To promote the sequestration of blue carbon, resource managers rely on best-management practices that have historically included protecting and restoring vegetated coastal habitats (seagrasses, tidal marshes, and mangroves), but are now beginning to incorporate catchment-level approaches. Drawing upon knowledge from a broad range of environmental variables that influence blue carbon sequestration, including warming, carbon dioxide levels, water depth, nutrients, runoff, bioturbation, physical disturbances, and tidal exchange, we discuss three potential management strategies that hold promise for optimizing coastal blue carbon sequestration: (1) reducing anthropogenic nutrient inputs, (2) reinstating top-down control of bioturbator populations, and (3) restoring hydrology. By means of case studies, we explore how these three strategies can minimize blue carbon losses and maximize gains. A key research priority is to more accurately quantify the impacts of these strategies on atmospheric greenhouse-gas emissions in different settings at landscape scales.
Blue Carbon & Sequestration
Blue carbon, the carbon fixed by vegetated coastal ecosystems including seagrasses, is reported to have a large potential to sequester atmospheric carbon dioxide. Planting, expanding or protecting seagrass meadows has, accordingly, been proposed as a form of geoengineering. Seagrasses are reported to account for up to 18% of the carbon burial in the world's oceans, which is on the same order of magnitude as other proposed geoengineering techniques, including iron fertilization. International protocols have been developed to quantify carbon sequestration in seagrass meadows, with a view to awarding carbon credits under the Verified Carbon Standard. Unfortunately, because these protocols do not adequately account for post-depositional processes in marine sediment, they significantly overestimate carbon capture by seagrass beds and give an incorrect view of its distribution. Specifically, neglecting biomixing and remineralization of carbon in surface sediments biases burial rates high, while using sediment carbon inventory (soil carbon stock) over the top 1 m as a proxy for burial rate incorrectly identifies areas of high carbon burial. Seagrass beds likely provide a limited setting for geoengineering, because they generally comprise slowly-accumulating, fine to medium sand, which captures organic carbon less efficiently than fine-grained sediments or rapidly-accumulating delta deposits. While there is no question that seagrass meadows provide valuable habitat, nor that they are disappearing rapidly, their contribution to the global burial of carbon has not yet been established. The danger of geoengineering with seagrasses before reliable assessment methods have been established is that overestimated carbon offsets could lead to a net increase in emissions of carbon dioxide to the atmosphere.
Old growth mangroves in existing protected areas store more carbon than restored forests or plantations. Carbon storage in such forests has economic value independent of additionality, offering opportunities for policy makers to ensure their maintenance, and inclusion in climate change mitigation strategies. Mangrove forests of the Everglades National Park (ENP), South Florida, though protected, face external stressors such as hydrological alterations because of flooding control structures and agriculture impacts and saltwater intrusion as a result of increasing sea level rise. Moreover, decreased funding of Everglades’ restoration activities following the recent economic crisis (beginning 2008) threatens the restoration of the Greater Everglades including mangrove dominated coastal regions. We evaluate several economic and ecological challenges confronting the economic valuation of total (vegetation plus soil) organic carbon (TOC) storage in the ENP mangroves. Estimated TOC storage for this forested wetland ranges from 70 to 537 Mg C/ha and is higher than values reported for tropical, boreal, and temperate forests. We calculate the average abatement cost of C specific for ENP mangroves to value the TOC from $2–$3.4 billion; estimated unit area values are $13,859/ha–$23,728/ha. The valuation of the stored/legacy carbon is based on the: 1) ecogeomorphic attributes, 2) regional socio-economic milieu, and 3) status of the ENP mangroves as a protected area. The assessment of C storage estimates and its economic value can change public perception about how this regulating ecosystem service of ENP mangrove wetlands (144,447 ha) supports human well-being and numerous economic activities. This perception, in turn, can contribute to future policy changes such that the ENP mangroves, the largest mangrove area in the continental USA, can be included as a potential alternative in climate change mitigation strategies.
Coastal dunes support biodiverse habitats of conservation interest and provide other essential but often overlooked benefits to society, such as carbon sequestration, thanks to their high soil carbon accumulation rates. The recently established coastal dune Natura 2000 network in the Italian Adriatic coast aims at protecting dune habitats diversity, yet its capacity to provide other ecosystem services, and the potential trade-offs with biodiversity provision have so far not been evaluated. In this paper we conduct this analysis for a key ecosystem service: carbon storage and sequestration. We i) quantify soil carbon stocks and sequestration within four coastal dune EU habitat types along the Adriatic Natura 2000 network; ii) upscale these data to create an inventory of carbon stocks for all dune Natura 2000 sites in the study area; iii) collate biodiversity data of the selected EU habitat types using plant diversity measures as surrogates of coastal dune biodiversity and iv) explore the trade-offs between carbon storage and biodiversity value for the selected habitats. Italian Adriatic coastal dune Natura 2000 sites sequester 4998 t of CO2e per year, with the majority in wooded dunes. Wooded dunes showed significantly higher soil carbon density than the other dune habitats, and had a much greater area, but they were characterized by lower species richness. By contrast, the endangered fixed dunes, which survive in few residual patches along the study area, showed the highest plant diversity for both total species richness and dune focal species, but had a much lower carbon density and extent. Although further analyses of additional services would be desirable for a more comprehensive assessment, these findings suggest that conservation actions should favor restoration of the natural dune zonation, since it guarantees both dune species diversity and carbon storage. The carbon stocks and EU habitat type extents produced in this study constitute the first systematic inventory for dune systems in the Mediterranean.
Designing a marine monitoring program that detects CO2 leaks from subsea geological storage projects is challenging. The high variability of the environment may camouflage the anticipated anisotropic signal from a leak and there are a number of leak scenarios. Marine operations are also costly constraining the availability of measurements. A method based on heterogeneous leak scenarios and anisotropic predictions of chemical footprint under varying current conditions is presented. Through a cost function optimal placement of sensors can be given both for fixed installations and series of measurements during surveys. Ten fixed installations with an optimal layout is better than twenty placed successively at the locations with highest leakage probability. Hence, optimal localizations of installations offers cost reduction without compromising precision of a monitoring program, e.g. quantifying and reduce probabilities of false alarm under control. An optimal cruise plan for surveys, minimizing transit time and operational costs, can be achieved.
The ocean provides ecosystem services (ES) that support humanity. Traditional single-issue management largely failed to protect the full suite of ES. Ecosystem-based management (EBM) promotes resilient social-ecological systems that provide ES. To implement EBM, an ES approach is useful: (1) characterize major ES provided (magnitude, geographic extent, monetary value, trends, and stakeholders), (2) identify trade-offs, (3) determine desired outcomes, and (4) manage anthropogenic activities accordingly. Here we apply the ES approach (steps 1–2) to an open ocean ecosystem, the eastern tropical Pacific (ETP), an area of 21 million km2 that includes waters of 12 nations and the oceanic commons, using 35 years (1975–2010) of fisheries and economic data, and 20 years (1986–2006) of ship-based survey data. We examined commercial fisheries, carbon storage, recreational fishing, and biodiversity as the major provisioning, regulating, cultural, and supporting ES, respectively. Average catch value (using U.S. import prices for fish) for the 10 most commercially fished species was $2.7 billion yr−1. The value of carbon export to the deep ocean was $12.9 billion yr−1 (using average European carbon market prices). For two fisheries-depleted dolphin populations, the potential value of rebuilding carbon stores was $1.6 million (cumulative); for exploited fish stocks it was also $1.6 million (an estimated reduction of 544,000 mt). Sport fishing expenditures totaled $1.2 billion yr−1, from studies of three popular destinations. These initial, conservative estimates do not represent a complete summary of ETP ES values. We produced species richness maps for cetaceans, seabirds, and ichthyoplankton, and a sightings density map for marine turtles. Over 1/3 of cetacean, seabird, and marine turtle species occur in the ETP, and diversity (or density) hotspots are widespread. This study fills several gaps in the assessment of marine and coastal ES by focusing on an oceanic habitat, utilizing long-term datasets, mapping the spatial distribution of ecological components, and concentrating on an area beyond Europe and the USA. Our results improve our understanding of ETP ES, highlight their variety, and offer a new perspective for a fisheries-dominated system. This study sets the stage for further analyses of trade-offs, which can inform decisions about resource management and biodiversity conservation.
Coastal “blue carbon,” (carbon sequestered in salt marsh, mangroves, and seagrasses) is a newly recognized benefit. The National Oceanic and Atmospheric Administration (NOAA), with partners, has been exploring and developing new policy opportunities for coastal conservation using the climate benefits of these ecosystems. We detail NOAA's efforts (federal and international, market and non-market) to leverage blue carbon for coastal conservation including: (1) how blue carbon is or could be incorporated into U.S. federal policies (both existing and new policy activities); (2) market-based policy solutions including the development of a Verified Carbon Standard methodology for carbon credits for wetland restoration and two landscape assessments of the climate mitigation benefits of watershed-scale restoration; and (3) international efforts to build a North American community of practice for blue carbon science and policy with the Commission for Environmental Cooperation, Canada, and Mexico, and an assessment of where blue carbon can be incorporated into international policy frameworks (including the Intergovernmental Panel on Climate Change (IPCC) Wetlands Supplement and the United Nations Framework Convention on Climate Change (UNFCCC)). Protecting coastal carbon leads to co-benefits including resilience to storms and erosion, and fishery benefits, thus blue carbon is a “triple win” for climate mitigation, adaptation, and conservation.
This study analyzed the past and future climate mitigation benefits of habitat restoration in Tampa Bay, and identified opportunities for enhanced ecosystem management that can provide agencies and community members in the region with information to support coastal management planning and prioritize restoration and climate adaptation planning.
As initiatives are taken in Sweden to evaluate the geological potential for carbon dioxide storage in the adjacent Baltic Sea, experiences from elsewhere may provide lessons about perceptions of and potential opposition toward carbon capture and storage (CCS). A comprehensive analysis of storage feasibility needs to include the issue of social acceptance. The knowledge of CCS is low in Sweden however and there are no Swedish CCS projects to learn from. This paper therefore draws on lessons from other large-scale energy projects that are embedded in similar Baltic Sea contexts to complement lessons on CCS acceptance provided in the literature. The aim of this study is to facilitate an understanding of acceptance of potential future CO2 storage initiatives in the Swedish Baltic Sea region and to analyze what contextual factors are likely to be determinative of the outcome of these and similar projects. The study identifies climate change as one such key contextual factor, which can often be used both to support and oppose a large-scale energy project. Furthermore, the study finds that there are perceptions of uncertainties regarding the regulatory framework that need to be adressed in order to facilitate the planning of CCS projects in the region.
The Southern Ocean archipelago, the South Orkney Islands (SOI), became the world's first entirely high seas marine protected area (MPA) in 2010. The SOI continental shelf (~44 000 km2), was less than half covered by grounded ice sheet during glaciations, is biologically rich and a key area of both sea surface warming and sea-ice losses. Little was known of the carbon cycle there, but recent work showed it was a very important site of carbon immobilization (net annual carbon accumulation) by benthos, one of the few demonstrable negative feedbacks to climate change. Carbon immobilization by SOI bryozoans was higher, per species, unit area and ice-free day, than anywhere-else polar. Here, we investigate why carbon immobilization has been so high at SOI, and whether this is due to high density, longevity or high annual production in six study species of bryozoans (benthic suspension feeders). We compared benthic carbon immobilization across major regions around West Antarctica with sea-ice and primary production, from remotely sensed and directly sampled sources. Lowest carbon immobilization was at the northernmost study regions (South Georgia) and southernmost Amundsen Sea. However, data standardized for age and density showed that only SOI was anomalous (high). High immobilization at SOI was due to very high annual production of bryozoans (rather than high densities or longevity), which were 2x, 3x and 5x higher than on the Bellingshausen, South Georgia and Amundsen shelves, respectively. We found that carbon immobilization correlated to the duration (but not peak or integrated biomass) of phytoplankton blooms, both in directly sampled, local scale data and across regions using remote-sensed data. The long bloom at SOI seems to drive considerable carbon immobilization, but sea-ice losses across West Antarctica mean that significant carbon sinks and negative feedbacks to climate change could also develop in the Bellingshausen and Amundsen seas.