Recycling Efficiencies of Organic Carbon, Nitrogen, Phosphorus and Reduced Sulfur in Rapidly Depositing Coastal Sediments

Abstract

Studies of the biogeochemical cycles of C, N, P and S in organic-rich coastal sediments such as those found in Cape Lookout Bight reveal direct linkages between the recycling of these elements as well as differential behaviour associated with other factors such as the nature of organic matter sources, sediment accumulation rates and bioturbation. In general we observe that: i) Remineralization of C, N and P is tightly coupled and supported by a reactive fraction of the total organic matter which may represent from less than 30% to almost 100% of that deposited. This reactive fraction has a low atomic C/N ratio close to that of fresh plankton. ii) The recycling of organic P following remineralization is controlled by adsorption/ precipitation processes involving iron and manganese oxyhydroxides. Phosphorus is less efficiently recycled than organic C and N as a result of these processes and exhibits more pronounced seasonality in fluxes as a result of changes in surface sediment redox conditions. iii) Rates of sulfate reduction are directly coupled to availability of reactive organic matter. However, the net retention and burial of reduced sulfur is largely controlled by bioturba- tion and availability of reduced iron.