© 2011 pearson education, inc. ap environmental science mr. grant lesson 71 freshwater systems

© 2011 Pearson Education, Inc.

AP Environmental Science

Mr. Grant

Lesson 71

Freshwater Systems


Objectives:

• Define the term aquifer.

• Describe the distribution of fresh water on Earth and the major types of freshwater systems.


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.


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.


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


Freshwater systems… another look

All Earth's water, liquid fresh water, and water in lakes and rivers.

http://ga.water.usgs.gov/edu/gallery/global-water-volume.html


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


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


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


The Ogallala Aquifer

Its water has allowed farmers to create the most bountiful grain-

producing region in the world


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


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



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


Water is renewed and recycled as it moves through the hydrologic cycle



Rivers shape the landscape Braided river = an interconnected series of

watercourses that run through steep slopes



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



Oxbow lake = water body formed when erosion cuts off and isolates the oxbow into a U-shape


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


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.


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


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


Lakes and ponds are ecologically diverse systems Eutrophic lakes and ponds have high-nutrient and

low-oxygen conditions Eutrophication may result from human pollution


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


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


Wetlands include marshes, swamps, bogs, and seasonal pools

Species in vernal pools are adapted to seasonal drying


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


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.

© 2011 pearson education, inc. ap environmental science mr. grant lesson 71 freshwater systems

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