Study On Carbon Sequestration By Seawater Olivine Addition And Its Impact On Microbial Community Struture

Human activities have emitted large amounts of CO2 since the industrial revolution,causing global climate change.Reducing fossil fuel CO2 emission and enhancing CO2 sequestration are vital to coping with climate change.Carbon dioxide removal(CDR)technology is considered to play an important role in ensuring sustainable development and has become an international research hotspot.Enhancing olivine weathering is one of the most promising CDR methods.The ocean accounting for 71%of the global surface area is the largest active carbon pool on the earth and has great carbon sink potential.Studies about the olivine dissolution rate and carbon sequestration model have been carried out by many researchers,but the model based on the dissolution rate of olivine in natural seawater is still insufficient.In addition,marine microorganisms play a pivotal role in the biogeochemical cycle.Bacteria and eukaryotic microalgae are important components of marine microorganisms,while the influence of olivine addition on bacterial and eukaryotic microalgal communities and the mechanism are poorly understood.CO2 sequestration potential of the coastal area in China based on the olivine dissolution rate in natural seawater and the influence of olivine addition on the bacterial and eukaryotic microalgal community in coastal seawater were studied in this thesis.The main conclusions are as follows:(1)The dissolution rate of olivine and the CO2 sequestration potential in the coastal area of China were studied based on the laboratory olivine addition experiment.The results showed that the dissolution of olivine was non-stoichiometric.The dissolution models characterized by alkalinity and silicate release were best described by the combined model,in which the early rapid dissolution was followed by linear dissolution.The dissolution constants obtained fro1 alkalinity and silicate release were 1.9 μmol m-2 day-1 and 0.6 μmol m-2 day-1,respectively.In a hypothetical one-time application of 10 cm-thick olivine sand in the coastal area of China,parameter values for dissolution constants obtained from alkalinity release were implemented in the shrinking particle model for olivine dissolution.The simulation showed that the carbon sequestration rate was up to 3.8 Tg CO2 year-1,and the total CO2 sequestration was 371 Tg,indicating great potential for carbon sink.(2)Based on 16S rRNA high-throughput sequencing technology,this thesis studied the response of marine bacterial communities to olivine addition in coastal seawater of Muping Marine Ranch.The addition of olivine had an influence on the particle-attached bacterial community,while there was no significant influence on the free-living bacterial community.In this study,olivine powders might provide more opportunities for particle-attached bacteria to colonize and the dramatic changes around the olivine microenvironment increased the relative abundance of Bacilli,Clostridia and Bacteroidia which could facilitate biofilm development.In addition,the addition of olivine increased the relative abundance of anaerobic bacteria Muribaculaceae and facultative anaerobic bacteria Dubosiella in the particle-attached bacterial community,suggesting that the complex structure of biofilm limited oxygen diffusion.(3)Based on 18S rRNA high-throughput sequencing technology,this thesis studied the influence of olivine addition on the succession of the eukaryotic microalgal community under natural light condition in coastal seawater of Aoshan Bay.The results showed that the diatomea species in spring and autumn had different responses to olivine addition,indicating that the succession of eukaryotic algal community was also regulated by the initial nutrient levels in the spring and autumn incubation experiments.The addition of olivine in the spring experiment did not influence the relative abundances of the diatomea species.Skeletonema marinoi was the dominant diatomea in the later stage of olivine addition experiment in spring,which might be due to its small size and high phosphate absorption rate.Skeletonema marinoi had a high competitive advantage in the later stage of spring incubation experiment when phosphate was limited,and the addition of olivine had no significant influence on its dominant position.The relative abundance of Thalassiosira increased after olivine addition in autumn,which might be due to the silicate released by olivine.Olivine addition significantly influenced eukaryotic non-diatom species in spring and autumn.The increase of the relative abundance of Chrysochromulina in the later stage of the spring incubation experiment might be related to the high pH after olivine addition.In autumn,the relative abundance of Noctiluca was affected by Thalassiosira and maintained at a relatively high level,which might be due to the predatory effect of Noctiluca on Thalassiosira.The network analysis indicated that the addition of olivine in spring and autumn strengthened the relationship among algae,and there were more nodes and correlations in the network.In addition,the interactions among algae were further dominated by positive correlations.(4)Based on 16S rRNA and 18S rRNA high-throughput sequencing technology,the influence of olivine addition on the relationship between bacteria and algae under natural light condition was studied in coastal seawater of Aoshan Bay.Both olivine addition and eukaryotic algal community succession induced by olivine addition had impacts on bacterial communities,but the latter had a higher impact on bacterial community than the former.The relative abundances of Candidatus Actinomarina,NS4 marine group and Marivivens increased after olivine addition.Candidatus Actinomarina strongly correlated with Thalassiosira,indicating the interaction between Candidatus Actinomarina and Thalassiosira.The high relative abundance of the NS4 marine group in the later stage might be related to the release of dissolved organic carbon caused by the decay of Thalassiosira and other algae.At the initial stage of olivine addition,the high relative abundance of particle-attached bacteria such as Marivivens indicated that olivine might provide more opportunities for bacteria to colonize,but the negative correlations between the Marivivens and alkalinity,pH,suggested that the microenvironment formed by olivine might be not conducive to their growth.In summary,this thesis explored the CO2 sequestration potential of olivine in the coastal area of China by using the shrinking particle model and explored the effects of olivine addition on marine bacterial and eukaryotic algal communities.The thesis preliminarily explored the influence of olivine addition on coastal microbial ecology,which should provide a scientific basis and reference for ocean alkalinity enhancement.