2005 BES Annual Meeting Presentation and Poster Abstracts
Breakdown of Sycamore Leaf Litter in Small Urban and Forested Streams: The Effects of Altered Hydrology and Landscape Position
Ken Belt, Christopher Swan, Richard Pouyat
Abstract: The influx of particulate organic matter to headwater streams, normally from riparian sources, is important to aquatic food webs and is crucial to maintaining functional streams. However in urban catchments, where 1) the density of drainage pathways (the “streetscape”) is great, 2) temperatures and atmospheric characteristics are different, and 3) the diversity of litter taxa is great, the quality and quantity of litter destined for stream ecosystems is likely highly altered. Understanding how urbanization and trees interact to alter organic matter transport and cycling in urban receiving streams is needed to assess the degree of retention and types of carbon losses to the atmosphere and to downstream aquatic ecosystems. This research investigated the rate at which urban Sycamore leaf litter (Platanaceae, a common riparian and urban landscape tree) breaks down in a forested (Baismans Run) and a suburban (Gwynns Falls at Gwynnbrook Rd.) catchment. Exponential decay curves from in-situ leaf bag experiments for eight different leaf source/landscape types (rural/urban/suburban settings) and landscape positions (gutter, residential and riparian) were constructed and exponential decay coefficients were estimated to determine which types had higher mass loss rates. Suburban & urban Sycamore sources almost all lost mass faster than the riparian litter and were faster than literature values. Among riparian sources from locations along the urban-rural gradient, decay rates were similar for the forested stream, but in the suburban stream (with flashy hydrology), the suburban and urban riparian leaves had faster breakdown rates than those from the proximal and distal rural sites. Surprisingly, there was not a general trend of faster decay rates for the suburban stream. If urban and suburban leaf litter generally breaks down faster than riparian litter (especially with flashy hydrology), urban catchment fluxes of organic matter (particulate and dissolved) may be higher to both downstream aquatic systems and to the atmosphere (as CO2) than in natural systems.