Utilization of hydrodynamic modeling in predicting water quality and Brook Trout habitat: reclamation of a mine impacted Boreal Shield Lake

Abstract

Mining operations in Ontario are subject to regulatory limits on effluent release into surrounding waterbodies designed to preserve aquatic life. However, said guidelines may not always be enough to prevent damage to the local ecosystem. This study examined Cleaver Lake, Ontario, an 18 m deep shield lake downstream of a copper/zinc mine active from 1987 – 1999. Mine activity resulted in increased levels of chemical constituents that created density induced stratification prohibitive of seasonal lake turnover (meromixis). This condition persisted for more than a decade after closure. Resulting hypoxic conditions of deeper waters caused extirpation of fish such as Brook Trout (Salvelinus fontinalis) that require cool water and high dissolved oxygen (DO). The water quality and hydrodynamics of the effluent receiving lake were modeled via CE-QUAL-W2 for the open water season of 2017. The model combined bathymetrical data with inflow, outflow, and meteorological measurements, in-situ multiprobe and data logger measurements of water quality characters like DO and temperature, chemical concentrations of potentially problematic metals (zinc = (81 ± 23) μg/L & copper = (3.7 ± 0.63) μg/L) and density altering compounds from samples collected on site to make real-time predictions of Brook Trout habitat. The model has accurately represented the recently observed recovery from a meromictic state. The objectives of this project were to: (1) assess current Brook Trout habitat with CE-QUAL-W2; (2a) predict potential future habitat based on what-if scenarios such as a return to elevated levels of chemical effluent received via industry activity and (2b) elevated air temperatures due to climate change. Minimum survivable habitat availability for Brook Trout was shown to be 69.97% in the unmodified model, reduced to 64.47% in the operational industry scenario, and 7.3% in the climate change scenario.