More microbial activity, not abrasive flow or shredder abundance, accelerates breakdown of labile leaf litter in urban streams

AbstractUrban land use degrades stream ecosystems, but the nature and mechanisms of its effects on ecological processes, such as leaf breakdown, are poorly understood. Leaf litter breakdown has pivotal effects on energy and nutrient flows in stream ecosystems. Our goals were to test the effect of catchment urbanization on breakdown rates of leaves of 2 common riparian species in southeastern Australia and to identify the mechanisms responsible for changes in breakdown rates. Catchment urbanization was quantified as the percentage of catchment covered by impervious surfaces with connection to streams via stormwater sewers (effective imperviousness [EI]). Eucalyptus obliqua and Pittosporum undulatum leaf packs were placed in 6 streams that ranged from 0 to 20% EI. Packs were left for up to 69 d and, upon removal, were analyzed for mass loss, microbial activity, and abundance of associated shredding macroinvertebrates. Stream nutrient concentrations, temperature, and abrasive flow were measured as potential ...