22. Sediment rain
1-11/2 hr x 2
FROM PROJECT REEF ED
Concepts
Aim
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Great Barrier Beet Marine Park Authority
Sediment
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To
find out whether the amount of sediment raining down is different on
Distribution
different parts of the reef flat.
Interaction
Skills
Observing
Purpose:
Measuring
Recording
To measure the amount of sediment that falls from the
Analysing
sea water on organisms on the reef.
Attitudes
Interest in
methods of
enquiry in
science
You will need
•
Reef-walking gear
• Small plastic specimen tubes (about 2cm diameter) with holes drilled near
upper rim (35 mm film canisters or cut down vinegar bottles can be used. The
holes can be drilled with a hot nail.)
• Strong twine or wire
• Air photo of reef-top (optional)
•
Knotted 20m rope (optional)
• A suitable permit
• Small boat for use at night tide (optional)
This activity requires two sessions each of about 1-11/2 hours on the reef flat at low
tide. One session should be at the beginning of your trip, the other at the end.
The amount of sediment raining down from above may affect the
4
distribution of plants and animals on a reef. If different amounts of
sediment rain down on different parts of the reef, this could possibly be
one factor influencing the relative distribution of corals and fleshy algae
on a reef flat.
What to do
1. Across the reef flat, put out a series of open plastic tubes attached to fixed
objects (e.g. boulders, iron slabs). The tubes should be held in place using, for
example, wire or tape threaded through holes near the top of the tube.
The mouths of the tubes should all be at the same tidal level (e.g. slightly
below the upper limit of coral growth on the reef flat). It may be useful to set
out the sediment traps along a transect line if used for other study.
2. After a number of days, collect the tubes. (Or check the tubes daily at low tide
and, if a boat is available, at high tide.)
3. Compare the amount of sediment in the tubes. Is there any systematic
variation in amount across the reef flat? Is there any variation in the size of the
sediment in the tubes, i.e., do some tubes contain coarser sediment than
others?
4. Discuss your findings and their possible significance with others in your group.
We acknowledge
the help of A Cribb, Botany Department, University of Queensland with this
activity.
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