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© 2011 Pearson Education, Inc.
AP Environmental Science
Mr. Grant
Lesson 71
Freshwater Systems
© 2011 Pearson Education, Inc.
Objectives:
• Define the term aquifer.
• Describe the distribution of fresh water on Earth and the major types of freshwater systems.
© 2011 Pearson Education, Inc.
Aquifer:
A wet underground layer of water-bearing permeable rock or unconsolidated materials (gravel, sand, silt, or clay) from which groundwater can be usefully extracted using a water well.
Define the term aquifer.
© 2011 Pearson Education, Inc.
Describe the distribution of fresh water on Earth and the major types of freshwater systems.
• Of all the water on Earth, only about 1% is readily available for our use.
• Groundwater is contained within aquifers.
• A watershed is the area of land drained by a river system.
• The main types of freshwater ecosystems include rivers and streams, lakes and ponds, and wetlands.
© 2014 Pearson Education, Inc.
Freshwater Systems
Water may seem abundant, but drinkable water is rare
Fresh water = water that is relatively pure, with few dissolved salts—only 2.5% of total water Most is tied up in glaciers, ice caps, and aquifers
One part in 10,000 is easily available for our use
© 2011 Pearson Education, Inc.
Freshwater systems… another look
All Earth's water, liquid fresh water, and water in lakes and rivers.
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Freshwater Systems
Water is renewed and recycled as it moves through the water cycle Precipitation sinks into the ground or runs off into
rivers to form lakes or enter oceans
Rivers interact with ponds, wetlands, and coasts
Groundwater exchanges with rivers and ponds
Water moves organisms, sediments, and chemicals
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
Groundwater plays key roles in the hydrologic cycles Surface water = water located atop Earth’s surface
Groundwater = water beneath the surface held in pores in soil or rock 20% of the Earth’s freshwater supply
Aquifers = porous, spongelike formations of rock, sand, or gravel that hold water Zone of aeration = pore spaces partly filled with water
Zone of saturation = spaces are filled with water
Water table = boundary between the two zones
Recharge zone = any area where water infiltrates Earth’s surface and reaches aquifers
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
Groundwater plays key roles in the hydrologic cycles Confined (artesian) aquifer = water-bearing,
porous rocks are trapped between less permeable substrate (clay) layers Water here is under great pressure
Unconfined aquifer = no upper layer to confine it Readily recharged by surface water
Groundwater’s average age is 1400 years It may be tens of thousands of years old
The Ogallala Aquifer is the world’s largest known aquifer Current water use for irrigation is not sustainable
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The Ogallala Aquifer
Its water has allowed farmers to create the most bountiful grain-
producing region in the world
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Researchers mapping underground water reserves in Africa find huge reservoirs, but warn this may not be a magic bullet solution to the continent's increasing need for fresh water.
Much of the water in this region is located deep underground, 100 – 250 m below the surface. MacDonald warns this inaccessibility might make it almost impossible to use the reserves for irrigation or to provide drinking water for new urban centres across the continent.
Northern Africa Aquifer
© 2014 Pearson Education, Inc.
Surface water converges in river and stream ecosystems
Surface water accounts for just 1% of fresh water Vital for us and Earth’s ecological systems
Runoff = water that flows over land Water merges in rivers and ends up in a lake or
ocean
Tributary = a smaller river slowing into a larger one
© 2014 Pearson Education, Inc.
Surface water converges in river and stream ecosystems
Watershed (drainage basin) = the area of land drained by a river system (river and its tributaries)
Surface water becomes groundwater through infiltration
Groundwater becomes surface water through springs or human-drilled wells 1.9 trillion L (492 billion gal) each day in the United
States
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
Water is renewed and recycled as it moves through the hydrologic cycle
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Surface water converges in river and stream ecosystems
Rivers shape the landscape Braided river = an interconnected series of
watercourses that run through steep slopes
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Surface water converges in river and stream ecosystems
Meandering river = river in flatter areas Water rounding a bend
erodes soil from the outer bank
Sediment is deposited on the inside of the bend
Rivers form oxbows, areas where river bends become exaggerated
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Surface water converges in river and stream ecosystems
Oxbow lake = water body formed when erosion cuts off and isolates the oxbow into a U-shape
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Surface water converges in river and stream ecosystems Floodplain = areas nearest to a river’s course that
are flooded periodically Frequent deposition of silt makes floodplain soils
fertile Good areas for agriculture
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Surface water converges in river and stream ecosystems Riparian = describing riverside areas that are
productive and species-rich Damming prevents large floods and river meanders
Rivers and streams host diverse ecological communities Algae, insects, fish, amphibians, birds, etc.
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Lakes and ponds are ecologically diverse systems Lakes and ponds are bodies of open, standing water
Littoral zone = region ringing the edge of a water body Rooted aquatic plants grow in this shallow part
Benthic zone = the entire bottom of the water body
Home to many invertebrates
Limnetic zone = open portion of the lake or pond where sunlight allows photosynthesis that produces oxygen Supports phytoplankton and zooplankton
Profundal zone = water that sunlight does not reach
Supports fewer animals because there is less oxygen
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
Lakes and ponds are ecologically diverse systems
Ponds and lakes may change over time Oligotrophic lakes and ponds have low-nutrient and
high-oxygen conditions
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Lakes and ponds are ecologically diverse systems Eutrophic lakes and ponds have high-nutrient and
low-oxygen conditions Eutrophication may result from human pollution
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Lakes and ponds are ecologically diverse systemsEventually, water bodies may fill completely in through the process of succession
The largest lakes are known as inland seas• Great Lakes, the Caspian Sea, Lake Baikal
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Freshwater wetlands include marshes, swamps, bogs, and vernal pools
Wetlands = systems in which the soil is saturated with shallow standing water with vegetation
Freshwater marshes = shallow water with plants that grow above the surface
Swamps = shallow water in forested areas Can be made by beavers
Bogs = ponds covered in thick floating mats of vegetation A stage in aquatic succession
Vernal pools = pools that form in spring then dry up
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Wetlands include marshes, swamps, bogs, and seasonal pools
Species in vernal pools are adapted to seasonal drying
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Freshwater wetlands include marshes, swamps, bogs, and vernal pools
Wetlands are extremely valuable for wildlife Louisiana’s coastal wetlands host 1.8 million
migratory birds each year
They provide valuable ecosystem services They slow runoff, reduce flooding, recharge aquifers,
and filter pollutants
People have drained wetlands, mostly for agriculture Southern Canada and the United States have lost
over half of their wetlands
Wetlands are affected when we withdraw water, build dams and levees, and introduce pollution
© 2014 Pearson Education, Inc.
Wetlands are valuable
Not all wetlands perform all functions nor do they perform all functions equally well.
Wetlands are among the most productive habitats in the world.