Evaluation of the biogeochemical capacity of sediments to process and dissipate N

Estuaries and coastal zones are shallow water bodies at the interface between fresh and marine aquatic environments, and highly dynamic environments controlled by physical processes and exposed to marine and continental influences. They host large energy and matter fluxes, supported by a few specific conditions: they are brackish, shallow and they can receive large nutrient amounts from the terrestrial side.

Eutrophication is a naturally occurring process in most coastal zones, however, over the last decades eutrophication has been dramatically increased by human activity in the catchment areas. Its impacts associated to climate change are unknown and poorly investigated.

Climate change, in particular in northern latitudes, is expected to affect patterns of ice formation and melting, precipitation and temperature regimes and may offset estuarine functioning via floods, storms, dissolved and particulate nutrient transport, heat waves, water stratification and prolonged low discharge periods. 

Aim:  Analyze the capacity of sediments to mineralize particulate N to NH4+, to oxidize it to NOx and to denitrify the produced NOx. Alternative N pathways as DNRA (dissimilatory nitrate reduction to ammonium), which recycles NH4+ and decreases the denitrification efficiency, will be measured. 

Where:  Different sedimentary environments in Gulf of Gdańsk, Sacca di Goro lagoon (Italy) and Norwegian fjords

When:  Two seasons will be compared: the spring and the summer, with high and low NO3 levels, respectively

How:  Intact sediment dark incubations along physico-chemical (e.g., depth and oxygen or organic matter availability), biological (e.g., bioturbation, primary producers’ growth forms) and latitudinal gradients (Italy, Poland, Norway)

Maps of the sampling site and the sampled station along the Vistula mouth

Denitrification is the process that removes NO3  from the system and it is controlled by the concentration of the substrates NO3 , dissolved organic carbon, and the presence of bioturbation.

Our results demonstrated that in the Vistula mouth denitrification is mainly driven by the organic matter content in the sediment.

Bioturbation increases the oxidized layers of the deep sediment (light brown color in the picture) due to the introduction of the oxic bottom water via bioirrigation of the burrows.

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