SEDIMENT SIZE ANALYSIS - Nutrient Analytical Services Laboratory

SEDIMENT SIZE ANALYSIS
NUTRIENT ANALYTICAL SERVICES
CHESAPEAKE BIOLOGICAL LABORATORY
FEBRUARY 2011
Method Description: This method uses sodium hexametaphosphate as a deflocculant
(breaks up the fines) and Ro-tap sieve technique to identify sediment
size classes of 2 mm through 63 microns. It does not differentiate between sizes
(phi) less than 63 microns.
Reagents: 0.5% Sodium hexametaphosphate (SHMP). Dissolve 5.0 g Sodium
hexametaphosphate in 1 Liter deionized water.
Equipment and Supplies:
Aluminum foil weighing pans (~15X20 cm)
47 mm GF/F pads, preweighed to 0.0001 g
Plastic Weigh boats (13X13 cm)
Four place analytical balance
Drying oven capable of maintaining 90 degrees C +/- 5 degrees C
600 mL beakers
Ro-tap Sieve
Sieves (21 cm diameter) 63 micron-2mm
Method:
1. Sediment samples usually come frozen in 8 oz glass jars.
2. Thaw the samples overnight (Six samples is a good quantity to work on at one
time).
3. Pre weigh aluminum foil weighing pans
4. Place the entire sample (at least 500 g wet weight) into a 600 mL beaker.
5. Add 0.5% sodium hexametaphosphate (SHMP, 5.0 g/L deionized water) until
the sample is completely covered.
6. Mix with glass stir rod and wait 5 minutes.
7. Carefully decant fluid (it will be very cloudy to begin with) through 63 micron
mesh and collect it in a container. Half gallon plastic milk jugs work well. By
carefully decanting the fluid, there will be a negligible amount of sand remaining
on the 63 micron mesh.

8. Repeat steps 4-6 until the fluid is clear. This may take up to several liters of
SHMP solution depending on the type of sediment.
9. Rinse what remains in the beaker thoroughly with deionized water.
10. Remove contents in the beaker to the pre-weighed aluminum foil dish and dry
at 80 degrees C.
To Determine The Amount of Fines
Measure the amount of SHMP used for a specific sample and
record on the bench sheet.
Filter at least two replicate aliquots for TSS measurements/sample
on a pre weighed 47 mm GF/F filter. Dry and weigh as per a normal TSS
measurement. Record on bench sheet.
Based on the TSS result (number of grams material for a given
volume), determine the amount of fine material for the entire sample.
Enter your work on the bench sheet.
Ro-tap Sieve Method
1. Record the dry weight of the sample.
2. Place the entire sample onto the first (most coarse) sieve.
3. Ro-tap for 15 minutes. Sieve sizes routinely used are 2.0 mm, 0.5 mm,
0.25 mm, 125 micron and 60 micron and the method allows for the
flexibility to add or subtract sieves depending on the project requirements.
4. Transfer material that is retained on each sieve to a pre-weighed large
plastic weighing dish. Use a tooth brush to loosen as much material as
possible. Record the sample+weighing dish weight on the bench sheet.
Calculation
Subtract the weigh dish weight from the total amount weighed for that sieved
fraction.
Add the amount determined from the SHMP procedure to the last fraction
(