Limited Australian data on sedimentary processes- C, N, P, Fe and Si diagenesis at the sediment/water interface- have been reviewed. These and the results of more recent work with benthic chambers indicate that the fractionation and transfer of N, P and Si from sedimentary particulates to pore waters control the speciation and concentrations of N, P and Si at the sediment- water interface and, ultimately, nutrients available for phototrophic growth. Oxygen and sulphate are quantitatively the most important oxidants recycling organic carbon. Secondary oxidants, such as nitrate (sourced from sedimentary nitrification or the overlying waters), are important for denitrification and the N balance. Iron is an intermediary in the nitrification and denitrification processes and also controls (in part) P fluxes across the sediment- water interface. The Port Phillip Bay environmental study demonstrated the contribution benthic chambers have made, so far, to studies of sediment- water exchange in Australian environments. These include the following: 1) defining the stoichiometry between the oxidation of organic carbon via oxygen, nitrate and sulphate reductions and the remineralisation of N, P and Si from sediments to overlying waters; 2) calculating net benthic respiration and nutrient (N, P and Si) fluxes (and speciation of N) to the water column; 3) identifying transport processes either advection (e.g. bioirrigation) or diffusion controlling metabolite transfers between the sediments and overlying waters; 4) investigating interactions between benthic flora and sediments; and 5) evaluating the controls and effects of benthic processes on water quality. The interpretations are more robust when combined with specific biomarker analyses of the most abundant organic matter source in the sediments, including its nature- fresh versus old and refractory. A limited survey of TOC content in Australian sediments found it to vary between < 1 % wt in unimpacted estuarine and shelf sediments to near 10% wt in a coastal lake in Western Australia impacted by activities in the catchment. Highest TOC was, however, found in mangrove sediments (2-15% wt ) in tropical Queensland. TOC:TN and TOC :TP ratios in sediments are not unique indicators of organic matter sources. The ratios probably reflect (i) mixed planktonic (predominantly diatomaceous) and other plant inputs of various aged and reworked organic matter; (ii) early diagenesis-specifically, denitrification, which results in the significant loss of N to the atmosphere as N, gas; and (iii) solute/particle interactions, specifically P and Fe cycling. P is trapped in oxic to suboxic sediments, but is liberated to the overlying waters when interfacial sediments become anoxic.
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