The uncertain future of mountaintop-removal-mined landscapes 2: Modeling the influence of topography and vegetation

Abstract

Erosion following human disturbance threatens ecosystem health and inhibits effective land use. Mountaintop removal (MTR) mined landscapes of the Appalachian Coalfields region, USA, provide a unique opportunity to quantify the geomorphic trajectory of disturbed lands. Here we assess how MTR-induced changes to topography and vegetation influence spatiotemporal erosion patterns by modeling landscape evolution in five mined watersheds. We use landscape evolution models starting from pre-MTR and post-MTR topographic data to isolate the influence of mining-induced topographic change. We then constrain ranges of erodibility from incision depths of gully features on mine margins, and use those estimates to model the influence of vegetation recovery trends on erosion. Results show that topographic alterations alone reduce total sediment flux from mined catchments. Model runs that incorporate the disturbance and recovery of vegetation in mined watersheds show that, in any scenario other than complete vegetation recovery, vegetation disturbance drives higher total sediment export from mined catchments than from unmined catchments. Scenarios with no vegetation disturbance or full recovery exhibit sediment fluxes that decline over time post-recovery, while those without full recovery experience fluxes that increase over time even after recovery is complete. Spatiotemporal erosion trends depend on 1) the extent of vegetation recovery and 2) the extent to which MTR has created slope–area disequilibrium in the landscape. Valley fills, headwater valleys that have been filled with waste rock, experience erosion rates orders of magnitude higher than those found in the unmined landscape, as do steep scarps left behind by mining. Rapid erosion of mined areas drives sediment accumulation in colluvial hollows, headwater stream valleys, and below mine scarps. Our numerical experiments suggest that reclamation practices focused on reducing hotspots of slope–area disequilibrium and controlling erosion during the first few decades of vegetation recovery would reduce the extent to which mined Appalachian watersheds experience different landscape evolution trajectories from unmined ones both during and long after the vegetation recovery period. Insights gained from MTR-influenced landscapes have the potential to improve mined land management as the renewable energy transition drives increased surface mining.