Road salt affects mitigation wetlands

Sacrificing one wetland for the sake of five others may be the way to go when planning constructed wetlands to replace those destroyed during road building, but a Penn State Erie biologist is monitoring the salinity of the wetlands to see how the salt affects animals and insects.

"I am currently doing research in wetlands that the Pennsylvania Department of Transportation constructed as mitigation wetlands to replace all the ones that were destroyed by the new road," says Dr. Pamela Silver, professor of biology, Penn State Erie, the Behrend College.

In November 2003, PennDOT completed a four-lane highway connecting Interstate 90 with the Erie waterfront. A portion of the road crossed the Penn State Erie campus. PennDOT asked researchers if they wanted to use the road building as an opportunity to do research.

"PennDOT has really gone out of their way to consider the environmental impact of what they have done," says Silver. "They have been extremely good about talking to the college to minimize the effects of having a road across campus and have gone out of their way to be as environmentally responsible as possible."

When building the section of road across the Behrend campus, PennDOT installed an elaborate drainage system beneath the road to collect all the runoff. The water goes to only one of the six constructed wetlands and eventually runs downhill through woodlands.

Silver is monitoring two PennDOT-installed data loggers to measure the amounts of salt that enter the designated runoff wetland and one other that is slightly affected by splashover from salt spreading and snow melting. The data loggers record salinity hourly.

"Salt levels in the runoff wetland reach peaks that are half as salty as sea water," Silver told attendees at the North American Benthological Meeting today (May 24) at the 2005 Joint Assembly in New Orleans. "We recorded peaks during the winter as high as 10 to 12 parts per thousand in the runoff wetland and 2.5 to 3 parts per thousand in the other affected wetland." Freshwater has zero salinity, while seawater has a salinity of about 28 parts per thousand.

Silver has also tested all six wetlands for salinity and looked in bottom sediment for non-biting midge populations because midges are good indicators of stress.

"Last year all the wetlands went back to zero salinity in mid spring," says Silver. "We are not sure if this will continue as we do not know if the baseline will creep up from salt deposited in the sediment."

She does not know if the salt levels will again fall back to zero in mid spring this year as Erie had its last snowfall on May 2 and had a three-foot snowfall in late April.

"PennDOT is between a rock and a hard place," says Silver. "Everyone knows that the salt is not good for the environment, but salting roads is a huge safety issue in a part of the country that gets 10 to 12 feet of snow every winter."

Silver's research does show a large decrease in non-biting midges in the designated runoff wetland. The effect on other species is not yet known. There was no decrease in midges from the slightly salty wetland. In general, freshwater organisms are not very salt tolerant. The Penn State researcher has students poised to look at the numbers and species of algae, amphibians, insects and bacteria in the salty and freshwater wetlands.

"We would like to know how big a hit these two wetlands are going to take from the salt. We see an effect on the midges in the runoff receiving wetland, but so far there is no effect on the slightly salty one," says Silver. "One thing we would like to see is what happens to bullfrog tadpoles and dragonflies that overwinter in the sediment mud."

The researcher would also like to sample the soil where the runoff eventually leaves the wetland to see if salt is building up there.

Source : Penn State