5-14 Sediment Cores, Tidal Wetlands, & Historical Fly-Ash Deposition: What coring methodology is most efficient and is there a potential fly-ash chemical signal within the estuarine environment in Salem, MA?

Session: Nearshore and Estuarine Research: Dynamics and Future Resiliency in the Coastal Zone (Posters)

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Abstract:

During coal combustion, a common by-product is a fine particulate matter known as fly ash (0.5-20 micrometers). Fly ash residuals can enter the environment through mishandling during facility production or disposal, resulting in airborne nonpoint-source contamination. Airborne fly ash may travel through the atmosphere and be deposited in surrounding environments via gravity or precipitation.

Tidal wetlands are known to serve as natural filters by burying contaminants with high sedimentation rates. This research aims to (1) investigate efficient field collection methods for identifying historical fly-ash deposition in tidal wetlands and (2) establish potential chemical signals of fly-ash contamination in wetland sediment profiles.

Salem, MA, was home to a coal-fired power plant that operated from 1952-2012. Composite and Push sediment cores (~20 centimeters [cm]) were collected within a tidal wetland environment in Salem, MA. The sediment profile consists of upper muds to coarse sands at depths. Sediment cores were sectioned downcore at 2cm intervals and processed via X-Ray Fluorescence to quantify concentrations of target trace metals (Arsenic [As], Chromium [Cr], Copper [Cu], & Lead [Pb]).

When comparing variations in downcore concentrations between coring techniques, the composite core displayed a lower mean concentration of As, Cr, and Pb (δ = μ_push - μ_composite: As = 1.09 ppm, Cr = 39.30 ppm, Pb = 10.94 ppm) and a higher mean concentration for Cu (δ: Cu = -30.84 ppm). Therefore, if using composite core methodology, researchers should be aware that they may report marginally higher As, Cr, and Pb concentrations and marginally lower Cu concentrations preserved within the sediment record. However, the mean trace metal concentrations for each coring methodology show no statistically significant differences (P > 0.05), indicating both techniques were effective at identifying chemical signals at depth within the wetland sediment. Therefore, research with similar objectives may select either core methodology based on resource availability.

At individual 2cm intervals downcore, elevated concentrations were identified with peaks exceeding the core’s mean value. Peaks in trace metal concentrations indicate potential signal of elevated historical fly-ash deposition. However, the wetland watershed also encompasses leather tanneries which can contribute As, Cr, Cu, & Pb to the environment. To definitively determine the presence of fly ash, these individual depths will be evaluated using additional fly-ash proxies, including sulfur isotopic composition and physical investigation.

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