Urban Water Quality 101: Turbidity, Part 2

Now that we know how the turbidity tube works and what can contribute to turbidity, lets see how the two sites from the last post measure up:

This site on Deer Creek has a turbidity between 10 and 15 NTU. If I were reporting this data, I would
probably call it 12 NTU. Notice that the black and white pattern is barely visible through the water.

This site on Deer Creek has a turbidity of less than 10 NTU. With as clear as the water is, the pattern is clearly visible;
if a longer tube were available, you could probably see through several more inches. This is the clearer of the two samples.

Surprised by the results?  The image on the top was taken in a shallow location with some suspended sediments.  The image on the bottom is a deeper pool with few suspended particles; the raindrops on the water's surface make the stream bottom appear more difficult to see.

So what does it all mean?  If we would measure turbidity of a local stream, what could that tell us?  Plenty!  If your stream is consistently at 10 NTU or less, you have a fairly clear stream.  If the spikes that you see hit about 50 or 60, then there might be some periodic erosion occurring, a bloom of small algae, or decomposition of leaf litter in a standing pool.

We could learn even more, especially if each turbidity measurement is paired with one or two other bits of data; a rainfall record, height on a stream gauge, or flow measurements (especially if you have a USGS gauge near your stream) would be particularly useful for comparison.  Take, for example, the graph below created using a fictitious data set. 

In this graph, the turbidity (in brown) increases each time the stream rises (in blue).  This indicates that there is either erosion occurring or that something being brought into the stream in runoff is clouding the stream.   Starting in late March, notice that the turbidity rises slowly to somewhere between 10 and 20, rises sharply when the water level rises, and then decreases when the stream falls again.  This might indicate that algae are blooming in the water column and then being washed away with each storm.


For more information on turbidity, check out page 182 of The Streamkeeper's Field Guide by Tom Murdoch and Martha Cheo (1996).  Many thanks to the Stream Team Program for providing this resource to me many moons ago - I've used it often!

You may also want to have a look at the EPA's page on Using a Secchi Disk or Transparancy Tube or their guidance on the Importance of Turbidity.

Urban Water Quality 101: Turbidity, Part 1

The first water quality topic I'd like to raise is turbidity - the cloudiness of the water.  It is one of the simplest measures of water quality to perform and it tells us a lot about our streams if we measure it often enough.

Just eye-balling the water to see if it is clear or cloudy is not enough.  Factors like water depth and lighting conditions can make a big difference in how clear water appears when you are standing streamside.  Take the following photos for example.  Which of these sites would you say has clearer water?  I'll share the answer in Part 2, so check back in a couple of days...

Two views of relatively clear water from Deer Creek in St. Louis County.  But which has clearer water?

The Missouri Stream Team Program provides Level 1 (and above) water quality monitors with turbidity tubes to measure the cloudiness of stream water.  These tubes function using the same general principle as the Secchi disk, a patterned platter that is lowered into the water on a rope.  This technique has been used for the past 145 years to measure water clarity in lakes and oceans.  The disk is lowered until the pattern can no longer be seen and then raised until the pattern is once again visible.  The average of the distance of the disk from the water surface for the two measurements is called Secchi depth.

A turbidity tube (top) and a Secchi disk  (bottom) share
the same black and white pattern.

A turbidity tube, on the other hand, is filled with stream water and the water is released slowly through a hole near the bottom.  When the pattern becomes visible as viewed through the water column from the top, the hole is covered and the clarity is determined based on the amount of water that remains in the tube.  The markings on the side indicate a turbidity value which is measured (on Stream Team equipment) in Nephelometric Turbidity Units (NTUs).  The lowest (clearest) value that can be measured using this equipment is 10 NTU.  The highest (cloudiest) value on the tube is 400 NTU, which corresponds to visibility to a depth of approximately 1 inch.

So, what makes water turbid?  There are really two things that contribute to turbidity: total dissolved solids and total suspended solids.  Many dissolved solids like road salt and nutrients like nitrate are clear and do not add to the turbidity; however, colored dissolved solids like humic acid or tannins can contribute to turbidity.  Suspended solids include any particles that are held in the water column, including soil particles and small algae.

Upcoming Event: Race for the Rivers Festival - August 27

If you are looking for an pleasant afternoon along the riverfront in historic St. Charles, then you couldn't pick a better day than Saturday, August 27th!  This is the date for this year's Race for the Rivers Festival.  The organizers are certainly grateful that Mother Nature seems to be cooperating and the Missouri River is not too high.

This event is run by the Greenway Network, a Stream Team Association (Stream Team 463) based in St. Charles, but committed to serving the St. Louis Region.  The Greenway Network is a grassroots, volunteer-based organization whose mission is to conserve natural resources, encourage sound management of the area's watersheds and protect the quality of life for all citizens.

The Races:
The Race for the Rivers Festival includes opportunities for paddlers of all strokes to challenge themselves and their competitors on the Mighty Missouri River.  They offer three races to accommodate various skill levels.  There are divisions for solo and tandem, canoe and kayak.  I paddled in the Clean Water Challenge in 2008 with Kelly White and had a blast.  I think I'll try it again this year!

• Race for the Rivers - a 65 mile race broken into two stretches: Washington, MO to Frontier Park on Saturday and Frontier Park to the Confluence with the Mississippi on Sunday.
• Clean Water Challenge - a 20 mile race beginning at  Weldon Spring and ending at Frontier Park on the festival grounds.
• The newest addition - a one-day, 41 mile race, from Washington, MO to Frontier Park. 

The Rides:
This year, Greenway Network has partnered with Trailnet to also offer Ride for the Rivers.  They offer two routes along the Katy Trail that begin and end at Frontier Park: 5 mile and 25 mile loops.

The Festival:
The highlight of this event for most folks is the festival.  You can easily spend a relaxing afternoon listening to music, watching the river go by and the paddlers floating in. The prime things to check out:

• Musical acts preforming on the main stage from noon till 7pm.
• Food and craft booths.
• Educational booths and activities for the kids.
• Watch the racers come in and enjoy the award ceremony.

I hope to see you there!!

Team of the Month - August 2011

A look at Stream Teams in the St. Louis area would be incomplete without a shout-out to the Mighty 211.  Led by Brian Waldrup and Bernie Arnold, the 500+ members of Stream Team 211 have removed several thousand tires from the bed and banks of the Meramec River and its tributaries.  They are experts at hauling waste of all sizes out of rivers of all sizes, including discarded chemical drums, hot water heaters, and large chunks of vehicles.

Bernie and Brian between a pile of tires and a dumpster of non-rubber trash at a clean-up in January 2011.

Each year, the Team holds major clean-ups on the lower 12 miles of the Meramec River in both winter and summer, regularly drawing about 100 volunteers.  They draw these kinds of crowds because not only are they good at what they do, they are also personable and very passionate!  They know how to excite others about Missouri streams.  When I did a Google search to dig up some extra information on these great folks, I found lots of great things, including their own YouTube video, featuring Brian!

The Mighty 211 is based in Arnold, MO, but they are always ready to help out other teams in need, especially where there is litter removal involved.  So the next time you go to a Stream Team event in the St. Louis area, have a quick look at the cars - you will likely see a "Mighty 211" sticker around somewhere!