Topic 4 Water

At the end of this subtopic 4.1 you should understand:

• Movements of water in the hydrosphere are driven by solar radiation and gravity. (4.1.1)

• The global hydrological cycle operates as a system with stores and flows.(4.1.2)

• The main stores in the hydrological cycle are the oceans (96.5%), glaciers and ice caps (1.7%),groundwater (1.7%), surface freshwater (0.02%), atmosphere (0.001%), organisms (0.0001%). (4.1.3)

• Flows in the hydrological cycle include transpiration, sublimation, evaporation, condensation, advection, precipitation, melting, freezing, surface run-off, infiltration, percolation, streamflow and groundwater flow. (4.1.4)

• The steady state of any water body can be demonstrated through flow diagrams of inputs and outputs. (4.1.6) 

• Human activities, such as agriculture, deforestation and urbanization, can alter these flows and stores. (4.1.5)

• Water has unique physical and chemical properties that support and sustain life. (4.1.7)

At the end of this subtopic 4.2 you should understand:

• Water security is having access to sufficient amounts of safe drinking water. (4.2.1)

• Social, cultural, economic and political factors all have an impact on the availability of, and equitable access to, the freshwater required for human well-being. (4.2.2) 

• Water scarcity refers to the limited availability of water to human societies. (4.2.5) 

• Mitigation strategies exist to address water scarcity. (4.2.8)

• Human societies undergoing population growth or economic development must increase the supply of water or the efficiency of its utilisation. (4.2.3)

• Water supplies can be increased by constructing dams, reservoirs, rainwater catchment systems, desalination plants and enhancement of natural wetlands. (4.2.4)

• Water conservation techniques can be applied at a domestic level. (4.2.6)

• Water conservation strategies can be applied at an industrial level in food production systems. (4.2.7)

At the end of this subtopic 4.3 you should understand:

• Phytoplankton and macrophytes provide energy for freshwater and marine food webs. (4.3.1)

• Humans consume organisms from freshwater and marine environments. (4.3.2)

• Demand for foods from freshwater and marine environments is increasing due to the growth in human population and changes in dietary preferences. (4.3.3)

• The maximum sustainable yield (MSY) is the highest possible annual catch that can be sustained over time, so it should be used to set caps on fishing quotas. (4.3.6)

• The increasing global demand for seafood has encouraged use of unsustainable harvesting practices and overexploitation. (4.3.4)

• Overexploitation has led to the collapse of fisheries. (4.3.5)

• Climate change and ocean acidification are having impacts on ecosystems and may cause collapse of some populations in freshwater or marine ecosystems. (4.3.7)

• Unsustainable exploitation of freshwater and marine ecosystems can be mitigated through policy legislation addressing the fishing industry and changes in consumer behaviour. (4.3.8)

• Marine protected areas (MPAs) can be used to support aquatic food chains and maintain sustainable yields. (4.3.9)

• Aquaculture is the farming of aquatic organisms, including fish, molluscs, crustaceans and aquatic plants. The industry is expanding to increase food supplies and support economic development, but there are associated environmental impacts. (4.3.10)

At the end of this subtopic 4.4 you should understand:

• Water quality is the measurement of chemical, physical and biological characteristics of water. Water quality is variable and is often measured using a water quality index. Monitoring water quality can inform management strategies for reducing water pollution. (4.4.3)

• Biochemical oxygen demand (BOD) is a measure of the amount of dissolved oxygen required by microorganisms to decompose organic material in water. (4.4.4)

• Water pollution has multiple sources and has major impacts on marine and freshwater systems. (4.4.1)

• Plastic debris is accumulating in marine environments. Management is needed to remove plastics from the supply chain and to clear up existing pollution. (4.4.2)

• Eutrophication occurs when lakes, estuaries and coastal waters receive inputs of mineral nutrients, especially nitrates and phosphates, often causing excessive growth of phytoplankton. (4.4.5)

• Eutrophication leads to a sequence of impacts and changes to the aquatic system.(4.4.6)

• Eutrophication can substantially impact ecosystem services. (4.4.7)

• Eutrophication can be addressed at three different levels of management. (4.4.8)