Purpose
To estimate the quantity of sediment deposited on a daily basis
(mg/cm2/day).
Materials for one sediment trap
One plastic garden tray
Two 2" x 7.5" (standard) bricks
Six 6" pieces of 2" PVC pipe
Twelve 2" PVC endcaps
PVC glue
Cable ties
#6 Melitta coffee filters
Six large plastic automotive funnels
to hold filters
Funnel rack (any plastic rack)
Scale (0.01 gm precision)
Optional:
Hobo light meter in underwater housing
(See Light Intensity Measurement method)
Assembly
Base
1. Cut 3 holes in the garden tray through which the 2"
PVC pipe will fit snugly.
2. Attach two bricks underneath the inverted garden
tray with cable ties, one on each uncut corner.
3. Attach optional equipment to base with cable ties.
Traps
1. Cut six 6" lengths of the 2" PVC pipe.
2. Glue one PVC endcap on each piece of pipe.
3. Label the bottom of each PVC pipe with permanent marker. (Coralline algae may
deposit on top and sides of pipe obscuring any markings in those areas.)
Deployment
Place assembled sediment traps flat on hard or sandy substrate. Avoid coral when possible.
In areas of potential surge or high wave action, cable tie sediment trap base to substrate.
Also avoid the bottom of sandy grooves that may experience bottom sediment churning in times
of greater water motion, causing high readings of sediment loading. Depending on the
turbidity and wave action in the area, sediment
traps should be collected weekly, bi-monthly or monthly.
Collecting Sediment Traps
Remove each PVC pipe carefully by reaching
under the base and pulling the trap down through
the hole. Cap the open end with the extra PVC endcap. If continuing the
sediment collection, insert new PVC pipes. (Note: do not transport new PVC pipes
capped as pressure makes it difficult to remove caps).
Lab Analysis
Sediments are rinsed, drained, and dried in #6 Melitta coffee filters held in plastic gas
funnels placed upright in drying racks.
1. Label one filter for each collected sample. Weigh filter 3 times. Average and
record weight in notebook.
2. Set funnels upright in drying racks. Put one preweighed filter in each funnel.
3. Carefully remove the cap from PVC pipe.
Pour sample into correspondingly marked filter, swirling PVC trap occasionally
to suspend sediments. Rinse trap with fresh water to wash any remaining
sediments into filter.
4. Allow sediments in filter to drain. Carefully rinse drained sediments in filter with
fresh water to remove any salts that may add to dry weight.
5. Let samples dry for 10 days to several weeks until a constant weight is achieved
(i.e. reweighing the sediments over several days producing the same results). Each sample
is then weighted over 3 different days and the results will be averaged to 0.01 grams.
6. If desired, sediments may be analyzed for grain size.
References
Brown, Eric, 1999. PhD dissertation, to be published. University of Hawaii.
Gardner, W.D., 1980. Field assessment of sediment traps. Jour. Mar. Res. 38:40-52.
