DECOMPOSITION OF PLANT MATERIALS IN MARINE SEDIMENT EXPOSED TO DIFFERENT ELECTRON ACCEPTORS (O2, NO3-, AND SO42-), WITH EMPHASIS ON SUBSTRATE ORIGIN, DEGRADATION KINETICS, AND THE ROLE OF BIOTURBATION

Abstract

Carbon mineralization of fresh and aged diatoms (Skeletonema costatum) and barley hay (Hordeum vulgare) was followed for 23 to 35 d in sandy and silty sediment. By the use of a thin-layer flow-through technique, it was possible to expose the sediment selectively for oxygen, nitrate or sulfate as electron acceptors in the terminal oxidation of organic carbon. Decomposition took place in two basic stages. Mineralization of the rapidly leachable fraction of the fresh materials occurred rapidly and with the same constant rate regardless of the electron acceptor available, indicating that the dissolved organic carbon released initially was labile and readily available for all heterotrophic respirers. In the case of diatoms, decay of the remaining, more refractory, particulate fraction of fresh and aged diatoms were strikingly similar, although both were degraded 5 to 10 times faster under oxic than anoxic conditions. Most of the particulate remains of diatoms after leaching apparently belong to one fraction, which maintains the same degradability even after prolonged aging. With respect to hay, the late divergence in rates of aerobic and anaerobic decay (a factor of 4 to 5 for aged hay only after 20 d) indicated that the larger hay particles (<500 μm) became exhausted in labile organic matter much slower through time than fine-particulate diatoms (~20 μm). anaerobic carbon mineralization rates of and hay particulates with sulfate nitrate as electron acceptors were similar or up to two times faster sulfate. the generally low levels dissolved all incubations after initial leaching phase suggest that limiting step decomposition under both aerobic decay is hydrolytic attack on complex particulate remains. based a volumetric model, we show exposure anoxic subsurface sediment containing partly degraded material oxygen via irrigated worm burrows by reworking may significantly enhance total oxidation. enhancement irrigation case increases linearly density (up 80%) higher density-independent (10%) when abundance above lower limit ~400 individuals m2.