INTRODUCTION TO ENVIRONMENTAL SCIENCES

LECTURE NOTES

Water Resources and Pollution

Water defines our planet, biology, and environment. Without it, neither we, nor any life as we know it, would exist. It is our planet's most distinctive, fundamental, and important resource.

I. Sources of Water

97.4% of the world's water is in the oceans: too salty for most uses. Another 2% is in the form of ice in glaciers and at the poles. Less than 0.01% is accessible, fresh, liquid water found in the atmosphere, streams, lakes, and underground.

Water moves through the various reservoirs of the hydrologic cycle. May take thousands of years to do this. Much of it is nonrenewable on a human time scale.

Water not distributed equally. Some places have excess (Canada; 20% of world's fresh water); others have very little (Middle East). Leads to confrontations between nations over access to adequate supplies of fresh water. Abundant water often located where there are few people (Amazon) or visa-versa (Southern California)

Often get short periods of excess precipitation leading to flooding followed by long periods of little precipitation causing droughts: a feast or famine situation.

In eastern U.S. there is a general water surplus, although much of it is polluted. Western U.S. has a general water deficit. Situation getting worse as population shifts to the west and as climate warms up. This has led to numerous and protracted legal battles over water rights.

A. Surface Water

Precipitation that does not infiltrate into the ground is known as surface runoff, which flows into lakes, rivers, stream, swamps, etc. Land is divided into distinct drainage basins or watersheds. These areas drain into a specific stream or lake.

Surface water is the most easily accessible where available. Often it is polluted.

B. Groundwater

This water has percolated down, filling the voids in soils, sediments, and rocks.

Zone of aeration (vadose zone; water and air in voids) above is separated from zone of saturation (only water in voids) below by the water table (top surface of the groundwater). This may extend down thousands of feet until voids close up.

Water table may move up or down depending on the balance between the inflow (recharge) and outflow (discharge) of water.

Most groundwater held in layers of high porosity and permeability. Known as aquifers. May be unconfined (aquifer extends to the surface) or confined (aquifer bounded on top and bottom by low porosity and permeability material. Groundwater moves slowly (meters/year) through aquifers from high elevation (or pressure) to low.

Confined (artesian) aquifers have water under pressure. They are cut off from surface recharge and pollution by overlying aquiclude (low porosity and permeability layer), except where aquifer is exposed at the surface. Known as a recharge area. These may be affected by local pollution and covering with impermeable material (buildings, parking lots, etc).

C. Human Uses of Water

Has increased about 500% since 1950. Will double again by 2025 at which point we will be using essentially 100% of all reasonably accessible fresh water.

Most water (65%) is used for irrigation where it is lost to the local hydrologic cycle (consumed) due to evaporation and infiltration. Value varies from place to place.

Another 25% used for energy and industrial production. Most returned to the local hydrologic cycle but often it is polluted. Only 10% used for drinking, bathing, flushing, cooking, etc. (municipal and domestic water supplies).

II. Water Shortages: Causes and Solutions

Almost half of the world's population faces chronic water shortages due to climate, prolonged drought, soil desiccation (due to loss of vegetation), or overpopulation. Another 20% of the world's population uses water that is polluted. There are five basic ways to increase water supplies, each with their own pros and cons.

A. Dams and Reservoirs

Pros: Large year-round capacity, used for flood control, used for recreation, and can generate electricity without pollution. Some of these uses conflict with one another.

Cons: Large evaporative loss, loss of habitat and displacement of people due to flooding by reservoir, may cause earthquakes, risk of collapse and catastrophic downstream flooding, blocks fish migration, traps sediment, causing increased downstream erosion and loss of beaches, and expensive to build and maintain.

B. Intrabasin or Watershed Transfer

Pros: Take water from where it is abundant to where it is scarce. This may be the only large supply of fresh, non-polluted water available to large populations. Examples are the New York City and Southern California water supply systems.

Cons: May require the construction of dams and reservoirs (see above), may destroy river and lake habitats in basins where water is being taken due to reduced flows (i.e. Aral Sea and Colorado River), and they are very expensive systems ($100+ billion).

C. Withdrawal of Groundwater

Pros: Largest single source of unpolluted fresh water. Provides about 50% of drinking water and 40% of irrigation in the U.S.

Cons: Lower water tables, aquifer depletion, aquifer destruction, subsidence, saltwater intrusion, increased pollution, drying up of streams and lakes.

Parts of the Ogallala Aquifer (source of most water for agriculture in central U.S) will dry up by 2050. Withdrawing groundwater at 4X its replacement rate in the U.S.

D. Desalination

Pros: Done by distillation or filtration. 7,500 installations in 120 countries provide 0.1% of human consumption.

Cons: Expensive (3-10X more than standard sources), requires large amounts of energy to make, leaves large amount of concentrated waste brines and salts behind.

E. Improving Efficiency of Water Use

Pros: Roughly 2/3 (1/2 in the U.S.) of the world's fresh water is wasted, largely through leaks and evaporation. Reducing this to 15% would keep water demand at present levels well into the next century and reduce the need to use other methods.

Best way to cut water use is to reduce irrigation evaporation. Typically 40-50% of the water never reaches the plant roots (in some places 90%). Center-pivot and drip irrigation systems lose much less water. Efficiencies of 90-95% are possible. Also grow crops requiring less water (fruits, vegetables) in areas where it is scarce.

Can also reuse gray water (non-sewage waste water; 75% of the water discharged from the home) and treated sewage for irrigation. Industry can recycle wastewater. Also, water needed for processing recycled metals is much less than the amount needed for processing original ores.

Homeowners can use low-flow showerheads and toilets. Lawns can be replaced with plants requiring less water. Public water supplies can fix their leaks. These methods can save up to 50% of domestic use and 25% of industrial use.

Cons: Start-up costs may be high, but payback times are short. Usually it is much cheaper to pay for conservation than to pay for new water supply systems.

III. Too Much Water: Flooding

Two types, coastal and stream. The former is caused by coastal storms, sea level rise, and coastal development. The latter usually caused by excess precipitation or snow and ice melt. Both are natural processes often enhanced by human actions.

Streams naturally overflow their banks and flood their adjacent floodplain. People settle there because of fertile soils (due to the sediment deposited by floods), abundant water, flat land, and the stream can be used for transportation. Civilizations start along rivers, but this puts people in harms way.

A. Human Impacts on Flooding

Human activities increase frequency and severity of floods. Destroy vegetation, increasing soil erosion and surface runoff.

Build levees, dams, floodwalls, and channelize streams to try to control floods and protect property. Make things worse by blocking off floodplain. Bigger floods result. Build more flood-control structures. Make things even worse. Cycle repeats.

Flood-control structures are equally good at keeping water in the floodplain as keeping it out. Once breached they often prolong the flood. In many instances, solving the flooding problem in one area only makes it worse in another.

In the U.S. we spend billions of dollars every year on flood control and still wind up with billions of dollars in damages. Also destroying natural habitats along streams.

B. Alternative Ways to Reduce Flooding Risks

We are now rethinking the logic of flood control. Ultimately may be cheaper to let streams go back to their natural condition and move the people out of flood-prone areas. Practice floodplain management (i.e. people control) rather than flood control.

Restrict development in flood-prone areas, zone out activities not consistent with flooding, create a natural floodway, make flood insurance more expensive and harder to get (in another words, stop encouraging people to live and work on floodplains).

IV. Water Pollution

Any biological, chemical, or physical change in water quality that has a harmful effect on living organisms or makes it unsuitable for desired uses. Usually human caused.

A. Pollutant Types

1) Disease causing agents or pathogens, including bacteria, viruses, protozoa, parasites. These come from raw sewage and animal waste and they may be responsible for 80% of the disease in developing countries. Measured by the amount of colliform bacteria present.

2) Oxygen demanding organic wastes: can be decomposed by aerobic bacteria. Cause a reduction in dissolved oxygen, suffocating oxygen-consuming organisms (fish). Measured by biological oxygen demand (BOD).

3) Water-soluble inorganic chemicals, including acids, salts, and metals. Make water unfit to consume and use for irrigation. Also can harm organisms and cause material corrosion.

4) Inorganic plant nutrients (nitrates and phosphates) from fertilizers. Cause excessive algal and plant growth that lower oxygen levels when they decompose.

5) Organic chemicals, including oil, gasoline, plastics, pesticides, solvents, detergents. Present health risks to humans and other organisms.

6) Water-soluble radioactive isotopes: These (and many other chemicals) often bioaccumulate in fish and other organisms at the top of the food chain.

7) Sediment or suspended matter (particulates) from soil and other solids. Disrupt photosynthesis and transports large amounts of other, adsorbed pollutants. Also silt up lakes, rivers, and reservoirs, increasing flood risk.

8) Thermal pollution: from the cooling of industrial and power plants. Lowers solubility of oxygen and makes organisms more susceptible to other pollution types.

9) Genetic pollution caused by the introduction of nonnative or exotic species.

All of the different pollutant type can be discharged from point (specific location) or nonpoint (no single location; large area) sources. Point-source pollution is usually easier to identify, monitor, measure, and control. Most water pollution in the U.S. now comes from nonpoint sources. Little has been done to control it.

B. Stream Pollution

Streams usually can recover from many types of pollution due to dilution from fresh water and bacterial decay. Takes some time and distance downstream to recover to normal conditions. Efficient if stream flow is not reduced. Nondegradable pollutants remain for long periods of time.

Since 1970, water pollution control laws have reduced pollution amounts entering surface waters from point sources in the U.S. and other industrialized nations. Rivers such as the Hudson, Delaware, Cuyahoga, Thames, Seine, have recovered and now support robust fish and bird populations and can be used for recreation.

Problems still exist in controlling nonpoint source pollution and accidental and industrial discharges. Storm runoff can overwhelm wastewater treatment plants. Developing countries and Eastern Europe have increasing levels of stream pollution.

C. Lake Pollution

Lakes have less dilution due to water stratification and low flow. Pollution recovery can take years rather than the days typical for streams.

Less dilution also leads to more bioaccumulation through the food chain. Even low pollution amounts in the water lead to large levels in top-level predators.

Large amounts of nutrient-rich agricultural runoff and other human discharges cause cultural eutrophication. May result in algal blooms, oxygen depletion, and fish kills. Many lakes (about 50%) near urban areas in the U.S. are eutrophic. This is the case for Centennial Lake. Lakes can recover if nutrient input is stopped or controlled.

Great Lakes are example of how lakes can recover if pollution is controlled. Since 1972, over $20 billion has been spent on reducing pollutants. Lakes have recovered to pre-1970 conditions and continue to improve, although nonpoint sources are still a problem and many fish still are not edible. A big concern now is from the invasion of numerous nonnative species.

D. Groundwater Pollution

It has the longest recovery times from pollution due to low flow, dispersion and dilution, colder temperatures, and lower bacteria levels. May take thousands of years to cleanse itself of degradable wastes and nondegradable waste is permanent. For all intents and purposes, once groundwater is polluted, it stays that way indefinitely.

25% of the U.S. groundwater is contaminated. All major aquifers in New Jersey are.

Groundwater contaminated from a number of sources, both on the surface and buried. Often attempts to control surface water pollution (injection or ponding of hazardous waste) results in groundwater pollution. Unconfined aquifers are more susceptible to contamination from the surface than confined ones.

Cleaning groundwater is very expensive (millions of dollars per aquifer) and time consuming. Better to prevent the contamination to begin with. Can do this by monitoring and controlling leaks from landfills, underground storage tanks, injection wells, waste ponds, etc. Should also require insurance to pay for spill remediation and ban the underground storage of hazardous waste.

E. Ocean Pollution

Oceans are capable of diluting, dispersing, and degrading huge amounts of pollutants, particularly in the deep ocean. Shallow continental shelves much more susceptible to pollution impacts and environmental degradation.

The most polluted areas are coastal regions where raw sewage and industrial wastes are dumped directly into the water. 35% of U.S. sewage dumped into marine waters.

Agricultural runoff near the mouths of large rivers (Mississippi) cause algal blooms (red, brown, and green tides) and create "dead zones" due to oxygen depletion.

Chesapeake Bay has become very polluted due to large population and agriculture in its drainage basin and also because of low tidal flushing rates (1%). Many areas of the bay have become eutrophic and even anoxic (no dissolved oxygen). Since 1983 the Chesapeake Bay Program has attempted to address this problem. Almost $1 billion spent so far. Many pollutants have been reduced, typically by about 10-15%. Billions more will be required to reduce levels by the 40% needed to return the bay to a more natural condition.

Although some ocean dumping has been banned in the U.S., industrial waste, dredge spoils, and sewage sludge are still dumped in the world's oceans. Dumping of sewage and garbage has been restricted from merchant and cruise ships. Many countries now ban the dumping of toxic and radioactive wastes, at least within their territorial limits. Many of these treaties and conventions are very hard to monitor and enforce.

Petroleum and its refined products are a major ocean pollutant, either accidentally from spills or well leaks, or from deliberate discharges. Natural oil seeps also contribute. Ships also clean out tanks and bilges at sea. Total discharges are many times (100-1000X) that spilled from the Exxon Valdez in 1989 (10+ million barrels). May take 3-10 years for marine life to recover from a large oil spill.

Ocean pollution can be reduced by separating sewage and storm runoff, improving sewage treatment of the waste that is dumped, restricting ocean dumping, regulating and restricting coastal development and industrialization, requiring double hulls for oil tankers, recycling used oil, and improving oil cleanup techniques

Since all waters eventually make it to the oceans, reducing stream, lake, and groundwater pollution will automatically reduce ocean pollution. In addition, as much as 33% of ocean pollution comes from the atmosphere so reducing air pollution also reduces ocean pollution.

V. Preventing and Reducing Water Pollution

A. Nonpoint Sources

Leading cause of water pollution is agriculture. Need to control runoff and reduce use of chemical pesticides, herbicides, and fertilizers. Use natural, organic, and biological methods to replace these where possible. Plant vegetation buffer zones around fields to filter runoff. Recycle animal wastes for fertilizer. Control soil erosion (and many other problems that are caused by soil erosion) by revegetation.

B. Point Sources

In most of the world sewage and industrial wastes are not required to be treated. In developed countries most of this is required by law to be treated to some extent.

In the U.S. the Clean Water Acts of 1972 and 1977 and the Water Quality Act of 1987 form the regulatory basis for controlling surface water pollution. Has helped greatly by almost doubling the number of lakes and stream (now about 65%) that are swimmable and fishable. Goal is 100%. In order to do this laws will have to be strengthened and by providing more funds for monitoring and enforcement.

Individual septic systems need to be upgraded and maintained regularly.

In urban areas, storm and sewage lines need to be separated so storm runoff doesn't cause system to overflow and raw sewage to be dumped into surface waters.

All urban waste should undergo both primary (screening and filtering of solids) and secondary (aeration, bacterial decomposition of organics, and disinfection) sewage treatment. Despite the requirements of the Clean Water Acts, many U.S. cities are still not utilizing secondary sewage treatment, either partially or totally.

Secondary treatment still leaves sewage with 3-5% of the oxygen demanding waste and suspended solids, 50% of the nitrogen, 70% of the phosphorous, 30% of the metals and organic chemicals, and virtually all of radioactive and persistent organic compounds. These can be removed by a series of specialized treatments known as advanced (tertiary) sewage treatment. Advanced treatment can be very costly (2-4X secondary treatment alone) and, therefore, is not commonly done.

Sludge from sewage treatment used as organic fertilizer (54%) or compost (9%). Rest is dumped in landfills or incinerated. Creates problems from the bacteria, organic chemicals, and metals the sludge contains.

Artificial and natural wetlands can be used to naturally treat wastewater. Wetlands effectively clean and filter sewage while providing needed natural habitats. Also reduce the cost of sewage treatment. Process can also be done indoors in a greenhouse-type setting. Systems work well for smaller towns and in rural areas.

C. Drinking Water Issues

Worldwide, total cost of cleaning up surface water to provide clean drinking water and prevent spread of sanitation-related diseases is estimated at $500+ billion.

In the U.S., municipal drinking water must meet standards of the 1974 Safe Drinking Water Act. Established maximum contaminant levels (MCL) for many pollutants. MCL for many more still not established. Private wells do not have to meet federal standards, largely due to expense and opposition of owners. As a result, 1 in 5 Americans drink potentially unsafe water, resulting in about 7 million annual illnesses and 1,200 deaths. Could be corrected for less than $100 per household on average.

Bottled water often is less clean than available municipal or private well supplies unless it meets IBWA or National Sanitation Foundation requirements. Home water purifiers usually not needed or do not perform as advertised.

D. Sustainable Use of Water

Clean, fresh water often is a finite resource that must utilized in a sustainable way. Need to extract groundwater no faster than it is being replaced. Need to integrate water use, treatment, and unavoidable pollution within a drainage basin. Need to reduce the amount of pollutants. Need to clean and reuse polluted water. Need to prevent pollution before it occurs rather than trying to clean it up after the fact.