Calculating Damage to Alpine Brown Trout Using Equivalency Analysis

Abstract

This hypothetical case study presents a method of calculating environmental damage to brown trout caused by hard rock mine pollution in an alpine river. In this scenario, heavy metals are released into a river as a consequence of the failure of a tailings dam impoundment at a hard rock mine, with subsequent adverse impacts to a brown trout fishery through impairment of water and sediment quality. This hypothetical tailings dam failure is assumed to have occurred in May 2014, with subsequent fish population studies conducted in 2014, 2015, and 2016. Brown trout populations recover slowly after the incident and, through linear extrapolation, we assumed that the impacted river would return to pre-release baseline trout populations by 2030. Primary remediation actions were assumed to include repairing the tailings dam and removing tailings from proximal areas of stream channel and floodplain, but interim losses were assumed to occur prior to and following implementation of the primary remediation. To assess environmental damages for these interim losses, we used an equivalency analysis with trout density as the metric to quantify damages and remediation credits. In-stream habitat enhancement was selected as the preferred remediation approach to compensate for interim loss. Habitat enhancements that would increase trout density include emplacement of structures such as large woody debris or boulders, plunge pool construction, and riparian revegetation. We estimated post-remediation increases in trout densities and quantified the credit per hectare of stream remediation. Finally, we calculated the amount of remediation (number of hectares) and associated potential costs required to offset the damage.