For seagrass characteristics, 15cm diameter cores were collected at
randomly chosen locations during low tide within each sampling site in
triplicate. Seagrass biomass was separated from sediment using a
coarse mesh bag. Seagrasses were separated by species and shoots were
counted. Leaves were counted on each shoot, measured and scraped of
any epiphytes. Aboveground and belowground components were separated
and dried at 50C until a constant weight was achieved. Dry weight of
above- and belowground components were recorded. The dried leaf
samples were homogenized and ground to a fine powder using a motorized
mortar and pestle. Powdered samples were analyzed for total carbon (C)
and nitrogen (N) content using a CHN analyzer (Thermo Flash EA, 1112
series). Total phosphorus content was determined by a dry-oxidation,
acid hydrolysis extraction followed by a colorimetric analysis of
phosphate concentration of the extract. Homogenized leaf samples were
additionally analyzed for δ13C using EA-IRMS techniques; high
temperature catalytic combustion was used to combust the organic
carbon to CO2, which was then measured on a Finnigan MAT Delta C IRMS
in a continuous flow mode. Isotopic ratios (R) were reported in the
standard delta notation (‰ ): δ (‰) = [(Rsample/Rstandard)-1]×1000.
These results are presented with respect to the international standard
Vienna Pee Dee Belemnite (V-PDB). Analytical reproducibility of the
reported values, based on sample replicates, was better than ±0.08‰.
Soil cores were collected at randomly selected locations within each
site in duplicate by driving a manually operated piston core (6cm
diameter) into the soil until 1m depth or the depth at which the
piston core could no longer be inserted. A depth of one meter was
chosen for straightforward comparison to existing soil carbon
inventories and is not associated with a known period of accumulation.
This method yielded samples of ~9 cm3 along the depth profile, while
minimizing compaction. Sediment samples of a known wet volume were
dried and weighed to calculate dry bulk density (g dry soil mL wet
soil-1). Soil samples were homogenized using a motorized mortar and
pestle then analyzed for Corg and Cinorg
