What is Turbidity?

For many lakes and streams, turbidity is the most important environmental issue affecting individual water bodies.  But what is turbidity, and where does it come from?

Turbidity is the amount of particles suspended in the water that absorb or scatter light.  Examples of turbidity-causing particles are: industrial pollution, suspended inorganic and organic soil, phytoplankton (algae), and zooplankton.

A stream overflows its banks, flooding the surrounding land after heavy rain. The brown, turbid water now carries nutrients that can harm the lake downstream and cause algae blooms.

Causes of Turbidity

Some turbidity is natural; if it weren’t for some particles in the water, there would be almost no aquatic life.  However, turbidity is often excessive, but where does this extra turbidity come from?

Wave caused resuspension of sediment is produced when the energy from waves disturbs the bottom of lakes and rivers.   Shallow lakes and reservoirs are most susceptible to this type of disturbance.  Resuspension of sediment can also be caused by prop-wash from recreational boating or commercial shipping. 

Activity of bottom-feeding fish. Fish that feed in the bottom sediments are a natural, healthy part of the ecosystem. Bottom feeding fish dig up sediment as they look for their food: plants, invertebrates, or decaying organic matter.  A small population of native white suckers is not going to cause problems, but when the invasive common carp population becomes excessive, they continually disturb the bottom, releasing both sediment particles and dissolved nutrients that will feed algae growth.  During spawning, common carp and other species can increase turbidity on their spawning grounds. 

Algal Growth One of the main problems is excessive algal growth in nutrient-rich waters.  Phytoplankton needs nutrients to grow.  If a water body has excessive phosphorus and nitrogen, algae can quickly grow to levels that can block out the light and reduce the amount of light to rooted aquatic plants.  Large algae populations produce excessive amounts of oxygen during the day and deplete the oxygen supply at night.  Zooplankton living in the water column also absorb light, leading to turbidity.  We often consider them beneficial because they consume algae and are a link in the food chain that leads to fish and wildlife that people enjoy.

Algae can also cause turbid conditions. Clear river water (right) with high nutrient content has caused an algae bloom as it moves through a shallow lake.

Erosion from the landscape.  The countryside naturally erodes, and soil makes its way to the sea, but the ground disturbed by agriculture and construction practices dramatically accelerates the process.  Particles of soil on exposed farm fields are picked up by wind and water and carried into lakes and rivers.  At unprotected construction sites, rain and snowmelt also wash these solids into surface waters.  Often these particles transport nutrient pollution that will lead to excessive algal growth.  The particles can also contain chemical pollutants that can harm aquatic environments.  Stream banks and lakeshores are always eroding and forming, but land use along the shore, and waves from the wakes of boats speeds erosion of the shores, adding to the water body’s turbidity.  Rip-rap is often used to reduce shoreline erosion.

During heavy rainfall, sediment is being washed off the surrounding farm fields and into the local lakes immediately increasing the turbidity of the water. Nutrients brought in with the soil particles will later feed algae, further adding to the turbid state.

Feedback Loops

Turbidity breeds more turbidity in a cascading feedback loop.  Turbid conditions reduce aquatic plant life.  Aquatic plants promote clear water conditions by filtering out nutrients, and holding in sediment.  As aquatic plants are lost, fewer nutrients are taken out of the water and are leftover to fuel algae blooms.  Without the rooted plants, the bottom sediments are easily disturbed by waves adding to turbidity.  The loss of plants and increased turbidity creates conditions that favor bottom-feeding rough fish.  Their increased population disturbs even more sediment and harms remaining aquatic plants.  This cascading effect can turn a lake or river system into a turbid nightmare.  It can be difficult to reverse the feedback loop, and sometimes it is economically or socially impossible to fix.  It is crucial to prevent lakes and rivers from going into a turbid state in the first place. 

Measuring Turbidity

Several tools can be used to measure the turbidity of lakes and streams.  The most commonly used is the Secchi disk, because of its ease of use and it is inexpensive.  A Secchi disk is a weighted circle that hangs off a rope and is divided into four alternating white and black parts.  The disk is lowered into the water column until it disappears from view.  When it disappears, the depth is noted, then the disk is brought back up until it can be seen again, depth noted, and then averaged with the first one.  The accuracy of the disk is affected by cloud cover, the angle of the sun, and the waves on the surface.  The Secchi disk fails in areas where it is shallow, and the disk hits bottom before it disappears from view. 

Although Secchi disk readings can be adversely affected by a number of factors it is still highly useful, because they are a standard used throughout the world.  They are also helpful because they are economical, so the number of readers and readings can be increased, smoothing out the errors over time.  

A turbidity tube works in the same way as a Secchi disk except that water from the lake or river is poured into a long tube with a small disk affixed to the bottom.  Water is let out of the tube until the disk can be seen.  If water is very clear and the tube isn’t long enough then an accurate reading cannot be made. 

Monitoring water quality using a turbidity tube.

A special turbidity meter can also be used.  A sample of water is taken from the waterbody and put in a devise that passes light through the sample.  The machine measures the light lost as it passes through the sample.  Turbidity meters have to be calibrated with turbidity standard solutions.  These meters eliminate the inaccuracies caused by changing environmental conditions.

Another way to measure turbidity is to use a light meter.  The meter is calibrated at the water’s surface, where it can correct for cloudy conditions.  Then the light is measured at several depths.  Waves and angle of the sun can still throw off readings. 


Turbidity is one of the most important factors facing the health of aquatic systems.  Some large rivers, such as the Amazon River, are naturally turbid, and life has evolved around those conditions.  Turbidity can degrade through feedback loops that are very hard to break and reverse.  Since it is so difficult to break these loops, it is crucial to never get to the point of a turbid state in the first place. 

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What is a graminoid plant?

A graminoid is a grass, or grass-like plant.  The leaves are typically blade-shaped, and the flowers are plain by most human standards.  Many people walking by a grass in bloom, would not even recognize that the plant was in flower.   Not all botanists completely agree on what a graminoid is. For instance, some exclude the cattails. 

graminoid plant
Fox-Tail Barley is a graminioid.

Graminoids include these plant families:

True Grasses –  Poaceae

Sedges, bulrushes – Cyperaceae

Rushes- Juncaceae

Cattails – Typhaceae

Graminoids grow pretty much everywhere other plants do on land, from hot deserts to wetlands, forests, tundra, and of course, grasslands.  Most graminoids are pollinated by the wind, but some get help from insect pollinators.  They distribute their seeds by dropping them next to the parent plant. Sometimes they will be carried off by rodents and dropped further from the plant if the seeds are not eaten.  There are always exceptions to the rule in nature, though.

Graminoid plant species dominate many wetlands: Phragmites, wild rice, burreed, and tussock sedge are just a few examples.  Without graminoids, wetlands and other ecosystems would be very different.   Birds, mammals, invertebrates, and other wildlife rely on graminoids for food, cover, and nest-building materials. Thick stands of grasses or sedges are great places to hide or build a nest and raise young.  The seeds dropped by many species are nutritious sources of food for ducks, sparrows, rails, and small mammals.  Masses of roots, leaves, and stems are heaped together by muskrats to make their lodges.     

Graminoids in Sedge Meadow
Graminoids in a sedge meadow: Tussock Sedge (Carex strict) and the grasses are Bluejoint grass (Calamagrostis canadensis).

Graminoids grown in and out of wetlands provide most of the food for humanity either directly or indirectly.  Wheat, rice, corn, oat, and a host of other grains are grass seeds we eat without much modification or ground into flour to make breads and pastas.  Wild grasses and domestic grains provide feed for cattle, hogs, and chickens, and we eat them.  Without our graminoid friends, we would starve.  Domestic rice and wild rice are both wetland grasses that have, and continue to be, one of the primary sources of calories for cultures worldwide. 

Field of Winter Wheat

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What is a sedge?

A sedge is a grass-like plant (graminoid) in the sedge family (Cyperacea).  Most would look down the sedges while walking through the woods or a wetland and just think they are grasses.  While they fill much the same ecological role as the true grasses (Poaceae/Gramiae) they are botanically unique.  

One thing that most people learn about sedges is the saying “sedges have edges” This refers to the triangular-shaped cross-section of many sedge species.  If you roll the base of the majority of the sedge species, particularly the Carex and Cyperaceae, between your fingers, you feel the edges plainly.  If you were to cut the stem in cross-section, you would notice the triangular shape.

A tussock or hummock if you prefer formed by Tussock Sedge (Carex Stricta), a member of the sedge family.

There are many exceptions to the rule.  Most importantly there are other plants like Common Bur reed, and Sweet Flag have triangular stems that are not in the sedge family.  Then there are those species like softstem bulrush that have perfectly round stems.  Beware the “sedges have edges saying”, it is a good start, but not a 100% rule. 

The flowers and seed of sedges differ from the grasses, and I would refer you to any good botany book for more information and detailed drawings.   For wetland plants of the Midwest I would recommend A Great Lakes Wetland Flora.  http://www.amazon.com/Great-Lakes-Wetland-Flora-complete/dp/1478194693

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What is Riprap

Alternative spellings and terms: rip rap, rip-rap, rock armor

You often see the shores of lakes, ponds, rivers, and other waterbodies lined with piles of rock to prevent erosion, protection for manmade structures, or just to give some sense of order to a shoreline.  These rocks are called riprap.  Rocks are stronger than soil or sand, reducing erosion from waves and ice, but they come with many problems.  Although in landscaping riprap is usually composed of locally available rock, it can be specially formed concrete or broken up concrete, bricks, or other debris from demolition.   

Pond Shoreline Riprap
Rock riprap prevents erosion of the shoreline of ponds when shallow rooted turf grasses are grown up to the water’s edge. All the spaces between rocks provide some hiding places for animals it can also trap and kill small turtles

Benefits of Riprap

Not all is bad when it comes to riprap.  In very high energy situations it reduces the erosion of shorelines.  This reduces sediment and nutrients that enter the surface water.  When in the water these pollutants would block light, smother plants and animals, and fuel algae blooms. 

While rip-rap can be a deathtrap for some animals, the spaces in the rocks can provide some hiding places for frogs and small mammals.  In the water riprap, it can provide a unique habitat for insects, crayfish, and other invertebrates. 

Habitat can also be protected with the aid of riprap.   In my area, the Lake Winnebago system has seen catastrophic sedge meadow wetland loss due to high water levels from dam construction.  Over 10,000 acres of floating wetland mats have ripped out and floated into open water where it disintegrates.  Lining the wetland with rock armor has stopped this type of erosion, but also prevents the natural interaction between wetland and lake.  Still, it is much better to have wetlands than shallow, turbid open water that has largely replaced them.

Riprap is preferable to seawalls.  As their name implies, a seawall is a vertical or near-vertical hard structure on a lake or river’s shore.  Seawalls are constructed of concrete, stone, metal, or wood.  Seawalls offer the ultimate in shoreline protection, but they also direct the power of the waves back into the lake where they can erode the bottom sediments.  Seawalls prevent turtles, frogs, muskrats, ducklings, and other critters from getting out of the lake, and can be detrimental to wildlife populations.  Seawalls also provide no places for young fish and invertebrates to hide. 

Negative Aspects of Riprap

Riprap has many negative attributes deriving from the fact that it is just plain unnatural.  Rocky shorelines do occur in nature, but soil and the roots of the lakeshore vegetation are usually intertwined with the rocks.  The gaps between rocks in riprap can permanently trap turtles, particularly hatchling turtles, as they move from nest to water.  Riprap creates a barren landscape at shorelines that would otherwise be well vegetated.  This natural vegetation is often enough to prevent most erosion, while at the same time providing valuable habitat for many species of wildlife.

Overuse of riprap also increases channelization of rivers and prevents the formation of unique habitats such as oxbow lakes and ponds. Rivers are meant to wander!   The high piles of rock can prevent floodwaters from flowing from rivers into adjacent wetlands that help store the excess water.  The same flooded wetlands are visited by fish such as Northern Pike, which spawn there.  Riprap can prevent the migration of these spawning fish.

Whether the installation of riprap is necessary or not, it can be improved to lessen its negative impacts. The easiest of this is to use smaller rocks to fill the gaps between the large ones where turtles can become trapped.  Planting native plants or allowing the riprap to become colonized with native vegetation wipes out many of the negative impacts.

Riprap Maintenance

Like any manmade structure, riprap requires maintenance.  The heavy rocks can sink into the soft sediments in the water or the water-soaked shoreline soils.  Ice, waves, and plain old gravity will pull the rocks into the lake or river over time.  Local governments and natural resource agencies may look at this movement as filling in a water body and may require the landowner to remove and re-pile the riprap to its original location.  Placement and movement of riprap during maintenance are regulated by state and federal statutes in many situations. 


In many situations, riprap is helpful or even necessary, but far too often it is installed because people think they need it or because it just looks nice.  It is difficult to change the minds of those who like the order and simplicity of manicured lawns and squared off properties.  Only those with a keen interest in nature may come over to the disordered beauty of natural shorelines.

Old, broken slabs of concrete form this riprap. While a good way to reuse waste, the angles of the slabs can cause the waves to undermine them.


Riprap can be interesting too.  In my hometown of Oshkosh, Wisconsin, the lumber mills that formed the early industry of this city are long gone, but many of the foundations of those mills are broken and dumped along the edge of the Fox River and Lake Winnebago, where they protect the shore from wave and ice erosion.  In some cases, the concrete contains the remains of even older industries.  I once found a broken marble sink that was thrown into the concrete when it was formed. Our riprap contains evidence that our society even throws away its industry, but now I’m going off on a tangent.   

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Swamp Aerial Video

I just finished editing and uploading my last video from last summer.  This aerial video is a low altitude flight over a wetland in NE Wisconsin.  It is late September and the leaves of the trees are just beginning to change color.  Many of the trees in view Green Ash and a number of other species whose leaves turn a shade of yellow.  Not as stunning as a northern hardwood forest with maples and other trees, but still a sight to behold.

So that’s the last of the summer videos.  I’m looking forward to doing many more this summer. I hope you enjoyed this one.  Thanks for watching.

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Spring is Coming!

Dagget's Creek Meltwater

Daggett’s Creek filled with melt water from farm fields.

This week the temperature was warm and the kids were in school, so I took the opportunity to get outside and enjoy the sun after a very cold February. I hope to be getting out a lot this year to experience more of nature and work on my photography, so I am adding a new feature.  It is sort of review of the previous week, largely in photographs that will show what is happening in the natural world.  It may be only a photo or two by the time December rolls around, we shall see, but it should be rather rich in the warmer months.

High Cliff State Park Panoramic

Panoramic view from the observation tower at High Cliff State Park

This week I visited High Cliff State Park near Sherwood Wisconsin.  High Cliff features the ruins of a lime kiln used to bake the local limestone to produce lime to make cement.  The old ruins are home to a number of European Starlings, and this day they were calling and singing from small trees growing on the top of one of the old stone building.  The video below show the silhouette of the birds, and sounds of their calls with a few other species in the background.

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Drainage Ditch Flight

Latest edit of a low altitude flight over sedge meadows I made last June.  These ditches run through Poygan State Wildlife Area in Wisconsin.  Some were dug to help drain nearby farmland and some were dug decades ago for ducks and other wildlife.

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Cooper’s Hawk on Birdfeeder

Cooper's Hawk

Cooper’s Hawk (Accipiter cooperii) on the Birdfeeder

The Cooper’s Hawk (Accipiter cooperii) has become a much more common site in urban areas in my lifetime.  The Cooper’s Hawk feeds almost exclusively on other birds so the House Sparrows and other common city birds are great food source.  We often feed these birds, which no doubt increases the population size.  The population of small birds then attracts and feeds the Cooper’s Hawks, so we indirectly feed those too.

The Coopers Hawk is well adapted to hunting fast moving birds in trees.  They have relatively short wings to fit through the tree branches and a long tail that allows it to change direction quickly and sharply.

Not long ago these hawks were shot, and poisoned by DDT, which greatly reduced their numbers.  Today their populations are on the rise because of the end of those practices and somewhat our feeding of the little birds.

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Frog on Ice

A couple of days ago I took a walk down by a small spring-fed creek.  The air temperature was about 4°F (-16°C), but since the creek is fed by numerous springs the stream was nearly free of ice.  Winter time in one of these spring-fed trout streams is really interesting.  While all the world around is in a deep freeze life goes on in the water.

Frog on Ice
A Green Frog was crawling around both in and out of water in below freezing temperatures. The spring-fed stream stays warm enough to keep many different animals active all winter. Notice the freshly killed flying insects on this cold day in February.

While I was taking photographs next to the stream I saw a Green Frog crawling through the shallow water of a muck filled back water of the stream where spring water seeps up through the ground.  The amphibian was half in the water and half in the cold air where condensation had froze into hoarfrost on old grass stems only millimeters above the water’s surface.  No hibernation for this frog. The frog was very cold, and when I approached it just got down low in the mud and stayed still.  I took some photographs while trying to keep my winter pack boots from overfilling with water and mud.  I got a few different angles and so I left the frog in peace.

I made my way back to shore and resumed my photography.  A few minutes later I happened to look down at my bootlaces and found them to be encased in ice.  Later when I got back the car I tried to get them off, but couldn’t untie the laces.

Even though a Wisconsin winter is bitter cold at times the aquatic insects are still busy eating algae, detritus and each other.  Some of these stream invertebrates are so bold as to grow wings and fly in February.  When I looked at the photo of the frog later I could see to tiny flying insects lying dead on the surface of the water.  It may seem odd that insects would try to fly in the winter to mate, but in makes sense.  In winter there are very few birds around, no bats and no aerial insect predators like dragonflies.  The winter hatching insects must brave the cold, and I wonder if the ones I found suddenly froze to death just above the water’s surface.

After my visit to Emmons Creek I went to another larger, but mostly frozen over trout steam, where  I took this underwater video of the Waupaca River.

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What Good is a Grass Fire?

Cattail Marsh Fire

Flames reach for the sky as a cattail marsh burns out of control.

The benefits of fire may be somewhat obvious, but there are others we forget today.  People throughout the world have used fire to alter their environment to their benefit.  On a small scale, traditional fires may have cleared a portion of forest for a garden, but hunter-gathers may have changed a few acres to tens of thousands to their benefit.

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