COLONIZATION AND PROCESSING OF LEAF-LITTER BY MACROINVERTEBRATE SHREDDERS IN STREAMS OF CONTRASTING PH

1. Leaf litter processing rates and macroinvertebrate shredder assembl ages in leaf packs were compared in four streams on the Allegheny plat eau in the central Appalachian Mountains, U.S.A.; these streams were c haracterized by different bedrock geology and streamwater pH. 2. Leaf litter processing rates were fastest in the neutral streams, slowest i n the acidic stream, and intermediate in the most alkaline stream. 3. Slower processing rates in the acidic stream were associated with lowe r total shredder biomass, made up predominantly by small leuctrid and nemourid stoneflies. 4. The differences in processing rates between th e more alkaline stream and the neutral streams were not associated wit h differences in shredder biomass, but appeared to be related to taxon omic differences in the shredder assemblages. Insects were dominant in the neutral streams, and amphipods were dominant in the more alkaline stream.