unit 9

• Water


  Can exist in three forms - solid, liquid and vapour
• Liquid water mainly exists in parts of the Earth where the temperature lies between 0oC and 100oC
• Water


  • It is a universal solvent - it carries dissolved nutrients into tissues of organisms and flushes waste products out
  • It plays an important role in diluting pollutants
  • It has a high heat capacity which means that it can absorb a great deal of heat without significant temperature change
  • This high heat capacity allows it to have a moderating effect on climate
  • Evaporation of water is an effective cooling process
  • Water expands when it freezes, facilitating the breakup of rocks leading to soil formation
  • Water has a high wetting ability
  • Solid water (ice) has a lower density than liquid water and will float, allowing aquatic life to exist in lakes and streams during winter
• Organisms


  Are made up mostly of water (H2O)
• Percentage of water in organisms

  • Trees are approximately 60% water
  • Animals are approximately 50-65% water
  • Approximately 60% of a human's body weight is water
• Uses of water


  • Domestic use (cooking, drinking, cleaning, bathing, washing etc.)
  • Industrial use (as raw material; washing and cooling)
  • Agricultural use (irrigation - 70% of water used worldwide)
  • Transport (rivers/oceans used as a source of conveying heavy and bulky goods over long distances)
  • Recreation/Tourism (lakes and coastlines are tourist attractions; water sports are becoming increasingly popular)
• Where water is stored

  • Ocean, seas and bays (97% of the earth's water is salty (saline))
  • Ice caps, glaciers and permanent snow (3% of the earth's water is fresh water)
  • Groundwater aquifers
  • Surface water bodies (e.g. rivers, lakes, streams, wetlands)
  • Soil moisture (small amounts)
  • Atmosphere (very small amounts)
  • Living organisms (very small amounts)
• Surface water


  Fresh water found on the Earth's surface in streams and rivers etc.
• Groundwater


  Precipitation that infiltrates the ground and percolates downward through pores, fractures, crevices and other voids in the soil until it reaches a depth where the ground is filled, or saturated, with water
• Saturated zone


  The area that is filled with water
• Water table


  The top of the saturated zone
• Aquifer


  The underground porous layers of rock where groundwater is stored
• Recharge area


  Any area of land through which water passes into an aquifer
• In Jamaica, 84% of the available fresh water comes from groundwater, which is extracted by pumping wells (approx. 500 in Jamaica)
• Watershed


  An area of land that drains water into bodies of surface water
• Functions of watersheds


  • Forested watersheds act as giant sponges increasing infiltration
  • They release water slowly, moderating flooding and maintaining stream flows in dry periods
  • They control soil erosion thereby improving water quality
  • They are habitats for many species
  • They regulate rainfall on a small scale (via transpiration)
• Causes of watershed destruction

  • Unsuitable hillside agricultural practices
  • Deforestation
  • Illegal settlement on hillsides
  • Illegal forest fires
  • Illegal quarrying
• Effects of watershed destruction

  • Decreased tree cover
  • Increased soil erosion
  • Decreased recharging of groundwater
  • Increased siltation of waterways
  • Increased flooding and loss of habitats
• Approximately 1.2 billion people (1/5 of the world's population) live in areas that experience a physical scarcity of water
• By 2025, 1.8 billion people will be living in countries or regions with absolute water scarcity, and two-thirds of the world's population could be living under water stressed conditions
• With the existing climate change scenario, almost half the world's population will be living in areas of high water stress by 2030, including between 75 million and 250 million people in Africa. In addition, water scarcity in some arid and semi-arid places will displace between 24 million and 700 million people
• Sub-Saharan Africa has the largest number of water-stressed countries of any region
• Ways to increase water supply

  • Desalinisation
  • Towing icebergs
  • Cloud seeding
• Water is scarce in some areas not because it is physically unavailable but because its quality has been degraded as a result of pollution
• Categories of water pollutants

  • Sediment
  • Oxygen demanding waste
  • Pathogens (disease-causing agents)
  • Inorganic plant nutrients
  • Synthetic organic compounds
  • Inorganic chemicals
  • Water soluble heavy metals
  • Thermal pollution
• Eutrophication


  The enrichment (over nourishment) of aquatic ecosystems by nutrients
• Characteristics of un-enriched (oligotrophic) water bodies

  • Clear water
  • Support small populations of aquatic organisms
• Characteristics of eutrophic water bodies

  • Cloudy water due to presence of vast numbers of algae and other organisms
  • Supported by the nutrients
• Point source pollution


  Pollutants discharged into the environment through pipes, sewers or ditches from specific sites e.g. factories or sewage treatment plants
• Non-point source pollution


  Land pollutants that enter bodies of water over large areas rather than a single point e.g. agricultural run-off, mining wastes, construction sediments and soil erosion
• Major sources of human-induced water pollution

  • Agriculture (pesticides, fertilizer run-off, animal wastes, plant residues, soil erosion)
  • Municipalities (domestic activities - sewage, run-off from storm sewers, streets, traffic emissions)
  • Industries (different pollutants depending on industry)
• Sustainable water use practices

  • Conservation (including the use of technological devices)
  • Recycling
  • Rainwater harvesting
  • Efficient sewage treatment
  • Proper solid waste disposal
  • Soil conservation
  • Reduce population growth
• Oxygen demanding wastes


  Increase in biological oxygen demand of water which may cause aquatic organisms to suffocate if they are not able to migrate to another location
• If adequate oxygen is available, oxygen demanding substances can be degraded by microorganisms usually present in water. If oxygen becomes depleted, decomposition is limited to what can be done by anaerobic decomposers. Water plants may be killed, and animals may be killed or forced to migrate
• Pathogenic organisms


  Cause disease in humans who drink the water e.g. cholera, botulism, dysentery, hepatitis A, gastroenteritis, fasciolopsiasis
• Most bacteria are well controlled in public drinking water, but certain viruses, especially those that cause hepatitis, still cause human disease. More effective means of removing viruses during purification are needed
• Inorganic chemicals and minerals

  Increase the salinity and acidity of water and render it toxic
• Synthetic organic chemicals


  Can cause birth defects, cancer, neurological damage, and other illness. Because these substances are not biodegradable, chemical or physical means must be used to remove them during waste treatment. Many such substances become magnified (increased in concentration) as they are passed along food chains
• Plant nutrients


  Causes excessive and sometimes uncontrolled growth of aquatic plants, primarily algae. Algae may cover the surface of water bodies blocking out sunlight from benthic plants such as seagrasses and may lead to low oxygen content in the water due to the action of decomposers breaking down the additional algae which requires a lot of oxygen. Decomposing algae also imparts undesirable odours and tastes to drinking water
• Removal of excess phosphates and nitrates from water during waste treatment may be done in quaternary water treatment where nutrient-containing waters are led into a reed pond which will absorb the nitrates and phosphates. This is usually a costly exercise to maintain and is not often done