Dissolved organic carbon production and consumption in anoxic marine sediments: A pulsed-tracer experiment

The degradation of phytoplankton and seagrass organic carbon (OC) in sulfat e-reducing (SR) and methane-producing (MP) sediments was tracked by measuri ng concentrations of particulate OC (POC), hydrolysis products (HP), fermen tation products (FP), and inorganic end products (EP). This experiment used the novel approach of amending sediment with organic substrates having del ta C-13 values unique from that of the OC pool originally present in the se diment. As a result, we could monitor changes in the dynamic dissolved OC p ool and gain insight into processes that control the fate of OC. Rates of h ydrolysis, fermentation, and terminal metabolism were greater in the phytop lankton-amended treatments than in the seagrass-amended treatments during t he period of active decomposition. At the end of the incubation, concentrat ions of HP and FP in amended treatments were not significantly different fr om those in the controls. An analysis of the delta C-13 values of HP from t he amended treatments indicated that the addition of fresh organic matter s timulated the decomposition of carbon present in the sediment at the time o f collection. Hydrolysis of this carbon accounted for greater than or equal to 50% of the total carbon hydrolyzed in the sediment amended with seagras s.