LATE HOLOCENE HIGH MARSH STRATIGRAPHY OF ESSEX RIVER MARSH SEDIMENTS, NORTHEASTERN MASSACHUSETTS

The Essex River is a mesotidal estuarine system in northeastern Massachusetts with previously unexplored, well-developed Holocene marsh sediments. Two cores were recovered from the high marsh terrace, approximately 5 km inland from Castle Neck and 0.25 km from each other. At each location, two 1-meter drives were taken from the same hole. Due to compaction, ~1.2 meters of sediment were recovered. This study aims to document the late Holocene marsh stratigraphy and to analyze downcore variations in magnetic susceptibility and heavy metal contaminants.

Three distinct stratigraphic units were recognized within the cores. Basal unit 3 consists of medium to dark brown muds with plant macrofossils interspersed with sandy beds. Unit 3 is between 13-59 cm recovered. The top of unit 3 gradationally is overlain by unit 2 which contains darker, more organic-rich sediments with higher concentrations of plant macrofossils. It is 60 cm in thickness landward and 104 cm seaward, as is expected due to late Holocene transgression. Finally, unit 1 sharply overlays unit 2, is massive, light brown, and has very abundant plant macrofossils. Unit 1 is 11 cm in thickness in both sections.

In addition, concerns about heavy metal contamination were explored utilizing a Niton XL5 Plus handheld X-ray fluorescence (XRF) analyzer, measuring every 2 cm downcore for the upper section, then at 8 cm intervals below. Concentrations of arsenic, chromium, copper, lead, nickel, and zinc were compared to sediment quality guidelines (Long et al. 1995). None of the metal concentrations analyzed downcore exceeded the Effects Range Median (ERM), suggesting that biological effects of these metals are likely minimal. Magnetic susceptibility was measured using a Bartington MS-2 magnetic susceptibility meter, and remained low throughout the cores, as would be expected for organic-rich marsh sediment.

Initial examination of units 1 and 2 revealed the presence of moderate amounts of benthic foraminifera that are in the process of being taxonomically identified.