Abstract
Seagrass meadows are highly productive habitats that provide important ecosystem services in the coastal zone, including carbon and nutrient sequestration. Organic carbon in seagrass sediment, known as “blue carbon,” accumulates from both in situ production and sedimentation of particulate carbon from the water column. Using a large-scale restoration (>1700 ha) in the Virginia coastal bays as a model system, we evaluated the role of seagrass, Zostera marina , restoration in carbon storage in sediments of shallow coastal ecosystems. Sediments of replicate seagrass meadows representing different age treatments (as time since seeding: 0, 4, and 10 years), were analyzed for % carbon, % nitrogen, bulk density, organic matter content, and 210Pb for dating at 1-cm increments to a depth of 10 cm. Sediment nutrient and organic content, and carbon accumulation rates were higher in 10-year seagrass meadows relative to 4-year and bare sediment. These differences were consistent with higher shoot density in the older meadow. Carbon accumulation rates determined for the 10-year restored seagrass meadows were 36.68 g C m-2 yr-1. Within 12 years of seeding, the restored seagrass meadows are expected to accumulate carbon at a rate that is comparable to measured ranges in natural seagrass meadows. This the first study to provide evidence of the potential of seagrass habitat restoration to enhance carbon sequestration in the coastal zone.
Highlights
Seagrass meadows are essential coastal ecosystems that provide many ecosystem services such as improved water quality and light availability, increases in biodiversity and habitat, sediment stabilization, and carbon and nutrient accumulation [1,2,3]
There was no significant difference in average % organic matter (OM) between 0-year (HI) and 4-year treatments, but there was a significant difference in average % OM between 0-year (SB) and 10-year treatments (F230,240,80,240 = 35.20; p < 0.0001) (Table 1)
Bulk density (BD) of sediment cores decreased significantly with age treatment, with 0-year (SB) treatment at 1.61 g cm-3 having the highest density compared to the 10-year treatment at 1.30 g cm-3 (F240,80,240,230 = 60.59; p < 0.0001) (Table 1)
Summary
Seagrass meadows are essential coastal ecosystems that provide many ecosystem services such as improved water quality and light availability, increases in biodiversity and habitat, sediment stabilization, and carbon and nutrient accumulation [1,2,3]. In order to partially mitigate seagrass decline, restoration in areas with suitable habitat is an effective option that has the potential to reestablish lost carbon stores and sinks, as well as other important ecosystem services seagrass meadows provide. Carbon accumulation in marine sediments provides longterm storage of organic carbon and has been referred to as “blue carbon” to distinguish it from carbon in terrestrial sinks [9]. Low oxygen, low sediment hydraulic conductivity, and slower microbial decomposition rates facilitate carbon burial and the accumulation of carbon stocks in these coastal sediments [11,15,16]
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