introduction - Pennsylvania Natural Heritage Program

encountering a more dense layer of rock, and eventually emerges at the surface. Groundwater dissolvesminerals from the bedrock layers through which it flows, and thus may substantially influence the chemicalenvironment of a seepage wetland. Seeps in Clearfield County are expected to be fairly acidic, as thebedrock is predominantly sandstone, which contains few soluble minerals. They are typically shaded byforest canopy, and thus provide consistently cool and wet habitat conditions which certain plant and animalspecies thrive upon. Many species of salamanders use seeps, and typical plant species are jewelweed(Impatiens sp.), bee balm (Monarda sp.), slender manna-grass (Glyceria melicaria), golden ragwort(Senecio aureus), wood sorrel (Oxalis acetosella), scabrous sedge (Carex scabrata), northern awned sedge(Carex gynandra), mad-dog skullcap (Scutellaria lateriflora), marsh pennywort (Hydrocotyle americana),a sedge (Carex torta), marsh marigold (Caltha palustris), false nettle (Laportea canadensis), woodhorsetail (Equisetum sylvaticum) and golden saxifrage (Chrysosplenium americanum).Wetlands and MiningWhere mining has occurred in the upland areas above any wetland that receives seepage inputs, drainagethrough the disrupted bedrock layers will typically contaminate these groundwater flows with dissolvedmetals (mainly iron, aluminum, and manganese) and acids. Upon reaching the surface and encounteringoxygen in the air, some of the metal compounds convert to solid form, thus accumulating in seepage areasas the orange (iron), bluish-white (aluminum), or black (manganese)-colored sediment characteristicallyassociated with mining drainage. Aluminum, manganese, and high acidity are all toxic to aquatic life; ironis less toxic. However, the accumulation of sediments of any of the metals degrades aquatic habitats byblocking light needed by aquatic plants and microorganisms, and clogging the tissues of aquatic animals.The impacts of abandoned mine discharges (AMD) on a particular wetland will depend on theconcentration of the contaminants in the discharge and the volume of the discharge, relative to the overallvolume of the wetland.14