Marsh construction techniques influence net plant carbon capture by emergent and submerged vegetation in a brackish marsh in the northwestern Gulf of Mexico
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Coastal marshes play an important role in global carbon cycles, yet coastal development has led to widespread losses of marsh habitat. To address this problem, many coastal wetlands have been restored or created over the past several decades using a variety of construction techniques, but it is unclear if net plant carbon capture in constructed marshes is equal to that of reference marshes, or if rates of plant carbon capture are influenced by marsh construction techniques. To comparatively assess relative carbon capture by emergent and submerged vegetation in constructed and reference marshes, we measured standing biomass and carbon content in above- and belowground emergent plant tissue and submerged vegetation in three constructed areas (2-3 years old) and one reference area in a brackish marsh in the northwestern Gulf of Mexico in 2009 and 2010. We also used aerial photographs to construct a GIS database of emergent and submerged vegetation coverage. These data were combined to estimate net annual plant carbon capture per square meter of marsh vegetation in each constructed and reference area. This index of carbon input to wetland vegetation suggests that rates of carbon capture by emergent aboveground vegetation and submerged aquatic vegetation were similar in constructed and reference areas. However, submerged vegetation captured less carbon (0.1-0.3kgm -2) than emergent vegetation (0.2-1.7kgm -2), and constructed areas contained an order of magnitude less emergent habitat than the reference area. Consequently, the annual carbon production of entire constructed areas (emergent+submerged vegetation; 0.1-1.2kgm -2) was always less than half that of the reference area (0.8-2.5kgm -2). Therefore, although productivity of emergent and submerged vegetation in constructed and reference areas was similar, the smaller ratio of land to water in the constructed areas reduced their annual rate of plant carbon capture at a larger spatial scale. To more closely mimic rates of plant carbon capture in reference marsh habitats, constructed marsh designs should aim to replicate the ratio of land to water in adjacent reference marshes. 2012 Elsevier B.V.
