MODERN RATES OF EROSION AND GEOLOGIC RECORD OF STORMS AND HURRICANE LANDFALLS ALONG THE NORTHERN SHORE OF THE DELAWARE ESTUARY

Analysis of aerial photos from 1930 to 2007 and recent lidar data document that the northern shoreline of the Delaware Bay is retreating at the average rate of ~2 m/yr. The fast eroding features along the shore are headlands while the lowest rates of erosion of 0.2 m/yr were documented within the embayments.

The stratigraphic record of salt marsh sediments reconstructed along 2 km long stretch of the shore revealed a geologic record of coastal erosion and recovery that might be related to historical and pre-historical storms and hurricanes landfalls. Stratigraphic cross-sections document the presence of 7 mineroclastic units deposited within salt-marsh peat sequence. Grain-size analysis, plant macrofossils and foraminifera assemblages preserved in sediments were used to reconstruct paleoenvironmental changes along the shoreline while radiocarbon dates of salt marsh plants provided a chronological record of these changes. Mineroclastic units of consistent thicknesses were deposited above abrupt contacts and suggest that eroded marsh deposits were replaced by a regressive sequence of tidal mud, low marsh peat and high marsh peat. Radiocarbon dates of Sp. Alterniflora rooted into tidal mud deposits provided the chronological framework of salt marsh recovery after erosion. Some of the marsh recovery sequences correlate well with late Holocene overwash fans deposited along the Atlantic coast of New Jersey (Donnelly et al. 2001, 2004). During the last century the mid-estuarine shoreline was impacted by environmental changes at least twice. Both events resulted in changes of sedimentation pattern and may be results of historical hurricane landfalls (1906, 1938 or 1954) or winter storm of 1956 or 1962. Increased in mineralogic sediment influx during the last century may also be result of anthropogenic impact on marshes.