Posts Tagged 'mitigation'

Metal fractionation in marine sediments acidified by enrichment of CO2: a risk assessment

Highlights

• Acidification related to CO2 leakages modifies the geochemistry of metals.
• Mobilization of metals from sediment into the water column is associated with their speciation.
• Sediments from Huelva Estuary have relevant concentrations of As, Cu, Pb and Zn.
• Risk assessment code analysis revealed that Zn presents the highest potential risk.

Abstract

Carbon-capture and storage is considered to be a potential mitigation option for climate change. However, accidental leaks of CO2 can occur, resulting in changes in ocean chemistry such as acidification and metal mobilization. Laboratory experiments were performed to provide data on the effects of CO2-related acidification on the chemical fractionation of metal(loid)s in marine-contaminated sediments using sequential extraction procedures. The results showed that sediments from Huelva estuary registered concentrations of arsenic, copper, lead, and zinc that surpass the probable biological effect level established by international protocols. Zinc had the greatest proportion in the most mobile fraction of the sediment. Metals in this fraction represent an environmental risk because they are weakly bound to sediment, and therefore more likely to migrate to the water column. Indeed, the concentration of this metal was lower in the most acidified scenarios when compared to control pH, indicating probable zinc mobilization from the sediment to the seawater.

Continue reading ‘Metal fractionation in marine sediments acidified by enrichment of CO2: a risk assessment’

An assessment of direct dissolved inorganic carbon injection to the coastal region: a model result

The amount of carbon dioxide (CO2) in the atmosphere has increased in the past 60 years and the technology of carbon capture and storage (CCS) has recently been extensively studied. One of the strategies of CCS is to directly inject a high dissolved inorganic carbon (DIC) concentration (or high partial pressure of carbon dioxide, pCO2) solution into the ocean. However, the carbonate dynamics and air-sea gas exchange are usually neglected in a CCS strategy. This study assesses the effect of a DIC-solution injection by using a simple two end-member model to simulate the variation of pH, DIC, total alkalinity (TA) and pCO2 between the river and sea mixing process for the Danshuei River estuary and Hoping River in Taiwan. We observed that the DIC-solution injection can contribute to ocean acidification and can also lead the pCO2 value to change from being undersaturated to oversaturated (with respect to the atmospheric CO2 level). Our model result also showed that the maximum Revelle factors (Δ[CO2]/[CO2])/(Δ[DIC]/[DIC]) among varied pH values (6–9) and DIC concentrations (0.5–3.5 mmol kg−1) were between pH 8.3 and 8.5 in fresh water and were between 7.3 and 7.5 in waters with a salinity of 35, reflecting the changing efficiency of dissolving CO2 gas into the DIC solution and the varying stability of this desired DIC solution. Finally, we suggest this uncoupled Revelle factor between fresh and salty water should be considered in the (anthropogenic) carbonate chemical weathering on a decade to century scale.

Continue reading ‘An assessment of direct dissolved inorganic carbon injection to the coastal region: a model result’

Adaptation strategies to climate change in marine systems

The world’s oceans are highly impacted by climate change and other human pressures, with significant implications for marine ecosystems and the livelihoods that they support. Adaptation for both natural and human systems is increasingly important as a coping strategy due to the rate and scale of ongoing and potential future change. Here, we conduct a review of literature concerning specific case studies of adaptation in marine systems, and discuss associated characteristics and influencing factors, including drivers, strategy, timeline, costs, and limitations. We found ample evidence in the literature that shows that marine species are adapting to climate change through shifting distributions and timing of biological events, while evidence for adaptation through evolutionary processes is limited. For human systems, existing studies focus on frameworks and principles of adaptation planning, but examples of implemented adaptation actions and evaluation of outcomes are scarce. These findings highlight potentially useful strategies given specific social–ecological contexts, as well as key barriers and specific information gaps requiring further research and actions.

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Model‐based assessment of the CO2 sequestration potential of coastal ocean alkalinization

The potential of coastal ocean alkalinization (COA), a carbon dioxide removal (CDR) climate engineering strategy that chemically increases ocean carbon uptake and storage, is investigated with an Earth system model of intermediate complexity. The CDR potential and possible environmental side effects are estimated for various COA deployment scenarios, assuming olivine as the alkalinity source in ice‐free coastal waters (about 8.6% of the global ocean’s surface area), with dissolution rates being a function of grain size, ambient seawater temperature, and pH. Our results indicate that for a large‐enough olivine deployment of small‐enough grain sizes (10 µm), atmospheric CO2 could be reduced by more than 800 GtC by the year 2100. However, COA with coarse olivine grains (1000 µm) has little CO2 sequestration potential on this time scale. Ambitious CDR with fine olivine grains would increase coastal aragonite saturation Ω to levels well beyond those that are currently observed. When imposing upper limits for aragonite saturation levels (Ωlim) in the grid boxes subject to COA (Ωlim = 3.4 and 9 chosen as examples), COA still has the potential to reduce atmospheric CO2 by 265 GtC (Ωlim = 3.4) to 790 GtC (Ωlim = 9) and increase ocean carbon storage by 290 Gt (Ωlim = 3.4) to 913 Gt (Ωlim = 9) by year 2100.

Continue reading ‘Model‐based assessment of the CO2 sequestration potential of coastal ocean alkalinization’

Assessing carbon dioxide removal through global and regional ocean alkalinization under high and low emission pathways (update)

Atmospheric carbon dioxide (CO2) levels continue to rise, increasing the risk of severe impacts on the Earth system, and on the ecosystem services that it provides. Artificial ocean alkalinization (AOA) is capable of reducing atmospheric CO2 concentrations and surface warming and addressing ocean acidification. Here, we simulate global and regional responses to alkalinity (ALK) addition (0.25 PmolALK yr−1) over the period 2020–2100 using the CSIRO-Mk3L-COAL Earth System Model, under high (Representative Concentration Pathway 8.5; RCP8.5) and low (RCP2.6) emissions. While regionally there are large changes in alkalinity associated with locations of AOA, globally we see only a very weak dependence on where and when AOA is applied. On a global scale, while we see that under RCP2.6 the carbon uptake associated with AOA is only ∼ 60 % of the total, under RCP8.5 the relative changes in temperature are larger, as are the changes in pH (140 %) and aragonite saturation state (170 %). The simulations reveal AOA is more effective under lower emissions, therefore the higher the emissions the more AOA is required to achieve the same reduction in global warming and ocean acidification. Finally, our simulated AOA for 2020–2100 in the RCP2.6 scenario is capable of offsetting warming and ameliorating ocean acidification increases at the global scale, but with highly variable regional responses.

Continue reading ‘Assessing carbon dioxide removal through global and regional ocean alkalinization under high and low emission pathways (update)’

Seagrass habitat metabolism increases short-term extremes and long-term offset of CO2 under future ocean acidification

The role of rising atmospheric CO2 in modulating estuarine carbonate system dynamics remains poorly characterized, likely due to myriad processes driving the complex chemistry in these habitats. We reconstructed the full carbonate system of an estuarine seagrass habitat for a summer period of 2.5 months utilizing a combination of time-series observations and mechanistic modeling, and quantified the roles of aerobic metabolism, mixing, and gas exchange in the observed dynamics. The anthropogenic CO2 burden in the habitat was estimated for the years 1765–2100 to quantify changes in observed high-frequency carbonate chemistry dynamics. The addition of anthropogenic CO2 alters the thermodynamic buffer factors (e.g., the Revelle factor) of the carbonate system, decreasing the seagrass habitat’s ability to buffer natural carbonate system fluctuations. As a result, the most harmful carbonate system indices for many estuarine organisms [minimum pHT, minimum Ωarag, and maximum pCO2(s.w.)] change up to 1.8×, 2.3×, and 1.5× more rapidly than the medians for each parameter, respectively. In this system, the relative benefits of the seagrass habitat in locally mitigating ocean acidification increase with the higher atmospheric CO2 levels predicted toward 2100. Presently, however, these mitigating effects are mixed due to intense diel cycling of CO2 driven by aerobic metabolism. This study provides estimates of how high-frequency pHT, Ωarag, and pCO2(s.w.) dynamics are altered by rising atmospheric CO2 in an estuarine habitat, and highlights nonlinear responses of coastal carbonate parameters to ocean acidification relevant for water quality management.

Continue reading ‘Seagrass habitat metabolism increases short-term extremes and long-term offset of CO2 under future ocean acidification’

The ability of macroalgae to mitigate the negative effects of ocean acidification on four species of North Atlantic bivalve

Coastal ecosystems can experience acidification via upwelling, eutrophication, riverine discharge, and climate change. While the resulting increases in pCO2 can have deleterious effects on calcifying animals, this change in carbonate chemistry may benefit some marine autotrophs. Here, we report on experiments performed with North Atlantic populations of hard clams (Mercenaria mercenaria), eastern oysters (Crassostrea virginica), bay scallops (Argopecten irradians), and blue mussels (Mytilus edulis) grown with and without North Atlantic populations of the green macroalgae, Ulva. In 6 of 7 experiments, exposure to elevated pCO2 levels (~ 1,700 µatm) resulted in depressed shell- and/or tissue-based growth rates of bivalves compared to control conditions (p < 0.05) whereas rates were significantly higher in the presence of Ulva in all experiments (p < 0.05). In many cases, the co-exposure elevated pCO2 levels and Ulva had an antagonistic effect on bivalve growth rates whereby the presence of Ulva under elevated pCO2 levels significantly improved their performance compared to the acidification only treatment (p < 0.05). Saturation states for calcium carbonate (Ω) were significantly higher in the presence of Ulva under both ambient and elevated CO2 delivery rates (p < 0.05). Collectively, the results suggest that photosynthesis and/or nitrate assimilation by Ulva increased alkalinity, fostering a carbonate chemistry regime more suitable for optimal growth of calcifying bivalves. This suggests that large natural and/or aquacultured collections of macroalgae in acidified environments could serve as a refuge for calcifying animals that may otherwise be negatively impacted by elevated pCO2 levels and depressed Ω.

Continue reading ‘The ability of macroalgae to mitigate the negative effects of ocean acidification on four species of North Atlantic bivalve’


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Ocean acidification in the IPCC AR5 WG II

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