© 2011 pearson education, inc. freshwater systems and resources

© 2011 Pearson Education, Inc.

Freshwater Systems and Resources


This lecture will help you understand:

• Water’s importance to people and ecosystems

• Water’s distribution• Use and alteration of

freshwater systems• Problems of water supply

and solutions• Problems of water quality

and solutions• How wastewater is treated


Gambling with water in the Colorado River basin

• 7 states share the Colorado river• Droughts and overuse are

threatening supplies• Las Vegas, Nevada, needs more

water than it is allotted• Other states will let Las Vegas

drill for underground water• Drilling threatens the area’s

ecology and people• This issue will end up in Nevada’s

Supreme Court


The Colorado River

• The Colorado River originates in the Rocky Mountains- Draining into the Gulf of

California• Its waters chiseled the Grand

Canyon- But it has been reduced to a

mere trickle• Dams provide flood control,

recreation, and hydroelectric power- 30 million people use the

water


Freshwater systems

• Water may seem abundant, but drinkable water is rare• Freshwater = relatively pure, with few dissolved

salts- Most is tied up in glaciers, ice caps, and aquifers


Water is renewed and recycled

• As water is cycled it redistributes heat, erodes mountains, builds river deltas, maintains ecosystems and organisms- It also shapes civilizations and political conflicts

• Surface water = on Earth’s surface- 1% of freshwater

• 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)


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


Water Cycle Scramble


Rivers and streams wind through landscapes

• Rivers shape the landscape• Braided river = an interconnected series of watercourses

that run through steep slopes• Meandering river = rivers in flatter areas

- Water rounding a bend erodes soil from the outer bank- Sediment is deposited on the inside of the bend- Rivers become exaggerated oxbows


Rivers shape the landscape

• Oxbows = areas where river bends become exaggerated

• Oxbow lake = erosion cuts off and isolates the oxbow into a U-shaped water body


A river may shift course over time

• Floodplain = areas nearest to the river’s course that are flooded periodically- Frequent deposition of silt makes floodplain soils

fertile- Good areas for agriculture

• Riparian = riverside areas that are productive and species-rich

• Rivers and streams hosts diverse ecological communities- Algae, insects, fish, amphibians, birds, etc.


Lakes and ponds are ecologically diverse

• Lakes and ponds = 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 = extends along the bottom of the water

body - Home to many invertebrates

• Limnetic zone = open portion of the lake or pond where sunlight allows photosynthesis

• Profundal zone = water that sunlight does not reach - Supports fewer animals because there is less oxygen


A typical lake


Lakes vary in their nutrients and oxygen

• Oligotrophic lakes and ponds = have low nutrient and high oxygen conditions

• Eutrophic lakes and ponds = have high nutrient and low oxygen conditions

• Eventually, water bodies fill completely in through the process of succession

• The largest lakes are known as inland seas- Great Lakes, The Caspian Sea


Wetlands include marshes, swamps, bogs, and seasonal pools

• Wetlands = the soil is saturated with shallow standing water

• Freshwater marshes = shallow water- Plants 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

Species in vernal pools are adapted to seasonal drying


Wetlands are valuable

• Wetlands are extremely valuable for wildlife- They slow runoff, reduce flooding, recharge aquifers,

and filter pollutants• People have drained wetlands, mostly for agriculture

- Southern Canada and the U.S. have lost over half of their wetlands

• In 2006 the Supreme Court told the Army Corps of Engineers it must create guidelines to determine when wetlands are valuable enough to protect by law


Groundwater plays a key role

• Groundwater = water beneath the surface held in pores in soil or rock- 20% of the Earth’s freshwater supply

• Aquifers = porous, sponge-like formations of rock, sand, or gravel that hold water - Zone of aeration = pore spaces are 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


A typical aquifer


There are two categories of aquifers

• Confined (artesian) aquifer = water-bearing, porous rocks are trapped between less permeable substrate (clay) layers - Is under great pressure

• Unconfined aquifer = no upper layer to confine it- Readily recharged by surface water

• Groundwater’s average age is 1,400 years- It may be tens of thousands of years old

• Groundwater becomes surface water through springs or human-drilled wells


The Ogallala Aquifer

• The world’s largest known aquifer

• Underlies the Great Plains of the U.S.

Its water has allowed farmers to create the most bountiful grain-producing region in the world


Water is unequally distributed across Earth

• Water is unevenly distributed in space and time- Different areas possess different amounts of water- People erect dams to store water

Many densely populated areas are water-poor and face serious water shortages


QUESTION: Review

The picture shows a(n):

a) Braided river

b) Meandering river

c) Oxbow

d) River delta


QUESTION: Review

The area of a lake that rings the edge and contains rooted plants is called the _______ zone.

a) Littoral

b) Benthic

c) Limnetic

d) Profundal


QUESTION: Review

An unconfined aquifer is defined as:

a) An aquifer that traps porous rocks between layers of less permeable substrate

b) An aquifer that traps porous rocks under one layer of less permeable substrate

c) An aquifer with porous rocks resting on bedrock

d) An aquifer with no upper layer


QUESTION: Review

Why do governments subsidize irrigation?

a) It promotes food self-sufficiency.

b) Governments have to or food could not be grown.

c) Governments want to lower water tables.

d) Governments do not subsidize irrigation.


QUESTION: Review

Which of the following statements is NOT true about dams?

a) They change habitat.

b) They generate electrical power.

c) They have created more farmland upstream.

d) Pollutants are trapped in reservoirs.


QUESTION: Review

Which of the following is a point source of water pollution?

a) A factory

b) Roads

c) Agricultural fields

d) All are point sources


QUESTION: Review

Which of the following type of water pollution causes the most severe human health problems?

a) Nutrient pollution

b) Pathogens

c) Toxic chemicals

d) Sediment pollution


QUESTION: Review

Which statement is NOT correct regarding using artificial wetlands to treat wastewater?

a) Water first undergoes primary treatment.

b) Microbes decompose pollutants.

c) Cleansed water cannot be released into waterways.

d) They are good areas for wildlife.


QUESTION: Interpreting Graphs and Data

In this figure of a wastewater treatment facility, what is the first step in treatment?

a) Physical screening to remove large debris

b) Aeration in basins

c) Secondary clarification

d) Piping the treated water into a river


QUESTION: Viewpoints

During times of drought, conflicts erupt between farmers (who need water for irrigation) and ecologists (who want water left in rivers to protect wildlife). Who should have the highest priority?

a) Farmers - they need the water for their crops.

b) Wildlife - animals will die without water.

c) Farmers should be paid subsidies to withdraw water from other places.

d) Farmers should be paid to plant different crops that do not require so much water.


QUESTION: Weighing the Issues

Should cities in dry areas, such as Las Vegas, be allowed to increase their populations, so that they will require more water?

a) Yes; it’s un-American to limit what cities can do.

b) Yes; but make the people pay the true cost of water.

c) Yes; but only if the people are required to use drastic conservation measures.

d) No; enough is enough, and cities in arid environments simply cannot continue growing.

© 2011 pearson education, inc. freshwater systems and resources

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