This document provides instructions for measuring soil organic carbon in mangrove sediments. It describes taking sediment samples at varying depth intervals, drying the samples, and measuring their bulk density and organic carbon concentration. An equation is given to calculate the soil organic carbon in megagrams per hectare for each interval by multiplying the bulk density, depth, and percent carbon. A table shows an example of these calculations being performed to obtain a total soil carbon value for a mangrove soil profile with a depth of 200 centimeters.

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USDA Forest Service, Research & Development
Pacific Southwest Research Station
Belowground protocol
USAID RDMA Mangrove Workshop April 23-May10, Trang, Thailand

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Mangroves 101
Mangrove soil
% Org. Carbon
Organic Carbon content (%)
5 10 15 20
Depth(cm)
-300
-250
-200
-150
-100
-50
0
mean, 95% CI

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USDA Forest Service, Research & Development
Pacific Southwest Research Station

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A
F
E
D
CBA
F
E
D
CB
0-15 15-30 30-50 50-100 100-300

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Sediment samples should be dried to
constant weight at 60 oC as soon as
possible
Jars and sediments are weighed
to the nearest 0.1 g. Sediments
are then removed and jars
reweighed

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Mortar and pestle ($)
Whiley Mill ($$$)
Coffee Bean Grinder ($$$)

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To accurately measure soil carbon we must know:
1) Soil depth
2) Soil bulk density
3) Organic carbon concentration

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Soil depth

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Soil depth

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Equation for soil bulk density:
Soil bulk density (g m-3) =
Oven-dry sample mass (g)
Sample volume (m3)
Soil -Bulk density
- C content
rθ
r2
2 ( )180
π
θ - sin θ*π*r2 -
( )Sample length
collected ( )*5 *

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Interval Actual Interval Dry wt (g) Vol (cm3) Bulk Density (g/cm3)
0-15 5-10 52.57 74.30 0.71
15-30 20-25 52.78 74.30 0.71
30-50 42.5-47.5 60.54 74.30 0.81
50-100 70-75 47.06 74.30 0.63
>100 150-155 47.06 74.30 0.63

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Interval Actual Interval Dry wt (g) Vol (cm3) Bulk Density (g/cm3)
0-15 5-10 52.57 74.30 0.71
15-30 20-25 52.78 74.30 0.71
30-50 42.5-47.5 60.54 74.30 0.81
50-100 70-75 47.06 74.30 0.63
>100 150-155 47.06 74.30 0.63

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Soil -Bulk density
- C content
0.0003833 m3
Dry combustion method

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Soil Carbon (Mg ha-1) = bulk density (g cm-3) * soil
depth interval (cm) * % carbon content
FOR EACH SEDIMENT INTERVAL:

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Soil Carbon (Mg ha-1) = bulk density (g cm-3) * soil
depth interval (cm) * % carbon content
FOR EACH SEDIMENT INTERVAL:
Interval Actual
Interval
Bulk Density
(g/cm3)
Soil interval
(cm)
% C
content
Soil C (Mg ha-1)
0-15 5-10 0.71
15-30 20-25 0.71
30-50 42.5-47.5 0.81
50-100 70-75 0.63
>100 150-155 0.63
TOTAL
1. Total peat depth depth = 200 cm
2. 1,000,000 g = 1 Mg
3. 100,000,000 cm2 = 1 ha

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Soil Carbon (Mg ha-1) = bulk density (g cm-3) * soil
depth interval (cm) * % carbon content
FOR EACH SEDIMENT INTERVAL:
Interval Actual
Interval
Bulk Density
(g/cm3)
Soil interval
(cm)
% C
content
Soil C (Mg ha-1)
0-15 5-10 0.71 15 10
15-30 20-25 0.71 15 10
30-50 42.5-47.5 0.81 20 10
50-100 70-75 0.63 50 10
>100 150-155 0.63 200 10
TOTAL
1. Total peat depth depth = 200 cm
2. 1,000,000 g = 1 Mg
3. 100,000,000 cm2 = 1 ha

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Soil Carbon (Mg ha-1) = bulk density (g cm-3) * soil
depth interval (cm) * % carbon content
FOR EACH SEDIMENT INTERVAL:
Interval Actual
Interval
Bulk Density
(g/cm3)
Soil interval
(cm)
% C
content
Soil C (Mg ha-1)
0-15 5-10 0.71 15 10 106.14
15-30 20-25 0.71 15 10 106.56
30-50 42.5-47.5 0.81 20 10 162.97
50-100 70-75 0.63 50 10 316.71
>100 150-155 0.63 200 10 633.41
TOTAL 1325.78
1. Total peat depth depth = 200 cm
2. 1,000,000 g = 1 Mg
3. 100,000,000 cm2 = 1 ha