Detritus from leaves and stems of Spartina spp. at different decomposition stages constitute the major source of OM in intertidals from SW Atlantic bays and estuaries. Spartina spp. roots, in addition to their secretion of LOC that fuel microbial activity, efficiently transport oxygen to anoxic sediments, having a great impact on sediment diagenesis.Thus, the interaction among
macrofauna, macrophytes and microbial activities could have a significant effect on the OM preservation in marine and coastal sediments. The structure of roots, in turn, stabilize the substrate and reduce the maintenance of burrows,consequently reducing reworking rates and probably decreasing the vertical turnover rate ofmaterials during crab burrowing. Although we did not directly assess the effects of plants on OM processing, our results showed higher rates of net sediment metabolism (i.e., CO2 production) in saltmarsh sediments than in mudflat, suggesting an impact of vegetation on microbial activity in both bioturbated and non-bioturbated sediments. Also, our results showed that bioturbation enhanced the whole benthic metabolism about 8000% in the saltmarsh, but only about 200% in the mudflat. This is a somewhat surprising result, since TOC content was similar at both zones and reworking rates are slow in the saltmarsh, so we would expect a smaller bioturbation effect in this intertidal zone.