Home About Me Chemistry 10 ESS Home IB Chemistry
Topic 4: Water and Aquatic Food Production Systems and Societies

4.1 Introduction to Water Systems
Significant Ideas:
  • The hydrological cycle is a system of water flows and storages that may be disrupted by human activity.
  • The ocean circulatory system (ocean conveyor belt) influences the climate and global distribution of water (matter and energy).
Knowledge & Understanding:
  • Solar radiation drives the hydrological cycle.
  • Fresh water makes up only a small fraction (approximately 2.6% by volume) of the Earth’s water storages.
  • Storages in the hydrological cycle include organisms, soil and various water bodies, including oceans, groundwater (aquifers), lakes, rivers, atmosphere, glaciers and ice caps.
  • Flows in the hydrological cycle include evapotranspiration, sublimation, evaporation, condensation, advection (wind-blown movement), precipitation, melting, freezing, flooding, surface runoff, infiltration, percolation, and stream-flow or currents.
  • Human activities such as agriculture, deforestation and urbanization have a significant impact on surface runoff and infiltration.
  • Ocean circulation systems are driven by differences in temperature and salinity. The resulting difference in water density drives the ocean conveyor belt, which distributes heat around the world, and thus affects climate.
Application & Skills
  • Discuss human impact on the hydrological cycle.
  • Construct and analyse a hydrological cycle diagram.
PPT: 4.1 Intro to Water Systems
National Geographic Video: Why Care about Water?
Interactive Water Cycle
Water Cycle Rap
Calculate your Water Footprint
Interactive Tool Looking At Water Availability and Usage Around the World
Practice Problems: Estimating Water Budgets
Video: Human Impacts on Water Cycle
NASA: Great Ocean Conveyor Belt
4.2 Access to Fresh Water
Significant Ideas:
  • Construct and analyse a hydrological cycle diagram.
  • Freshwater resources can be sustainably managed using a variety of different approaches.
Knowledge & Understanding:
  • Access to an adequate freshwater supply varies widely.
  • Climate change may disrupt rainfall patterns and further affect this access.
  • As populations, irrigation and industrialization increase, the demand for fresh water increases.
  • Freshwater supplies may become limited through contamination and unsustainable abstraction.
  • Water supplies can be enhanced through reservoirs, redistribution, desalination, artificial recharge of aquifers and rainwater harvesting schemes. Water conservation (including grey-water recycling) can help to reduce demand but often requires a change in attitude by the water consumers.
  • The scarcity of water resources can lead to conflict between human populations, particularly where sources are shared.
Application & Skills
  • Evaluate the strategies that can be used to meet an increasing demand for fresh water.
  • Discuss with reference to a case study, how shared freshwater resources have given rise to international conflict.
PPT: 4.2 Access to Freshwater
Documentary: A World Without Water
Interactive: The Hidden Water We Use (National Geographic)
Interactive: Global Water Footprint of Key Crops
Green Facts: Water Resources - Be sure to select level 3 for questions and detail at IB level
UNEP: Vital Water Graphics
BBC: 8 Radical Solutions for the Water Shortage
Water Conflicts Around the World
River Case Studies - Completed by You
Bagmati River - Kaja
Indus River - Baber
Colorado River - Hollys
Kelani River - Ade
Murray River - Jace
Tagus River - Sira
Congo River - Merci
Yellow River - Fyad
Yumuna River - Rohan
Nile River - Michael
Mississippi River - Theo
Han River - Kevin
Teesta/Brahmaputra River - Jazilah
Ganges/Padma River - Saneyha
4.3 Aquatic Food Production Systems
Significant Ideas:
  • Aquatic systems provide a source of food production.
  • Unsustainable use of aquatic ecosystems can lead to environmental degradation and collapse of wild fisheries.
  • Aquaculture provides potential for increased food production.
Knowledge & Understanding:
  • Demand for aquatic food resources continues to increase as human population grows and diet changes.
  • Photosynthesis by phytoplankton supports a highly diverse range of food webs.
  • Aquatic (freshwater and marine) flora and fauna are harvested by humans.
  • The highest rates of productivity are found near coastlines or in shallow seas, where upwellings and nutrient enrichment of surface waters occurs.
  • Harvesting some species, such as seals and whales, can be controversial. Ethical issues arise over biorights, rights of indigenous cultures and international conservation legislation.
  • Developments in fishing equipment and changes to fishing methods have led to dwindling fish stocks and damage to habitats.
  • Unsustainable exploitation of aquatic systems can be mitigated at a variety of levels (international, national, local and individual) through policy, legislation and changes in consumer behaviour.
  • Aquaculture has grown to provide additional food resources and support economic development and is expected to continue to rise.
  • Issues around aquaculture include: loss of habitats, pollution (with feed, antifouling agents, antibiotics and other medicines added to fish pens), spread of diseases and escaped species (some involving genetically modified organisms).
Application & Skills
  • Discuss with reference to a case study, the controversial harvesting of a named species.
  • Evaluate strategies that can be used to avoid.
  • Explain the potential value of aquaculture for providing food for future generations.
  • Discuss a case study that demonstrates the impact of aquaculture.
PPT: 4.3 Aquatic Food Production Systems
PBS Case Studies: Salmon, Blue Fin Tuna & Shrimp Aquafarming
Montery Bay Aquarium: Fishing and Farming Methods
How to Choose Sustainable Fish to Eat
List of Case Studies on Specific Fish Species
Case Study: Fish diversity and fish consumption in Bangladesh
Documentary: The Last Fish
Video: Tragedy of the Comons
Video: Case Study of Canadian Cod Overfishing
4.4 Water Pollution
Significant Ideas:
  • Water pollution, both to groundwater and surface water, is a major global problem, the effects of which influence human and other biological systems.
Knowledge & Understanding:
  • There are a variety of freshwater and marine pollution sources.
  • Types of aquatic pollutants include floating debris, organic material, inorganic plant nutrients (nitrates and phosphates), toxic metals, synthetic compounds, suspended solids, hot water, oil, radioactive pollution, pathogens, light, noise and biological pollutants (invasive species).
  • A wide range of parameters can be used to directly test the quality of aquatic systems, including pH, temperature, suspended solids (turbidity), metals, nitrates and phosphates.
  • Biodegradation of organic material utilizes oxygen, which can lead to anoxic conditions and subsequent anaerobic decomposition, which in turn leads to formation of methane, hydrogen sulfide and ammonia (toxic gases).
  • Biochemical oxygen demand (BOD) is a measure of the amount of dissolved oxygen required to break down the organic material in a given volume of water through aerobic biological activity. BOD is used to indirectly measure the amount of organic matter within a sample.
  • Some species can be indicative of polluted waters and can be used as indicator species.
  • A biotic index indirectly measures pollution by assaying the impact on species within the community according to their tolerance, diversity and relative abundance.
  • Eutrophication can occur when lakes, estuaries and coastal waters receive inputs of nutrients (nitrates and phosphates), which results in an excess growth of plants and phytoplankton.
  • Dead zones in both oceans and fresh water can occur when there is not enough oxygen to support marine life.
  • Application of figure 3 to water pollution management strategies includes: 1- reducing human activities that produce pollutants (for example, alternatives to current fertilizers and detergents) 2- reducing release of pollution into the environment (for example, treatment of waste water to remove nitrates and phosphates) 3- removing pollutants from the environment and restoring ecosystems (for example, removal of mud from eutrophic lakes and reintroduction of plant and fish species).
Application & Skills
  • Analyse water pollution data.
  • Explain the process and impacts of eutrophication.
  • Evaluate the uses of indicator species and biotic indices in measuring aquatic pollution.
  • Evaluate pollution management strategies with respect to water pollution.
PPT: 4.4 Water Pollution
Water Pollution Guide
Video: Water Pollution
National Geographic: Chasing Rivers The Ganges
Procedure for Measuring BOD
Video: Using Biotic Indices
Video: Eutrophication
Eutrophication Song