Table 1.
Direct and indirect effects of human activity on the carbon sequestering capacity of coastal ecosystems.
Figure 1.
Historic salt marsh habitat loss.
(A) High densities of eroded S. reticulatum burrows characteristic of consumer-driven die-off accelerate erosion and calving. (B) Results of GIS habitat loss analysis. Die-off marshes lost significantly more creek bank habitat between than healthy marshes between 1976 and 2005. (C) Results of GIS creek bank retreat analysis. Creek banks at die-off marshes also retreat more rapidly than healthy marsh creek banks over three decades.
Figure 2.
Schematic drawing of a typical die-off marsh creek bank.
Experimental zones are labeled with brackets. Abandoned S. reticulatum burrows in the low marsh quickly collapse without maintenance, while active burrowing and herbivory create a characteristic grazing border at die-off marshes. Ungrazed S. alterniflora above the denuded border contributes to peat toughness, but becomes vulnerable to S. reticulatum grazing as the grazing front migrates into the higher marsh. (Credit: E. Suglia)
Figure 3.
Creek bank surveys and field experiment results in three experimental zones of marsh creek banks.
(A) S. reticulatum burrowing is largely restricted to the grazing front where substrate toughness (B) and remnant cordgrass concentrate S. reticulatum activity. (C) S. reticulatum most successfully burrow in substrate at the grazing front and are unable to start or maintain burrows in the hard vegetated zone or the soft die-off zone, respectively. (D) S. reticulatum burrowing and herbivory make the grazing front the site of greatest erosion, explaining patterns of creek bank calving and sediment loss.
Figure 4.
Calving surveys at die-off marshes on Cape Cod, MA.
(A) S. reticulatum burrow density is highest on and behind calves, suggesting that burrowing weakens peat, leading to calving. Calving does not occur where burrow densities are low. (B) Burrows on and behind calves are also larger than in uncalved areas. Despite a lack of maintenance, burrows on calves erode due to tidal flow, releasing previously sequestered carbon into the water column.
Table 2.
Radiocarbon analyses of sediment samples at the base of vertical peat faces on die-off banks.