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The Yahara River
May 10, 2019

Looking below the surface for landscape resilience

Written By: Tom Ziemer

Climate and land use wield profound influence on the utility of an ecosystem. But there’s also an unseen—and largely overlooked—factor that can shape environmental benefits such as crop yield, soil retention and water quality.

In a recently published paper in the journal Nature Sustainability, a University of Wisconsin-Madison team featuring Professor of Civil and Environmental Engineering Steven Loheide and PhD graduate Sam Zipper demonstrated the impact of groundwater on a range of “ecosystem services,” an umbrella term that encompasses all the benefits humans derive from the environment.

The upshot? Groundwater matters, particularly for creating more resilient landscapes in the face of changes in climate, land use and population density. The study shows that strategic groundwater management could potentially buffer the effects of climate change, and Loheide adds that efforts to model changes to ecosystem services should start factoring in the influence of groundwater.

“When people think about how we manage the landscape, they think about what the surface of the land looks like,” says Zipper, who shared first authorship on the paper and earned his PhD in freshwater and marine sciences under Loheide in 2015. “And I think the key message of our paper is that if you’re going to be doing that management in an effective way, you have to look into the subsurface as well. Things that are happening below ground that are hard to see, that are pretty much invisible, can have a very large effect on the things that we as society care about.”

The researchers used biophysical modeling to quantify the effects of groundwater on ecosystem services throughout the Yahara Watershed, which includes Madison. The group focused on eight ecosystem services they identified as particularly relevant to the region: crop production, grass production, freshwater supply, groundwater quality, surface-water quality, flood regulation, climate regulation and soil retention.

“It’s our backyard,” says Loheide, who leads the Hydroecology Lab at UW-Madison. “It’s a watershed that we’re very familiar with, and we used that as an exemplar of urbanizing watersheds in the Upper Midwest.”

The researchers found the influence of groundwater varied significantly across the watershed, depending on land cover, soil type and, most importantly, water table depth. The latter refers to the point at which the subsurface is saturated, where groundwater lurks.

For areas with a water table depth of roughly 8 feet or less, the group discovered that small changes in groundwater depth rendered disproportionately large effects on those ecosystem services. While measures of some services exponentially increased or decreased as groundwater crept closer to the surface, others like crop yield and carbon storage shot up and then dropped.

Climate conditions—wet, dry or average—also heavily influenced the ecosystem services.

In other words, there’s no one-size-fits-all solution for land managers or other decision makers, who need to consider the characteristics of their land and then prioritize specific ecosystem services.

“The tricky part is that conditions that can be good for some ecosystem services are bad for others,” says Zipper. “You have to balance those tradeoffs.”

Zipper is a postdoctoral fellow at the University of Victoria and McGill University in Canada and will join the Kansas Geological Survey as a research scientist in August 2019. He shared first authorship of the paper with Jiangxiao Qiu, who received his PhD in zoology from UW-Madison and is now an assistant professor of landscape ecology at the University of Florida. Other collaborators included Melissa Motew, a graduate research assistant in the Nelson Institute for Environmental Studies at UW-Madison; Eric Booth, an assistant research scientist in the Department of Agronomy at UW-Madison; and Christopher Kucharik, a professor of agronomy and environmental studies at UW-Madison.

The study was part of the National Science Foundation-funded Water Sustainability and Climate Project at UW-Madison, which focused on safeguarding the future of the Yahara Watershed.