Environmental impacts of leakage from sub-seabed CO2 storage

Informations

Funding country

Norway

Acronym

-

URL

-

Start date

1/1/2016

End date

12/31/2019

Budget

861,000 EUR

Fundings

Abstract

RESULTS Mobilization of Metals: Our results indicate that mobilization of metals from sediment is definitely a function of sediment types, its organic contents, and especially geological characters (minerals composition). As expected the lowest pH applied during the experiments (pH 6.3) was creating more mobility of metals (such as Hg, Pb, and U), especially from weakly adsorbed fraction. The CO2-exposure induced a decrease in pH from 8.0 to 6.9 and an increase in DIC by 380 µmol/kg in both experiments. The results of experiments under pH 6.9 indicate that two elements which showed significant mobilization are arsenic (As) and cadmium (Cd) both of which are known environmental toxicants. To follow Fe and Mn is essential which are important indicators for redox changes in the sediment and they are serving as a shuttle to carry other surface-active elements. Our results also indicate that even residual fractions of some metals showed signs of mobilization during the CO2 leakage test at pH 6.9, which was not expected. On the other hand, some metals such as Fe and Mn mobilized in some fraction but accumulated in the sediment as other forms, this shows that CO2 leakage will cause a transformation of metals from one fraction into other and has potential to change the sediment chemistry. Significant differences in the response to CO2-exposure are observed between the two sediment types tested. 10.5% of the total CaCO3-minerals were dissolved in the Trondheimsfjord sediment meanwhile the calcite and dolomite within the Barents Sea sediment were unaffected by the CO2-exposure. Cd mobilization in these two sediment types shows completely different patterns and their correlations with carbonate minerals are different, which is an expression of different mineral composition of these two sample sites. Impact on macrofauna and microbial community in the sediment: Results of TrykkCO2 showed that adults specimens of Astarte sp. were not affected under pH 7. Experimental CO2 leakage caused no lethal effects or bioaccumulation of toxic elements in the organism. They could grow in a normal way. The results of TrykkCO2 results reveled a gradual impact of CO2 leakage on the bacterial composition as well as bacterial activity. This evidence was clearly observed the last experiment testing Barents Sea sediments (Fig. 5). Even, after the CO2 leakage, bacteria did not show any recovery stage to initial status. Changes in the relative abundance of Pseudomonas, Flavobacteria, desulfuromonadales, and geobacteraceae or Rodobactaerlaes may confirm alterations on biogeochemical cycles in sediments. Results based on bacterial activity were also found in experiment 2 testing Trondheim fjord sediments. Therefore, results suggested that bacterial community may be impacted in any location. Impact on DOC characterization: The impact of low pH on organic carbon characterization was also observed during our experiment, our results suggest the changes in the charge of organic carbon during the experiment in CO2 treatment. Positively charged DOC will be dominant under CO2 treatments and some increase in recalcitrant DOC (less available for bacterial decomposition) under CO2 treatment has been observed. If this results will be confirmed after detailed data analysis, which is going on right now, this may have some consequences for microbial carbon decomposition which is an important process of the biological carbon capture and storage (B-CCS) mechanism in the marine environment. Results of the models: The results of TOUGHREACT model with appropriate top and bottom boundary conditions for the two cases (Distal and Local) confirm the hypothesis and suggest that pH, dissolved Fe(II) and Ca profiles may be the best indicators of leakage, and potentially the best indicators to distinguish local versus distal leakage locations based on their spatial and temporal trends. BROM was applied for studying of consequences of a 2-hours long discharge of gaseous CO2 with a rate of 11 l/min (Fig.9). CO2 bubbles disappear immediately after the stop of the leak, while changes in pH, pCO2 and TIC that can be detected for several days after the but leak in a very small distance from the leaking point (< 10 m ). In conclusion, our results clearly show that mobilization of metals from sediment, and the response of microbial communities to CO2 leakage are definitely a function of sediment types, its organic contents and especially sediments geological characters (minerals composition).