SUBSURFACE GEOLOGIC CONTROLS ON ISOLATED WETLANDS IN THE PINELANDS OF NEW JERSEY

Isolated wetlands are present within persistent canopy openings throughout pitch pine forests of the New Jersey Pinelands in the range of tens-to-hundreds of meters in size. Some of these wetlands are vernal ponds that support sensitive amphibian species while others are perennially saturated with modest accumulations of peat. In an effort to understand the mechanism for the formation and maintenance of these wetlands, variations in the subsurface geology were studied using ground penetrating radar and electrical resistivity tomography. Geophysical transects were completed around three canopy gaps from 20 m – 200 m in diameter to investigate patterns suggestive of a common mode of formation. The ground penetrating radar achieved deep penetration signal penetration (up to 30 meters below the surface), high vertical resolution for pinpointing the locations of interfaces (better than 0.25 meters) and the ability to identify for changes in the velocity of the signal using common mid-point collection methods. The electrical resistivity surveys were effective at identifying areas of high conductivity noted as signal attenuation in the ground penetrating radar data. These near-surface geophysical data, along with direct sampling, were used to identify stratigraphic interfaces and variations in sediment texture in the subsurface below the canopy gaps. The dipping reflectors and areas of high signal attenuation noted in the ground penetrating radar and resistivity data may indicate variable groundwater chemistry or lithology. Evidence suggests that these geologic variations may influence infiltration, drainage and hydroperiod effectively acting as subsurface controls on the surface vegetation communities in the isolated wetlands.