Figure 6 - available via license: Creative Commons Attribution 4.0 International
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LC50 plots for sea hare (top) and isopod (bottom) mortality at each treatment group. 50% mortality is indicated by the 400 dashed line.
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Marine carbon dioxide removal (mCDR) approaches are under development to mitigate the effects of climate change with potential co-benefits of local reduction of ocean acidification impacts. One such method is ocean alkalinity enhancement (OAE). A specific OAE method that avoids issues of solid dissolution kinetics and the release of impurities into...
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Context 1
... average, 50% mortality (LC50) of the sea hares was observed after the first water refresh (between day 0.5 and day 1) in the high treatment group (pH 9.3) and after 1.5 days (between day 1 and day 2.5) in the medium treatment group (pH 8.8) (Fig. 6 top). In the low treatment group (pH 8.3), LC50 was reached in only one of the three rounds of experiment, at day 3, and never reached in the control group (pH 7.8) (Fig. 6 ...
Context 2
... the first water refresh (between day 0.5 and day 1) in the high treatment group (pH 9.3) and after 1.5 days (between day 1 and day 2.5) in the medium treatment group (pH 8.8) (Fig. 6 top). In the low treatment group (pH 8.3), LC50 was reached in only one of the three rounds of experiment, at day 3, and never reached in the control group (pH 7.8) (Fig. 6 ...
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Marine carbon dioxide removal (mCDR) approaches are under development to mitigate the effects of climate change by sequestering carbon in stable reservoirs, with the potential co-benefit of local reductions in coastal acidification impacts. One such method is ocean alkalinity enhancement (OAE). A specific OAE method is the generation of aqueous alk...
Citations
... Although ∆pH ≈ 0.6 is high near the source and has the potential to cause localized ecosystem impacts [39,40], the pH levels of 8.6 is still well below the water quality protective standard of 9 in Washington, US, and drops rapidly to 8.1 or lower within the nearfield mixing zone ≈100 m (0.01 km 2 ), which lies within natural variability of pH in Sequim Bay [41]. The transects show that within Sequim Bay, there is elevation in background levels of pH and TA due to the longer residence and constrained flushing, but levels drop off further once the plume travels outside of Sequim Bay. ...
Marine CO2 removal (CDR) using enhanced-alkalinity seawater discharge was simulated in the estuarine waters of the Salish Sea, Washington, US. The high-alkalinity seawater would be generated using bipolar membrane electrodialysis technology to remove acid and the alkaline stream returned to the sea. Response of the receiving waters was evaluated using a shoreline resolving hydrodynamic model with biogeochemistry, and carbonate chemistry. Two sites, and two deployment scales, each with enhanced TA of 2997 mmol m⁻³ and a pH of 9 were simulated. The effects on air-sea CO2 flux and pH in the near-field as well as over the larger estuary wide domain were assessed. The large-scale deployment (addition of 164 Mmoles TA yr⁻¹) in a small embayment (Sequim Bay, 12.5 km²) resulted in removal of 2066 T of CO2 (45% of total simulated) at rate of 3756 mmol m⁻² yr⁻¹, higher than the 63 mmol m⁻² yr⁻¹ required globally to remove 1.0 GT CO2 yr⁻¹. It also reduced acidity in the bay, ΔpH ≈ +0.1 pH units, an amount comparable to the historic impacts of anthropogenic acidification in the Salish Sea. The mixing and dilution of added TA with distance from the source results in reduced CDR rates such that comparable amount 2176 T CO2 yr⁻¹ was removed over >1000 fold larger area of the rest of the model domain. There is the potential for more removal occurring beyond the region modeled. The CDR from reduction of outgassing between October and May accounts for as much as 90% of total CDR simulated. Of the total, only 375 T CO2 yr⁻¹ (8%) was from the open shelf portion of the model domain. With shallow depths limiting vertical mixing, nearshore estuarine waters may provide a more rapid removal of CO2 using alkalinity enhancement relative to deeper oceanic sites.
Marine carbon dioxide removal (mCDR) approaches are under development to mitigate the effects of climate change by sequestering carbon in stable reservoirs, with the potential co-benefit of local reductions in coastal acidification impacts. One such method is ocean alkalinity enhancement (OAE). A specific OAE method is the generation of aqueous alkalinity via electrochemistry to enhance the alkalinity of the receiving water by the extraction of acid from seawater, thereby avoiding the issues of solid dissolution kinetics and the release of impurities into the ocean from alkaline minerals. While electrochemical acid extraction is a promising method for increasing the carbon dioxide sequestration potential of the ocean, the biological effects of increasing seawater alkalinity and pH within an OAE project site are relatively unknown. This study aims to address this knowledge gap by testing the effects of increased pH and alkalinity, delivered in the form of aqueous NaOH, on two eelgrass epifauna in the US Pacific Northwest, Taylor's sea hare (Phyllaplysia taylori) and eelgrass isopod (Idotea resecata), chosen for their ecological importance as salmon prey and for their role in eelgrass ecosystems. Four-day experiments were conducted in closed bottles to allow measurements of the evolution of carbonate species throughout the experiment, with water refreshed twice daily to maintain elevated pH, across pHNBS (NBS standard scale) treatments ranging from 7.8 to 9.3. Sea hares experienced mortality in all pH treatments, ranging from 37 % mortality at pHNBS 7.8 to 100 % mortality at pHNBS 9.3. Isopods experienced lower mortality rates in all treatment groups, ranging from 13 % at pHNBS 7.8 to 21 % at pHNBS 9.3, which did not significantly increase with higher pH treatments. These experiments represent an extreme of constant exposure to elevated pH and alkalinity, which should be considered in the context of both the natural variation and the dilution of alkalinity experienced by marine communities across an OAE project site. Different invertebrate species will likely have different responses to increased pH and alkalinity, depending on their physiological vulnerabilities. Investigation of the potential vulnerabilities of local marine species will help inform the decision-making process regarding mCDR planning and permitting.
Rapid development and deployment of marine carbon dioxide removal (mCDR) approaches will be required to prevent the worst consequences of climate change and meet national treaty obligations under the Paris agreement. However, approaches to monitor the efficacy and environmental safety of mCDR are not being developed with the same intensity as the technology. Verification will be required to convince a sceptical public and regulatory community of the overall benefit of mCDR as well as provide the regulatory community a basis for risk assessments that will be required for at scale deployments. In this perspective, we posit that genomics-based approaches can be used to assess the efficacy of carbon sequestration and monitor for the possibility of unintended consequences. By adopting these approaches, it will be feasible to develop the evidence portfolio necessary to underpin assessments of the risks, benefits and trade-offs involved in responsible deployment of mCDR.
