A raindrop falls from the warm, spring air and hits the hard concrete of a street with a thud. It is met by other raindrops, all of which are rapidly headed downstream. They flush the streets, mixing with months of salt and sand, forming a slurry of dirty water.

Beige and grey homes checker the landscape. Oaks, elms, and ginkgos alternate in a row overhead. The trees cast long shadows over the curb.

With a steep drop, darkness surrounds the slurry. Now restricted in a tunnel, the slurry hastily continues below the City of Fitchburg. It is dumped into Swan Creek and winds past fields of agricultural land until…

Light.

Billows of sunlight peer through trees overhead. Songbirds chirp, and a broad expanse of dark soil and plants lie ahead.

Welcome to the Waubesa Wetlands.

Wetlands are nature’s water treatment facility. The incoming slurry slows and disperses into the warm vegetation. Some of the slurry is filtered through the soil to become groundwater. Some is used by the plants and released into the air as water vapor. Some continues downstream to adjacent waterbodies. Yet, all of the water comes out cleaner than it arrived. This purification is one of the important services provided by a wetland.

Wetlands provide natural infrastructure for people by protecting water quality and by reducing floods. But these ecosystem services often go unnoticed.

Nick Miller, science director for The Nature Conservancy in Wisconsin, says “there’s a growing body of research that wetlands provide ecosystem services, and they do this to a greater degree than other resources.”

But, “not all wetlands provide the same services to the same extent,” says Miller. Soil type, vegetation, and water all play a role. The location of the wetland and how land is used upstream are very important.

A wetland surrounded by pristine forest absorbs water from its surrounding area, acting as a sponge. It stores water for times of drought and provides a clean source of drinking water for plants, animals, and people downstream.

Now compare this to the Waubesa Wetlands, downstream of the City of Fitchburg. The Waubesa Wetlands convert an incoming slurry into clean water, acting more like a filter than a sponge. Clean water is slowly released into its neighbor, Lake Waubesa.

Whether a wetland is a filter or a sponge depends upon its location within its watershed, or area of land that drains to a common stream or lake. As Miller states, “the position of the wetland within its watershed affects how and whether it provides various services. The land use context and the condition of the surrounding watershed affect each wetland’s functional performance.”

So that’s why Miller co-developed Wetlands by Design, a free, web-based decision support tool. The tool shows specific opportunities for wetland restoration and protection in Wisconsin by comparing the quality of a wetland relative to other wetlands within its watershed.

Wetlands by Design can be used in two directions. “People and groups interested in wetland services may choose to work in a watershed with the greatest losses and therefore the greatest need. Or they may choose to work where there’s the least amount of loss, adding value to that watershed,” says Miller.

Wetlands by Design highlights the best wetlands that accomplish a particular goal, such as the wetlands that filter the most slurry water. Released in December, 2017, the tool is already being used by graduate students at the University of Wisconsin – Madison in the Waubesa Wetlands watershed. With Wetlands by Design and other computer tools, the graduate students will determine whether services provided by the Waubesa Wetlands will be lost as the upland City of Fitchburg expands.

“It’s not a prescriptive tool; instead, it provides information to assist in decision-making and a way to tell the story,” says Miller.

That story is always adapting, and for the Waubesa Wetlands, the plot is still being written.

After a winding journey, the incoming slurry is greeted by warm wetland vegetation. The wetland says its welcoming remarks. “Welcome to the Waubesa Wetlands, named one of the highest quality wetlands in the state,” the wetland chimes. “As a border patrol, we make sure only clean water enters Lake Waubesa. Get ready to be filtered.”