Energy and the Environment-A Coastal Perspective

This section will address the methods by which carbon deposits are stressed to emission, along with the ways in which these coastal ecosystems vary. For reference, it should be stated that the brunt of the disturbances is felt by the top one meter of sediment, and therefore the following regards near-surface carbon.

Seagrass ecosystem degradation often results from a decline in water quality that occurs because of over-exposure to nutrients and organic sediments released by various organisms, and less frequently results from the anthropogenic activities of trawling, dredging, and dropping anchors within these networks. The aforementioned disturbances lead to the release of carbon deposits from the underlying sediments to the surrounding water network or atmosphere (Orth RJ, 2006). Tidal marshes suffer from conversion to arable land usable for agricultural practices, thus heavily effecting underlying sediments because of extensive oxidation that occurs as a result of diking and draining efforts that disturb these ecosystems (Barbier EB, 2011). Finally, mangroves owe their decline to the common transformation of these networks into aquacultures. This causes the near-surface range to be almost entirely disturbed as a result of digging activities, which in turn leads to further oxidation of exposed sediments. The detrimental effects of maintaining these aquacultures can become even longer lasting if not maintained properly, as over-harvest and expansion practices can increase the extent of erosion and subsequently increase exposure of underlying sediments to oxidative environments (Kristensen E, 2008).

Seagrass Beds

Of the three types of vegetated coastal ecosystems, it was observed that mangroves contribute the largest portion of carbon dioxide release, as they possess the greatest withheld carbon stock per-hectare and are thus responsible for about half of these emissions. Coming in second for global blue carbon emission totals, seagrasses contain the least amount of carbon per-hectare, yet contribute the next largest amount due to their greater global presence in terms of area covered. Tidal marshes then contribute the least to these CO₂ emission totals because they occupy the smallest global area, even though they possess a mid to upper carbon stock (Simon Thrush, 2012).

Tidal Marsh

The “social cost of carbon”, or SCC, as defined by the U.S. government, places the global economic expense at $41 per ton for each subsequent unit of carbon dioxide added to the atmospheric carbon pool (according to the value of the U.S. dollar in 2007) (United States Government, 2010). At this rate, the study by Simon Thrush et al places the estimated global cost resulting from degradation of vegetated coastal ecosystems at a range of $6.1 to $42 billion per annum, which relies on conservative measures (United States Government, 2010). Taken on any side of this range, this figure displays that there is a high economic stake to maintain the underlying sediments in these coastal regions, proving that conservation and monitoring of habitat conversion and land-use of these ecosystems is of greater economic benefit (and of greater ‘scientific importance’) than restoration attempts that are being conducted currently, which generally are not capable of sequestering as much carbon and preventing cycling into the atmosphere.

Mangroves

Citations

• Barbier EB, Hacker SD, Kennedy C, Koch EW, Stier AC, et al. (2011) The value of estuarine and coastal ecosystem services. Ecological Monographs 81: 169–193.
• Kristensen E, Bouillon S, Dittmar T, Marchand C (2008) Organic carbon dynamics in mangrove ecosystems. Aquatic Botany 89: 201–219.
• Orth RJ, Carruthers TJB, Dennison WC, Duarte CM, Fourqurean JW, et al. (2006) A global crisis for seagrass ecosystems. Bioscience 56: 987–996.
• 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.
• United States Government (USG) (2010) Technical Support Document: Social Cost of Carbon for Regulatory Impact Analysis Under Executive Order 12866. United States Environmental Protection Agency website. Available at: http://www.epa. gov/otaq/climate/regulations/scc-tsd.pdf.