Riparian areas are fundamental to aquatic ecosystems by regulating temperature and light regimes, and providing allochthonous subsidies critical to the survival of aquatic and terrestrial species. On a global scale, increased rates of anthropogenic disturbance from agricultural activities and urbanization have caused the degradation of aquatic habitats. As a result, billions of dollars have been spent on stream restoration projects to protect aquatic resources; however, fundamental ecosystem processes like litter decomposition are rarely addressed. We conducted a litterbag experiment in a degraded high desert stream proposed for large-scale restoration to test the effects of reach location, canopy cover, and temperature on the rates of leaf litter breakdown attributed to microbial activity and macroinvertebrate shredders. Results from coarse mesh litterbags indicated that total leaf breakdown rates per degree-day were significantly faster in upstream, less degraded reaches, associated with higher abundance of shredders. In contrast, the main driver of leaf mass loss due to microbial activity in fine mesh litterbags was water temperature, which was significantly warmer in downstream reaches. Location effects, including temperature differences between upstream and downstream reaches, also depended on canopy cover and leaf species. Overall, the relative proportion of leaf mass loss attributed to microbial activity increased with increasing cumulative degree-days, while leaf mass loss attributed to shredders decreased. Reduced leaf processing rates by shredders in the degraded downstream reaches could further affect the timing and availability of suspended food resources to other detritivore and higher-level consumers downstream. These shifts in microbial and shredder-mediated leaf litter processing could have bottom-up effects via heterotrophic energy pathways, especially in degraded streams subject to warming. Furthermore, the significant variation in litter decomposition we observed underscores the importance of measuring ecosystem function across multiple scales within a given stream in order to assess relative levels of degradation and guide future restoration efforts.
Year manuscript completed
Year degree awarded
stream, riparian area, degradation, ecosystem function, litter decomposition, restoration
Master of Science
Jesse D. Jones College of Science, Engineering and Technology
Rothenbuecher, Carla, "EFFECTS OF STREAM DEGRADATION ON ECOSYSTEM FUNCTION ARE MEDIATED BY LOCAL MICROBIAL AND MACROINVERTEBRATE LEAF LITTER PROCESSING" (2016). Murray State Theses and Dissertations. 3.