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

This paper reviews research on fluxes of carbon in Australian floodplain ri vers. 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, ripa rian sources dominate carbon pools in catchment streams. On floodplains, pr imary production by river red gum (Eucalyptus camaldulensis) forests is sim ilar to 600 gC m(-2) year(-1). Total primary production by aquatic macrophy tes 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 debr is (similar to 6 kgC m(-2)). Floods may release 50 gDOC m(-2) from leaf lit ter. Export of this DOC (dissolved organic carbon) may be substantial relat ive to autochthonous production in river channels. Sediments deposited on f loodplains 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 similar to 1 gC m(-2) day(-1)). Flow and its interaction with geomor phology control carbon fluxes in rivers. Decreased inputs of floodplain car bon, following river regulation and physical disturbances to catchments and floodplains, may have resulted in many Australian rivers being dominated b y algal production.