that pollinators are generally tolerant to lead levels in the Twin Cities, although certain hotspots of pollution may stress caterpillars, resulting in smaller adults. In addition, “butterfly species with larger geographic ranges tolerated significantly greater concentrations of lead, arsenic, and cadmium in their tissues,” she notes. 

Also, in studying hair and skin samples from museum specimens of local mammals dating back to 1910, she and her colleagues found a steady decrease in levels of lead and other heavy metals after a peak in the first two decades.

“This may be initially from decreased coal burning and later from banning leaded gasoline and paint in the 1970s,” she says. "This is good news – our efforts to reduce pollution are working, and you can see it in the animals that live alongside us." 

Too much of a good thing: nutrient and salt pollution

Trees offer many benefits, but those adjacent to streets shed leaves packed with nutrients nitrogen and phosphorus onto roadways, where runoff can carry them into lakes and streams.  

“Too much nitrogen or phosphorus can cause blooms of harmful algae, oxygen loss, and diminished biodiversity," says Finlay.

Runoff also carries road salt into lakes, where it can interfere with the phenomenon of turnover, in which strong spring and autumn winds mix a lake from top to bottom. This aerates the whole water column, allowing sufficient oxygen to reach fish, especially species that need the colder water in the deep layers. 

One victim of turnover loss is Brownie Lake, the northernmost of Minneapolis’s Chain of Lakes. The main culprit: road salt from nearby Highway I-394. 

Working with the Minnesota Pollution Control Agency, Finlay and Hobbie found that efforts to increase the canopy of trees must be balanced with work to manage nutrient pollution, such as street sweeping. 

Such efforts can help cities meet stormwater regulations.

“Cities above a certain size are required to take steps to minimize their stormwater impacts,” Finlay says. “This is mandated by the Environmental Protection Agency, and efforts are administered by states.” 

 A blast (at racism) from the past

As part of the University’s Mapping Prejudice Project, MSP LTER researchers studied where real estate developers imposed racial covenants to keep Twin Cities neighborhoods white-only. This happened as the cities and park systems were developing. 

The researchers found large disparities in access to urban nature across the Metro Area (see similar research for more on this). Residents of color were kept out of neighborhoods with amenities like parks and trees. This project has spurred numerous efforts to identify and root out racial covenants across Minnesota.

As they share their data from these and other projects, the University’s MSP LTER researchers enable public officials at all levels to gain the tools they need to fulfill their responsibilities as environmental stewards — to everyone’s benefit.  

Make a gift to support clean water research through the Driven to Discover Preserving Lakes and Rivers Fund