- Sediment reduces the
amount of light penetrating the water, depriving the plants
of light needed for photosynthesis.
- Sediment particles absorb warmth from the
sun and thus increase water temperature. This can stress some
species of fish.
- Settling sediment can bury and suffocate
fish eggs and bury the gravel nests they rest in.
- Suspended sediment in high concentrations
can dislodge plants, invertebrates, and insects in the stream
bed. This affects the food source of fish, and can result
in smaller and fewer fish.
The stream-bottom sediments on the left provide spaces
for fish to lay eggs and for invertebrates to live and
hide. Excess erosion has deposited fine grained sediments
on the stream bottom to the right. There are no spaces
available for fish spawning or for invertebrate habitat.
- Excess sediment from
eroding soils contains organic matter that contributes to
oxygen depletion in the water as it is decomposed.
- Eroding soils also contribute the nutrients
nitrogen, and especially phosphorus. In low nutrient streams
and recovering waters such as Duluth's streams and Lake Superior,
these can contribute to algal growth and oxygen depletion.
- Suspended sediment in high concentrations
irritates the gills of fish, and can cause death.
- Sediment can destroy the protective mucous
covering the eyes and scales of fish, making them more susceptible
to infection and disease.
- Sediment may carry toxic agricultural and
industrial compounds such as heavy metals and pesticides.
If these are released in the habitat they can cause abnormalities
or death in the fish.
- Sediment loads in our waterways often result
in further increased erosion and instability of stream banks,
causing stream channels to become wider and shallower, which
leads to warmer water temperature.
from "Turbidity: A Water Quality Measure", Water
Action Volunteers, Monitoring Fact sheet Series, UW-Extension,
Environmental Resources Center. It is a generic, un-calibrated
impact assessment model based on Newcombe, C. P., and J.
O. T. Jensen. 1996. Channel suspended sediment and fisheries:
a synthesis for quantitative assessment of risk and impact.
North American Journal of Fisheries Management. 16: 693-727.
Where does excess sediment come from?
Sediment is a natural part of the ecosystem. Streams transport
sediment washed in from the watershed and deposit it on natural
bars or into the larger rivers and lakes that they empty
into. Problems occur, however, when activities such as
road construction, building construction, landscaping, logging, or poorly
managed farming remove the protective vegetative covering from soils.
Loose sediments are then free to wash into the streams
with surface water runoff during rain storms. The dirt and sand
that builds up on city streets is also a source of sediment,
as this gets washed into streams through the storm water
The streams, themselves, can also be a source of excess
sediment.As stream flows increase, the increased amount
of water leads to stream bank erosion. The sediment that was a part of
the stream bank then enters the stream, further increasing the
suspended sediment concentrations and loads. Stream flows
increase when we remove forests, fill in wetlands or add
impervious surfaces (click here to read more).
How can sediment pollution be controlled?
In order to minimize the amount of sediment free to wash into streams during construction and
landscaping activities, a sediment control plan must be created and implemented
before there is a problem. First-off, minimizing the amount
of land disturbed can significantly reduce the amount
of erosion, and reduces the area where sediment needs to be controlled.
Sediment management techniques include installing silt fences,
structural modifications, diversion ditches, sediment traps
and basins. In order to be effective, these techniques
must be properly installed and, of equal importance, maintained
over the duration of the project. Once construction activities
are complete, mulch and vegetation should be applied to
bare surfaces as soon as possible to anchor the soil in
Big construction projects aren't the only source of sediment
pollution. Homeowners can help by minimizing vehicle traffic
on vegetated surfaces during muddy, wet conditions. Avoid
sweeping the sand, grit and roadsalt
left over from winter road maintenance back onto the street.
It will drain into the storm drains and end up in the streams.
Also, stockpiles of sand, gravel and soil for those summer
projects should be placed in areas that are not natural
watercourses during storms. They should be located far enough away from
those watercourses (including roads and driveways) that they
cannot wash into them during big storms. Also, covering
these piles with a tarp will keep the rain from eroding
How do we measure suspended sediment in streams?
DuluthStreams staff estimate total suspended sediment concentration
(TSS) in several ways ranging from simple transparency
tubes to complex automated sensors.
The simple, inexpensive transparency tubes are the cornerstone
of the State's Volunteer
Stream Monitoring Program. Middle School Young Scientists
used them to monitor Tischer Creek from October 2002 through