PERIGLACIAL LEGACY OF VERNAL POOLS IN THE RIDGE AND VALLEY PROVINCE OF CENTRAL PENNSYLVANIA

Wetland depressions are elliptical shaped basins that are typically isolated from other bodies of water. They are often filled only in the spring and early summer, thus may be called vernal pools. We recognize the presence of wetland depressions in predictable landscape positions in the Ridge and Valley physiographic province in central Pennsylvania: in headwater saddles on shale nestled between adjacent sandstone ridges. The wetlands are distinct and unique features of the central Pennsylvania landscape that most often are not recognized in the National Wetland Inventory. These types of pools are important breeding habitats for a broad range of flora and fauna and their headwater position emphasizes the need for protection to maintain water quality at downstream locations. However, the lack of recognition presents a challenge to land managers and any effort to conserve these important habitats.

In this project more than 150 shale saddles (potential depression hosts) have been identified through a swath of central Pennsylvania, 94 of which have been visited to confirm the presence or absence of wetlands. Here we present the results of the (ongoing) field surveys, evaluation of remotely sensed imagery and topographic maps, and intensive studies at two centrally located sites that include: standard field soil descriptions, geochemical analyses of the soil columns and cores, and ground penetrating radar surveys. A common characteristic of the depressions is the total absence of boulders or cobbles at the land surface which otherwise mantle the surrounding landscape. These efforts and results have led to the development of a conceptual model for the formation of the wetland depressions as pingo scars that developed during and after the Last Glacial Maximum. The conceptual model may provide a tool for predicting the location of these important features in otherwise obscure landscape positions.