Ev Sci Ch 10

Ev Sci Ch 10

Water Resources and Water Pollution

Chapter Questions

• Why is fresh water in short supply?

• How can people increase freshwater supplies?

• How can people use fresh water more sustainably?

• How can people reduce water pollution?

Why is fresh water in Short supply?

People often manage fresh water poorly

• Water covers 71% of earth’s surface

• People withdraw excessive amounts of water from rivers and aquifers.

• --This has degraded water quality

• --Reduced fish populations

• --Hastened extinction of aquatic species

• --Degraded aquatic ecosystem services

Most of Earth’s freshwater is not available

• .024% of planet’s water supply is available to people as liquid fresh water.

• Canada has 20% of the world’s freshwater

Groundwater

• Much of Earth’s freshwater is stored in the ground

• Spaces in soil and rock close to surface holds little moisture

• Zone of saturation - completely filled with freshwater deep below earth’s surface

• Top of groundwater zone is water table.

Groundwater

• Deeper down are aquifers - underground caverns and porous layers of sand, gravel, rock

• --Recharge slowly

Surface water

• Surface water - Freshwater from rain and melted snow that flows or is stored in lakes, reservoirs, wetlands, streams, and rivers.

• Precipitation that does not infiltrate the ground or return to the atmosphere is surface runoff

Surface water

• Two thirds of annual surface runoff into rivers and streams is lost in seasonal floods

• Remaining one third is reliable surface runoff - regarded as a stable source of fresh water from year to year

• Experts think that people are likely to remove up to 90% of reliable runoff by 2025.

Surface water

• Virtual water - freshwater that is used to produce food and other products

• Virtual water makes up large part of your water footprint

• Water footprint - rough measure of volume of fresh water you use directly and indirectly to support your lifestyle.

Freshwater shortages will grow

• More than 30 countries face stress from freshwater scarcity

How can people increase freshwater supplies?

Aquifers are being depleted

• Water tables are falling in many areas because aquifers are being depleted faster than they are being replenished.

• As water tables drop, energy and costs of pumping water rise sharply

• Withdrawing too much groundwater can cause land to collapse

• --Subsidence - land above an aquifer sinks.

• ---Damages roadways, sewage lines, and building foundations

• Overpumping in coastal areas can bring saltwater into freshwater aquifers, which makes the water undrinkable

Dams provide benefits and create problems

• Dams are built to control flow

• Dammed water creates an artificial lake, or a reservoir

• Dam-and-reservoir system captures and stores surface runoff from a river’s watershed.

Dam and Reservoir system

• This system releases water as needed to control floods, generate electricity, and supply freshwater for irrigation and for use in towns and cities

• Provide water for recreational activities

Dams (continued)

• Dams have increased annual reliable surface runoff by 33%

• Dams impair ecosystem services that rivers provide

• Reservoirs have limited life spans

• --Typically fill up with sediments in 50 years

Removing salt from seawater is costly and harmful

• Desalination - process of removing dissolved salt from ocean water or from brackish water in aquifers or lakes

• Two methods used for desalination

• --Distillation - heating salt water until it evaporates to separate salt then cooling steam

• --Reverse Osmosis - force saltwater through a membrane filter with pores small enough to remove salt

Issues with this

• Costly because removing salt requires a lot of energy

• Pumping large amounts of seawater through pipes requires chemicals to sterilize the water and prevent algae growth, which kills marine organisms

• Produces huge quantities of salt waste that require proper disposal. Dumping into the ocean causes rise in salinity of those waters and threatens food resources and aquatic life

• Desalination is only used in water short countries that can afford high cost

How can people use fresh water more sustainably?

Reducing freshwater losses

• Educate people

• --Improve irrigation practices, repairing infrastructure, increasing water reuse

• Irrigation

• --Highly inefficient currently

• --Flood irrigation - water pumped from groundwater or surface water source into unlined ditches and flows to crops.

• ---Uses too much water

• --Drip irrigation (more efficient) - Use pipes or tubes to deliver water directly to plant roots.

Industries and Homes

• Household water use, for drinking, washing, and cooking accounts for only about 5 percent of world water use.

• Simple steps, such as taking shorter showers, fixing leaks, and washing cars, dishes, and clothes as efficiently as possible, can go a long way toward forestalling the water shortages that many authorities predict.

• Water-conserving appliances, such as low-volume showerheads and efficient dishwashers, can reduce water consumption greatly

Communities are starting to recycle water

• Reclaimed stormwater, and even water from sewage treatment plants, can be filtered, purified, and re-used.

• Most treated wastewater— some almost clean enough to drink—is sent to the sea.

• Despite a growing population, the United States is now saving some 144 million liters (38 million gal) per day

Water Pollutants

• Pollution includes point sources and nonpoint sources

• Point sources -  Factories, power plants, sewage treatment plants, underground coal mines, and oil wells

• -- discharge pollution from specific locations, such as drainpipes, ditches, or sewer outfalls

Water Pollutants

• Nonpoint sources - diffuse, having no specific location where they discharge into a particular body of water

• --Harder to monitor and regulate because origins are hard to identify

• -- runoff from farm fields and feedlots, golf courses, lawns and gardens, construction sites, logging areas, roads, streets, and parking lots.

Biological pollution includes pathogens and waste

• Pathogens

• --(disease-causing) organisms

• --The main source of these pathogens is untreated or improperly treated human wastes

• --sewage treatment plants and other pollution-control techniques have reduced or eliminated most of the worst sources of pathogens in inland surface waters.

Biological pollution includes pathogens and waste

• Detecting specific pathogens in water is difficult, time consuming, and costly, so water quality is usually described in terms of concentrations of coliform bacteria

• Coliform bacteria - any of the many types that commonly live in the colon, or intestines, of humans and other animals

Biological oxygen demand

• The amount of oxygen dissolved in water is a good indicator of water quality and of the kinds of life it will support

Inorganic pollutants include metals, salts, and acids

• Some toxic inorganic chemicals are naturally released into water from rocks by weathering processes

• Humans accelerate the transfer rates in these cycles thousands of times above natural background levels by mining, processing, using, and discarding minerals

Metals

• Currently the most widespread toxic metal contamination in North America is mercury

• Americans are warned not to eat more than one meal of wild caught fish per week

• Top marine predators tend to have especially high mercury content

Acids and Bases

• Acids are released as by-products of industrial processes

• Coal mining is an especially important source of acid water pollution.

• Thousands of kilometers of streams in the United States have been acidified by acid mine drainage, some so severely that they are essentially lifeless

Is bottled water safer?

• Every year, Americans buy about 28 billion bottles of water at a cost of about $15 billion with the mistaken belief that it’s safer than tap water

• Health experts say that municipal water is often safer than bottled water

Municipal Water over Bottled Water?

• Most large cities test their water supplies every hour for up to 25 different chemicals and pathogens

• Requirements for bottled water are much less rigorous

• A recent survey of bottled water in China found that two-thirds of the samples tested had dangerous levels of pathogens and toxins.

• Average energy cost to make the plastic, fill the bottle, transport it to market, and then deal with the waste would be “like filling up a quarter of every bottle with oil,”

Sediment is one of our most abundant pollutants

• Farming and urbanization, greatly accelerate erosion and increase sediment loads in rivers

• Cropland erosion contributes about 25 billion metric tons of soil, sediment, and suspended solids to world surface waters each year.

• Makes purification of drinking water more costly

• Thermal pollution - degradation of water quality by any process that changes ambient water temperature

• --aquatic organisms tend to be poorly adapted to rapid temperature changes

Water treatment and remediation

• The cheapest and most effective way to reduce pollution is to avoid producing it or releasing it in the first place.

• Industry can reduce pollution by recycling or reclaiming materials that otherwise might be discarded in the waste stream

• Impaired water can be destroyed

Impaired water can be destroyed

• Bay in Minamata, Japan, was so strongly associated with mercury poisoning that the condition was named Minamata disease in the 1950s.

• Over 2,000 people were affected, officially. When mercury discharges were banned, mercury concentrations eventually became diluted, and in 1997 the bay was declared clean.

How do we treat municipal waste?

• Municipal water = Water that comes from a public water supply system

• Most developed countries require that cities and towns build municipal water treatment systems to purify the human and household waste.

• Most rural households use septic systems, which allow solids to settle in a tank, where bacteria decompose them

3 levels of treatment of quality in municipal water

• Primary treatment physically separates large solids from the waste stream with screens and settling tanks.

• Secondary treatment, in which aerobic bacteria break down dissolved organic compounds.

• Tertiary treatment removes dissolved metals and nutrients, especially nitrates and phosphates, from the secondary effluent

Legal protections for water

• The clean water act was ambitious, popular, and largely successful

• Passage of the U.S. Clean Water Act of 1972 was a bold, bipartisan step that made clean water a national priority.

• Goal of the Clean Water Act was to return all U.S. surface waters to “fishable and swimmable” conditions.

• Quality in the United States has significantly improved on average over the past quarter century

• $54 billion in federal funds and more than $128 billion in state and local funds for municipal sewage treatment facilities.