Sources, transport, and fate of terrestrial organic matter inputs to small Puget Lowland streams: effects of urbanization, floods, and salmon

Abstract

Urbanization can alter various structural and functional properties of aquatic systems including flow, water quality, habitat, energy regimes, and biotic interactions. This study evaluated the effects of urbanization on the delivery and processing of terrestrial organic matter from riparian vegetation along small streams. Changes in the quantity, quality, and time of delivery of organic matter and nutrients as well as organic matter transport and decomposition within small streams with altered physical, chemical, and biological processes due to urbanization were assessed. In many cases, urbanization has changed riparian vegetation from conifer to deciduous trees, altering the amount and timing of organic matter inputs. In some locations, development has led to the modification or removal of riparian trees, reducing total organic matter inputs. Urban streams transport organic matter farther, limiting availability for macroinvertebrate and microbial processing that may otherwise buffer increasing nutrient levels. Finally, red alder leaves decompose faster in urban streams, although the effects of flooding in 2003 and large salmon runs in 2002 were larger than the effect of urbanization. Urbanization alters the inputs, transport, and decomposition of organic matter in small streams, which could affect nutrient delivery to downstream water bodies like Puget Sound.