Spatial variability of the soil microhabitat in disturbed and undisturbed headwater wetlands of Pennsylvania

Since the 18th century US wetlands have been altered due to their position in a matrix of anthropogenic land changes. Although we know that land change affects wetlands through hydrologic modification, accelerated sedimentation, and shifts in vegetative community composition, less is understood, about the critical levels beyond which these stressors alter soil microhabitat parameters and their associated wetland ecosystem processes. Natural wetlands tend to exhibit high levels of soil microhabitat spatial variability; however, we suspect that stressors reduce the soil microhabitat variability at spatial scales within a wetland, leading to net changes in the nutrient source-sink dynamics of the wetland as a whole. An ongoing study aims to characterize differences in the soil microhabitat of eight headwater wetlands across an anthropogenic disturbance gradient. Forty-five, 1-m² sampling blocks, ranging in distance from 1 to 40 m apart are being assessed for soil moisture, soil texture, extractable soil organic carbon, nitrate and ammonium. To accommodate the large number of assays, we developed a high-throughput infrared spectroscopic technique for assessing organic matter in methanolic extracts. Preliminary soil-moisture and organic-horizon depth data support our hypothesis; using spatial statistics these parameters are significantly more variable in wetlands that have received low levels of disturbance than in wetlands that have been highly disturbed. We will relate the spatial differences found in soil microhabitat parameters to differences in the vegetation and microtopography, two wetland traits that can be managed. This characterization study should help guide efforts to restore and maintain functions of the remaining US headwater wetlands.