Water and Its Pollution

Lecture 9

A Glimpse Into Water’s Unique Properties

Liquid water dissolves a variety of compounds

- known as the universal solvent

- is easily polluted by water-soluble wastes

- in living organisms: carry dissolved nutrients; flush waste products

Main Uses of Water

1. Domestic Use- domestic and municipal use account

for 6 - 8% of worldwide withdrawals

- improved water supply helps reduce diseases

- humans are approx. 70% water

Main Uses of Water cont’d

2. Industrial Use

- worldwide withdrawals of water for energy production &

industrial processing is ~ 23%

- most water is used for cooling & cleaning

- it takes 100,000 gallons (380,000 litres) to make an automobile

Main Uses of Water cont’d

3. Agricultural Use- consumes the greatest quantity of

fresh water

- globally ~ 69% of the water withdrawn is used for irrigation

- irrigation water efficiency is < 30%

Main Uses of Water cont’d

4. Transport

- use of seas and rivers

- e.g., river barges, freight ships

Main Uses of Water cont’d

5. Recreation / Tourism

- use of seas and rivers

- e.g., rafting, canoeing, snorkeling, swimming, river-boat casinos, scuba diving, cruise ships

WHERE IS OUR WATER STORED?

Watershed

- also called drainage basin or catchment area

- areas of land that drain into bodies of water

Surface Water

- precipitation that does not soak into the ground or return to the atmosphere

- forms streams, lakes, wetlands

Surface Runoff

- water flowing off the land into bodies of surface water

Groundwater

- water that sinks into the soil and is stored in slow flowing and slowly renewed underground reservoirs

- underground water

Groundwater Pollution

- groundwater is easy to deplete and pollute because it is renewed very slowly

- pesticides and nitrates are the most common contaminants

- pollution is caused from: landfills, underground storage tanks, hazardous waste dumps, leaking underground sewers, industrial-waste storage lagoons e.g. red mud lakes

Water Pollution

Water is becoming scarce in some parts of the world & its quality is being degraded.

8 Principal Water Pollutants

1. Sediment

2. Inorganic Plant Nutrients

3. Pathogens

4. Organic Chemicals

5. Inorganic Chemicals

6. Radioactive Chemicals

7. Thermal Pollution

8. Sewage

1. Sediment (or suspended matter)

- insoluble particles of soil and other solids that are suspended in water

- occurs mostly when soil is eroded from land

- biggest water pollutant

- clouds water

(lowers rate of photosynthesis)

2. Inorganic Plant Nutrients (excess nutrients)

- come from soil erosion and human & animal waste

- water-soluble nitrates and phosphates can cause excessive growth of algae

- causes eutrophication: over-nourishment of aquatic ecosystems with

plant nutrients

3. Pathogens (disease-causing agents)

- from sewage and livestock wastes

- include disease-causing bacteria, parasitic worms, protozoa and viruses

- greatest cause of sickness and death in LDCs

4. Organic Chemicals / Compounds

- include oil, gasoline, plastics, pesticides, cleaning solvents, detergents

- threaten human health

- harm aquatic life

5. Inorganic Chemicals

- consist of acids, salts & compounds of toxic chemicals, e.g., mercury, lead

- high levels can:

· make water unfit to drink

· harm aquatic life

· depress crop yields

· accelerate corrosion of equipment

6. Radioactive Chemicals

- can cause birth defects, cancer, genetic damage

- capable of being biologically amplified to higher concentrations as they pass through food webs

- e.g. DDT (Dichloro-Diphenyl-Trichloroethane)

PCBs (Polychlorinated Biphenyls)

7. Thermal Pollution

- is an increase in water temperature that has harmful effects on aquatic life

- generally caused by heat that is absorbed by water used to cool electric power plants

- water temperature increase lowers oxygen content

- aquatic organisms more vulnerable to disease

8. Sewage & other oxygen demanding wastes

- organic wastes that an be decomposed by aerobic bacteria

- can lead to depletion of oxygen and death of aquatic life

Sources of Water Pollution

Point Source

- single, identifiable source that discharges pollutants into the environment

- e.g., the drainpipe of a meat packing plant

Sources of Water Pollution cont’d

Non-point Source

- large or dispersed land areas, e.g., crop fields, streets & lawns, that discharge pollutants into the environment over a large area

• Agriculture

• Municipal Waste

• Industrial Waste

MAIN SOURCES OF WATER POLLUTION

AQUATIC ECOSYSTEMS UNDER THREAT

Coral Reefs

- the most threatened ecosystem in the coastal zone

- greatest threats come from eroded soil

produced by: deforestation

construction

agriculture

poor land management

Wetlands

- under severe human attack

- cut & converted to wood chips

- cut and drained for farmland & aquaculture ponds

- drained & dumped up for housing development

Oceans

- covers > 70% of Earth’s surface

- water evaporates as part of the water cycle

- mix and dilute many human-produced wastes to less harmful levels, if they are not overloaded

- affected by oil pollution

Sustainable Use of Water

• Conservation

• Recycling

• Rainwater harvesting

• Efficient sewage treatment

• Proper solid waste disposal

• Soil conservation

• Population control