How does urbanization alter the sources, transport, and fate of organic matter in small Puget Lowland streams?

Organic matter delivered to streams from riparian vegetation provides habitat and food resources for stream biota. Puget Lowland streams exhibit a wide variety of urbanization influences, including modification to riparian vegetation and changes to stream channel complexity. These changes alter the delivery of organic matter to small streams and what happens to that organic matter within the stream environment. More disturbed watersheds tend to have a greater proportion of deciduous vegetation than more natural systems with conifer-dominated riparian zones. Deciduous riparian forests produce 54% more nitrogen and 40% more phosphorus loads from litterfall inputs compared with conifer-dominated riparian areas. Shifts in the timing of inputs occur as well. Urban streams have lower pool/riffle ratios and higher reach-averaged velocities than less developed streams. Decreases in channel complexity result in less retention of surrogate leaf material near the litterfall source and enhanced organic matter transport in small urban streams. In addition, red alder leaf processing occurs faster in urban streams, primarily through enhanced abrasion rather than macroinvertebrate or microbial processing. Urban streams receive more leaf litter input than less developed streams. However, the lack of channel complexity does not retain the litter locally and enhanced abiotic processes lead to faster leaf processing. While more leaf litter of higher nutritional quality falls into urban streams, abiotic processes limit availability for biotic processes. These shifts in sources, transport, and fate alter nutrient processes and aquatic productivity within small Puget Lowland streams but also alter how much organic matter reaches downstream water bodies such as Puget Sound