PVC pipes of three sizes (10, 25, 4

PVC pipes of three sizes (10, 25, 40 mm in
diameter) corresponding to the three burrow size
classes were used (n = 6/size class). Soil deposited
into burrow mimics was also collected daily (two
tidal cycles) during a 5-d spring-tide period (July
30–August 3, 2007). Again, a total of 270 samples
were taken (3 sizes 9 3 habitats 9 5 d 9 6 replicates).
We filled PVC pipes with estuarine filtered
water to avoid overestimating sediment deposition
due to the incoming water. All water and soil in
burrow mimics were collected daily in plastic bottles,
and stored for 24 h. All supernatants were
drawn out, and remaining deposits were oven dried
at 60C to constant weight and weighed.
We combined the samples collected from each
burrow or burrow mimic over 5 days for analysis. A
total of 54 samples were taken for both excavation
and deposition (3 sizes 9 3 habitats 9 6 burrows or
burrow mimics). Total soil N (TN), total soil C (TC)
and total organic C (TOC) concentrations, salinity
and grain size were measured in the laboratory.
To examine background soil properties, six control
samples were taken from the top 5-cm soil (background
surface soil) and at a depth of 30 cm (background
subsurface soil) in small unburrowed areas
in Spartina and Phragmites marshes and mudflat
habitats with a 2-cm-diameter soil corer. The use of
the small unburrowed areas for sampling background
soil was to avoid sampling errors that might
be caused by the differences in other conditions rather
than crab burrowing. Thirty-six samples of
background soil (6 soil cores 9 2 depth 9 3 habitats)
were taken and used to compare with those of
the excavated and deposited soils.
To determine NO3-N and NH4-N concentrations,
10–50 g from each of 36 samples were frozen at
-10C until samples were analyzed. The soil for
determining inorganic N concentrations was also
used to calculate soil water content. Subsamples of
approximately 300 mg were used to determine TC,
TN and TOC concentrations. The remaining samples
were oven dried and used to measure soil
salinity and grain size. The total inorganic N (TIN)
concentration of the deposited soil was not measured.
Consequently, soil TIN, bulk density, and
water content were measured only in background
and excavated soils.