Development of ocean acidification endpoint characterization model for life cycle assessment

Ocean acidification, also referred to as the evil twin of global warming, occurs due to the CO2 absorption of the oceans from the atmosphere. Both the pH and carbonate saturations are altered with this absorption process. The optimal operating conditions of the biological systems in the marine environment are therefore no longer maintained. The marine species are reacting in various ways to this change, eventually leading to a loss in biodiversity. With the current trend in emissions, the pH levels of the oceans are expected to decrease from 8.1 to 7.8 by the end of the century. In combination with the other stressors, it is projected that OA will have a wide range of impacts on marine life and its services to humanity. The representation of these implications is limited in environmental assessment tools such as Life Cycle Assessment.

This research explores the relationship between the changing acidity of the oceans and marine biodiversity loss. This relation is quantified through utilizing the ecotoxicology impact assessment approach for LCA. Following this approach, an endpoint characterization model is developed for ocean acidification. The approach consists of the development and integration of fate, exposure, effect and damage models. The fate model, expressing the relation between the GHG emissions (CO2, CO, CH4) and change in acidity of the ocean is based on the work of Bach et al. (2016). The effect model has been developed by constructing species sensitivity distributions utilizing species response data from 5 taxonomic groups (mollusca, echinodermata, fish, cnidaria, crustacea) to obtain the potentially affected fraction of species with changing pH. Furthermore, 3 different categorizations (climate zones, calcification, exposure duration) were made to assess their effects on species responses. The results revealed that there is no significant difference in responses based on different exposure durations or climate zones. Calcifying species on the other hand is found to have a higher sensitivity to ocean acidification as the change in carbonate chemistry directly influences the shell and skeleton formation of these organisms. Lastly, these models were integrated into an endpoint characterization model for ocean acidification. From the 3 GHG emissions included within the scope of this research, CO2 has the highest (CFCO2 = 4.883 Γ— 104 (𝑃𝐷𝐹)π‘š3/π‘˜π‘”πΊπ»πΊ) and CH4 has the lowest (CFCH4 = 4.072 Γ— 104 𝑃𝐷𝐹)π‘š3/π‘˜π‘”πΊπ»πΊ) impact on marine biodiversity loss due to OA. These ecosystem damage indicators can be utilized in the impact assessment phase of the Life Cycle Assessment to translate the inventory results into impact on marine biodiversity.

Through the quantification of the impacts of ocean acidification, the effects of this major stressor on marine life can be better understood and targeted strategies can be developed. However, more research is required to increase the robustness of these models through expanding the species scope and incorporating temporal and geographical aspects into the models. Furthermore, the cascading effects of the changing ocean pH are still unknown and its consequences on ecosystems and socio-economic structures are unprecedented. To establish science-based targets and strategies to conserve the species richness in marine life, the extent of our understanding of the damage caused by anthropogenic actions needs to be further explored and estimated for the future.

GΓΌrdal Δ°., 2021. Development of ocean acidification endpoint characterization model for life cycle assessment. MSc thesis, Leiden University, 89 p. Thesis.

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