Environmental Biology Unit 5 Lecture 13

percentage of reliable surface water being withdrawn

34%

percentage of groundwater and surface water withdrawn in the U.S. used to cool electric power plants

41%

how many of the world's people are likely to lack access to clean water by the year 2025

3 billion

percentage of earth's surface covered by water

71%

The Colorado River

- Supplies water and electricity for about 40 million people
- Includes 14 dams and reservoirs
- Flows 2,300 kilometers through seven U.S. states
- Water supplied mostly from snowmelt in the Rocky Mountains
- Irrigates crops that help feed America

The Colorado River Issues

− Very little water is reaching the Gulf of California
− System has experienced severe drought since 1999
− Climate change expected to further reduce river flow

Freshwater

− One of the earth's most important forms of natural capital
− Used inefficiently and polluted
− Low cost encourages waste

We Are Managing Freshwater Poorly

Access to freshwater a global health issue
− An average of 9,300 people die each day from lack of access to safe drinking water
• Economic issue− Water vital for producing food and energy
• National and global security issue
• Environmental issue− Excessive withdrawal

Hydrologic cycle

− Movement of water in the seas, land, and air
− Distributed unevenly

Humans alter the hydrologic cycle

Withdrawing and polluting water and causing climate change

Zone of saturation

Spaces in soil below a certain depth are filled with water

Water table

Top of zone of saturation

Aquifers

Recharged naturally by precipitation or by nearby lakes, rivers, and streams

Surface water

− Surface runoff
− Watershed or drainage basin

Two-thirds of surface runoff lost to

seasonal floods

Reliable runoff

Remaining one-third is reliable source of freshwater

Water footprint

Volume of water used directly or indirectly

Virtual water

Water used to produce food and other products

Freshwater Resources in the United States

More than enough renewable freshwater
− Unevenly distributed and polluted

Freshwater Shortages

Will Grow

30% of the earth's land area

experiences severe drought

Groundwater withdrawals unsustainable in some areas

Being pumped from aquifers in some areas faster than it is renewed by precipitation

Widespread drilling of wells by farmers

− Accelerated aquifer overpumping
− Water tables falling

Ogallala Aquifer—largest known aquifer

− Irrigates the Great Plains
− Very slow recharge
− Water table dropping
-- Water pumped 10-40 times faster than recharge rate
− Government farm subsidies result in further depletion
− Biodiversity threatened in some areas

Harmful Effects of Overpumping Aquifers

• Limits food production and raises prices
• Widens gap between rich and poor
• Land subsidence− San Joaquin Valley in California
− Mexico City
• Groundwater overdrafts near coastal regions
− Contamination of groundwater with saltwater

Tapping Deep Aquifers

May contain enough water to provide for billions of people for centuries

Tapping Deep Aquifers major concerns

− Nonrenewable
− Little is known about the geological and ecological impacts of pumping deep aquifers
− No international treaties govern access
− Costs of tapping are unknown
− Water is contaminated

Large dam-and-reservoir systems

− Greatly expanded water supplies in some areas
− Disrupted ecosystems and displaced people

Main goal of a dam and reservoir system

− Capture and store runoff
− Release runoff as needed for:
Flood control
Generating electricity
Supplying irrigation water
Recreation (reservoirs)

Reservoirs

− Increase the reliable runoff available for use
− Displace people
− Impair ecological services of rivers
− Endanger plant and animal species
− Fill up with sediment within 50 years

Proposed actions for states using the Colorado river

− Enact strict conservation measures
− Phase out agricultural subsidies
− Shift water-thirsty crops to less arid areas
− Raise the price of freshwater

Desalination methods

distillation and reverse osmosis

desalination issues

high cost, high energy use, and large amounts of salty wastewater

Water Transfers

Transferring water from one place to another has greatly increased water supplies in some areas
− Has also disrupted ecosystems

Water Transfers Have Benefits and Drawbacks

China−
South-North Water Diversion Project
Diverts 6 trillion gallons of water per year
• California central valley− Aqueducts
• Water loss through evaporation and leaks
• Ecosystem degradation

The Aral Sea Disaster

Large-scale water transfers in dry central Asia have led to
− Wetland destruction
Desertification− Greatly increased salinity
− Fish extinctions and decline of fishing
− Blowing salt and dust destroying wildlife and crops
− Increased glacial melting in the Himalayas

The Aral Sea Disaster pt 2

Shrinkage of the Aral Sea has altered local climate
− Hot, dry summers, colder winters, and a shortened growing season
• Restoration efforts− Cooperation of neighboring countries
− More efficient irrigation
− Dike construction raised level of the northern sea
- Southern sea may dry up within a few years

Ways to use freshwater more sustainably

− Cut water waste
− Raise water prices
− Slow population growth
− Protect aquifers, forests, and other ecosystems that store and release freshwater

One-half to two-thirds of water is wasted

Evaporation, leaks, and inefficient use

Conserving Water Using Low-Tech Methods

Human-powered treadle pumps bring water into irrigation ditches
• Harvest and store rainwater
• Capture water from fog
• Use polyculture to create canopy vegetation− Reduces evaporation

Cutting Freshwater Waste in Industries and Homes

• Recycle water used in industry
• Use low-flow toilets, showerheads, and front-loading washing machines
• Fix leaks in the plumbing systems
• Use native plants in landscaping
• Use gray water
• Water meters reduce water use

Using Less Water to Remove Wastes

• Large amounts of freshwater used to flush away wastes
• Reuse wastewater− Less than 10% of wastewater is currently recycled
• Use waterless composting toilets

We can lessen the threat of flooding by

− Protecting more wetlands and natural vegetation in watersheds
− Not building in areas subject to frequent flooding

Floodplain

− Area flooded when a stream overflows its channel − Fertile soils for farming− Recharge groundwater and refill wetlands

Human activities that damage floodplains

− Vegetation removal− Draining of wetlands

Human activities that damage floodplains

Rising sea levels from global warming means more coastal flooding

Living Dangerously on Floodplains in Bangladesh

• Dense population on coastal floodplain
• Moderate floods maintain fertile soil
• Recent increased frequency of severe floods
• Destruction of coastal wetlands
− Mangrove forests cleared
− Increased storm damage
• Adapting: using more flood-tolerant crops

Reducing Flood Risks

• Rely more on nature's systems
− Wetlands
− Natural vegetation in watersheds
• Rely less on engineering devices
− Dams
− Levees
− Channelized streams

We can use water more sustainably

− Reduce water use
− Use water more efficiently
− Cut water losses
− Raise water prices
− Protect aquifers, forests, and other ecosystems that store and release water