Changes in Selected Metals Concentrations from the Mid-1980s to the Mid-2000s in a Stream Draining the Picher Mining District of Oklahoma

After abandonment in the late 1960s, the Picher mining district of Oklahoma, once the largest source of lead and zinc in the world, continued to be affected by severe environmental degradation, with scattered subsidence and abundant toxic metals such as cadmium and lead seeping from flooded underground mine workings and seeping and running off from as much as 60 million tons of mine tailings remaining at the land surface. Water-quality data collected during the mid-1980s and the mid-2000s at the Tar Creek at 22nd Street Bridge in Miami, Oklahoma streamflow-gaging station (USGS number 07185095), located downstream from much of the district, indicate that total concentrations of iron, manganese, and zinc significantly decreased between the two sampling periods. Those water-quality improvements probably are due to a combination of reclamation activities and natural attenuation processes such as stabilization of exposed minerals in flooded underground mine workings, progressive wind and water erosion of the most readily erodible metalliferous particles from tailings, and colonization of volunteer plants that reduce physical erosion of soils and tailings.