Benthic fluxes of dissolved silica are an important component of the marine Si cycle in the coastal zone

Borawska, Zuzanna; Szymczycha, Beata; Silberberger, Marc J.; Koziorowska-Makuch, Katarzyna; Szczepanek, Marta; Kędra, Monika

doi:10.1016/j.ecss.2022.107880

Cited by 6 publications

(3 citation statements)

References 84 publications

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“…However, the shallow sedimentary depocenters in the Baltic Sea display strong biogeochemical and physical seasonality, which leads to a highly complex chemical system governed by variable oxygen availability, bottom water temperatures, microbial activities, and organic matter degradation rates (Dale et al, 2011;Melzner et al, 2013;Perner et al, 2022). Moreover, the large benthic background fluxes induced by natural CaCO 3 input via continental erosion and diatom dissolution (Gasiunaite et al, 2005;Borawska et al, 2022;Wallmann et al, 2022) constitute further challenges for disentangling natural and enhanced weathering, as they might overprint potential fluxes induced by enhanced benthic weathering.…”

Section: Introductionmentioning

confidence: 99%

Disentangling artificial and natural benthic weathering in organic rich Baltic Sea sediments

Fuhr,

Wallmann,

Dale

et al. 2023

Front. Clim.

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Enhanced mineral dissolution in the benthic environment is currently discussed as a potential technique for ocean alkalinity enhancement (OAE) to reduce atmospheric CO2 levels. This study explores how biogeochemical processes affect the dissolution of alkaline minerals in surface sediments during laboratory incubation experiments. These involved introducing dunite and calcite to organic-rich sediments from the Baltic Sea under controlled conditions in an oxic environment. The sediment cores were incubated with Baltic Sea bottom water. Findings reveal that the addition of calcite increased the benthic alkalinity release from 0.4 μmol cm−2 d−1 (control) to 1.4 μmol cm−2 d−1 (calcite) as well as other weathering products such as calcium. However, these enhanced fluxes returned to lower fluxes after approximately 4 weeks yet still higher than the un-amended controls. Microbial activity appeared to be the primary driver for lowering pore water pH and thus enhanced weathering. In several sediment cores, pH profiles taken at the start of the experiments indicated activity of sulfur oxidizing Beggiatoa spp, which was verified by RNA-profiling of 16S rRNA genes. The pH profiles transitioned to those commonly associated with the activity of cable bacteria as the experiments progressed. The metabolic activity of cable bacteria would explain the significantly lower pH values (~5.6) at sediment depths of 1–3 cm, which would favor substantial calcite dissolution. However, a high abundance of cable bacteria was not reflected in 16S rRNA sequence data. Total alkalinity (TA) fluxes in these cores increased by a factor of ~3, with excess TA/calcium ratios indicating that the enhanced flux originated from calcite dissolution. The dissolution of dunite or the potential formation of secondary minerals could not be identified due to the strong natural flux of silicic acid, likely due to biogenic silica dissolution. Furthermore, no accumulation of potentially harmful metals such as nickel was observed, as highlighted as a potential risk in other studies concerning OAE. Given the complexity of sediment chemistry and changes of the benthic conditions induced by the incubation, it remains challenging to distinguish between natural and enhanced mineral weathering. Further investigation, including the identification of suitable tracers for mineral dissolution, are necessary to assess the feasibility of benthic weathering as a practical approach for OAE and climate change mitigation.

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Section: Introductionmentioning

confidence: 99%

Disentangling artificial and natural benthic weathering in organic rich Baltic Sea sediments

Fuhr,

Wallmann,

Dale

et al. 2023

Front. Clim.

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“…Coastal ecosystems with high biodiversity of habitats and benthic communities, especially lagoons, bays and estuaries, play a special role in marine regulatory processes [2,3]. Benthic organisms play a key role in the circulation of chemical elements and nutrients directly by physiological processes such as feeding, respiration and excretion, as well as indirectly by reworking the sediment matrix through bioturbation and bioirrigation [4][5][6][7][8][9]. These activities can be positive for the ecosystem in terms of sediment oxygenation and increasing the surface area available for microbial activity [10][11][12].…”

Section: Introductionmentioning

confidence: 99%

Role of Macrofaunal Communities in the Vistula River Plume, the Baltic Sea—Bioturbation and Bioirrigation Potential

Miernik

Janas

Kendzierska

2023

Biology

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Macrozoobenthos plays a key role in the transformation of inputs from rivers to the sea, such as nutrients, organic matter, or pollutants, and influences biogeochemical processes in the sediments through bioturbation and bioirrigation activity. The purpose of our study was to determine the structure of benthic communities, their bioturbation (BPC) and bioirrigation potential (IPC), and the vertical distribution of macrofauna in the Gulf of Gdańsk. The study revealed changes in the structure of benthic communities and, consequently, in the bioturbation and bioirrigation potential in the study area. Despite the presence of diverse and rich communities in the coastal zone, BPC and IPC values, although high, were formed by a few species. Both indices were formed mainly by the clam Macoma balthica and polychaetes, although the proportion of polychaetes in IPC was higher than in BPC. In the deepest zones, the communities became poorer until they eventually disappeared, along with all macrofaunal functions. Both indices changed similarly with distance from the Vistula River mouth, and there was a very strong correlation between them. We also demonstrated that the highest diversity of the macrofauna was observed in the upper first cm of the sediment, but the highest biomass was observed in deeper layers—at a depth of up to 6 cm, and single individuals occurred even below 10 cm.

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“…In the Baltic Sea, distinguishing between natural and EBW is difficult, given the substantial benthic background fluxes driven by natural CaCO 3 input from continental erosion for calcium and diatom dissolution for silica that can overshadow potential fluxes induced by enhanced benthic weathering (Gasiunaite et al, 2005;Borawska et al, 2022;Wallmann et al, 2022;Fuhr et al, 2023). Furthermore, the dissolution kinetics of both calcite and olivine remain largely unexplored in the brackish waters of the Baltic Sea, introducing uncertainty whether dissolution rates assumed in modeling studies based on standard seawater (Feng et al, 2017;Griffioen, 2017;Fakhraee et al, 2023) can be applied in this specific region.…”

Section: Introductionmentioning

confidence: 99%

Alkaline mineral addition to anoxic to hypoxic Baltic Sea sediments as a potentially efficient CO2-removal technique

Fuhr,

Wallmann,

Dale

et al. 2024

Front. Clim.

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Recent studies have begun to explore the potential of enhanced benthic weathering (EBW) in the Baltic Sea as a measure for climate change mitigation. To augment the understanding of EBW under seasonally changing conditions, this study aims to investigate weathering processes under anoxia to hypoxia in corrosive bottom waters, which reflect late summer conditions in the Baltic Sea. Dunite and calcite were added to sediment cores retrieved from Eckernförde Bay (Western Baltic Sea) with a constant flow-through of deoxygenated, CO2-enriched Baltic Sea bottom water. The addition of both materials increased benthic alkalinity release by 2.94 μmol cm−2 d−1 (calcite) and 1.12 μmol cm−2 d−1 (dunite), compared to the unamended control experiment. These excess fluxes are significantly higher than those obtained under winter conditions. The comparison with bottom water oxygen concentrations emphasizes that highest fluxes of alkalinity were associated with anoxic phases of the experiment. An increase in Ca and Si fluxes showed that the enhanced alkalinity fluxes could be attributed to calcite and dunite weathering. First order rate constants calculated based on these data were close to rates published in previous studies conducted under different conditions. This highlights the suitability of these proxies for mineral dissolution and justifies the use of these rate constants in modeling studies investigating EBW in the Baltic Sea and areas with similar chemical conditions. Generally stable pH profiles over the course of the experiment, together with the fact that the added minerals remained on the sediment surface, suggest that corrosive bottom waters were the main driving factor for the dissolution of the added minerals. These factors have important implications for the choice of mineral and timing for EBW as a possible marine carbon dioxide removal method in seasonally hypoxic to anoxic regions of the Baltic Sea.

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Benthic fluxes of dissolved silica are an important component of the marine Si cycle in the coastal zone

Cited by 6 publications

References 84 publications

Disentangling artificial and natural benthic weathering in organic rich Baltic Sea sediments

Disentangling artificial and natural benthic weathering in organic rich Baltic Sea sediments

Role of Macrofaunal Communities in the Vistula River Plume, the Baltic Sea—Bioturbation and Bioirrigation Potential

Alkaline mineral addition to anoxic to hypoxic Baltic Sea sediments as a potentially efficient CO2-removal technique

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