Energy and the Environment-A Coastal Perspective

Based upon the present data, it appears that the most immediate effect of vegetated coastal region degradation will be an increase of GHG emissions, as projections hold that these rates of release could be up to 50 times that of carbon sequestration, given the ecosystems were still intact (McLeod E, 2011). Luckily, the mechanism by which blue carbon acts to seize emissions is readily understood through scientific explanation.

Ocean’s Involvement in the Carbon Cycle

In these vegetated coastal regions, there exists an underlying layer of sediments that is organic-rich and therefore capable of withholding carbon, due to a relatively low presence of oxygen and other inhibitory compounds that relate to decomposition at depth below the surface. Although terrestrial ecosystems have also been observed to perform the same mechanism, it is notable that the efficiency and capacity of these ‘blue carbon’ sequestration sources is much greater, and thus stocks of stored carbon are much more abundant in the marine environments. When habitat conversion and land-use of these ecosystems occurs, the carbon residing in these deep sediment sinks becomes exposed to oxygen or is destabilized through another chemical reaction, and following microbial actions act to release the stored greenhouse gases to the above aquatic environment or atmosphere (Kristensen E, 2008). This process does not have a limiting factor. This means that the rate and amount of carbon released into the environment, generally occurring in the form of CO­₂ or CH₄ among other carbon species, is dependent upon the nature of land use and the type of underlying sediment.

Recent experiments have allowed for the production of data sets and figures that display the rate of carbon sequestration by the vegetation and top one meter of sediment in these areas. This is a major development because it reveals the emission rates for this so called ‘near-surface carbon’, which is the portion of the sediment that is most vulnerable to the subsequent effects of ecosystem alteration. In one study conducted by Simon Thrush et al, it was found that near-surface blue carbon became oxidized after disturbance and was then converted into the chemical species of CO₂, as well as into bicarbonate and carbonate ions, which equate to an increase of the active carbon dioxide occurrence in the ocean-atmosphere system (Simon Thrush, 2012). As this system relies on an equilibrium of partial pressure produced by differential levels of CO₂ existing between the atmosphere and oceans, the amount of carbon dioxide persisting in the atmosphere can be altered either through direct circulation between the two, or by the declining ability of the oceans to sequester carbon.

The study by Simon Thrush, et al. presents some of the most current estimations and projections resulting from habitat conversion and land-use of coastal vegetated ecosystems, but these are still conservative figures. This means that they remove uncertain variables from their calculations such as: deep sediment release, high-end area estimations, further speculative assumptions as to the ability of converted regions to retain at least 75% of near-surface carbon, and ambiguous measures of the effects of ecosystem distortions in producing new sediments that could further efforts of carbon sequestration. Given the above parameters, this study attributes an amount of 0.15 to 1.02 billion tons of carbon dioxide released to the atmosphere from blue carbon sinks each year, with the mean value lying at 0.45 billion tons.

Citations:

• McLeod E, Chmura GL, Bouillon S, Salm R, Bjork M, et al. (2011) A blueprint for blue carbon: toward an improved understanding of the role of vegetated coastal habitats in sequestering CO₂. Frontiers in Ecology and the Environment 9: 552–560.

• Kristensen E, Bouillon S, Dittmar T, Marchand C (2008) Organic carbon dynamics in mangrove ecosystems. Aquatic Botany 89: 201–219.

• Simon Thrush, et al. “Estimating Global “Blue Carbon” Emissions From Conversion And Degradation Of Vegetated Coastal Ecosystems.” Plos ONE 7.9 (2012): 1-7. Academic Search Complete. Web. 19 July 2013.