Litter breakdown and invertebrate detritivores in a resource - depleted Appalachian stream

We measured breakdown rates of leaves and small wood for the first three years in a stream in which detrital inputs were excluded for 7 years and in a reference stream located in the Appalachian Mountains of North Carolina, USA. Leaf and wood inputs were excluded using a gill-net canopy constructed over a 170-m section of stream. We hypothesized that red maple (Acer rubrum) and rhododendron (Rhododendron m i m a ) leaf breakdown rates would decline in the litter exclusion stream as shredder production decreased with each year of litter exclusion. In contrast, we expected faster wood breakdown rates in the litter exclusion stream as microbes and invertebrates shifted from leaves to wood as their primary organic matter resource. Consistent with our predictions, wood breakdown rates were significantly faster in the litter exclusion stream. We also found sigdicantly slower processing rates of maple leaves in the litter exclusion stream compared to the reference stream during years 2 and 3. Slower breakdown rates for red maple leaves in the litter exclusion stream were associated with lower shredder production and estimated consumption rates in years 2 and 3. Shredder production and consumption rate estimates were also lower in the exclusion stream for rhododendron leaves, but leaf breakdown rates were not affected. We also found that shredder production in litterbags was 3-4 x greater than in benthic substrates in the litter exclusion stream. In contrast, shredder production in litterbags was similar to that in benthic substrates in the reference stream. These differences were probably due to the relatively low availability of organic matter in benthic substrates in the litter exclusion stream. Our data show shredders track high quality organic matter resources (leaves) and contribute to their loss rate, illustrating the interdependence of stream organisms and terrestrial organic matter input. Key 'words: organic matter, decomposition, litter exclusion, detritus, resource island, aquatic macroinvertebrates, wood, streams. ' Authors' addresses: Institute of Ecology, University of Georgia, Athens, Georgia, USA 30602. Department of Entomology, University of Georgia, Athens, Georgia, USA 30602. * Author for correspondence. E-mail: eggerts @ sparc.ecology.uga.edu DOI: 10.1 127/0003-913612003/0156-0315 0003-91 36103101 56-031 5 $6.00 Q 2003 E. Schweizerbart'sche Verlagsbuchhandlung, D-7Ol76 Stuttgart 316 S. L. Eggert and J. B. Wallace