Mangrove forests have one of the highest capacities of any ecosystem to sequester carbon. Mangroves in the Red Sea exist in a uniquely saline, high temperature, nutrient limited environment and the effects on carbon storage and greenhouse gas (GHG) emissions from arid mangrove soils is understudied. The flux of carbon dioxide (CO2) and methane (CH4) has the potential to enhance or reduce the carbon storage capacity of mangroves, which is an important nature-based solution for carbon drawdown to limit global warming. To determine the magnitude of CO2 and CH4 flux from mangrove soil in the Red Sea, soil cores were incubated on a monthly basis for over a year in light and dark conditions. Soil properties such as salinity, organic carbon, water content, bulk density, and stable isotopes, along with environmental variables such as inundation frequency and temperature were measured to resolve the drivers and variation of GHG flux over time. Additionally, 16S and 18S rRNA metabarcoding was conducted to determine the relative influence of prokaryotes and eukaryotes in the microbial mat within this mangrove ecosystem, and the microbial contribution to GHG flux. Oxygen microsensors were used for fine-scale resolution of the microbial mat, to determine photosynthetic rates and oxygen profiles. Fluxes were found to be highly variable, with the highest correlation between GHG flux and soil water content (p<0.05). Both prokaryotic and eukaryotic components of the microbial mat had a significant relationship with GHG flux, with mixed impacts depending on the taxa. These findings show that Red Sea mangroves, despite their lower carbon storage capacity, are a negligible source of GHG to the atmosphere unlike other regions where GHG emissions offset a greater proportion of carbon storage potential. Additionally, the importance of the microbial mat in this ecosystem is demonstrated, and an important consideration for future studies on mangroves and their potential as a nature-based solution against global warming.

Seagrass, mangrove, saltmarshes and macroalgae - the coastal vegetated habitats, offer a promising nature-based solution to climate change mitigation, as they sequester carbon in their living biomass and in marine sediments. Estimation of the macrophyte organic carbon contribution to coastal sediments is key for understanding the sources of blue carbon sequestration, and for establishing adequate conservation strategies. Nevertheless,identification of marine macrophytes has been challenging and current estimations are uncertain. In this dissertation, time- and cost-efficient DNA-based methods were used to fingerprint marine macrophytes and estimate their contribution to the organic pool accumulated in blue carbon habitats. First, a suitable short-length DNA barcode from the universal 18S gene was chosen among six barcoding regions tested, as it successfully recovered degraded DNA from sediment samples and fingerprinted marine macrophyte taxa. Second, an experiment was performed to test whether the abundance of eDNA represents the content of organic carbon within the macrophytes; results supported this notion, indicating a positive correlation (R2 = 0.85) between eDNA and organic carbon. Third, using the chosen barcode, eDNA of marine macrophyte was identified from sediments of seagrass meadows and mangrove forests in the Arabian Red Sea, to further estimate contributions to the organic carbon pools. Estimations based on eDNA were compared against estimations of organic carbon based on stable isotope analyses from the same sediments; results from both methods were similar. In addition, this research provided the first quantitative evidence of the contribution of macroalgae to coastal and oceanic carbon pools. Hitherto, macroalgae have been ignored in blue carbon assessments because their fingerprinting was challenging and there was no evidence of their carbon export. The results of this dissertation demonstrate that eDNA offers an unprecedent taxonomic discrimination, and resolve the contribution of marine macrophytes to the organic pools in blue carbon sediments.

Seagrass meadows, or submerged aquatic vegetation, constitute an ecosystem with great importance to the coastal zone, and may be characterized as the most productive ecosystem on Earth. In addition to the provision of habitat for a wide variety of species, protection of the coastal zone and production of organic matter base for the marine trophic web, these environments have been recognized for their great capacity to store organic carbon in their soils and are, therefore, a priority area for the mitigation of increased carbon in the atmosphere. In spite of the great importance of these areas, there is little information about the soils of these ecosystems, mainly using an approach based on the genesis of its soils. Thus, this thesis covers 4 chapters aiming to: (i) evaluate changes in the characteristics of seagrass meadows publications in the last 50 years, identify knowledge gaps and priorities for future studies; (ii) to discuss the paradoxical lack of information on Brazilian seagrass meadows soils, stimulate studies to understand their characteristics and contribute to the correct inclusion of seagrass meadows soils in the Brazilian System for Soil Classification; (iii) characterize and investigate soils of seagrass meadows along the Brazilian coast, in order to understand the pedogenetic processes within these soils; and (iv) identify variations in the biogeochemical processes related to the dynamics of Fe, Mn and S along the Brazilian coast, aiming to provide an improved basis for the understanding of this ecosystem and subsidies for the use and protection policies of these coastal areas. / As pradarias marinhas (seagrasses), ou vegetação aquática submersa, constituem um ecossistema de grande importância para a zona costeira, caracterizando-se como o ecossistema mais produtivo da Terra. Além de fornecer habitat para uma grande variedade de espécies, favorecer a estabilidade costeira e produzir matéria orgânica base para a teia trófica marinha, estes ambientes têm sido reconhecidos pela grande capacidade de armazenar carbono orgânico em seus solos e são, portanto, prioritários para as medidas de mitigação do aumento de carbono na atmosfera. Apesar da grande importância desse ecossitema, há pouca informação a respeito dos solos onde estes ecossistemas estão inseridos, principalmente utilizando uma abordagem baseada na gênese dos solos. Esta tese contempla 4 capítulos cujos objetivos visam avaliar as mudanças nas características das publicações sobre pradarias marinhas nos últimos 50 anos, identificando lacunas de conhecimentos e prioridades para estudos futuros; discutir a paradoxal ausência de informação sobre os solos das pradarias marinhas do Brasil, estimulando estudos para o entendimento de suas características e contribuindo para a correta inclusão de solos de pradarias marinhas no Sistema Brasileiro de Classificação de solos; caracterizar e investigar os solos das pradarias marinhas ao longo da costa brasileira, com vistas a entender os processos pedogenéticos atuantes nestes solos; e Identificar variações nos processos biogeoquímicos relacionados à dinâmica de Fe, Mn e S ao longo da costa brasileira, com a finalidade de fornecer base para o entendimento deste ecossistema e subsídios para as políticas de proteção e de uso destas áreas costeiras.

Seagrass meadows, or submerged aquatic vegetation, constitute an ecosystem with great importance to the coastal zone, and may be characterized as the most productive ecosystem on Earth. In addition to the provision of habitat for a wide variety of species, protection of the coastal zone and production of organic matter base for the marine trophic web, these environments have been recognized for their great capacity to store organic carbon in their soils and are, therefore, a priority area for the mitigation of increased carbon in the atmosphere. In spite of the great importance of these areas, there is little information about the soils of these ecosystems, mainly using an approach based on the genesis of its soils. Thus, this thesis covers 4 chapters aiming to: (i) evaluate changes in the characteristics of seagrass meadows publications in the last 50 years, identify knowledge gaps and priorities for future studies; (ii) to discuss the paradoxical lack of information on Brazilian seagrass meadows soils, stimulate studies to understand their characteristics and contribute to the correct inclusion of seagrass meadows soils in the Brazilian System for Soil Classification; (iii) characterize and investigate soils of seagrass meadows along the Brazilian coast, in order to understand the pedogenetic processes within these soils; and (iv) identify variations in the biogeochemical processes related to the dynamics of Fe, Mn and S along the Brazilian coast, aiming to provide an improved basis for the understanding of this ecosystem and subsidies for the use and protection policies of these coastal areas. / As pradarias marinhas (seagrasses), ou vegetação aquática submersa, constituem um ecossistema de grande importância para a zona costeira, caracterizando-se como o ecossistema mais produtivo da Terra. Além de fornecer habitat para uma grande variedade de espécies, favorecer a estabilidade costeira e produzir matéria orgânica base para a teia trófica marinha, estes ambientes têm sido reconhecidos pela grande capacidade de armazenar carbono orgânico em seus solos e são, portanto, prioritários para as medidas de mitigação do aumento de carbono na atmosfera. Apesar da grande importância desse ecossitema, há pouca informação a respeito dos solos onde estes ecossistemas estão inseridos, principalmente utilizando uma abordagem baseada na gênese dos solos. Esta tese contempla 4 capítulos cujos objetivos visam avaliar as mudanças nas características das publicações sobre pradarias marinhas nos últimos 50 anos, identificando lacunas de conhecimentos e prioridades para estudos futuros; discutir a paradoxal ausência de informação sobre os solos das pradarias marinhas do Brasil, estimulando estudos para o entendimento de suas características e contribuindo para a correta inclusão de solos de pradarias marinhas no Sistema Brasileiro de Classificação de solos; caracterizar e investigar os solos das pradarias marinhas ao longo da costa brasileira, com vistas a entender os processos pedogenéticos atuantes nestes solos; e Identificar variações nos processos biogeoquímicos relacionados à dinâmica de Fe, Mn e S ao longo da costa brasileira, com a finalidade de fornecer base para o entendimento deste ecossistema e subsídios para as políticas de proteção e de uso destas áreas costeiras.

Coastal marine sediments have recently been identified as globally important stocks of organic carbon (Corg) that, if compromised, could significantly exacerbate global greenhouse gas emissions. While resource managers and policy makers are eager to incorporate this ecosystem service into seagrass ecosystem valuation frameworks, similar to those already in existence for terrestrial forests, there has been insufficient information regarding how environmental conditions and seagrass ecology control carbon storage. These include the influence of the seagrass to the production and preservation of soil organic matter, the fate of stored carbon following conversion of coastal wetlands, and the interactions between organic and inorganic carbon cycling. This dissertation intends to to understand the drivers of Corg storage and preservation to better prioritize and evaluate the worth of seagrasses to large scale carbon cycles and greenhouse gas mitigation planning. Long-term experiments and thorough field surveys reveal that seagrasses are not categorically necessary nor sufficient for long-term Corg storage. Soil Corg stocks as well as their recalcitrance and breakdown rates are all correlated with sediment grain size, where muddy, fine sediments have higher Corg stocks that are less likely to breakdown. Sediment grain size can be influenced by the presence of seagrasses at some sites, likely where the leaf canopy can modify local hydrology enough to create a depositional environmental that wouldn’t otherwise exist. However, similar depositional environments that collect and store Corg can be obtained through local geomorphological features and natural hydrology, independent of benthic flora. This distinction has important implications on how soil C is managed to continue its preservation. The relation between seagrass Corg and CO2 can be blurred by calcification and carbonate dissolution processes that occur concurrently, and have direct but antagonistic effects on CO2. Carbonate processes are dependent on local environmental factors, though augmented by biological processes, thus the ability of carbonate processes to interfere with seagrass Corg storage and loss is limited to geographic areas where processes can occur. Warm, shallow waters, like those in Florida Bay, encourage calcification, though the magnitude of soil inorganic and organic carbon interaction can vary locally as well. Seagrasses are declining globally thus additional ecosystem value via greenhouse gas mitigation could greatly benefit conservation efforts. To make conservation efforts worthwhile to greenhouse gas mitigation, these findings help to consider and prioritize sites where risk and impact of Corg lost is more severe.

Seagrass is a valuable and important habitat, providing services such as coastal protection, supporting fisheries, and carbon sequestration. However, it is challenging to map accurately, as remote sensing has limits to how deep in the water column it can penetrate, and uncertainties such as distinguishing between algae and seagrass. Seagrass can exist at depths of theoretically 90 m deep in ultraoligotrophic waters, meaning that there is much of this habitat that cannot be mapped by remote sensing. Green turtles are an ideal candidate to help find seagrass blue carbon resources in the Red Sea. They go through an ontogenetic dietary shift to become almost completely herbivorous, and have a high fidelity to foraging sites. In this study we aim to assess the use of green turtles Chelonia mydas in discovering seagrass blue carbon. We use telemetry from 53 turtles tagged over 2018, 2019, and 2021 to map their foraging areas. 50 out of the 53 (94.34%) foraging sites had not been visited by previous seagrass studies in the Red Sea. We visited 18 locations in 14 of these foraging sites to ground truth them, and all 14 foraging sites (100%) had seagrass present. Comparatively, 18 out of 30 sites where seagrass was indicated by the remote sensing-based Allen Coral Atlas showed no seagrass. The turtles were seen to favour travelling shorter distances, thus it will be necessary to expand the area of tagging in order to achieve complete coverage of the Red Sea. Approximately 1/3 of the visited sites were deeper than 8 m, and so out of range of remote sensing, showing that considerable blue carbon resources may be discovered with the use of turtles. Samples were taken for carbon stock estimation from the ground truthed sites. A mean carbon stock of 4.89 ± 0.83 kg Corg m-2 was estimated for 1 m depth sediment. In the future it is important to develop methods for mapping the surface areas of the deep and inaccessible seagrass habitats that the turtles discover.

During the last decade, the academic interest for Earth’s natural carbon sinks and their role concerning climate change has increased. Today, many scientists around the world are trying to calculate different ecosystem’s potential to sequester and store carbon dioxide from the atmosphere. As a newcomer to the scientific arena, the term ‘blue carbon’ has been well received by scientists in the field. ‘Blue carbon’ highlights the carbon captured and stored by productive ecosystems along the world’s coasts. The term refers to coastal wetlands – such as mangrove forests, salt marshes and seagrass meadows – and it came to life as the scientific community recognized these ecosystems’ significant potential as effective carbon sinks. New research indicates that these ecosystems’ complex and vertical root systems can store much larger amounts of carbon in the soil than any other terrestrial ecosystem. By studying this subject, scientists are trying to understand how these ecosystems can help us in the quest of removing excessive carbon dioxide from the atmosphere. The goal of this thesis is to conduct a literature review, aiming to analyse and compile the new research on ‘blue carbon’ that has been published during the last 10 years. The paper aims to investigate whether the ecosystem’s potential as carbon sinks differ from each other, and what threats they will face in the future. It will additionally review if scientists have been able to unite around any predictions about what the future for ‘blue carbon’ – and its role in mitigating climate change – will look like. / Under det senaste decenniet har intresset kring naturliga kolsänkors potential och roll i att mildra klimatförändringar ökat. Idag är det många forskare som arbetar med att beräkna mängden kol som olika ekosystem runt om världen kan lagra i sin biomassa och i jorden under dess rötter. Som en nykomling på den vetenskapliga arenan, har termen ’blue carbon’ blivit väl mottaget av forskare inom området. ’Blue carbon’ syftar på det kol som fixeras och lagras av de produktiva ekosystemen längs världens kuster. Termen refererar till kustbelägna våtmarker – så som mangroveskogar, saltträsk och sjögräsbäddar – och introducerades efter att den vetenskapliga världen erkänt deras imponerande potential som kolsänkor. Ny forskning tyder på att deras avancerade och vertikala rotsystem kan lagra mer koldioxid i marken än vad vanliga terrestra skogar kan. Genom att studera detta ämne försöker forskare att förstå hur dessa ekosystem kan hjälpa oss att avlägsna överskottet av koldioxid från atmosfären. Målet med denna uppsats är att utföra en litteraturstudie och analysera, samt sammanställa den nya forskningen om ’blue carbon’ som publicerats de senaste 10 åren. Uppsatsen kommer undersöka hur stor skillnad det är mellan de olika ekosystemen och vilka hot de står inför i framtiden. Dessutom kommer den undersöka ifall forskare kommit närmre i att enas kring förutsägelser om framtiden för ’blue carbon’, och hur dess roll i att mildra klimatförändringarna kommer se ut.

Prussian blue (PB) nanoparticles were synthesized from FeCl3.6H2O, K4[Fe(CN)6].3H2O, and from Fe(NO3)3.9H2O and K4[Fe(CN)6].3H2O, and then characterized by Fourier transform infrared (FT-IR), Ultraviolet-visible spectroscopy, X-ray diffraction (XRD), Energy dispersive spectroscopy (EDS), Scanning electron microscopy (SEM), Raman spectroscopy and thermogravimetric analysis. Graphene oxide and carbon nanotubes were also synthesized and characterized. PB nanoparticles, carbon nanotubes (CNT), graphene oxide (GO) and cetyltrimethylammonium bromide (CTAB) were sequentially deposited onto glassy carbon electrode surface to form chemically modified electrode for the detection of hydrogen peroxide (H2O2) and dopamine. The following electrodes were fabricated, GC-PB, GC-MWCNT, GCGO, GC-CTAB, GC-MWCNT-PB, GC-GO-PB and GC-CTAB-PB. Cyclic and Square wave voltammetric techniques were used to measure the hydrogen peroxide detectability of the electrodes at pH ranges of (3 - 7.4) in 0.1M phosphate buffer solution, in the absence or presence of 25 μL of H2O2. The GC-CNT-PB, GC-GO-PB,GC-CTAB-PB electrodes showed a good response for the detection of hydrogen peroxide in both acidic and neutral media while the GCPB electrode only showed good response in acidic media.

Seagrasses are considered highly important CO2 sinks, with the capacity to store substantial quantities of organic carbon in the living biomass and sediments, and thereby acting as a buffer against climate change. In this thesis, I have studied carbon storage variability in temperate and tropical seagrass habitats and identified factors influencing this variation. In addition, as seagrass areas are decreasing worldwide, I have assessed effects of different anthropogenic disturbances on carbon sequestration processes. The result from this thesis showed that there was a large variation in carbon storage within and among temperate, tropical and subtropical regions. The highest organic carbon stocks were found in temperate Zostera marina meadows, which also showed a larger carbon storage variability than the subtropical and tropical seagrass habitats. The tropical and subtropical seagrass meadows had inorganic carbon pools exceeding the organic carbon accumulation, which could potentially weakens the carbon sink function. The variability in organic carbon stocks was generally strongly related to the sediment characteristics of the seagrass habitats. In Z. marina meadows, the strength of the carbon sink function was mainly driven by the settings of the local environment, which in turn indicates that depositional areas will likely have higher organic carbon stocks than more exposed meadows, while in the tropics seagrass biomass was also influencing sedimentary carbon levels. Furthermore, locations with large areas of seagrass were associated with higher carbon storage in tropical and subtropical regions, which could be related to increased accumulation of both autochthonous and allochthonous carbon. In an in situ experiment, impacts on carbon sequestration processes from two types of disturbances (with two levels of intensity) were tested by simulating reduced water quality (by shading) and high grazing pressure (through removal of shoot biomass). At high disturbance intensity, reductions in the net community production and seagrass biomass carbon were observed, which negatively affected carbon sequestration and could impact the sedimentary organic carbon stocks over time. In the treatments with simulated grazing, erosion was also seen, likely due to an increase in near-bed hydrodynamics. When experimentally testing effects of increased current flow on organic carbon suspension in Z. marina sediment, a ten-fold release of organic carbon with higher current flow velocities was measured, which resulted in an increase in the proportion of suspended organic carbon by three times in relation to other sediment particles. Therefore, periods with enhanced hydrodynamic activity could result in a removal of organic carbon and thereby likely reduce the seagrass meadows’ capacity to store carbon. The findings of this thesis add to the emerging picture that there is a large natural variability in seagrasses’ capacity to store carbon, and highlight how human-induced disturbances could negatively affect the carbon sink function in seagrass meadows. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.</p>

Shallow seagrass ecosystems frequently experience physical disturbance from vessel groundings. Specific restoration methods that modify physical, chemical, and biological aspects of disturbances are used to accelerate recovery. This study evaluated loss and recovery of ecosystem structure in disturbed seagrass meadows through plant and soil properties used as proxies for primary and secondary production, habitat quality, benthic metabolism, remineralization, and nutrient storage and exchange. The efficacy of common seagrass restoration techniques in accelerating recovery was also assessed. Beyond removal of macrophyte biomass, disturbance to seagrass sediments resulted in loss of organic matter and stored nutrients, and altered microbial and infaunal communities. Evidence of the effectiveness of restoration actions was variable. Fill placement prevented additional erosion, but the resulting sediment matrix had different physical properties, low organic matter content and nutrient pools, reduced benthic metabolism, and less primary and secondary production relative to the undisturbed ecosystem. Fertilization was effective in increasing nitrogen and phosphorus availability in the sediments, but concurrent enhancement of seagrass production was not detected. Seagrass herbivores removed substantial seagrass biomass via direct grazing, suggesting that leaf loss to seagrass herbivores is a spatially variable but critically important determinant of seagrass transplanting success. Convergence of plant and sediment response variables with levels in undisturbed seagrass meadows was not detected via natural recovery of disturbed sites, or through filling and fertilizing restoration sites. However, several indicators of ecosystem development related to primary production and nutrient accumulation suggest that early stages of ecosystem development have begun at these sites. This research suggests that vessel grounding disturbances in seagrass ecosystems create more complex and persistent resource losses than previously understood by resource managers. While the mechanics of implementing common seagrass restoration actions have been successfully developed by the restoration community, expectations of consistent or rapid recovery trajectories following restoration remain elusive.