Leaf breakdown in urban and forested streams: effects
of leaf type and shredder exclusion.
Paul, Michael J., N. Davis, Y. Kurian, and N.
Stewart. Department of Biology, Howard University,
415 College Street, NW, Washington, DC 20059.
Leaf breakdown has been studied in a variety of
different ecosystems, yet little is known about how
it differs between urban and forested streams.
Defining that difference is fundamental to a complete
understanding of carbon cycling in urban streams.
Previous work suggests faster leaf breakdown in
southern Piedmont urban streams is due to greater
physical fragmentation. We extended that study to
the mid-Atlantic Piedmont and compared breakdown of
black oak and dogwood leaves in urban and forested
streams within the Baltimore Ecosystem Study. We
also measured the effect of large macroinvertebrates
using large (1 cm) and small mesh (1 mm) leaf packs.
Leaf packs were deployed in streams and sampled
through time. Packs were dried and weighed to
estimate leaf loss. Invertebrates were sorted,
identified to family, and enumerated. Respiration of
20 leaf disks (0.5 cm diameter) was used to estimate
microbial activity on leaves. Dogwood decayed faster
than black oak, in keeping with previous results.
Urban dogwood leaves exhibited faster decay rates
than dogwood leaves in forest streams. Leaves of
both species decayed more slowly in small mesh than
large mesh bags, although the effect was more
pronounced in forest streams. The results suggest
that decay rates for some species do appear faster in
mid-Atlantic urban streams than forested streams.
Respiration and invertebrate data suggest that
increased rates cannot be attributed to greater
microbial or insect activity, but appear more related