Geochemical and Toxicological Investigation of the Hogarth and Caland Pit Lakes, Former Steep Rock Iron Mine Site

The closure of the Steep Rock Iron Mines near Atikokan, Ontario, Canada in the late 1970s left behind an area of severe environmental concern. The subsequent flooding of the pit mines resulted in the formation of two adjacent pit lakes, Hogarth and Caland. As water levels in the two pit lakes continue to rise, the water columns are exposed to differing proportions of various wall rocks. The geochemical influence is likely the major control on the unique and dynamic water chemistries of the two pit lakes.;Although both pit lakes have near-neutral pH, Hogarth has greater concentrations of dissolved ions including Ca2+, Mg2+, and SO42- than Caland. While dissolved ions increase in depth in both pit lakes, Caland is a meromictic lake with an anoxic sulfate-saline monimolimnion that is separated from the oxygenated freshwater mixolimnion by the chemocline. Both lakes have low concentrations of dissolved metals. Hogarth water produced chronic toxic effects in Daphnia sp. (Goold, 2008) while the freshwater lens of Caland was host to the Snow Lake Fish Farm which produced rainbow trout (Oncorhynchus mykiss) from the early 1980s until about 2008.;To investigate this geochemical influence of the wall rocks on pit lake water chemistry, a column experiment was conducted to empirically predict the influence of the varying types and proportions of wall rocks on the water chemistry of the two pit lakes as they fill and eventually merge. A mixing series of water from the two pit lakes was exposed to the relative types and proportions of rock lining the pits to mimic the filling and eventual joining of the two pit lakes. Although most water quality parameters varied little under the geological influence, the column experiment predicted that three main reactions will influence future pit lake water quality: (1) pyrite oxidation, (2) weathering of potassium feldspar, and (3) carbonate dissolution and precipitation. In the columns these reactions caused changes in pH indicative of buffering processes and increases in potassium, barium, and strontium concentrations.;To predict future impacts that pit lake water under geochemical influence would have on aquatic fauna, toxicity tests with the resultant column water were conducted using the duckweed, Lemna minor. After total frond counts were found to give a conservative estimate of toxic response, several alternative endpoint analyses were used: dry weights, chlorophyll a content, and total frond surface area. The dry weight measurements were determined to be inconclusive due to large variation among similar treatments. After controlling for the influence of dry weight using ANCOVA, chlorophyll a content was found to be significantly different from the controls in most treatments indicating that water from Hogarth impacts the growth rate of Lemna minor. The total frond surface area measurements confirmed that water from Hogarth significantly reduced the growth of the aquatic macrophye with water from a depth of 2 m (mixed with 30 m water from Caland) causing a greater reduction in overall frond surface area than water from 30 m (mixed with 2 m water from Caland).;These experiments show that if the water quality of the two pit lakes is allowed to progress naturally under the geological influence of the various rock types lining the pit lake walls, chronic toxic effects are very likely to be seen in aquatic flora and fauna that may become established in the pit lakes. If the combined pit overtops into the Seine River system along the historical flow path of the former Steep Rock Lake, the water quality of the combined pit lake will likely have a negative impact on downstream aquatic communities.