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Effect of a controlled sub-seabed release of CO2 on the biogeochemistry of shallow marine sediments, their pore waters, and the overlying water column

Effect of a controlled sub-seabed release of CO2 on the biogeochemistry of shallow marine sediments, their pore waters, and the overlying water column
Effect of a controlled sub-seabed release of CO2 on the biogeochemistry of shallow marine sediments, their pore waters, and the overlying water column
The potential for leakage of CO2 from a storage reservoir into the overlying marine sediments and into the water column and the impacts on benthic ecosystems are major challenges associated with carbon capture and storage (CCS) in subseafloor reservoirs. We have conducted a field-scale controlled CO2 release experiment in shallow, unconsolidated marine sediments, and documented the changes to the chemical composition of the sediments, their pore waters and overlying water column before, during and up to 1 year after the 37-day long CO2 release. Increased levels of dissolved inorganic carbon (DIC) were detected in the pore waters close to the sediment-seawater interface in sediments sampled closest to the subsurface injection point within 5 weeks of the start of the CO2 release. Highest DIC concentrations (28.8 mmol L?1, compared to background levels of 2.4 mmol L?1) were observed 6 days after the injection had stopped. The high DIC pore waters have high total alkalinity, and low ?13CDIC values (?20‰, compared to a background value of ?2‰), due to the dissolution of the injected CO2 (?13C = ?26.6‰). The high DIC pore waters have enhanced concentrations of metals (including Ca, Fe, Mn) and dissolved silicon, relative to non-DIC enriched pore waters, indicating that dissolution of injected CO2 promotes dissolution of carbonate and silicate minerals. However, in this experiment, the pore water metal concentrations did not exceed levels considered to be harmful to the environment. The spatial extent of the impact of the injected CO2 in the sediments and pore waters was restricted to an area within 25 m of the injection point, and no impact was observed in the overlying water column. Concentrations of all pore water constituents returned to background values within 18 days after the CO2 injection was stopped.
Carbon capture and storage, CO2 leakage, Sediment biogeochemistry, Release of metals, Environmental impact
1750-5836
80-92
Lichtschlag, Anna
be1568d9-cc63-4f85-bd38-a93dfd7e245f
James, Rachael H.
79aa1d5c-675d-4ba3-85be-fb20798c02f4
Stahl, Henrik
bdd6e6a3-906e-4714-855a-3634cf0d471b
Connelly, Douglas
d49131bb-af38-4768-9953-7ae0b43e33c8
Lichtschlag, Anna
be1568d9-cc63-4f85-bd38-a93dfd7e245f
James, Rachael H.
79aa1d5c-675d-4ba3-85be-fb20798c02f4
Stahl, Henrik
bdd6e6a3-906e-4714-855a-3634cf0d471b
Connelly, Douglas
d49131bb-af38-4768-9953-7ae0b43e33c8

Lichtschlag, Anna, James, Rachael H., Stahl, Henrik and Connelly, Douglas (2015) Effect of a controlled sub-seabed release of CO2 on the biogeochemistry of shallow marine sediments, their pore waters, and the overlying water column. International Journal of Greenhouse Gas Control, 38, 80-92. (doi:10.1016/j.ijggc.2014.10.008).

Record type: Article

Abstract

The potential for leakage of CO2 from a storage reservoir into the overlying marine sediments and into the water column and the impacts on benthic ecosystems are major challenges associated with carbon capture and storage (CCS) in subseafloor reservoirs. We have conducted a field-scale controlled CO2 release experiment in shallow, unconsolidated marine sediments, and documented the changes to the chemical composition of the sediments, their pore waters and overlying water column before, during and up to 1 year after the 37-day long CO2 release. Increased levels of dissolved inorganic carbon (DIC) were detected in the pore waters close to the sediment-seawater interface in sediments sampled closest to the subsurface injection point within 5 weeks of the start of the CO2 release. Highest DIC concentrations (28.8 mmol L?1, compared to background levels of 2.4 mmol L?1) were observed 6 days after the injection had stopped. The high DIC pore waters have high total alkalinity, and low ?13CDIC values (?20‰, compared to a background value of ?2‰), due to the dissolution of the injected CO2 (?13C = ?26.6‰). The high DIC pore waters have enhanced concentrations of metals (including Ca, Fe, Mn) and dissolved silicon, relative to non-DIC enriched pore waters, indicating that dissolution of injected CO2 promotes dissolution of carbonate and silicate minerals. However, in this experiment, the pore water metal concentrations did not exceed levels considered to be harmful to the environment. The spatial extent of the impact of the injected CO2 in the sediments and pore waters was restricted to an area within 25 m of the injection point, and no impact was observed in the overlying water column. Concentrations of all pore water constituents returned to background values within 18 days after the CO2 injection was stopped.

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Accepted/In Press date: October 2014
Published date: July 2015
Keywords: Carbon capture and storage, CO2 leakage, Sediment biogeochemistry, Release of metals, Environmental impact
Organisations: Geochemistry, Marine Geoscience

Identifiers

Local EPrints ID: 370556
URI: http://eprints.soton.ac.uk/id/eprint/370556
ISSN: 1750-5836
PURE UUID: 3b101bbe-56fa-49b9-9fa3-8fb5bc9567e7

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Date deposited: 29 Oct 2014 10:17
Last modified: 21 Oct 2019 19:18

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