What is a river system?
A river and all its tributaries together make up a river system
How do ponds and lakes form?
When water collects in hollows and low-lying areas of land.
Source of water: rainfall, melting snow and ice, runoff. Others fed by rivers or groundwater
Lakes can be formed either by a natural process (volcano) or by human efforts. A river channel can form a lake as it changes over time, depressions created by ice sheets that melted at the end of the Ice Age,movements in the Earth's crust, volcanoes, dams
What changes can occur in lakes?
Seasonal Changes - in summer, the sun warms the upper layer of water. The warm water floats on top of the cooler, In the fall the top layer cools off and becomes denser and sinks. This causes the lake waters to mix. The mixing or lake turnover causes material to rise from the lake bottom. Lake turnover refreshes the supply of nutrients the lake.
Long term Changes - organisms in a lake release waste into the water. Wastes and remains of dead organisms contain nutrients such as nitrates and phosphates. Algae feed on nutrients. Over many years, the nutrients build up in the lake. As this happens eutrophication causes more algae to grow, a thick, green scum forms on the surface of the water. This is present in ponds as well
the streams and smaller rivers that feed into a main river
the land area that supplies water to a river system
ridge of land that keeps one watershed separate from another. Streams on each side of the divide flow in different directions. The Continental Divide, is the longest divide in North America.
A man made lake that stores water for human use
are substances such as nitrogen and phosphorus tht enable plants and algae to grow
Over many years, the nutrients build up in the lake. As this happens eutrophication causes more algae to grow, a thick, green scum forms on the surface of the water.
How can a body of fresh water die
1- Eutrophication - When the algae layer becomes so thick that it blocks out the sunlight, plants in the lake or pond can no longer carry out photosynthesis. They stop producing food and oxygen, and they die.Eventually a grassy meadow takes the place of the former lake or pond.
2. When water leaves a pond more rapidly than it enters. This can happen when the sourse of water is cut off by erosion
3. Streams and rivers carry sediments into ponds or lakes. Over a long period of time, they can fill in the body of water.
What kinds of materials can build up over time at the bottom of a lake
Material from decaying plants and animals
How are lakes different from ponds
both are fresh "still or standing" water
ponds are smaller and shallower than lakes. Muddy bottom often covered with weeks. Sunlight usually reaches to the bottom of all parts of a pond so it has plants growing on the bottom.
Lakes usually have areas where the water is too deep for sunlights to reach the bottom and can be very large. The lake bottom may be sand, pebble or rock. Deep lakes have few organisms living in the bottom. May have clams, mollusks and worms and large fish