Following a watershed's winding path to sustainability

March 12, 2012 By Cheryl Dybas
A dot on a map of the United States, Cherokee Marsh in Wisconsin is central to the Yahara watershed. Credit: City of Madison, Wisconsin

Cherokee Marsh, it's called, this sunken enclave surrounded by cattails and bulrushes.  The marsh is a mere dot on a map of the state of Wisconsin, but its importance reaches far beyond the wetland's edge.

The Yahara River flows through Cherokee Marsh, swirling through coontail, sago pondweed, glade mallow and other plant species along the Yahara watershed as it goes.  Its next stop is the twins of Madison: Lakes Mendota and Monona.

The river and its watershed provide Madison with critical "ecosystem services" such as quality and flood protection, says Chris Kucharik, a scientist at the University of Wisconsin-Madision.

But the marsh, the twin lakes that lie downstream and the river that runs through them may be threatened by the effects of climate and land-use change.

The National Science Foundation (NSF) awarded Kucharik and colleagues a Water, and Climate (WSC) grant to study how ecosystem services may be sustained in a regional watershed such as the Yahara, and how the watershed is affected as climate, land cover, urban areas and human demands on the environment change.

"The Yahara watershed," says Kucharik, "is a perfect example of water-related issues in the Upper Midwest."

How is the Yahara faring? Lakes Mendota and Monona may be the eyes that are the windows to its soul.

Among the most urgent challenges facing the world today is how to ensure the adequate supply and quality of water, say scientists like Kucharik, especially in light of burgeoning human needs and climate variability and change.

Despite water's importance to life on Earth, major gaps exist in our understanding of water availability and quality, and of the effects of a changing climate and human activities on the planet's water system.

The Yahara River watershed extends through the city of Madison, Wis., and beyond. Credit: Blake Draper

NSF awarded 17 grants through the WSC program to better understand how Earth's water cycle works. NSF's Directorates for Geosciences; Biological Sciences; Social, Behavioral & Economic Sciences, and Engineering variously support WSC. The U.S. Department of Agriculture/National Institute of Food and Agriculture also currently support WSC.

The awards are for studies of the water system using observations at specific sites, in combination with models that allow for extrapolation to other regions and integration with different Earth processes.

"We need to determine how our 'built' water systems and our governance systems can be made more reliable, resilient and sustainable," says Tim Killeen, NSF assistant director for Geosciences.

"They must meet diverse and often conflicting needs," says Killeen, "such as consumption of water for energy generation, industrial and agricultural production, and other requirements."

Along with Kucharik, an agronomist and climatologist, scientists working on the NSF WSC Yahara watershed project are limnologist Steve Carpenter, ecohydrologist Steven Loheide, forest and wildlife ecologist Adena Rissman and landscape ecologist Monica Turner, all at the University of Wisconsin-Madison.

"Madison is a moderate-sized city that's growing quickly," says Kucharik. "It's one of the best examples of the issues surrounding urbanization. We have increasing water use due to a growing population; climate change happening, which is likely to foster extreme weather events; and it's in an agricultural watershed."

When you start putting all this together, Kucharik asks, what might it mean for the future of the Yahara watershed in terms of quality of life and the sustainability of the environment?

The Yahara watershed encompasses marshes and lakes, prairies and forests. Credit: Blake Draper

"With the interplay of agriculture, cities, industry and nature across the landscape, the contribution of direct-and-obvious, as well as indirect-and-subtle, interactions determines resilience to change," says Tom Torgersen, NSF lead program director for WSC. "This type of research is key to determining what needs to be done to ensure sustainability."

The Yahara watershed is largely agricultural--corn, soy and dairy products--but includes a densely populated urban area and remnant native vegetation. 

A mix of urban areas, croplands, forests, pastures, wetlands and prairie makes for a complex environment, especially when coupled with the region's water resources, says Kucharik.

Stresses on the ecosystem services of the Yahara watershed are typical of many agricultural landscapes.

Groundwater extraction, loss of wetlands, reduced water infiltration and increased runoff from impervious surfaces like roads alter the Yahara's hydrology and increase local and regional flood frequency.

Nitrates from agriculture contaminate groundwater, and phosphorus loads from non-point, diffuse runoff are greater than those prior to widespread farming.

Aerial view of a rural farm surrounded by cornfields in the Yahara watershed. Credit: Michael Forster Rothbart, UW-Madison

Use of pesticides and fertilizers contribute to increased "flashiness" of runoff from heavy rainfall during storms, as well as to water quality issues in the area's lakes.

"More than 35 years of data for these lakes, assembled by NSF's North Temperate Lakes Long-Term Ecological Research site, have allowed us to develop models of lake response to changes in hydrology and in nutrient inputs," says Carpenter.

Climate change is making its presence in the Yahara watershed known. Since 1950, the number of extremely cold days has declined. 

Many species of plants flower sooner in spring. "There's an early-season 'green-up' of some three to six days in the Madison area," says Kucharik.

In summer, water use by human residents of the watershed increases. The city acts as an urban heat island, making temperatures even higher.

"These factors all combine to challenge the sustainability of freshwater resources and other ecosystem services throughout the region," Kucharik says.

Initial findings by project scientists reveal that in 2011, dry conditions in mid-summer created potential water stresses for the Yahara watershed's natural and human systems. 

In the long-term, however, the region has experienced higher water tables and a rising trend in precipitation amounts.

"Historical water table elevations are being reconstructed using a high-resolution model," says Kucharik. "We're combining the results with a review of historical aerial photos of water features in the upper part of the watershed."

This rising water table may be causing low-oxygen root conditions in some farm fields.  Indices indicate a decrease in corn production, for example.

Project scientists monitor a network of 160 or more temperature-and-humidity sensors collecting continuous data across and beyond the urban landscape of Madison.

Combined with information from a mobile temperature-sensing unit, the results will provide a level of detail the researchers believe is unique in local climate and urban heat island studies.

"The results will advance our understanding of Earth's water resources," says Killeen, "and with it, our predictive capability not only for the availability of water, but for the future of life on our planet."

"We have the opportunity to change management practices while the Yahara watershed is still relatively healthy," says Kucharik. "Let's not wait until its mainstem river is only a trickle."

Or until the reeds of Cherokee Marsh have dried up, scattering the watershed's heart to the four winds.

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