Syllabus concepts to know

• 4.4.1 Water pollution has multiple sources and has major impacts on marine and freshwater systems.
• 4.4.2 Plastic debris is accumulating in marine environments.
• 4.4.3 Water quality is the measurement of chemical, physical and biological characteristics of water.
• 4.4.4 Biochemical oxygen demand (BOD) is a measure of the amount of dissolved oxygen required by microorganisms to decompose organic material in water.
• 4.4.5 Eutrophication occurs when lakes, estuaries and coastal waters receive inputs of mineral nutrients, especially nitrates and phosphates, often causing excessive growth of phytoplankton.
• 4.4.6 Eutrophication leads to a sequence of impacts and changes to the aquatic system.
• 4.4.7 Eutrophication can substantially impact ecosystem services.
• 4.4.8 Eutrophication can be addressed at three different levels of management.
• 4.4.9 There is a wide range of pollutants that can be found in water.
• 4.4.10 Algal blooms may produce toxins that threaten the health of humans and other animals.
• 4.4.11 The frequency of anoxic/hypoxic waters is likely to increase due to the combined effects of global warming, freshwater stratification, sewage disposal and eutrophication.
• 4.4.12 Sewage is treated to allow safe release of effluent by primary, secondary and tertiary water treatment stages.
• 4.4.13 Some species are sensitive to pollutants or are adapted to polluted waters, so these can be used as indicator species.
• 4.4.14 A biotic index can provide an indirect measure of water quality based on the tolerance to pollution, relative abundance and diversity of species in the community.
• 4.4.15 Overall water quality can be assessed by calculating a water quality index (WQI).
• 4.4.16 Drinking water quality guidelines have been set by the World Health Organization (WHO), and local governments can set statutory standards.
• 4.4.17 Action by individuals or groups of citizens can help to reduce water pollution.