The Effects of Historic Iron Mining on Wetland Areas in the St. Louis River Basin

Land-use changes on the scale caused by iron mining on the Mesabi Iron Range in northeastern Minnesota have the potential to cause substantial changes to groundwater flows that feed rivers, lakes, and wetlands, especially those close to mining areas. The Iron Range is within the St. Louis River Basin (SLRB) and broad understanding of the groundwater flow system and interactions between groundwater and surface waters in this region is limited. This poster will present our approach to modeling groundwater-surface water interactions and how wetland extent and groundwater flux to wetlands changes between modern and premining model scenarios.

In cooperation with Tribal representatives from five bands of Minnesota Chippewa and Ojibwe, the U.S. Geological Survey produced a series of models of the SLRB to explore how groundwater flows to rivers, lakes, and wetlands may have changed as a result of human alteration of this landscape. The first is a regional scale (10,032 square mile) two-dimensional (2-D) analytic element model of the St. Louis River basin, which provided defensible model boundary conditions to a detailed three-dimensional (3-D) finite-difference (MODFLOW) model of modern conditions along the Iron Range. A pre-mining scenario was constructed from the modern conditions model by removing all known mining features and restoring the land surface to pre-iron-mining conditions. The premining and modern conditions MODFLOW model scenarios simulate horizontal and vertical flow of groundwater. These models use the Unsaturated Zone Flow (UZF) package to parse apart recharge into that which reaches the aquifer and that which returns to the surface via seepage and rejected recharge, such as in wetlands. Preliminary comparisons of the results these two scenarios show reduced wetland extent in the immediate vicinity of the Iron Range under modern conditions. Results of the final model runs will be presented and discussed.