The wetland disturbance index: Links with soil and water nitrate concentrations

Human activities have increased deleterious nitrogen inputs to terrestrial and aquatic ecosystems. The lessening of nitrogen inputs to streams can be achieved through the protection and restoration of riparian zones, including headwater wetlands. However, although headwater streams and their associated habitats account for the majority of the drainage area of rivers in Pennsylvania (U.S.A.), it is unknown how nitrogen cycling rates vary in headwater wetlands that differ in anthropogenic disturbance level. Thirteen forested headwater wetland sites within the Upper Juniata watershed, a major drainage basin of the Susquehanna-Chesapeake watershed, were selected based on a previously described, rapid assessment/disturbance index. The objective of this study was to determine whether relative soil nitrogen availability was correlated with a disturbance gradient created from the rapid assessment/disturbance index. Soil nitrogen at each site was collected with free ion exchange resin bags and analyzed for ammonium and nitrate. Results indicated that the disturbance index was predictive of relative soil nitrate availability (R2=0.69, p<0.05). We conclude that the disturbance index is an effective, rapid assessment tool that could be used by managers to locate headwater wetlands with potentially high soil nitrate availability.