Freshwater Sources and Storage

Earth's Freshwater

  • Life on Earth needs water; oceans have 97% of Earth's water, but organisms need freshwater.
  • Lesson focus: the 3% of water that's not in oceans; where it's found and stored.
  • Vocabulary: divide, freshwater, groundwater, reservoir, river system, runoff, tributary, watershed, wetland.

The Water Cycle

  • Water circulates through air, land, and oceans; evaporation, condensation, precipitation, runoff.

Freshwater Distribution

  • Freshwater: water not in oceans/seas (ice sheets, lakes, rivers, groundwater, vapor).
  • Only about 3% of Earth's water is freshwater; 75% frozen, most of the rest underground.
  • Small amount in atmosphere as water vapor.

Ice Sheets

  • Approximately 75% of Earth's fresh water.
  • Ice sheet: glacial land ice, extending over 20,000 square miles.
  • Largest ice sheets: Greenland and Antarctica.
  • Icebergs: pieces that break off and melt in warmer waters.

Rivers and Lakes

  • Important freshwater sources for transport, habitats, and economic activities (fishing, tourism).
  • Provide drinking water and nutrients.
  • Hydroelectricity: power generation using water movement.
  • Great Lakes: have 20% of the fresh water in the world's lakes.

Groundwater

  • Largest source of usable freshwater, located underground.
  • Rain and snow filter through soil and rocks.
  • Used by 51% of the US population as drinking water.
  • Vital for irrigation and feeds lakes/rivers.

River Systems

  • Rivers start in mountains from rain/snow runoff, forming streams.
  • Runoff: rainfall or melted snow running across the ground.
  • Streams combine into small rivers, then larger rivers.
  • Tributaries: streams/small rivers that join larger rivers.
  • River system: river and all its tributaries.

Watersheds

  • Watershed: land area supplying water to a river system (also called drainage basins).
  • Water sheds from the land after rain/snow, channeled into soil, groundwater, creeks, streams.
  • Size varies from acres to encompassing large river systems.

Divides

  • Watersheds separated by ridges called divides.
  • Divides have higher elevation; water flows opposite directions on each side.
  • Continental Divide (Great Divide): separates Pacific and Atlantic watersheds; located in the Rocky Mountains.

Ponds

  • Small bodies of still fresh water, smaller and shallower than lakes.
  • Sunlight reaches the bottom, allowing plant growth throughout.
  • Form from collected rainfall or melted snow, fed by rivers or groundwater.

Lakes

  • Larger, deeper bodies of still fresh water than ponds.
  • Sunlight doesn't reach the bottom, limiting plant growth to the shore.
  • Deeper water is cold and dark, with fewer organisms.
  • Formed by filled low-lying areas, glacial depressions, or crust movement.
  • Reservoirs: man-made lakes created by dams (e.g., Lake Mead).

Wetlands

  • Land covered with water part or all of the year.
  • Form in low-lying areas or where groundwater surfaces.
  • Help filter water, improve water quality, minimize pollution.
  • Sheltered areas rich in nutrients, providing wildlife habitats.
  • Control flooding by absorbing runoff and maintain surface water flow.

Types of Freshwater Wetlands

  • Marshes: grassy wetlands covered by shallow water, often on shores of lakes/rivers.
  • Swamps: flooded forests, usually in warm, humid climates.
  • Bogs: cool northern areas, highly acidic, with thriving mosses in depressions left by ice sheets.

Coastal Wetlands

  • Mixture of saltwater and freshwater (salt marshes, mangrove forests).
  • Prevent flooding, hold water, and protect inland habitats with root systems.