Application of the paleolimnological method in the environmental assessment of effluent-influenced freshwater sediment: an example from northern Nova Scotia

Abstract

A former estuary in Pictou Co., Nova Scotia began receiving effluent in 1967 from a pulp mill. In 1972 a dam was installed, and the estuary was transformed into a freshwater pond. A paleolimnological approach was applied to the bulk geochemical assessment of the sediment that has accumulated at the site. This study focused on the organic sediment that has accumulated since 1972 and identifying the sources of metals that were identified as representative of impact at the site. Samples were obtained by gravity coring, and bulk geochemical analysis was accomplished using pXRF, carbon ©, nitrogen (N) and stable isotope analyses. Sediments were also obtained from a nearby freshwater lake and parallel analyses provided baseline reference concentrations for all bulk geochemical parameters. Data was analyzed in R and plotted using QGIS. At both the receiving pond and reference site, metal concentrations generally exceeded Interim Sediment Quality Guidelines; a strong local geogenic and atmospheric contribution is inferred. Chromium was identified as a metal uniquely representative of industrial activity at the site and may be a good indicator for effectiveness of remediation efforts. Metal concentrations were generally highest at the top of the receiving pond sediment and may be indicative of increasing effluent influence through time. Total C, N and stable isotope data indicated dominantly terrestrial organic input indicating that the receiving pond sediment is anomalous and may strongly influence the retention of metals. Results of this study demonstrate that geogenic and local atmospheric contribution to metal load at contaminated sites must be determined if site assessment, remediation and rehabilitation techniques are to be effective.

Publication
Science Atlantic: Environment