Paleolimnological Reconstruction of the Environmental Impact of the Deloro Industrial Site on Moira Lake (Ontario)

Abstract

Historical industrial activity at Deloro (1866-1961) included both mineral exploration and mineral processing practices which produced over 650,000 m3 of waste material ultimately dumped on site. Previous studies on the Moira River system including examination of surface waters, sediments, and sediment porewaters identified Moira Lake as an affected lacustrine system. The contamination resulted in elevated levels of arsenic (As), cobalt (Co), and nickel (Ni) in the lake sediments. This study used paleolimnological techniques, including geochemical tools, to evaluate the impact of the metal contamination on the lake system. The data collected showed increased concentrations of As, Co, and Ni with respective concentrations ranging from 50-900mg/kg, 21-1500mg/kg, and 41-1400mg/kg coinciding with the years of operation of Deloro determined via 210Pb dating. The bulk of the sedimentary As occurred as inorganic As(V) with higher As(III) in the deeper sediments and minor occurrences of As(-I) at shallow depths as indicated by XANES. The As was determined to be almost exclusively hosted in iron oxides (98-100%) via SEM-MLA. Under reducing conditions, As bound to iron-oxides may be released as dissolved As via reductive dissolution and diffusion through porewaters. The presence of As(-I) is a potential result of secondary re-precipitation of dissolved As. Increased chlorophyll-a concentrations and a shift in the cladoceran assemblage from one dominated by pelagic Bosminids to one dominated by littoral Chydorids and pelagic Daphniids suggested a response to a regional stressor. The primary and secondary production suggested that, although changes coincided with the onset Deloro, there was another driving factor thought to be nutrient enrichment and/or climate change.