The impact of induced redox transitions on nutrient diagenesis in coastal marine sediments (Gulf of Trieste, northern Adriatic Sea)
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Sequential nutrient regeneration and organic matter (OM) degradation were studied in surface coastal sediments of the Gulf of Trieste (northern Adriatic Sea).
Materials and methods
In situ benthic chambers were used under normoxic, anoxic and reoxic conditions. Diffusive benthic fluxes were calculated from pore water modelling using a diffusion-advection-reaction model.
Results and discussion
Intensive NH4 + and PO4 3− anoxic regeneration was subsequently slower in prolonged anoxia. NH4 + production was probably also a consequence of dissimilatory nitrate reduction to NH4 +. The presence of laterally pumping of oxygenated water by benthic infauna can explain the presence of NO3 − in anoxia. Anoxic phases were characterized by enhanced dissolution of biogenic Si. Reoxygenation was characterized by enhanced bioturbation. Nitrification caused NH4 + decrease. P precipitated quickly as carbonate fluorapatite and FePO4 and adsorption of P onto Fe-hydroxides could also occur. Diffusive fluxes at the sediment-water interface (SWI) revealed high anoxic NH4 + effluxes, while PO4 3− fluxes were very low. High NH4 +/PO4 3− flux ratios in anoxic and reoxic phases suggested an excess of benthic inorganic N.
Nutrient budgets at the sediment-water interface of this sandy coastal sediment showed intensive anoxic recycling of inorganic N, but low P and Si cycling in all redox phases.
KeywordsGulf of Trieste Modelling Nutrients Redox changes Sediments
This research was conducted in the framework of the Austrian Science Fund (FWF) project P21542-B17 entitled “Low dissolved oxygen events in the Northern Adriatic: in situ experimental insights into benthic responses before, during and post-anoxia”. This part of the research was also supported financially by the Research Programme P1-0143 and the Young Researcher Programme of the Slovenian Research Agency (ARRS). We thank M. Stachowitsch, M. Zuschin, I. Gallmetzer and A. Haselmair for the technical and diving support. Authors also thank R. Pain for the linguistic corrections.
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