Chemical Evidence of Environmental Changes and Anthropogenic Influences in a Bay of Fundy Saltmarsh
Keywords:contamination, iron, metals, macrofossil, paleo-reconstruction, pyrite, salinity, sulphur
A 4.3 m vibracore, retrieved from a Bay of Fundy saltmarsh, was analysed for total extracted S, Fe, Mn, Pb, Zn, Cu and Organic C. Macrofossils were also identified in several key samples from the core. Results showed stable concentrations of all elements except for surficial enrichment of Zn, Cu and Pb and four down-core maxima in Fe, S and Mn concentrations. There was an anomalous elevation of Zn, Pb and Cu concentrations coinciding with the second down-core peak of Fe, S and Mn. Macrofossil analysis revealed a transition from fresh- or brackish water species to Spartina alterniflora and later to Spartina patens. The earliest salt marsh sediments, located at 334 cm, were radiocarbon dated at 2560 ± 60 yr BP. Both paleoenvironmental and more recent historical interpretations were made from the data. The simultaneous presence of S. alterniflora rhizomes and a rise in Fe end S concentration suggests a low marsh environment existed at a depth of 224-237 cm. The two uppermost concentration maxima are most likely the result of the presence of a redox boundary within the sediment matrix and, therefore, an active site of geochemical processes. Zinc, Cu and Pb concentrations showed an increase above background levels from 30 cm upwards. The positive correlation between the macrofossil and chemical data, combined with the discovery of surficial contamination at a relatively pristine site, dearly demonstrates the usefulness of chemical analysis as a method for paleoenvironmental reconstruction and determination of anthropogenic influences.