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More in depth look at Turbidity
back to the list
of parameters
Turbidity is a measure of the amount of suspended particles in the water. Algae, suspended sediment, and organic matter particles can cloud the water, making it more turbid. The easiest way to think about turbidity is to ask: how clear is the water? If water is very clear, that means the turbidity is very low. The more cloudy or dirty, the higher the turbidity.
Why is it Important?
High turbidity levels can have many negative impacts on a creek
or river. Here are some examples:
· Suspended particles can block sunlight from reaching
algae in the water, decreasing photosynthesis.
· Suspended particles can also absorb heat, raising the temperature of the water.
· Suspended sediments can clog the gills of fish, making it difficult for them to breathe.
· When suspended sediments settle to the bottom, they can smother fish eggs and insects that live in the bottom of the creek.
· Suspended sediments can also carry pathogens, pollutants, and nutrients.
· Suspended particles can also absorb heat, raising the temperature of the water.
· Suspended sediments can clog the gills of fish, making it difficult for them to breathe.
· When suspended sediments settle to the bottom, they can smother fish eggs and insects that live in the bottom of the creek.
· Suspended sediments can also carry pathogens, pollutants, and nutrients.
There are several methods for measuring turbidity. The
method we use at Stream Team is a Turbidity Meter (also called a nephelometer).
We fill up a clear tube with a water sample, and place it inside the meter.
The meter shoots a beam of light through the sample, and measures how
much the light is scattered. As the amount of suspended particles increases,
more light is scattered and the turbidity readings increase. The units
for turbidity are nephelometric turbidity units, or NTUs.
Natural Factors:
· High concentrations of microscopic algae caused by elevated nutrient levels
· Suspended sediment from erosion and sediment transport
· Seasonal weather, especially large storm events
Human Factors:
· Erosion due to removal of vegetation, land grading, stream alterations, etc.
· Excessive nutrient loading
What are expected turbidity levels?
· High concentrations of microscopic algae caused by elevated nutrient levels
· Suspended sediment from erosion and sediment transport
· Seasonal weather, especially large storm events
Human Factors:
· Erosion due to removal of vegetation, land grading, stream alterations, etc.
· Excessive nutrient loading
What are expected turbidity levels?
Expected turbidity levels vary according to the type of
water body being monitored. This table shows what can be expected in 4
different situations:
Groundwater < 1 NTU Water bodies with moderate plant and animal life 1-10 NTU Water bodies enriched with nutrients, supporting much planktonic life 10-50 NTU Winter storm flows in creeks and rivers 20-1000 NTU
We would generally place our Stream Team sites in the
second category down, meaning that we should expect turbidity levels to
be between 1-10 NTU.
Stream Team turbidity results
Stream Team turbidity results
Good news! In both Ventura
and Goleta Stream Teams, we typically
find very low turbidity levels, between 0 and 5. Many sites, particularly
in Ventura, consistently read a perfect 0.0 NTU! During major storm events,
however, these levels can climb drastically. For example, in May 2003,
we sampled during a storm and found turbidity levels so high that they
were out of the range of our meters! The highest level that our meters
were able to read on this day was 756 NTU. WOW! That's high!