Coldwater Spring's cool wetland

It looks like just a shallow pond, but there’s a story behind and beneath Coldwater Spring’s north wetland.

Often overlooked, overshadowed by the iconic springhouse and burbling creek, the north wetland sits modestly by the park’s northern edge, tucked between the oak grove and prairie, guarded by a towering cottonwood.

Where the wetland sits now, once a building stood. Bureau of Mines Building 9 was the agency’s library, a resource of papers and information. Former BOM staffers say it was a library with soggy basement. So why did the Bureau build there? Well, they didn’t. The agency didn’t have money to build, so instead, they hauled an building from the Iron Range and set it downclose to the sprawling headquarters building where most Bureau staffers worked.

When the National Park Service began restoring the park, step one was demolishing of all twelve Bureau of Mines buildings, including the soggy library. Construction crews began tearing down the library in late December 2011, but the basement was still sodden. Crews began pumping out the water, but within days, water had seeped back.

The Park Service realized the library was sitting atop a natural wetland. When they tested the water, the wetland’s northwest corner seemed to be a rare kind of wetland -- a calcareous fen. Minnesota is one of just ten states with calcareous fens, which require very particular conditions — the right mix of non-acidic soil, lots of cold groundwater with calcium and magnesium but not much oxygen. Neither Hennepin nor Ramsey County had any such fens. These finicky fens sometimes feature uncommon plants like brook lobelia, shrubby cinquefoil and fringed gentian.

The Park Service wants to nurture the potential fen. To avoid altering the wetland’s acidic balance, they didn’t remove the library’s foundation. They set limestone steps in the northwest corner by the fen and across the wetland by the massive cottonwood.  The steps make it easy for visitors to see and touch the wetland’s waters. School kids can do simple experiments to test the water.

There’s no guarantee that the north wetland will support a calcareous fen, but it’s possible. What’s certain is that where an old building once stood is now home to a wetland, fringed with grasses and native plants. A wetland where whitetail deer browse and drink, where woodchucks scurry into a nearby hole, where an eagle sometimes perches on the cottonwood’s tall branches. It’s one of eight wetlands at Coldwater, all made by natural groundwater seeps.
It looks like just a shallow pond, but there’s a story behind and beneath Coldwater Spring’s north wetland.