Mining can affect the physical structure of streambed habitat by changing the amount and size of sediment supplied to streams. Resulting changes in stream channel shape and bed grain size influence the viability and composition of aquatic ecosystems. Here I review mining effects on stream sediment dynamics as a function of the timescale over which they appear, with the goal of identifying knowledge gaps that present opportunities to quantify and forecast mining effects on aquatic ecosystems.
Short-term (minutes to years) effects are observed where mining activities directly interact with the riparian corridor. Examples include hydraulic gold placer mining in the Sierra Nevada, burial of headwater streams by mountaintop removal/valley fill coal mining in Appalachia, and modern river sand mining for construction materials. These effects commonly include elevated turbidity, changes in river-bed grain size, and rapid changes in channel form. Medium-term effects occur wherever near-channel mining landforms can source sediment to the river channel over years to centuries and include many small-scale, off-channel forms of mining, such as Appalachian bench-and-highwall coal mining and early gold mining in the Colorado Rockies. This intermediate timescale also encompasses corollary effects of mining, such as deforestation, that themselves influence stream processes by triggering pulses of water and/or coarse sediment. Long-term (centuries, millennia, and longer) effects occur primarily where mining has caused extensive and dramatic changes to the topography such that natural erosion trajectories are supplanted by novel landscape evolution pathways. Topographic effects of modern, large-scale surface mining fall into this category because altered topography causes streams in mined watersheds to experience perturbations to their water and sediment regimes over timescales longer than most human planning efforts.
Important knowledge gaps arise from the immense variability in 1) how mining affects the land surface as a function of the target deposit, physiographic setting, ecosystem, and regulatory environment, and 2) how land-surface processes filter the expression of mining-driven alterations in streambed habitat structure. Progress along these lines may enhance our ability to effectively balance society’s needs for minerals, energy, and functioning aquatic ecosystems.