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- Ekeroth, Nils, 1982-
(författare)
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Benthic fluxes of biogenic elements in the Baltic Sea : Influence of oxygen and macrofauna
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis investigates how benthic fluxes of phosphorus (P), nitrogen (N), and silicon (Si) change upon oxygenation of anoxic soft bottoms in the brackish, eutrophicated Baltic Sea. Direct measurements in situ by benthic landers demonstrated that fluxes of dissolved inorganic P (DIP) from anoxic bottom sediments in the Eastern Gotland Basin are higher than previously thought (Paper I). It is argued that the benthic DIP flux has a much larger influence on the DIP inventory in the Baltic proper than the external sources. Similarly, benthic fluxes of DIP and dissolved inorganic N (DIN) from anoxic sediment in the coastal Kanholmsfjärden Basin, Stockholm archipelago, were sufficiently high to renew the pools of these nutrients below the upper mixed layer in roughly one year (Paper II).A natural inflow of oxygen rich water into the deep, and previously long-term anoxic part of Kanholmsfjärden Basin, increased the P content in the sediment by 65% and lowered DIP and dissolved silica (DSi) concentrations in the pore water. These changes, as well as the large increases in benthic effluxes of these solutes following de-oxygenation of the bottom water, suggest that they are influenced similarly by changing oxygen conditions.Experimental results in papers III and IV show that common benthic macrofauna species in the Baltic Sea can stimulate benthic release of DIN and DSi, as well as dissolved organic and particulate bound nutrients. Thus, if benthic oxygen conditions would improve in the Baltic, initial effects on benthic–pelagic nutrient coupling will change due to animal colonisation of currently azoic soft bottoms.A new box corer was designed (Paper V) which can be used to obtain highly needed virtually undisturbed samples from soft bottom sediments – if lowered slowly and straight into the bottom strata – as demonstrated by in situ videography and turbidimetry. The commonly used USNEL box corer caused severe biasing during sediment collection.
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- Ekeroth, Nils, 1982-, et al.
(författare)
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Recolonisation by macrobenthos mobilises organic phosphorus from reoxidised Baltic Sea sediments
- 2012
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Ingår i: Aquatic geochemistry. - : Springer Science and Business Media LLC. - 1380-6165 .- 1573-1421. ; 18:6, s. 499-513
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Tidskriftsartikel (refereegranskat)abstract
- In recent decades, eutrophication has increased the extent of hypoxic and anoxic conditions in many coastal marine environments. In such conditions, the nutrient flux across the sediment–water interface is a key process controlling the biogeochemical dynamics, and thereby the level and character of biological production. In some areas, management attempts to drive the ecosystem towards phosphorus (P) limitation, which calls for reliable knowledge on the mechanisms controlling P-cycling. We report a well-controlled laboratory experiment on benthic fluxes of P, when shifting from a state of hypoxic and azoic sediments to oxic and zoic bottom conditions. Adding any of three types of macrobenthic fauna (mysid shrimp, pontoporeid amphipod and tellinid clam) to oxygenated aquarium sections resulted in benthic P fluxes that differed consistently from the azoic control sections. All species caused liberation of dissolved organically bound P (DOP) from the sediment, in contrast to the azoic systems. The shrimp and the amphipod also resuspended the sediment, which resulted in a release of P bound to particles (>0.45 μm). Dissolved inorganic phosphate (DIP) was released during hypoxic conditions, but was taken up after oxygenation, irrespective of the presence or absence of bottom fauna. In the presence of fauna, the uptake of DIP roughly equalled the release of DOP, suggesting that the benthic efflux of DOP following oxygenation and bottom fauna (re)colonisation might be considerable. This is an hitherto overlooked animal-controlled nutrient flux, which is missing from coastal marine P budgets.
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