Poster: 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 to hydrology.