Determining Water Clarity (or visibility)

Visibility in a body of water is the distance through which you can still see something.

The distance you can see through water can be affected by several things.

A few things that affect water clarity are listed on the next slide.

Go on to the next slide.

Things that affect clarity

Amount of algae in the water Dirt from erosion Churned up sediment from the bottom of

the body of water Amount of small organisms living in the

water Take a moment to write these things down

on your activity report.

Testing Visibility Visibility through a body of water can be tested with a device called a “Secchi (seh-key) disc.”

A Secchi disc is pictured here. The disc is attached to a rope and lowered into water until it is no longer visible.Go on to the next slide

Using a Secchi Disc

There is a Secchi disc apparatus set up by the entrance to the laboratory.

You will use the device to determine the depth of visibility in the water sample provided.

Go on to the next slide

Why measure visibility in water?

The visibility through a sample of water can provide us with valuable information about the ecosystem of the body of water.

Lake Ontario is currently suffering from an overpopulation of zebra mussels that eat the microorganisms in the water.

Go on to the next slide

Secchi disk activity

You will be doing this activity with the Secchi disk by the door to the lab.

Take out the binder in your drawer and turn to the Secchi disk activity section.

Once you complete the Secchi disk activity, you may go on to the next slide.

An Underwater Ecosystem

Algae, or “phytoplankton,” has a significant affect on the amount of visibility in water.

The next slide has a diagram of a food chain in Lake Ontario. Write down the creatures that zebra mussels eat, and what eats zebra mussels.

Go on to the next slide

Trout, SalmonWarm waterSport fish

Large, exoticZooplankton

AlewifeJuvenile Fish

GobiesSturgeon

Zooplankton(Tiny animals)

Zebra MusselsQuagga Mussels

Phytoplankton(Microscopic

Plants)

SunlightNutrients

Use this chart to find out some information about all of the different lake organisms. You can write down your observations on your worksheet.

A disturbed balance

The picture to the right is a zebra mussel.

The zebra mussel is a species that is not native to the great lakes. The best explanation is that the zebra mussels came into the lakes on ships.

Go on to the next slide.

Zebra Mussels Zebra mussels do not have many natural predators in the Great Lakes.

The lake sturgeon, which is pictured to the right, is one of the only predators of zebra mussels in Lake Ontario.

Finish writing your observations on the worksheet.

Once you are done, go on to the next activity!

Trout are freshwater fish that are related to salmon. They are a part of a subdivision of the salmon family called “Salmoninae.” The Lake Trout used to be the primary

predator of Lake Ontario, but almost reached extinction in the lake due to over-fishing and environment destruction.

Return to Food Chain

The Alewife is a small fish that is second in command in the Lake Ontario food chain. It feeds on zooplankton

(Tiny aquatic animals)

Return to Food Chain

Return to Food Chain

The pictures on this slide are some of the large zooplankton that can be found in Lake Ontario. Zooplankton are sometimes called

“brine shrimp.” They can be visible with the naked eye or microscopic.

Return to Food Chain

Gobies are an aggressive species of bottom dwelling fish

that are not native to Lake Ontario. They were brought here in the ballast of cargo

ships.

Lake Sturgeon can grow to be very large in size. (six to eight feet) They are an endangered species because they

used to be hunted heavily for their caviar. (eggs)

Return to Food Chain

Zooplankton are microscopic creatures that are one of the building blocks of

the Lake Ontario food chain. The population of zooplankton can fluctuate extremely rapidly based on the chemistry of the water. If there is pollution in the water, the zooplankton are some of

the first to feel it.

Return to Food Chain

The creature on the left is a zebra mussel. The Zebra Mussel originated in the

Caspian Sea, which is Bordered by Russia. It was brought to the United States by cargo ships.

The image on the right is a Quagga Mussel. The Quagga mussel prefers

cold and deep waters. It too was brought to the United States from

Russia in the ballast tanks of oceanliners.

Return to Food Chain

Phytoplankton are microscopic plants. They

are responsible for the basis

of food production in Lake Ontario.

Go On To Next Slide

Return to Food Chain

Sunlight is needed for plants to do photosynthesis to make

food.