The Impact of Urban Land Use on Aquatic Diversity

photo of a student surveying a pond

Catherine Lewis sampling a pond. Photo: Erin Crone

Equipped with waders and nets, members of professor Dan Preston’s UW–Madison aquatic ecology lab set out this summer to learn what is living in and around 101 ponds throughout Dane County. The lab group sampled both natural and artificial ponds in diverse sites such as parks and green spaces, neighborhoods, agricultural fields, and golf courses.

Several Arboretum sites, including Teal Pond, Curtis Pond, and Wingra Springs, were sampled to understand their water chemistry and amphibian, fish, invertebrate, and zooplankton communities. The group sampled frogs, toads, and salamanders via visual and auditory observations and sampled amphibian larvae using a dip net and seine. Different species of amphibians breed at different times of year, so each site was sampled twice during the summer to ensure a more comprehensive representation of amphibian life.

Sampling in highly urbanized Dane County gave the lab group the opportunity to study effects of urban land use and pollutants on aquatic diversity. While data is still being processed, preliminary analysis by postdoctoral researcher Erin Sauer suggests that higher levels of urbanization may have a detrimental impact on amphibian communities in the sample ponds.

Threats in the sample sites include pollution from garbage and road runoff; destruction of riparian buffers (the vegetated areas around a pond’s edge); algae blooms and decreased oxygen levels exacerbated by fertilizer runoff; erosion; and invasive species. Among the freshwater invaders were common aquarium pets such as goldfish and Chinese mystery snails. Junior Catherine Lewis spearheaded a project examining the impacts of these golf-ball sized snails on the aquatic invertebrate communities that share the same ponds.

Photo: Erin Crone

However, this is not to say that urban areas necessarily provide poor habitat. For example, in certain artificial golf course ponds, the group discovered a surprising diversity of animals such as tiger salamander larvae, a variety of adult and tadpole frogs, and several species of fish and turtles such as sunfish, bullhead catfish, and a very large softshell turtle.

Large snapping turtle
Blake Cwynar holds a large snapping turtle. Photo: Ethan Plumier

The ponds dotting the Arboretum also support an abundance of species. Adult green frogs and American toads were commonly observed, as well as green frog, toad, and tree frog tadpoles. Frogs and small fish like stickleback predominately inhabited ponds like those within Curtis Prairie, Teal Pond, and Wingra Springs. At locations such as the stormwater pond near Manitou Way, the group found communities of larger fish like sunfish but no sign of larval amphibians. Painted and snapping turtles were also seen in Arboretum ponds. To supplement the pond amphibian and reptile sampling, seniors Ethan Plumier and Blake Cwynar conducted live trapping using coverboards, pitfall traps, and turtle traps in several Arboretum locations. These surveys added common garter, red-bellied, and Dekay’s brown snakes to the group’s list of Arboretum reptile sightings.

While summer pond surveys are complete, lab members are staying busy identifying aquatic macroinvertebrate and zooplankton samples and analyzing relationships within the dataset. So far, findings suggest that ponds within the Arboretum and throughout Dane County may provide critical habitat for amphibians, fish, and countless other species. Ongoing goals for this project are to portray the biodiversity within these understudied urban habitats, study relationships between various organisms in pond communities, and better understand human impacts on these systems to promote effective urban freshwater management. Studying urban aquatic ecosystems, as well as valuing and protecting them, is essential to the continued persistence of species living in areas of ever-expanding human influence.

—Erin Crone, master’s student in forest and wildlife ecology, UW–Madison, and Arboretum Research Fellow