SEDIMENT DYNAMICS IN THE ALBEMARLE-PAMILICO ESTUARINE SYSTEM, NORTH CAROLINA: A STORM DRIVEN SYSTEM?

The Albemarle-Pamlico estuarine system (APES) is the second largest estuarine complex in the nation. The APES, a product of rising sea level (e.g. drowned-river estuarine system), includes several major and minor embayed tributaries. The physical processes operating within this wind-dominated, microtidal estuarine system have been well documented, however, little data exists regarding sedimentation rates and the influence of major storms (ie., hurricanes, nor’easters, etc.). As part of a larger USGS-ECU-NCGS cooperative research program, we have begun to elucidate the sediment dynamics of the APES.

Over the last 3 years, we have collected over 50 sediment cores from regions of organic rich mud (ORM) accumulation within the system. Several sites have been revisited in order to evaluate temporal variability. Three of these sites were reoccupied following the crossing of Hurricane Isabel.

The sediments are being analyzed for a number of geochemical tracers aimed at quantifying the rates of accumulation and potential sources of sediment. The tracers being used include radionuclides (²³⁴Th, ⁷Be, ¹³⁷Cs, and ²¹⁰Pb), carbon (d¹³C) and nitrogen (d¹⁵N) isotopes, and C:N ratios. The short-term radionuclides, ²³⁴Th and ⁷Be, provide information on shallow sediment reworking and mixing over short time scales (days to months). ¹³⁷Cs and ²¹⁰Pb are used to establish a geochronology of sedimentation and examine changes in sedimentation rates over time. Carbon and nitrogen isotopes and C:N ratios provide a geochemical signature of the dominant sediment source.

Radioisotopic data indicates significant and rapid changes in sedimentation rates, potentially associate with major storm events. Time series data demonstrate a significant loss of sediments from Albemarle Sound prior to Hurricane Isabel. Cores collected days after the crossing of Hurricane Isabel show a significant (»10 cm) depositional event in Albemarle Sound, thought to be from massive shoreline erosion. However, we must first evaluate the spatial heterogeneity of these tracers in order to confirm this unusual sedimentation pattern. Geochemical tracers in Pamlico Sound also portray a fairly dynamic environment, with periods of rapid deposition and significant mixing in the surficial sediments.