Elevated sedimentary removal of Fe, Mn, and trace elements following a transient oxygenation event in the Eastern Gotland Basin, central Baltic Sea

Velde, Sebastiaan van de; Hylén, Astrid; Kononets, Mikhail; Marzocchi, Ugo; Leermakers, Martine; Choumiline, Konstantin; Hall, Per; Meysman, Filip J. R.

doi:10.1016/j.gca.2019.11.034

“…(b) Water-column profiles of oxygen. Data from SMHI (SMHI, 2019; year 2014, station BY15), Hall et al (2017;year 2015, station F) and van de Velde et al (2020b;years 2016-2018. (c) Bottom-water oxygen (O2) concentrations measured by the benthic chamber lander (average ± standard deviation).…”

Section: Site Characteristicsmentioning

confidence: 99%

“…Upon arrival at the stations, a CTD (SBE 911, Sea-Bird Scientific) with a high-accuracy oxygen sensor (SBE 43, Sea-Bird Scientific) was deployed to record water-column profiles of salinity, temperature and oxygen (van de Velde et al, 2020b).…”

Section: Water-column and Benthic In-situ Flux Measurementsmentioning

confidence: 99%

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Hylen¹

2021

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Phosphorus fertilisation (eutrophication) is expanding oxygen depletion in coastal systems worldwide. Under lowoxygen bottom-water conditions, phosphorus release from the sediment is elevated which further stimulates primary production. It is commonly assumed that re-oxygenation could break this 'vicious cycle' by increasing sedimentary phosphorus retention. Recently, a deep-water inflow into the Baltic Sea created a natural in-situ experiment that allowed us to investigate if temporary re-oxygenation stimulates sedimentary retention of dissolved inorganic phosphorus (DIP). Surprisingly, during this three-year-long study, we observed a transient but considerable increase, rather than a decrease, in the sediment efflux of DIP and other dissolved biogenic compounds. This suggested that the oxygenated inflow elevated the organic matter degradation in the sediment. As a result, the net sedimentary DIP release per m 2 was 35-70% higher over the years following the re-oxygenation than before. In contrast to previous assumptions, our results show that inflows of oxygenated water to anoxic bottom waters can increase the sedimentary phosphorus release. IntroductionEutrophication is one of the main causes of oxygen depletion in coastal systems worldwide (Breitburg et al., 2018;Diaz and Rosenberg, 2008). Excess input of nutrients from land stimulates primary production, resulting in a higher delivery of organic matter to deeper coastal waters and the seafloor (Breitburg et al., 2018;Middelburg and Levin, 2009). Oxygen is consumed as this organic matter is degraded and in severe cases, anoxia can develop. Depletion of oxygen can lead to decreasing biodiversity and thereby a loss of important ecosystem functions and services (

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“…The detection limit was 0.5 µM. Data from Hall et al (2017) and van de Velde et al (2020b). *no measurement.…”

Section: Site Characteristicsmentioning

confidence: 99%

“…Sediment-water fluxes of nutrients and dissolved inorganic carbon (DIC) were subsequently measured using the Gothenburg benthic chamber lander (Kononets et al, 2020). Deployment of the lander during these samplings has been described in detail elsewhere (Hall et al, 2017;van de Velde et al, 2020b). Briefly, the lander carried four incubation chambers incubating 400 cm 2 of sediment with overlying water each.…”

Section: Water-column and Benthic In-situ Flux Measurementsmentioning

confidence: 99%

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Hylen

¹

2021

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Phosphorus fertilisation (eutrophication) is expanding oxygen depletion in coastal systems worldwide. Under lowoxygen bottom-water conditions, phosphorus release from the sediment is elevated which further stimulates primary production. It is commonly assumed that re-oxygenation could break this 'vicious cycle' by increasing sedimentary phosphorus retention. Recently, a deep-water inflow into the Baltic Sea created a natural in-situ experiment that allowed us to investigate if temporary re-oxygenation stimulates sedimentary retention of dissolved inorganic phosphorus (DIP). Surprisingly, during this three-year-long study, we observed a transient but considerable increase, rather than a decrease, in the sediment efflux of DIP and other dissolved biogenic compounds. This suggested that the oxygenated inflow elevated the organic matter degradation in the sediment. As a result, the net sedimentary DIP release per m 2 was 35-70% higher over the years following the re-oxygenation than before. In contrast to previous assumptions, our results show that inflows of oxygenated water to anoxic bottom waters can increase the sedimentary phosphorus release. IntroductionEutrophication is one of the main causes of oxygen depletion in coastal systems worldwide (Breitburg et al., 2018;Diaz and Rosenberg, 2008). Excess input of nutrients from land stimulates primary production, resulting in a higher delivery of organic matter to deeper coastal waters and the seafloor (Breitburg et al., 2018;Middelburg and Levin, 2009). Oxygen is consumed as this organic matter is degraded and in severe cases, anoxia can develop. Depletion of oxygen can lead to decreasing biodiversity and thereby a loss of important ecosystem functions and services (

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Enhanced benthic nitrous oxide and ammonium production after natural oxygenation of long‐term anoxic sediments

Hylén

¹

,

Bonaglia

²

,

Robertson

³

et al. 2021

Limnology & Oceanography

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Coastal and shelf sediments are central in the global nitrogen (N) cycle as important sites for the removal of fixed N. However, this ecosystem service can be hampered by ongoing deoxygenation in many coastal areas. Natural reoxygenation could reinstate anoxic sediments as sites where fixed N is removed efficiently. To investigate this further, we studied benthic N cycling in previously long-term anoxic sediments, following a large intrusion of oxygenated water to the Baltic Sea. During three campaigns in 2016-2018, we measured in situ sediment-water fluxes of ammonium (NH þ 4 ), nitrate (NO À 3 ), oxygen (O 2 ), dissolved inorganic carbon, and NO À 3 reduction processes using benthic chamber landers. Sediment microprofiles of O 2 , nitrous oxide (N 2 O), and hydrogen sulfide were measured in sediment cores. At a permanently oxic station, denitrification to N 2 was the main NO À 3 reduction process. Benthic N 2 O production appeared to be linked to nitrification, although no net N 2 O fluxes from the sediment were detected. At newly oxygenated sites, dissimilatory NO À 3 reduction to NH þ 4 comprised almost half of the total NO À 3 reduction. At these stations, the removal of fixed N was inefficient due to high effluxes of NH þ 4 . Sedimentary N 2 O production was associated with incomplete denitrification, accounting for 41-88% of the total denitrification rate. Microprofiling revealed algae aggregates as potential hotspots of seafloor N 2 O production. Our results show that transient oxygenation of euxinic systems initiates benthic NO À 3 reduction, but may not lead to efficient sedimentary removal of fixed N. Instead, recycling of N compounds is promoted, which may accelerate the return to anoxia.

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Elevated sedimentary removal of Fe, Mn, and trace elements following a transient oxygenation event in the Eastern Gotland Basin, central Baltic Sea

Cited by 28 publications

References 97 publications

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Enhanced benthic nitrous oxide and ammonium production after natural oxygenation of long‐term anoxic sediments

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