13

Water Resources: Preserving

Our Liquid Assets and

Protecting Aquatic

Ecosystems

Chapter Outline

The Hydrological Cycle

Water Issues Related to Supply and Demand

Where is Water Used and Where Does It Come From?

Drought and Water Shortages

Impacts of the Water Supply System

Impacts of Excessive Groundwater Withdrawals

Impacts of Dams and Reservoirs

Creating a Sustainable Water Supply System

Flooding: Problems and Solutions

Causes of Flooding

Controlling Floods

Wetlands, Estuaries, Coastlines, and Rivers

Wetlands

Estuaries

Barrier Islands

Coastal Beaches

Wild and Scenic Rivers

Key Terms

hydrological cycle evaporation transpiration

evapotranspiration absolute humidity relative humidity

condensation nuclei precipitation surface waters

ground water stable runoff drought

water table saltwater intrusion subsidence

sinkholes aquifer recharge zones watersheds

wetlands xeriscape gray water

black water flooding flood plains

levees streambed channelization watershed management

estuaries barrier islands coastal beaches

jetties beach drift longshore currents

longshore drift wild rivers scenic rivers

recreational rivers

Objectives

1. Draw a sketch of the hydrological cycle showing its major processes and components.

2. Define the following terms: “evaporation,” “transpiration,” “evapotranspiration,” “absolute humidity,” and “relative humidity.”

3. Summarize the major sources of human use of water in the United States and globally.

4. Define the following terms: “surface waters,” “ground water,” “stable runoff,” and “drought.”

5. Discuss the potential impacts of excessive groundwater withdrawal.

6. Summarize the impacts of dams and reservoirs on the environment.

7. Discuss the ways the present system of water supply and use can be made more sustainable.

8. Summarize the major causes of flooding and how watershed management can reduce flooding.

9. List the major aquatic life zones associated with surface waters.

10. Discuss important legislation affecting aquatic habitats discussed in this chapter.

11. Discuss why wetlands are more than just important areas of habitat for aquatic plants and animals.

12. Define the terms: “wild rivers,” “scenic rivers,” and “recreational rivers.”

13. Discuss how you can personally conserve water.

Lecture Outline

The Hydrological Cycle - Water is a renewable resource purified and distributed in the hydrological cycle.

A. The hydrological or global water cycle consists of two phases, evaporation and precipitation.

B. The cycle is driven by winds generated by solar energy.

Water Shortages - Water shortages are a function of uneven distribution, excessive demand and inefficient use.

A. Where Is Water Used, and Where Does It Come From?

1. Globally, agriculture and industry are the major users of water.

2. Most water comes from surface water supplies: rivers, streams, and lakes.

3. Withdrawal of water in excess of the stable runoff typically results in severe water shortages and hardships for people and many species.

B. Drought and Water Shortages

1. While droughts appear to be natural causes of water shortages, human activities may increase their frequency and severity.

2. Droughts reduce water supplies and create significant social, economic, and environmental problems.

C. Impacts of the Water Supply System

1. Water is withdrawn from groundwater and surface water sources, but very little is returned directly to its source.

2. Water that is returned to its source is often laden with pollutants.

D. Impacts of Excessive Groundwater Withdrawals

1. Groundwater Overdraft - Groundwater overdraft is the removal of groundwater at a rate faster than it is replaced. Groundwater overdraft is responsible for several important problems:

a. Saltwater Intrusion - Saltwater intrusion is the movement of salt water from marine aquifers into freshwater aquifers. Salt water is then contaminating potable water supplies.

b. Subsidence - Removal of groundwater can cause soil compaction and sinks or sinkholes. These can affect large areas of land making them unsuitable for human use.

E. Impacts of Dams and Reservoirs

1. Dams have many positive benefits such as power generation, flood control, and water storage.

2. Dams can have a detrimental impact on fish and wildlife. They flood streams and can eliminate fish species that live and reproduce there. They also flood terrestrial habitats affecting large numbers of other species.

3. Dams can impact human activities and economies negatively. New dams can threaten recreational rivers and surrounding towns and their economies. Dams built in developing countries often flood valuable farmland and can encourage new epidemics of disease.

4. Dams can have downstream impacts on rivers, often changing the environmental conditions severely.

5. Water diversions as a result of dam projects can affect water quality and dewater downstream areas.

F. Creating a Sustainable Water Supply System

1. Water Conservation - traditional approaches to water problems have focused on supply: damming rivers and streams and pumping water from lakes and aquifers. A more sustainable approach is to conserve on the use side.

a. Agriculture and industry are the biggest users and efforts to conserve in these sectors should be given the highest priority.

b. Water projects are often subsidized by the government providing no incentives for conservation. Reducing the amount of irrigation water by improving efficiency or switching to crops that do not require irrigation are several strategies that could be employed.

c. Sustainable farming practices reduce the demand for watering and irrigation.

2. Water Recycling - Water can be purified and reused in industry, on farms, and even in our homes. Water recycling reduces pressure on surface and groundwater supplies and reduces water pollution.

3. Restoring Watersheds and Wetlands to Protect and Enhance Our Water Supplies - Restoring watersheds reduces siltation in reservoirs and rivers and enhances groundwater recharge. Wetlands are the natural filters for surface water and restoration of these areas will reduce pollution of surface and ground water.

4. Population Stabilization - Stabilizing or reducing human population size can reduce the demand on the water system.

5. Changing Government Policies to Create a Sustainable Water Supply System

a. Government policies should be revamped to require those who benefit from water projects to pay the full cost. The cost of a water project should include any environmental costs should problems arise as a result of the project.

b. Governments should establish building codes that include requirements for water conserving devices.

c. Alternative landscaping method requiring less water should be subsidized and encouraged (xeriscape).

d. Gray water systems should be installed to reduce water use. Building codes can require these be installed in new construction.

e. Government can control water prices and adjust water rates by time of day and encourage conservation.

f. Education can play an important function in reducing water use.

Flooding: Problems and Solutions - Despite widespread water shortages, flooding is a serious problem in many parts of the world.

A. Causes of Flooding - Human activities and land use patterns combine with heavy precipitation and other natural factors to produce floods.

B. Controlling Flooding - Structural flood-control devices and watershed management are two different approaches to controlling flooding.

C. Streambed channelization is an environmentally destructive technique. The construction of floodwall not only eliminates many important wetland areas but also prevents normal flooding and enrichment of the flood plain ecosystem. In addition, channelization has been shown to exacerbate the effects of flooding in downstream areas.

Wetlands, Estuaries, Coastlines, and Rivers - Surface waters are under assault. The destruction of these systems affects available water supplies but also eliminates important habitat for fish and other organisms.

A. Wetlands - These are flooded lands lying either inland or in coastal zones.

1. The Hidden Value of Wetlands - Wetlands function as valuable habitats and water-quality protectors.

2. Declining wetlands - Wetlands are destroyed in the United States and elsewhere for development and agriculture.

3. Protecting Wetlands - Various federal and state bills are designed to protect remaining wetlands in the United States, though enforcement, and thus effectiveness, is low.

B. Estuaries - Estuaries, or river mouths and bays, are critical habitat for many commercial species and wildlife. Estuarine zones are valuable also as water purifiers.

1. Damaging This Important Zone - Pollution, sedimentation, inflow reduction, and dredging/filling projects all harm estuarine zones and their life forms.

2. Protecting the Estuarine Zone - Pollution and erosion control, along with water conservation, will help protect the estuarine zone.

C. Barrier Islands - Barrier islands form in response to wave and wind patterns offshore. Development and beach-erosion control programs threaten both barrier islands and coastal beaches.

D. Coastal Beaches - Like barrier islands, coastal beaches are eroded by longshore currents.

1. Protecting coastlines may require measures to ensure a steady stream of sediment from rivers and a hands-off policy toward building levees.

E. Wild and Scenic Rivers

1. Rivers provide many benefits in addition to recreation. They are great reservoirs of diversity and should be respected as such. This means that interruption of in-stream flow is probably not a sustainable activity.

2. Many rivers or segments of rivers in the United States have been given protection against development by the Wild and Scenic Rivers Act. The wild or scenic river designation is often marked by controversy because so many interests vie for a river’s benefits.

3. Dammed and diverted to water-hungry, often wasteful consumers, a river becomes a symbol of unsustainable systems design.

Suggestions for Presenting the Chapter

· A visit to a local lake, river, estuary, or coastline to investigate the ecosystem is an excellent way to introduce your students to aquatic ecosystems.

· Instructors should stress that the health and sustainability of aquatic ecosystems is dependent on the sustainability of human activities using land as well as water.

· A trip to your local water plant and/or a wastewater/sewage treatment plant is an excellent activity. Students should know where and how their potable water is obtained and how wastewater is treated before returning to surface waters.

· Instructors should stress that human development directly influences our water resources. Pollution of ground and surface waters, water supply problems, and flooding are just some of the main issues associated with human development.