Spatial analyses of the risk of cumulative impacts of mining on Canadian rivers and communities using hydrological connectivity and discharge-related indices

Canada's vast freshwater systems are increasingly threatened by the cumulative impacts of industrial activities, particularly mining. Recent national investments in the extraction of critical elements, which are primarily driven by Canada's transition to clean energy, are expected to amplify these pressures. In this study, we endeavour to understand the cumulative impact of current mining activities on Canada's river system at a large scale. We develop and apply geospatial methodologies to evaluate how active mining operations affect river systems across the country and compare how these impacts are distributed between Indigenous and urban communities. Two novel indices were created: the Hydrologic Connectivity Cumulative Vulnerability Index (HCCVI), which identifies rivers affected by cumulative impacts by highlighting river reaches where impacts from multiple upstream mine types converge, and the Discharge-Adjusted Cumulative Vulnerability Index (DACVI), which adjusts cumulative upstream mining impacts in a river reach by the river discharge, which account for the ability of the river reach to buffer the cumulative stress. The HCCVI and DACVI indices were used to compare the spatial exposure of Indigenous and urban communities to hydrologically impacted river reaches, using proximity analysis and statistical testing. Findings from HCCVI showed no statistically significant difference in proximity between Indigenous and urban communities, although a higher percentage of Indigenous communities were located within 5 km of impacted rivers. In contrast, DACVI analysis revealed that urban communities have significantly higher average impact values; however, a notable portion of Indigenous communities also fall within moderate or high DACVI impact thresholds. Stratified DACVI analysis by mine type provided additional insights: urban communities were more exposed to rivers affected by coal mining, while Indigenous communities were more commonly situated near oil sands-impacted rivers. These findings underscore both group-level and localized environmental justice concerns and call for more nuanced, equity-driven approaches to cumulative impact assessment. Recommendations include incorporating empirical water quality data, accounting for anthropogenic flow modifications in future analysis, and supporting Indigenous-led environmental monitoring.