Short Virtual Presentation & Digital Poster 10th Australian Stream Management Conference 2021

Drivers of organic matter decomposition of headwater streams in an urbanizing region (#51)

Stephanie E Brown 1 , Matthew J Burns 1 , Sam J Imberger 1 , Belinda Hatt 1 , Ryan M Burrows 1
  1. Waterway and Ecosystem Research Group, University of Melbourne, Melbourne, Victoria, Australia
  1. Headwater streams often constitute >75 percent of stream networks and are critical for the integrity of downstream waters. They are major suppliers of freshwater, nutrients and material, can be biodiversity hotspots, and are areas of active biogeochemical processing. Headwater streams are under increasing stress and degradation from agriculture and urbanization, yet we lack a detailed or quantified understanding of how their key ecosystem processes, such as organic matter decomposition, vary across the landscape.
  2. We conducted organic matter decomposition experiments at 40 sites in the Melbourne region to understand how site and catchment characteristics influence rates of decomposition and microbial communities. Sites varied in catchment land cover, temperature, rainfall, geology and vegetation. We used cotton strips as a proxy for organic matter, leaving them to decompose in the stream for four weeks in autumn. We also collected measurements of hydrology, temperature, water biogeochemistry, and microbes for DNA analysis.
  3. We found organic matter decomposition was generally faster beneath the surface of intermittent and ephemeral headwater streams than at the streambed. Ongoing research is assessing how other study variables influence decomposition and the diversity of microbial communities across the landscape.
  4. Our results suggest that subsurface regions of headwater streams can be active zones for organic matter decomposition, sustaining this key ecosystem process even without persistent surface flow. This study contributes to the important cataloguing of decomposition rates in headwater streams, which is a critical step to enabling managers to use organic matter processing as an indicator of ecosystem health in Australia.
Download Full Paper