S E D I M E N T A T I O N R AT E
S10
What
What Is It?
BENCHMARK
Sedimentation refers to the process of depositing
Average
Average sediment deposition rates less
sediments (solid fragments of inorganic or organic
than 10 mg/cm2/d.
than
/d.
material, such as sand or mud) onto the seafloor.
TA R G E T
This process is usually quantified in terms of the
To be developed. At a minimum, should
To
amount of sediment accumulated over some specified
meet
meet the benchmark values.
area during some specified period of time (for example,
5 mg of sediment per cm2 per day).
RED FL AG
A sedimentation rate of 10 mg/cm2/d is often cited
Average sedimentation rates above
Average
as a general rule-of-thumb threshold for deleterious
10
10 mg/cm2/d for more than two
effects on corals34. Sensitivity to sediment
consecutive
consecutive sampling intervals.
accumulation varies among coral species. Small-polyp
species and corals with plate-like growth forms are
often more susceptible to the lethal effects of high
sedimentation.
species) do exist in areas of high sedimentation. An
abrupt change in sedimentation rate, lasting for an
Why
Why Do We Measure It?
extended period, is likely the most problematic to
As stationary, benthic (bottom-dwelling) animals,
coral reefs or species not accustomed to higher rates
corals have a real problem when excessive sediments
of sedimentation.
fall on their surface, interfering with phytosynthetic
High sedimentation rates can be indicative of stressful
and active feeding activities. Most corals can produce
mucus to trap and slough off sediments, but this has
conditions on the reef, potentially associated with
an energetic cost to the coral.
changes in land use (e.g., deforestation, agriculture
and aquaculture) or marine dredging operations.
Sediment accumulation and resuspension are natural
Many pollutants (pesticides, fertilizers, heavy metals)
processes that can be affected by anthropogenic
can be associated with these sediments, resulting in
activities (e.g., dredging operations, coastal land
additional perturbation of the benthic marine life.
clearing) and also by natural weather events (e.g.,
storms, cold fronts). High rates of sedimentation can
How
How Do We Measure It?
reduce coral growth rates, species richness, and
zonation patterns of corals and even seagrasses.
Researchers use sediment traps (often PVC tubes)
to collect particles raining down through the water
Some reefs (containing more sediment-tolerant
column onto the reef. The trapped particles are then
dried and weighed. Sometimes the particles are
separated into different particle types or size classes.
By knowing how much time it took to collect a certain
amount of sediment, analysts can calculate the rate
at which particulates are accumulating on the reef.
The MBRS SMP details a methodology for monitoring
sedimentation rates17.
Lisa Carnes
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