Oral Presentation Australian Society for Limnology Congress 2013

Aquatic organic carbon dynamics in massively altered landscapes: Past, present and future. (#48)

Darren P Giling 1 , Ralph MacNally 1 , Ross M Thompson 2
  1. Monash University, Clayton, VIC, Australia
  2. Institute for Applied Ecology, University of Canberra, Canberra, ACT, Australia
Landscapes globally have been greatly altered by agricultural land use. Restoring native vegetation has necessarily occurred at small spatial scales, with limited ability to address landscape scale effects. However, extensive replanting is an economically feasible option for climate change mitigation in emerging carbon-driven economies. Much replanting occurs in riparian zones, offering concomitant ecological health benefits for aquatic systems because riparian vegetation provides important subsidies of terrestrial organic carbon to streams. We measured organic carbon fluxes in riparian replantings on 13 agricultural streams over two years to assess if replanting affected in-stream organic carbon dynamics. We then up scaled to estimate fluxes from similar sized streams in an entire catchment (second and third order streams; approximately 30% of the network). We sought to assess the regional implications of incorporating additional trees in future landscapes. At reach scales we found that replanting vegetation increased the provision of leaf litter and doubled the standing stock of coarse particulate organic carbon in-stream within three decades. Combined with greater shading, this increased organic carbon processing and reduced net ecosystem productivity by 50%. At catchment scales changes in organic carbon fluxes were high per unit of stream, but small compared to the potential for terrestrial carbon storage. We predict that extensive replanting of riparian vegetation will cause agricultural streams to become more retentive of organic carbon. This reflects a restoration of terrestrial and aquatic processes towards that of past, forested catchments. Replanting riparian vegetation in agricultural landscapes can effectively return multiple benefits within decadal timescales.