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Impact of the 2014 Major Baltic Inflow on benthic fluxes of ferrous iron and phosphate below the permanent halocline in the southern Baltic Sea

Brocławik O., Łukawska-Matuszewska K., Bolałek J.

Oceanological and Hydrobiological Studies

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2018

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Vol. 47, No. 3

275--287

EN

The impact of 2014 Major Baltic Inflow (MBI) on ferrous iron (FFe(II)) and phosphate (FPO43–) benthic fluxes was investigated. Sampling took place few months after the MBI, in August 2015, and over one year after the inflow, in February 2016. Materials were collected from three sites (depth of 106–108 m) located in the Gdańsk Deep. Total dissolved iron, Fe(II), phosphate, H2S and sulfate were analyzed in bottom and pore water. Benthic fluxes were estimated using Fick’s first law. All fluxes were directed from sediment. FFe(II) ranged from 0.31 × 10–2 to 1.25 × 10–2 μmol m–2 hr–1 and FPO43– from 1.53 to 2.70 μmol m–2 hr–1. At the deepest site, FPO43– was similar in both seasons, while at two other sites fluxes in August 2015 were 40–50% smaller than in February 2016. The increase in bottom water oxygen after the MBI enhanced Fe(oxyhydr)oxides formation. As a consequence, bottom and pore water concentrations of Fe(II) and FFe(II), decreased. Adsorption of phosphate onto Fe(oxyhydr)oxides resulted in binding of P in surface sediment and lower FPO43– in August 2015. This was particularly evident at the shallowest site. The reductive dissolution of Fe(oxyhydr)oxides and desorption of P during the subsequent months resulted in higher FPO43– in February 2016.

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Phosphate exchange across the sediment–water interface under oxic and hypoxic/anoxic conditions in the southern Baltic Sea

Łukawska-Matuszewska K., Burska D.

Oceanological and Hydrobiological Studies

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2011

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Vol. 40, No.2

57-71

EN

Benthic fluxes of phosphate and phosphorus distribution in sediments from the southern Baltic Sea were investigated in spring and autumn in 2005 and 2007–2010. Strong spatial variability of phosphate fluxes was observed across the sediment–water interface. The highest values of phosphate flux from sediment (up to 37 μmol m-2 h-1), resulting from the high mineralization rate of organic matter and rapid phosphorus turnover due to macrofaunal activity and hydrodynamic conditions, were observed in the shallow area at depths ranging from 50 to 69 m. The rate of phosphate exchange in the transportation and accumulation bottom area with the water depth .72 m was several times lower (2.12 – 6.22 μmol m-2 h-1). In continuously hypoxic or anoxic sediments, phosphorus was preserved in the refractory organic form, and sediments were depleted of redox-dependent phosphorus forms. In shallow area with well oxygenated near-bottom water, phosphorus was present mainly in the calcium-bound form.

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Seasonal variability of benthic ammonium release in the surface sediments of the Gulf of Gdańsk (southern Baltic Sea)

Maksymowska-Brossard D., Piekarek-Jankowska H.

Oceanologia

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2001

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No. 43 (1)

113-136

EN

This paper describes the seasonal and spatial variations of diffusive sediment- water ammonium fluxes in the western part of the Gulf of Gdansk (southern Baltic). It assesses the potential environmental controls of these fluxes, such as the inflow of organic matter to bottom sediments and its quality, temperature-induced degradation of organic matter, and the redox potential of sediments. Ammonium fluxes, calculated using Fick's first law, were always in the direction from the sediment into the water column and differed significantly with respect to sediment type. Fluxes were most intensive in sediments with the highest silt-clay fraction located in the deepest parts of the study area. The mean annual diffusive fluxes of ammonium from sediments to near-bottom water were estimated at 5.24 tonnes km-2 year-1 for silty-clays, 1.85 tonnes km-2 year-1 for silty-sands and 1.03 tonnes km-2 year-1 for sandy sediments. There was a high seasonal variation, with the greatest ammonium release in summer and early autumn, when the temperature of near-bottom water was the highest. On the basis of the calculated diffusive ammonium fluxes, we estimated that approximately 2700 tonnes of N-NH4+ are released annually from the surface sediments of the western part of the Gulf of Gdansk, providing a minimum of 10% of the mineral nitrogen essential for primary production in surface waters. Our results are undoubtedly underestimated, as we disregarded advective ammonium fluxes, which in some areas of the Gulf of Gdansk could well be comparable to diffusive fluxes.