Effects of acid precipitation and acid mine drainage on leaf litter decomposition rates in central Appalachian streams

Acid precipitation and acid mine drainage have dramatically altered chemical conditions and biological assemblages in streams throughout the central Appalachians. The objectives of this study were to: 1- quantify differences in organic matter decomposition among reference streams, streams impacted by acid precipitation, and streams impacted by acid mine drainage; and 2- determine if lowered decomposition rates are the result of reduced microbial activity or reduced shredder abundance or both. We quantified water chemistry, organic matter decomposition, microbial activity, and macroinvertebrate community structure in 15 headwater streams in the Allegheny Plateau ecoregion (5 circum-neutral reference, 5 AMD, and 5 acid precipitation). Water chemistry and benthic invertebrate communities were sampled in spring and fall, and decomposition rates were quantified from leaf packs deployed for a period of 120 days. Microbial activity was measured as microbial respiration, ergosterol content, and capillary DNA sequencing. AMD resulted in dramatically altered macroinvertebrate assemblages and reduced overall OM decomposition. Decomposition rates in acid precipitation streams were intermediate to AMD and reference streams. Overall, decomposition rates were correlated with both benthic invertebrate diversity and microbes suggesting a combined role of shredders and microbial activity in these systems.