Allerton Mansion Pond Makeover

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The next time you visit the U of I’s Robert Allerton Park near Monticello, make time to observe the changes that are taking place around the Mansion Pond.

In the years between its creation in 1903 and the summer of 2003, a hundred years later, the natural value of the pond and surrounding area had become degraded. The small wetland connected to the stream that flows into the pond was choked with daylilies, which are a nuisance in natural areas. The upland surrounding the stream inflow had become overgrown with other invasive plants, Japanese honeysuckle, garlic mustard, and multiflora rose. And the pond itself was choked with algae and muddied by the rooting of common carp, which also prevented the growth of beneficial aquatic vegetation. In addition, the roots of trees growing on top of the dam were creating fissures that allowed water to seep through.

Over the course of the 2003-2004 academic year, sixteen U of I students investigated the problems facing the pond, and then devised strategies for resolving them. Their goal was to establish a healthy ecosystem emphasizing plants and wildlife native to the area, with attention to aesthetic values as well. Thus began a multifaceted restoration project that has continued in the years since with the assistance of hardworking summer interns. Visitors to Allerton can already enjoy many of the changes to the pond and surrounding area.

The inflow stream and edges of the pond are now graced by the growth of native plants, including cardinal flower, swamp milkweed, common arrowhead, and wild blue iris. The understory of the wooded upland has been opened up by the removal of invasive plants, which have been replaced by native wildflowers. Wildflowers have also replaced the trees that were removed from the top of the dam, which was reinforced and altered to better handle overflows.

With help from the Illinois Department of Natural Resources, the pond itself has been restocked—not with a typical mix of bass and bluegill, but rather some of the now rare nongame species native to the Sangamon River basin. At present, these include the ironcolor shiner and the lake chubsucker, neither of which you are likely to see since they shy away from the top of the pond. You should be able to observe the pond’s other new resident fish, the state-threatened starhead topminnow. It’s a two to three inch fish that is easy to see because it hangs out near the surface of the water, and easy to identify because it sports two very light spots, one on the top of its head and another on its back.

As the aquatic vegetation of the pond expands to provide cover for smaller fish, plans call for the introduction of native predator species, perhaps smallmouth bass and grass pickerel.

In the current absence of predatory fish, the amphibians that use the Allerton Mansion Pond are enjoying a population boom. You can see and hear bullfrogs and cricket frogs throughout the day, but the pond is also a breeding hotspot for grey treefrogs, chorus frogs, leopard frogs and two species of toads.

From a visitor’s perspective, perhaps the coolest aspect of the Allerton pond restoration project is the boardwalk just now under construction. When it’s finished, everyone will be able to enjoy an up-close view of this renewed ecosystem.