Surface Water

Groundwater definition?

Key Concepts

What is a river system?

How do ponds and lakes form?

What changes can occur in lakes?

Key Terms

Tributary

Watershed

Divide

Reservoir

Nutrient

Eutrophication

River Systems

Everyone knows that water flows downhill because of……….

Gravity

A river and all of its tributaries together make up a river system.

Please note the following parts of a river.

Watersheds

Just as all of the water in a bathtub flows toward the drain, all the water in a river system flows into a main river.

The land area that supplies water to a river system is called a watershed.

Watersheds are sometimes known as “drainage basins.”

As you can see from the Figure below, the Missouri and Ohio Rivers are quite large, yet they still flow into a larger River…the Mississippi River.

When rivers join other river systems, the area they drain become part of the largest river’s watershed. These are

found as imaginary lines around the region drained by all its tributaries. The watershed of the Mississippi River, the

largest river in the U.S. covers 1/3 of the country!

Divides

What keeps watersheds separate?

One watershed is separated from another by a ridge of land called a “divide.”

Notice the red lines that show the major Divides in the U.S.

Ponds and Lakes

Unlike streams and rivers, ponds and lakes contain still, or standing, water.

What is the difference between a pond and a lake?

There is no definite rule. However, normally the ponds are smaller and shallower than lakes.

Ponds and lakes form when water collects in hollows and low-lying area of land.

Where does the water come from?

Rainfall, melting snow and ice, or runoff from other lands. Others are fed by rivers or groundwater.

Ponds and lakes can also lose water. How do you think this could happen?

Overflow into rivers, or evaporation.

A pond might seem calm and peaceful, but they are normally a thriving habitat, full of organisms, fishes, and because sun can reach the bottom of a pond, plants and plantlike organisms.

Because the sun reaches the bottom, plants and algae use sunlight to make food through……….

photosynthesis.

The animals in the pond use the oxygen provided by the plants and algae.

Exploring a Pond

Exploring a Lake

Lakes are generally deeper and bigger than ponds. A lake bottom may consist of sand, pebble, or rock. Do we know why?

No sun reaches the bottom so……..

No photosynthesis takes place.

There are no plants, but clams, and worms move along the lake bottom feeding on food particles that drift down from the surface.

Some fish may also live down here feeding on the “bottom-dwellers” and also swim to the surface to feed on other fishes and even small birds.

Near the edge of a lake, the wildlife is similar to that of a pond because the sun can get to the bottom.

Sunlight, photosynthesis, plants, algae, small fish, water beetles,……all carry on the process that would occur in a pond.

Different Types of Lakes

Lake FormationRiver channels can form a lake as it

changes over time. Remember the oxbow lake…this cut-off loop results from changes occurred by obstacles in its path as it bends and loops.

Others, such as the Great Lakes, formed in depressions created by ice sheets that melted a the end of the Ice Age.

Reservoirs are lakes that stores water for human use.

What can of uses could that be?

Water for drinkingIrrigating fieldsRecreation.

How Lakes Can Change

Lakes change for many reasons.

They can change with the seasons, they can change with the amount of material that flows into the lakes that causes long term changes.

Unfortunately, these changes can sometimes lead to the death of the lake.

Seasonal Changes

Seasonal changes occur in mostly cooler, northern climates of North America.

In these lakes, the warm water floats on top of the cooler water on the bottom….why

Because of DENSITY.The warmer water is LESS DENSE than the

cooler water on the bottom.

As the water cools, it becomes denser and sinks……..this causes the layers of the water to mix.

This mixing is called “lake turnover.”

This also causes the nutrients on the bottom to come to the top.

Why are there nutrients in the bottom of the lake?

“Nutrients” are substances such as nitrogen and phosphorus that enable plants and algae to grow.

Where do these nutrients come from?

Long Term ChangesThe 2nd type of change happens over a long

period.

Organism release waste materials….yeah.that.These contain nitrates and phosphates and

over many years build up in a process called “eutrophication.”

Please look at the this process.

Eutrophication

Please remember that this process occurs in ponds as well as lakes.

Death of a body of Fresh Water

When the algae becomes so thick it blocks out the sunlight……what happens to the plants on the bottom.

Die.

What happens to the oxygen in the water when the plants die.

No more oxygen

What happens to the fish and other organisms in the water when there is no more oxygen.

Die.

These plants and animals pile up on the bottom and the lake or pond become shallower….the lake gets warmer…more plants may grow because sunlight reaches them…..more algae grows…then plants die…..then no oxygen…then no organisms….they die….dead plants and animals build up….lake becomes warmer… sunlight reaches bottom….more plants grow…then more al……..get the picture?

Eventually the lake will build up to where it is completely covered with plants, the water evaporates, and a grassy meadow is left.

Ponds and lakes can also dry up from lack of rain, either a drought or is cut off from a water supply.

Sediments can also flow into a lake or pond and fill them up with soil causing them to disappear.