Posts Tagged 'mitigation'

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Induction of lipid production through controlled acidification: a transcriptional insight into the metabolism of Scenedesmus obtusiusculus AT-UAM

Published 20 September 2024 Science Closed
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Highlights

  • Maximum lipid content and productivity were 62 % and 85.9 mg L−1d−1, respectively.
  • Controlled acidification altered gene expression during nitrogen depletion.
  • Up-regulation of genes in energy metabolism was observed in the conditions studied.
  • Down-regulation of lipid degradation and carbohydrate synthesis was observed.
  • ANIm analysis confirmed the identity of Scenedesmus obtusiusculus AT-UAM.

Abstract

Scenedesmus obtusiusculus AT-UAM was able to accumulate up to 62 % of lipids when controlled acidification was applied to a nitrogen-deplete culture. Under these conditions, up-regulation of genes related to lipid synthesis and central carbon metabolism (glycolysis, the tricarboxylic acid cycle, and the pentose phosphate pathway) was recorded. Additionally, genes related to photosynthesis were up-regulated in the nitrogen depletion and nitrogen depletion with controlled acidification conditions with respect to the control samples analyzed under nutritional sufficiency. The Pyani program was used to establish pairwise ANI values between reported and annotated NCBI genomes to uphold genomics similarity. ANI analysis confirms the previously observed identity of S. obtusiusculus AT-UAM with the 18S rRNA and ITS2 regions, and also provides a solid framework for understanding the genetic stability and lineage of the strain. Results obtained are encouraging for integrating biofuel production processes and carbon capture technologies. Specifically, the up-regulation of genes related to both lipid synthesis and photosynthesis under controlled conditions indicates the potential of S. obtusiusculus AT-UAM for efficient biofuel production while simultaneously sequestering carbon. These biochemical properties make this strain a promising candidate for sustainable energy solutions and environmental mitigation strategies.

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Acute hypercapnia at South African abalone farms and its physiological and commercial consequences

Published 19 September 2024 Science Closed
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Abalone Haliotis midae are distributed from the cold, hypercapnic waters of the dynamic Benguela Current Large Marine Ecosystem to the relatively warm, normocapnic waters of the Agulhas Current. The species supports an important fishery as well as a thriving aquaculture industry. Due to the relatively low capacity to regulate their acid–base balance and their need to calcify shell and radula, abalone are especially vulnerable to increasing ocean acidification. Exposure to acidified seawater, i.e., hypercapnia, also occurs during the farming operation and can originate from (a) changes in influent seawater, (b) pH decrease by accumulation of waste products, and (c) intentional hypercapnia for anaesthesia using CO2-saturated seawater for size grading. Currently, these are acute exposures to hypercapnia, but increasing ocean acidification can cause chronic exposure, if not mitigated. Wild South African abalone are already exposed to periodic hypercapnia during ocean upwelling events and will be more so in the future due to progressive ocean acidification. This study investigated the acute pH effects in isolation as an initial step in studying the acute physiological response of H. midae to provide a mechanistic basis for the design of complex multifactorial studies, imitating more closely what occurs on farms and in the natural habitat. The major findings relevant to the above conditions are as follows: 1. Acute exposure to hypercapnia induces a reversible, unbuffered respiratory acidosis. 2. The impact of acute hypercapnia is size-dependent and potentially fatal. 3. Exposure to extreme, short hypercapnia during anaesthesia causes a rapid imbalance in the acid–base state but a rapid subsequent recovery. LC50 for small, medium and large abalone range from pH 6.27 to 6.03, respectively, and sub-lethal levels from pH 6.8 to 6.2. These results can be used by abalone aquaculture farms to mitigate/avoid the impact of acute (and chronic) hypercapnia but also to standardise their anaesthesia method. They are also a proxy to estimate the effects on wild populations.

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Effect of copper and temperature on the photosynthetic physiological characteristics of Ulva linza under elevated CO2 concentrations

Published 18 September 2024 Science Closed
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Highlights

  • The growth of Ulva linza was reduced with increased CO2 and Cu at 5 °C.
  • Elevated CO2 alleviated toxic effects on thalli at high Cu concentrations at 15 °C.
  • The response of algal to Cu pollution, high CO2, and temperature was analyzed.

Abstract

Copper (Cu) is vital for macroalgae’s functions, but high concentrations can be toxic. Rising CO2 levels affect algal growth and Cu bioavailability. In this study, the results reveal that at 5 °C, low Cu increased Ulva linza growth, while high Cu and elevated CO2 decreased growth. At 10 °C, low Cu and elevated CO2 enhanced growth, but high Cu did not have a significant impact. At 15 °C, high Cu reduced growth, but elevated CO2 offset this effect. Furthermore, under elevated CO2 conditions, the chloroplast structure of the algae appeared to be denser, accompanied by a large amount of starch granules, compared to low CO2 conditions. These results emphasize that lower temperatures, in conjunction with elevated CO2 concentration, could intensify the toxic effects of high Cu concentrations on thalli. However, at higher temperatures, elevated CO2 concentration appeared to be capable of mitigating the detrimental effects of heavy metals on algae.

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Harmful algal blooms in eutrophic marine environments: causes, monitoring, and treatment

Published 6 September 2024 Science Closed
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Marine eutrophication, primarily driven by nutrient over input from agricultural runoff, wastewater discharge, and atmospheric deposition, leads to harmful algal blooms (HABs) that pose a severe threat to marine ecosystems. This review explores the causes, monitoring methods, and control strategies for eutrophication in marine environments. Monitoring techniques include remote sensing, automated in situ sensors, modeling, forecasting, and metagenomics. Remote sensing provides large-scale temporal and spatial data, while automated sensors offer real-time, high-resolution monitoring. Modeling and forecasting use historical data and environmental variables to predict blooms, and metagenomics provides insights into microbial community dynamics. Control treatments encompass physical, chemical, and biological treatments, as well as advanced technologies like nanotechnology, electrocoagulation, and ultrasonic treatment. Physical treatments, such as aeration and mixing, are effective but costly and energy-intensive. Chemical treatments, including phosphorus precipitation, quickly reduce nutrient levels but may have ecological side effects. Biological treatments, like biomanipulation and bioaugmentation, are sustainable but require careful management of ecological interactions. Advanced technologies offer innovative solutions with varying costs and sustainability profiles. Comparing these methods highlights the trade-offs between efficacy, cost, and environmental impact, emphasizing the need for integrated approaches tailored to specific conditions. This review underscores the importance of combining monitoring and control strategies to mitigate the adverse effects of eutrophication on marine ecosystems.

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Impacts of ocean acidification on marine ecosystems and mitigation strategies 

Published 30 August 2024 Science Closed
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This study explores the mechanisms of adaptation in aquatic species, including phenotypic plasticity, genetic evolution, and molecular mechanisms. Aquatic species exhibit significant phenotypic plasticity, allowing them to respond rapidly to environmental changes. Changes in gene expression related to osmoregulation and metabolic processes demonstrate how species adjust their physiological states to cope with varying conditions. Genetic evolution plays a crucial role in long-term adaptation, driven by processes such as mutation, natural selection, and genetic drift. Research shows that specific genes in marine mammals and freshwater prawns are crucial for their adaptation to aquatic environments. Molecular adaptations involve gene regulation, genomic changes, and epigenetic modifications. Studies on fireflies and marine diatoms provide insights into the genetic basis of adaptation to different environmental conditions.

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The potential of Southeast Florida’s coral reef tract to enhance climate resilience of ecosystems and communities

Published 4 June 2024 Science Closed
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Increasing anthropogenic greenhouse gas emissions have led to more heat being trapped in the atmosphere, raising our overall global temperature. The hottest recorded sea surface temperatures in Southeast Florida occurred in 2023 causing extreme coral bleaching and high mortality in part of the Florida Reef Tract (FRT). Coral reefs play a vital role in protecting coastal communities from storm surge and sea level rise, reducing wave energy by up to 97% across whole reefs. However, with increasing ocean acidity and thermal stress from climate change, coral ecosystems are struggling to maintain their structural complexity and overall health, much less provide substantial protection to human communities. Through a literature synthesis, environmental assessment, environmental justice analysis, and an analysis of risk management strategies, I assess the FRT’s potential to reduce flood risk from storm surge and sea level rise. This paper examines how the FRT can enhance climate resilience for both marine ecosystems and communities in Southeast Florida amidst climate change. My analyses find that coral reefs have significant wave attenuation potential only if structural complexity and carbonate accretion are high. I also find that coral reefs can reduce climate injustices in disadvantaged communities by reducing flooding from rising seas and greater storm surge. However, policies are needed to avoid climate gentrification in protected neighborhoods. I conclude that the five biggest impacts and threats to the FRT are climate change, loss of coral biodiversity, coral disease, pollution, and direct human activities such as dredging and fish trapping. Swift climate action and stringent policy are necessary to protect and sustain the benefits provided by the FRT. This includes quickly reducing greenhouse gas emissions to net zero, increasing restoration efforts, updating local sewage infrastructure to reduce pollution runoff, and implementing legislation that further promotes the protection of coral reefs.

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Processes controlling seawater acidification in offshore aquaculture system of China

Published 21 May 2024 Science Closed
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Highlights

  • Uncertainties exist in offshore acidification characterization.
  • Incorporating SGD into research on regulating acidification processes globally.
  • Incorporating SGD into studies of regulating seawater carbonate dynamics globally.
  • Mitigating seawater acidification requires cautious treatment and prevention.
  • Recommendations for the comprehensive development of sustainable aquaculture.

Abstract

The issue of seawater acidification has become a focal concern within China’s offshore aquaculture systems. This review systematically examines the processes influencing this phenomenon, with a particular emphasis on the lesser-known threat posed by submarine groundwater discharge (SGD). It presents strategies for mitigating seawater acidification and ensuring sustainable aquaculture. 1) Standardize seawater pH measurement and implement quality control in pH determination. Measuring calcium ion (Ca2+) to obtain aragonite saturation (Ωarag) in offshore aquaculture areas is recommended. 2) The research community has extensively recognized the influence of temperature effect, air-sea exchange, terrestrial input, biological production, and calcification on seawater acidification. However, the connection between SGD and acidification is a bottleneck in current research. Prioritizing quantitative methods to assess the impact of SGD on acidification and its contribution to acidification across all processes is essential. 3) Mitigating offshore acidification should focus on restraining human behavior rather than pollution control. Combining theoretical research with preventive measures can mitigating acidification. Sustainable aquaculture strategies should consider regional farming patterns, cost-effectiveness, and societal demands. While primarily focusing on acidification in Chinese aquaculture, insights gained may have broader implications for global acidification research and coastal management.

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Causes, effects and possible mitigation strategies of ocean acidification

Published 14 May 2024 Science Closed
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The process whereby the ocean’s pH falls as a result of absorbing carbon dioxide from the atmosphere is known as ocean acidification It is a major concern because it can have negative impacts on marine life and ecosystems. In this article, we review the causes of ocean acidification and its potential effects on marine organisms and ecosystems. We also discuss some possible strategies for mitigating ocean acidification, including the use of renewable energy sources and energy-efficient technologies, ocean alkalinity enhancement techniques, and ocean iron fertilization. Overall, This review highlights the need for continued research and action to address the challenges posed by ocean acidification. Objectives: This literature review aims to explore the causes, effects and possible mitigation strategies of ocean acidification. Method and results: The methods used in this literature review included a comprehensive search of the scientific literature on ocean acidification, using databases such as Google Scholars and the Web of Science along with other literature. Furthermore, the reference lists of pertinent papers were examined in order to find any further research that might have eluded during the first search. The inclusion criteria for the studies included in this review were that they must have been published in a peer-reviewed journal and must have focused on the effects of ocean acidification on marine organisms and ecosystems. Conclusion: Ocean acidification is a serious problem that would have massive implications for both the environment and the human lives that depend on it. The marine ecosystem has felt its effect in the forms of the decreasing population of calcifying marine organisms and possibly fishes as they are now more prone to predation due to its change in behavior. Massive changes of their population has the potential to disrupt the ecosystem dramatically.

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Impact of human disturbance on biogeochemical fluxes in tropical seascapes

Published 9 May 2024 Science Closed
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Highlights

  • Interest in biogeochemical fluxes in tropical seascapes surged in the past decade.
  • Mangroves have received the most attention among the three habitats of study.
  • Four anthropogenic drivers are identified for disrupting biogeochemical fluxes.
  • Mangroves and seagrasses buffer microbes, reducing disease in nearby corals.
  • Research on how mangroves and seagrasses mitigate ocean acidification is a priority.

Abstract

Tropical seascapes rely on the feedback relationships among mangrove forests, seagrass meadows, and coral reefs, as they mutually facilitate and enhance each other’s functionality. Biogeochemical fluxes link tropical coastal habitats by exchanging material flows and energy through various natural processes that determine the conditions for life and ecosystem functioning. However, little is known about the seascape-scale implications of anthropogenic disruptions to these linkages. Despite the limited number of integrated empirical studies available (with only 11 out of 81 selected studies focusing on the integrated dynamics of mangroves, seagrass, and corals), this review emphasizes the importance of biogeochemical fluxes for ecosystem connectivity in tropical seascapes. It identifies four primary anthropogenic influences that can disturb these fluxes-nutrient enrichment, chemical pollution, microbial pollution, and solid waste accumulation-resulting in eutrophication, increased disease incidence, toxicity, and disruptions to water carbonate chemistry. This review also highlights significant knowledge gaps in our understanding of biogeochemical fluxes and ecosystem responses to perturbations in tropical seascapes. Addressing these knowledge gaps is crucial for developing practical strategies to conserve and manage connected seascapes effectively. Integrated research is needed to shed light on the complex interactions and feedback mechanisms within these ecosystems, providing valuable insights for conservation and management practices.

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Countering the effect of ocean acidification in coastal sediments through carbonate mineral additions

Published 4 April 2024 Science Closed
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Along with its impact on calcifying plankton, ocean acidification also affects benthic biogeochemistry and organisms. Compared to the overlying water, fluid composition in sediments is altered through the effect of the mineralization of organic matter, which can further lower both pH and the carbonate saturation state. This can potentially be counteracted by the addition of carbonate minerals to the sediment surface. To explore the biogeochemical effects of mineral additions to coastal sediments, we experimentally quantified carbonate mineral dissolution kinetics, and then integrated this data into a reactive transport model that represents early diagenetic cycling of C, O, N, S and Fe, and traces total alkalinity, pH and saturation state of CaCO3. Model simulations were carried out to delineate the impact of mineral type and amount added, porewater mixing and organic matter mineralization rates on sediment alkalinity and its flux to the overlying water. Model results showed that the added minerals undergo initial rapid dissolution and generate saturated conditions. Aragonite dissolution led to higher alkalinity concentrations than calcite. Simulations of carbonate mineral additions to sediment environments with low rates of organic matter mineralization exhibited a significant increase in mineral saturation state compared to sediments with high CO2 production rates, highlighting the environment-specific extent of the buffering effect. Our work indicates that carbonate additions have the potential to effectively buffer surficial sediments over multiple years, yielding biogeochemical conditions that counteract the detrimental effect of OA conditions on larval recruitment, and potentially increase benthic alkalinity fluxes to support marine carbon dioxide removal (mCDR) in the overlying water.

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Response of ocean acidification to atmospheric carbon dioxide removal

Published 28 March 2024 Science Closed
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Artificial CO2 removal from the atmosphere (also referred to as negative CO2 emissions) has been proposed as a potential means to counteract anthropogenic climate change. Here we use an Earth system model to examine the response of ocean acidification to idealized atmospheric CO2 removal scenarios. In our simulations, atmospheric CO2 is assumed to increase at a rate of 1% per year to four times its pre-industrial value and then decreases to the pre-industrial level at a rate of 0.5%, 1%, 2% per year, respectively. Our results show that the annual mean state of surface ocean carbonate chemistry fields including hydrogen ion concentration ([H+]), pH and aragonite saturation state respond quickly to removal of atmospheric CO2. However, the change of seasonal cycle in carbonate chemistry lags behind the decline in atmospheric CO2. When CO2 returns to the pre-industrial level, over some parts of the ocean, relative to the pre-industrial state, the seasonal amplitude of carbonate chemistry fields is substantially larger. Simulation results also show that changes in deep ocean carbonate chemistry substantially lag behind atmospheric CO2 change. When CO2 returns to its pre-industrial value, the whole-ocean acidity measured by [H+] is 15%-18% larger than the pre-industrial level, depending on the rate of CO2 decrease. Our study demonstrates that even if atmospheric CO2 can be lowered in the future as a result of net negative CO2 emissions, the recovery of some aspects of ocean acidification would take decades to centuries, which would have important implications for the resilience of marine ecosystems.

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The rise, fall and rebirth of ocean carbon sequestration as a climate ‘solution’

Published 15 March 2024 Science Closed
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Highlights

  • Solutions to the climate crisis are not ahistorical.
  • Both social and technical processes explain their rise (or fall) on the agenda.
  • Thinking about ocean CDR closely co-evolved with scientific understandings of global climate change.
  • Ocean CDR methods have followed cycles of hype, controversy and disappointment.
  • Key sociotechnical configurations and narrative changes explain the new hype around ocean CDR.

Abstract

While the ocean has long been portrayed as a victim of climate change, threatened by ocean warming and acidification, it is now increasingly framed as a key solution to the climate crisis. In particular, the promising carbon sequestration potential of the ocean is being emphasised. In this paper, we seek to historicise the practices, discourses and actors that have constructed the ocean as a climate change solution space. We conceptualise the debate about the mitigation potential of the ocean as a contested site of governance, where varying actors form alliances and different sociotechnical narratives about climate action play out. Using an innovative quali-quantitative methodology which combines scientometrics with document analysis, observational fieldwork, and interviews, we outline three historical phases in the history of ocean carbon sequestration that follow recurring cycles of hype, controversy and disappointment. We argue that the most recent hype around ocean carbon sequestration was not triggered by a technological breakthrough or a reduction in scientific uncertainty, but by new socio-technical configurations and coalitions. We conclude by showing that how climate change solutions are put on the agenda and become legitimised is both a scientific and political process, linked to how science frames the climate crisis, and ultimately, its governance.

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Evaluating the values and limitations for coral and oyster reefs in coastal disaster risk reduction: a literature review

Published 12 March 2024 Science Closed
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Previous researchers have made efforts to link the limitations and values of coral and oyster reefs to coastal defence. However, given the context in which reef ecosystems interact with changing climate and human behaviours, synthesising the available information is necessary to know the status and actions needed to improve the situation. To comprehend and advance this field, we used a detailed review approach to examine 84 relevant previous papers to provide a comprehensive overview of the existing state of knowledge of the values and limitations of coral and oyster reefs in coastal disaster risk reduction. The results show that the literature on the economic valuation of oyster reefs in coastal disaster risk reduction is in its infancy and therefore needs more attention. Due to the lower threshold of environmental tolerance of corals, the ongoing and projected global warming circumstances will put coral reefs more at risk than oyster reefs. The severity of the associated consequences for humans will depend on socioeconomic disparity and poor governance among coastal communities. Individuals who rely on climate-susceptible livelihoods will suffer the most. The authors recommend collaborative studies involving local governments to investigate the possibility of making payment for the services of these organisms a requirement for living near them. Additionally, simulation and modelling studies on the reactions of corals and oyster reefs to short, medium, and long-term projected climate change and human influences are necessary.

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Is seaweed culture a sustainable approach to climate change adaptation?

Published 12 March 2024 Science Closed
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Seaweed culture is considered the prominent sector of worldwide food production that offers a range of prospects to address and adapt to climate change. Seaweed beds release carbon (C) that is deposited in soils or shipped to the deep ocean, acting as a carbon dioxide (CO2) sink. Seaweed is also utilized in whole or in part to produce biofuel, with possible C sequestration of around 1,500 tons CO2/km2 /year from avoided fossil fuel combustion. Seaweed cultivation reduces emissions in agriculture by promoting soil health, reducing the use of synthetic fertilizers, and reducing greenhouse gasses in livestock when used as feed. By attenuating wave energy and shielding coastlines, and by increasing pH and oxygenating the oceans, seaweed cultivation contributes to the mitigation of climate change by reducing the effects of acidification and oxygen depletion in the region. Potentials for increasing seaweed production are constrained by several factors, including the availability of suitable sites, competition for appropriate sites with other uses, technological systems that can withstand challenging maritime environments, and expanding potential markets for seaweed goods. Considering these limitations, seaweed culture can be changed to optimize climatic benefits, which could increase the income of seaweed producers if they are well compensated.

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A comprehensive assessment of electrochemical ocean alkalinity enhancement in seawater: kinetics, efficiency, and precipitation thresholds

Published 15 February 2024 Science Closed
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Ocean alkalinity enhancement (OAE) is a promising approach to marine carbon dioxide removal (mCDR) that leverages the large surface area and carbon storage capacity of the oceans to sequester atmospheric CO2 as dissolved bicarbonate (HCO3–). The SEA MATE (Safe Elevation of Alkalinity for the Mitigation of Acidification Through Electrochemistry) process uses electrochemistry to convert some of the salt (NaCl) in seawater or brine into aqueous acid (HCl), which is removed from the system, and base (NaOH), which is returned to the ocean with the remaining seawater. The resulting increase in seawater pH and alkalinity causes a shift in dissolved inorganic carbon (DIC) speciation toward carbonate and a decrease in the surface-ocean pCO2. The shift in the pCO­2 results in enhanced CO2 uptake or reduced CO2 loss by the seawater due to gas exchange. The net result of this process is the increase of surface-ocean DIC, where it is durably stored as mostly bicarbonate and some carbonate. In this study, we systematically test the efficiency of CO2 uptake in seawater treated with NaOH at beaker (1 L), aquaria (15 L), and tank (6000 L) scales to establish operational boundaries for safety and efficiency in scaling up to field experiments. Preliminary results show CO2 equilibration occurred on order of weeks to months, depending on circulation, air forcing, and air bubbling conditions within the test tanks. An increase of ~0.7–0.9 mol DIC/ mol added alkalinity (in the form of NaOH) was observed through analysis of seawater bottle samples and pH sensor data, consistent with the value expected given the values of the carbonate system equilibrium calculations for the range of salinities and temperatures tested. Mineral precipitation occurred when the bulk seawater pH exceeded 10.0 and Ωaragonite exceeded 30.0. This precipitation was dominated by Mg(OH)2 over hours to 1 day before shifting to CaCO3, aragonite precipitation. These data, combined with models of the dilution and advection of alkaline plumes, will allow for estimation of the amount of carbon dioxide removal expected from OAE pilot studies. Future experiments should better approximate field conditions including sediment interactions, biological activity, ocean circulation, air-sea gas exchange rates, and mixing-zone dynamics.

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The additionality problem of ocean alkalinity enhancement

Published 12 February 2024 Science Closed
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Ocean alkalinity enhancement (OAE) is an emerging approach for atmospheric carbon dioxide removal (CDR). The net climatic benefit of OAE depends on how much it can increase CO2 sequestration relative to a baseline state without OAE. This so-called “additionality” can be calculated as follows:

So far, feasibility studies on OAE have mainly focussed on enhancing alkalinity in the oceans to stimulate CO2 sequestration (COAE); however, the primary focus has not been on how such anthropogenic alkalinity would modify the natural alkalinity cycle and associated baseline CO2 sequestration (ΔCbaseline). Here, I present incubation experiments in which materials considered for OAE (sodium hydroxide, steel slag, and olivine) are exposed to beach sand to investigate the influence of anthropogenic alkalinity on natural alkalinity sources and sinks. The experiments show that anthropogenic alkalinity can strongly reduce the generation of natural alkalinity, thereby reducing additionality. This is because the anthropogenic alkalinity increases the calcium carbonate saturation state, which reduces the dissolution of calcium carbonate from sand, a natural alkalinity source. I argue that this “additionality problem” of OAE is potentially widespread and applies to many marine systems where OAE implementation is considered – far beyond the beach scenario investigated in this study. However, the problem can potentially be mitigated by dilute dosing of anthropogenic alkalinity into the ocean environment and the avoidance of OAE in natural alkalinity cycling hotspots, such as in marine sediments. Understanding a potential slowdown of the natural alkalinity cycle through the introduction of an anthropogenic alkalinity cycle will be crucial for the assessment of OAE.

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Evaluating the ability of macroalgae to create a chemical refuge for bivalves under ocean acidification conditions in closed-environment experiments

Published 26 January 2024 Science Closed
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Ocean acidification (OA) can impact aquaculture because reduced pH may negatively affect the calcification in bivalve species. Photosynthetic activity can naturally generate an OA buffering effect, favouring the calcification process by increasing the surrounding seawater pH. Therefore, the incorporation of macroalgae into bivalve farms may be a strategy to mitigate the impacts of acidification on the industry. In this study, we evaluated the modification of seawater chemistry by the metabolic activity of the blue mussel Mytilus chilensis and three macroalgae (Ulva sp., Chondracanthus chamissoi and Macrocystis pyrifera), in monocultures and co-cultures under ambient and acidified initial conditions in three closed-environment experiments. In all three experiments, photosynthesis and respiration modulated seawater chemistry, resulting in higher values of pH, oxygen concentrations, and aragonite saturation state (ΩAra) in macroalgal monocultures compared to mussel monoculture. In co-cultures, pH, oxygen concentrations and ΩAra were higher than in mussel monoculture but lower than in macroalgal monoculture. In co-cultures, the OA buffering effect (pH > 7.7, ΩAra > 1) was observed during daytime, but unfavourable conditions for calcification were observed during nighttime. These results are species-specific, with a greater capacity for pH increase for Ulva sp. and Ch. chamissoi and limited capacity for M. pyrifera in both initial pH treatments. Results of the enclosed environment experiments indicate that the presence of macroalgae in co-cultures did not guarantee favourable conditions for mussel calcification in acidified conditions.

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Early stage ecological communities on artificial algae showed no difference in diversity and abundance under ocean acidification

Published 24 January 2024 Science Closed
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Marine habitat-forming species create structurally complex habitats that host macroinvertebrate communities characterized by remarkable abundance and species richness. These habitat-forming species also play a fundamental role in creating favourable environmental conditions that promote biodiversity. The deployment of artificial structures is becoming a common practice to help offset habitat loss although with mixed results. This study investigated the suitability of artificial flexible turfs mimicking the articulated coralline algae (mimics) as habitat providers and the effect of ocean acidification (OA) on early stage ecological communities associated to flexible mimics and with the mature community associated to Ellisolandia elongata natural turfs. The mimics proved to be a suitable habitat for early stage communities. During the OA mesocosms experiment, the two substrates have been treated and analysed separately due to the difference between the two communities. For early stage ecological communities associated with the mimics, the lack of a biologically active substrate does not exacerbate the effect of OA. In fact, no significant differences were found between treatments in crustaceans, molluscs and polychaetes diversity and abundance associated with the mimics. In mature communities associated with natural turfs, buffering capability of E. elongata is supporting different taxonomic groups, except for molluscs, greatly susceptible to OA.

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Estuary is the promising site for olivine-dissolution engineering: Insight from olivine mineralogy

Published 22 January 2024 Science Closed
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To keep global warming below 1.5 °C to address the threats posed by global climate change, various geoengineering strategies based on increasing the negative carbon emissions in oceans have been proposed, considering the ocean the largest reservoir of carbon [1, 2]. Dissolution of silicate minerals, such as olivine, is one promising engineering that not only depletes carbon dioxide (CO2) but reduces ocean acidification. Olivine is the most abundant mineral in the earth’s upper mantle [3]. Olivine consists of a hexagonal close-packed array of oxygen atoms from Si-O tetrahedrons lying parallel to (100) (Figure 1) [4]. Olivine is a magnesium iron silicate with the formula (Mg2+, Fe2+)2SiO4 and has an orthorhombic crystal system. In olivine, the Mg2+ and Fe2+ ions form a complete isomorphic series, and forsterite and fayalite are the two end-member minerals of the olivine group. The Mg-O and Fe-O bonds in olivine have a much lower bond energy than thatof Si-O bonds [4]. Moreover, bridging oxygen atoms lack between Si and Mg, and thus Mg2+ is more easily released from the olivine’s surface during dissolution [5]. The dissolution reaction of olivine depends on H+ ions, which form an activated complex with Mg2+ and enhance its removal from the olivine’s surface, damaging its structures [5]. Therefore, the dissolution of olivine led to a significant increase in seawater alkalinity. And meanwhile, olivine dissolution also consumes CO2.

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Ocean alkalinity enhancement using sodium carbonate salts does not impact Fe dynamics in a mesocosm experiment

Published 11 January 2024 Science Closed
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The addition of carbonate minerals to seawater through an artificial Ocean Alkalinization Enhancement (OAE) process increases the concentrations of hydroxide, bicarbonate, and carbonate ions. This leads to changes in the pH and the buffering capacity of the seawater. Consequently, OAE could have relevant effects on marine organisms and in the speciation and concentration of trace metals that are essential for their physiology. During September and October 2021, a mesocosm experiment was carried out in the coastal waters of Gran Canaria (Spain), consisting of different levels of total alkalinity (TA). Different concentrations of carbonate salts (NaHCO3 and Na2CO3) previously homogenized were added to each mesocosm to achieve an alkalinity gradient between ∆0 to 2400 μmol L-1. The lowest point of the gradient was 2400 µmol kg-1, being the natural alkalinity of the medium, and the highest point was 4800 µmol kg-1. Iron (Fe) speciation was monitored during this experiment to analyse whether total dissolved iron (TdFe), dissolved iron (dFe), soluble iron (sFe), dissolved labile iron (dFe´), iron-binding ligands (LFe) and their conditional stability constants (K’FeL), could change because of OAE and the experimental conditions in each mesocosm. Observed iron concentrations were within the expected range for coastal waters, with no significant increases due to OAE. However, there were variations in Fe size fractionation during the experiment. This could potentially be due to chemical changes caused by OAE, but such effect being masked by the stronger biological interactions. In terms of size fractionation, sFe was below 1 nmol L-1, dFe concentrations were within 0.5-4.0 nmol L-1, and TdFe within 1.5-7.5 nmol L-1. Our results show that over 99 % of Fe was complexed, mainly by L1 and L2 ligands with k´Fe’L ranging between 10.92±0.11 and 12.68±0.32, with LFe ranging from 1.51±0.18 to 12.3±1.8 nmol L-1. Our data on iron size fractionation, concentration, and iron-binding ligands substantiate that the introduction of sodium salts in this mesocosm experiment did not modify iron dynamics. As a consequence, phytoplankton remained unaffected by alterations in this crucial element.

Continue reading ‘Ocean alkalinity enhancement using sodium carbonate salts does not impact Fe dynamics in a mesocosm experiment’

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