Leaf breakdown in streams receiving coal mine drainage in central Pennsylvania

We used breakdown of white oak and sugar maple leaves to indicate impairment of ecosystem function in streams receiving drainage from mines in the anthracite and bituminous coal regions of central Pennsylvania.  In each region, we studied a reference stream not affected by mine drainage, an impacted stream receiving inputs from active or abandoned mines, and a remediated stream with improved water quality following a history of mine drainage impact.  Impacted streams in each region showed very different physical and chemical conditions due to different mining practices and geochemical processes.  The impaired stream in the bituminous region was characterized by low pH (< 3.5), net acidity, and high concentrations of dissolved metals (iron, aluminum, manganese, and others).  The impaired anthracite stream was net alkaline, had higher pH (6 to 7), and lower dissolved metals concentrations but had extensive precipitates of metal hydroxides (especially iron) on stream substrata.  Despite dramatically different physical and chemical conditions, leaf breakdown was equally inhibited by mine drainage in both regions.  Leaf breakdown rates were 2x faster in reference and remediated streams compared to impacted streams, most likely due to higher microbial activity and shredder-detritivore abundance in reference and remediated streams compared to impaired streams.  Remediation of water quality does seem to allow leaf breakdown in formerly mine-impacted streams to return to normal rates.  Leaf breakdown can be used to assess streams affected by mine drainage, and recovery of this ecosystem process appears likely following water quality improvements and recovery of microbial and invertebrate abundances.