Environmental Considerations for Wet Mining Peatlands in Northwestern Ontario

Abstract

Signi cant changes in water quality were detected using a Before-After-Control-Impact (BACI) experimental design. Porewater showed increases in pH, alkalinity, conductivity (including Ca, Mg, K, Na), some metals (Sr, Ba, Mn, Fe) and total nitrogen (TN) in the mined and restored plot. Change in surface water total mercury (THg) was linked to total suspended solids (TSS) and limited to active phases of wet mining. The season mining ceased, TSS and THg concentrations in impacted surface waters were similar to reference site water (<5 mg L􀀀1 and <4 ng L􀀀1, respectively). Experimentally derived 28 day dry weight Biota-Sediment Bioaccumulation Factors (BSAFs) for THg using Lumbriculus variegatus exposed to site sediment ranged from 0.91 to 1.59, while indigenous benthos ranged from 1.2 to 6.8. The BSAFs for methylmercury (MeHg) ranged from 9.92 to 67.4 and benthos from 21.8 to 106. A kinetic trial with inorganic mercury (iHg) spiked sediment, showed tissue THg reached steady state (11.5 d, model BSAF=3.12). Both tissue and sediment MeHg for the same trial showed linear increases (model BSAF=8.38), suggesting an increase in MeHg concentration in sediment would result in a corresponding MeHg increase in L. variegatus tissue.