Sources, sinks and transformations of organic carbon in Australian floodplain rivers

Abstract

This paper reviews research on fluxes of carbon in Australian floodplain rivers. Except where cover is absent, and in-stream gross primary production is >1 gC m–2 day–1 and ratios of production to respiration are >1, riparian sources dominate carbon pools in catchment streams. On floodplains, primary production by river red gum (Eucalyptus camaldulensis) forests is ~600 gC m–2 year–1. Total primary production by aquatic macrophytes and biofilms in floodplain wetlands is >2500 gC m–2 year–1 and >620 gC m–2 year–1, respectively. Large pools of particulate organic carbon (POC) exist on floodplains as litter (>500 gC m–2) and coarse woody debris (~6 kgC m–2). Floods may release 50 gDOC m–2 from leaf litter. Export of this DOC (dissolved organic carbon) may be substantial relative to autochthonous production in river channels. Sediments deposited on floodplains during large floods represent a substantial sink of riverine POC (up to 280 gC m–2). Bacteria are responsible for rapid decomposition of DOC and POC in floodplain wetlands (sediment respiration and methanogenesis, both ~1 gC m–2 day–1). Flow and its interaction with geomorphology control carbon fluxes in rivers. Decreased inputs of floodplain carbon, following river regulation and physical disturbances to catchments and floodplains, may have resulted in many Australian rivers being dominated by algal production.