THE EFFECTS OF ATMOSPHERIC POLLUTANTS AND HYDROLOGY ON THE DEGRADATION OF PANNE VEGETATION BY INVASIVE SPECIES

Pannes, intradunal ponds kept wet by the water table or springs, exhibit diverse and extremely sensitive vegetation. These ecosystems are frequently threatened by encroaching anthropogenic activities; an excellent example being within the Indiana Dunes National Lakeshore (IDNL), where they have been placed on the second tier of conservation targets for recovery by the Chicago Wilderness Biodiversity recovery plan. They are home to plant species found nowhere else in Indiana. The pannes at the IDNL have been exposed to atmospheric pollutants emanating from the surrounding steel and energy production facilities over the last century. Since 1986, the native vegetation of this area is slowly disappearing and is being replaced by invasive species like Phragmites australis and Typha spp. The cause of the degradation of the native vegetation is subject to some debate, perhaps the result of the accumulation of nitrogen and heavy metals from upwind utility and steel production or fluctuations in the levels of Lake Michigan (tied to the hydrology of these proximal panne ecosystems).

To test these hypotheses, we took surface sediment samples from four of the 12 pannes at the IDNL, and analyzed these samples for nutrient and metal contents using standard geochemistry coupled with sequential extraction analyses (to characterize nutrient geochemistry). Two pannes at Sleeping Bear Dunes and two at Warren Dunes were also examined and are being used as control sites as they are situated far from the atmospheric pollutant sources near Chicago. A number of metals (Cd, Cr, Cu, Mn, Ni, Pb, Zn, Ba, Fe) and several biologically-relevant elements (P, S, C, N) are being determined at these sites. Results show that the zones in which the invasive species exist show a higher concentration of metal deposition as compared to other zones with native vegetation. Coupled with this geochemical approach are complementary ecological studies of panne vegetation, as well as analyses of hydrologic levels within the pannes and past projections of panne water table levels. The results provided by this study could assist in the development of guidelines relating to the management of the plant species that are being exposed to these high levels of atmospheric pollutants from the surrounding industries.