Influences of land use on leaf breakdown in southern Appalachian headwater streams: a multiple-scale analysis

Stream ecosystems can be strongly influenced by land use within watersheds. The extent of this influence may depend on the spatial distribution of developed land and the scale at which it is evaluated. Effects of land-cover patterns on leaf breakdown were studied in 8 southern Appalachian headwater streams. Using a GIS, land cover was evaluated at several spatial scales, including the watershed, riparian corridor, and subcorridors that extended upstream in 200-m increments for 2 km. Breakdown rate for American sycamore (Plantanus occidentalis) leaf packs varied significantly among sites (k = 0.0051-0.0180/d) but fell within the range reported in the literature for sycamore. Leaf breakdown rate increased at sites with high shredder density and biomass. Further, breakdown rate and shredder density and biomass were positively related to mean substrate particle size. Several instream variables were related to watershed-scale features, but leaf breakdown rate was not related to land cover at the watershed scale. Leaf breakdown rate was inversely related to % nonforested land within riparian subcorridors of similar to1 km. Results suggest that the distribution of shredders is critical to leaf processing in these streams. In some streams, increased sediment inputs resulting from agricultural activity or residential development in riparian corridors may limit the distribution of shredders and thus influence leaf breakdown rates. Alternatively near-stream development may alter the quality of allochthonous inputs to streams, and thus indirectly influence the distribution of shredders and instream processing.