Effects of oxygen on recycling of biogenic elements from sediments of a stratified coastal Baltic Sea basin

Benthic nutrient dynamics in the coastal basin Kanholmsfjarden, NW Baltic proper, were studied by in situ flux measurements and sediment samplings in 2010–2013. The benthic release of NH4 and DIP from anoxic sediments in Kanholmsfjarden were calculated to renew the standing stock inventories of DIN and DIP in the overlying water in roughly 1 year. Starting in summer 2012, mixing of oxygen-rich water into the deep part of the basin temporarily improved the oxygen conditions in the deepwater. During the 1 year oxygenated period, the total phosphorus inventory in the surficial sediment increased by 0.4 g Pm−2 or 65%. Thiswasmost likely due to stimulated bacterial P assimilation under oxygenated conditions. By July 2013, the bottomwater had again turned anoxic, and DIP and DSi fluxes were even higher than earlier in the study period. These high fluxes are attributed to degradation of sedimentary pools of P and Si that had accumulated during the bottom wateroxygenation in 2012. The strong correlation between DIP and DSi fluxes and the similar dynamics of DIP and DSi in the sediment pore water and near bottom water, suggest a similar redox dependency of benthic–pelagic exchange for these nutrients. © 2015 The Authors. Published by Elsevier B.V. This is an open