The biogeochemical cycling of dissolved organic nitrogen in estuarine sediments

Article Abstract:

Estuarine sediments and the biogeochemical cycling of dissolved organic nitrogen (DON) are discussed. A study has been carried out in three contrasting sites in Chesapeake Bay. Results suggest that the dissolved organic material (DOM) accumulating in the sediment pore waters was carbon-rich vs the DOM that was remineralized or escaped the sediment as benthic flux. DON escaping from the sediments may not be inherently refractory: a low C:N ratio was seen. Estuarine sediments, and maybe marine sediment overall, may not be a major source of ocean refractory DON.

United States, Statistical Data Included, Chesapeake Bay, Ocean, Oceans, Benthos, Benthic zone, Nitrogen cycle

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Rhythmic ammonium regeneration and flushing in intertidal sediments of the Sado estuary

Article Abstract:

Exposure to the atmosphere affects cycling of ammonium in intertidal sediments, according to a study conducted over a nine-hour period during a tidal cycle in the Sado estuary, Portugal. At the end of the exposure period, water flooded the sediment and approximately 75% of the ammonium was flushed into the water column. The sorbed pool had a faster build-up of ammonium in the sediment than the dissolved pool. Turnover of organic matter in estuary intertidal sediments is rapid, with residence times of 37.5 d for organic carbon and 43.4 d for nitrogen.

Portugal, Ammonium, Intertidal zonation, Intertidal areas

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Sedimentation, bioturbation, and Hg uptake in the sediments of the estuary and Gulf of St. Lawrence

Article Abstract:

The magnitude and timing of mercury (Hg) contamination in the St. Lawrence estuary and Gulf have been investigated using a biodiffusion model and radionuclide tracers to establish rates of sedimentation and mixing. A chloralkali plant on the Saguenay River that closed in 1976 released some 136 tonnes of Hg over 30 years of operation. About 100-130 tonnes are estimated to be present in the seduciments of the St. Lawrence Estuary.

Mercury, Mercury (Metal), Sedimentation and deposition, Deposition (Geology), Gulf of Saint Lawrence

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