Weight loss, carbon, nitrogen and sulfur dynamics during early diagenesis of organic matter in fresh and salt water marshes along the Delaware River and Bay
It has been widely believed that decomposition of organic matter in marine and near-marine environments is enhanced by a slow sedimentation rate and inhibited by rapid sedimentation. However, the influence on litter dynamics of rapid exhumation and reburial of organic matter by storms and bioturbation is not well known. Therefore, litterbag experiments were conducted and sediment cores were taken in Great Marsh and Raccoon Creek Marsh to measure the influence of rapid burial and exhumation on several aspects of early diagenesis.
Known weights of oven dried senescing Spartina alterniflora, Peltandra virginica and Zizania aquatica above ground biomass were sealed in polypropylene mesh bags and placed at the marsh surface, 10 cm and 40 cm below the marsh surface. To simulate rapid burial and exhumation of partially decomposed organic matter, some of the organic matter at 10 cm was switched with organic matter at the marsh surface six weeks into the experiment and some of the samples at 40 cm were transferred to the surface. Litterbags were retrieved at irregular time intervals, cleaned, oven dried, weighed and crushed to pass a 1/2 mm sieve. The weight loss, sulfur, carbon and nitrogen concentrations in each sample were determined.
Based on 461 days of monitoring, results from this study suggest that during the decomposer phase decomposition was faster at 10 cm than at the marsh surface. Transferring organic matter from one redox environment to another slows decomposition rate. Decomposition at all the three depths converged during the refractory phase after approximately 60% of the organic matter had been lost. Sulfur content analysis suggest that plant type and litter quality may be important during sulfur enrichment in organic matter. Sulfur accumulation in the decomposing organic matter was highest at 10 cm. In addition, sulfur accumulation was influenced by the litter type and litter quality. Sediment mixing is a common process in near shore environments and these sediments contain abundant organic matter from various vegetation types. This study provides evidence of some new factors which contribute to the understanding of chemical changes that occur during early diagenesis of marsh sediments.
0481: Soil sciences