MadSci Network: General Biology

Re: What causes water to become turbid?

Date: Tue Dec 4 16:22:39 2001
Posted By: Stacey Kohler, Secondary School Teacher, General Science, Kissimmee Middle School
Area of science: General Biology
ID: 1001529374.Gb

Water can become turbid, or cloudy, for many different reasons.  Fine 
sediments, such as silt, are easily disturbed and can hang suspended in the 
water for amazingly long periods of time.  A gentle current can be enough 
to keep these sediments suspended indefinitely.

Sometimes, water can be naturally dyed.  Here in Florida, we have many 
trees whose leaves contain tannin, the same chemical that makes tea brown. 
 And Tea Brown is the exact color of most Florida lakes and streams.  This 
can contribute to apparent turbidity.

By far the most common, and probably the most ecologically significant 
cause of turbidity, however, is organic growth.  Algae and other 
microorganisms can grow in the water, sometimes at tremendous rates.  This 
is one reason why turbidity is used as a test of water purity.  An 
interesting note is that water which is very pure often indicates a sick 
lake, since extremely low turbidity generallly indicates that something is 
killing off the aquatic organisms that cause the water to be cloudy.

Obviously pollution is a factor that can lead to turbid waters.  The 
pollution itself can cloud the waters, it can kill native shoreline 
vegetation that usually filters out run-off - which leads to siltification, 
and it can increase microbial growth by increasing the nutrients many kinds 
of algae need.

I hope this helps, and good luck on your experiment!

Your mad scientist,
S. Kohler

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