CHAP. 1.3 – SURFACE WATER

I. RIVER SYSTEMS A river system is a river with all of its tributaries (streams and small rivers). Many rivers such as the Rio Grande and the Mississippi River start as melted snow on the top of a mountain. The melted snow starts to run downhill and become a small stream.

The small stream will join up to another small stream to become a small river. The small river has more streams that keep joining it and it will become a large river.

A. TRIBUTARIES Def. of Tributaries: streams and smaller rivers that feed into a main river. Tributaries flow downward pulled by gravity toward the main river.

B. WATERSHEDS Def. of Watershed: a land area that supplies water to a river system. Watersheds are also known as drain basin. Look at the map on p. 21. Large rivers such as the Missouri River and Ohio River are tributaries. They drain into the largest river of the U.S.: the Mississippi River.

The area drained by the Missouri River and Ohio River joining the Mississippi River are watersheds. We are in the Mississippi River watershed. This watershed covers 1/3 of the U.S.

C. DIVIDES Def. of a divide: a ridge of land that separates one watershed from another watershed. Rivers on the sides of a watershed flow in different directions. For example, the Continental Divide is the longest divide in the U.S. Rivers west of the Continental Divide flow west toward the Pacific Ocean or the Great Dry Basin. Rivers east of the Continental Divide flow east toward the Mississippi River or the Gulf of Mexico.

II. PONDS AND LAKES Ponds and lakes are bodies of freshwater in which the water is still. Rivers and lakes are bodies of water where the water is moving. Ponds are smaller and shallower than lakes. As a result, sunlight is usually able to reach the bottom of ponds. Lakes are too deep for the sunlight to reach the bottom.

Ponds and lakes form when water collects in hollows and low-lying areas of land. The water itself comes from: 1. rain; 2. melting snow and ice; 3. water runoff from land; 4. rivers; and 5. groundwater. Water in ponds and lakes can leave through evaporation or flowing out into a river.

A. EXPLORING A POND Since ponds are shallow enough to have light reach the bottom, many plants grow down there such as seaweed and algae. These plants produce oxygen through photosynthesis. Many animals used the oxygen from the plants and eat the plants as a food source.

Plant’s Stoma Where CO2 enters and H20 leaves

B. EXPLORING A LAKE A lake bottom is very dark and consists of sand, pebble, or rock. The only things that live in the lake bottom are mollusks (clams), worms, and large body fish (pike and sturgeon). There are no plants because there is no light for photosynthesis to take place.

A pond bottom is covered with mud and algae A pond bottom is covered with mud and algae. Since there is light and plants, life is teeming at the bottom with beetles, loons, fish, frogs, crayfish, and water lilies. One can also find certain marsh grasses, willows, and maples that will provide shelter to the pond organisms. The pond bottom habitat is very similar to the lake shore habitat. Since the shore is shallow, light can reach the bottom and all the same life like a pond is there.

C. LAKE FORMATION Lakes can be formed by a natural process or man-made. Volcanic lakes are old volcano caters that fills with water. Glacier-Made Lakes are made in two steps: Ice sheets from the last Ice Age move land and leave large land depressions. As the ice melted, it filled the large land depressions.

Lakes can also be made from the Earth’s plates shifting to create deep valleys. These valleys fill with water. Man-made lakes are created by building a dam across a large moving river. The lake behind the dam is called a reservoir. Water in a reservoir is used for hydropower, recreation, drinking water, and irrigating fields.

III. HOW LAKES CAN CHANGE A. SEASONAL CHANGES Seasonal changes in lakes are very common in cool, northern areas of North America. During the summer, the sun warms the upper layers of water. This warm water floats on top of a cooler, denser layer. In the fall, the warm top layer cools off to become denser and sinks. This causes the top layer and lower layer to mix. This mixing is called ‘Lake Turnover’. Nutrient-rich materials from the bottom layer such as nitrogen and phosphorus come to the top. This will help plants and algae to grow at the shore.

B. LONG-TERM CHANGES Organisms in a lake constantly release waste products into the water. Also, many organisms die the lake water. The wastes and dead remains contain harsh elements such as nitrates and phosphates. These elements build up in a lake during a process called ‘eutrophication’. Algae feed on these elements causing a thick, green scum to form on the surface of the water.

Eutrophication can occur in ponds too.

C. DEATH OF A BODY OF FRESH WATER If the algae layers become too thick, it will block out sunlight. This will cause the death of all plants in the lake because they cannot undergo photosynthesis. With out oxygen and food from plants, fish and animals start to die in the lake as well. All this decaying matter falls to the bottom of the lake creating new layers and the lake starts to become shallower.

The sun warms this shallower water to evaporate all the water and to expose a mud layer. Plants take root in the mud layer and the lake now becomes a grassy meadow. Other ways in which a lake can die is through the water source being drained away or soil runoff from the land finally taking over the water.