What you’ll learn17 learning objectivesChoose one objective for a focused lesson, or study the complete topic.4.4.1Water pollution sources• Sewage, agricultural run-off, industrial effluent• Urban run-off, solid waste disposal, oil spillsSyllabus objective4.4.2Plastic debris accumulation• Marine environments• Oceanic gyres, microplastics enter food chainSyllabus objective4.4.3Water quality measurement• Chemical, physical, biological characteristics• Water quality index (WQI)• Parameters: dissolved O₂, pH, temperature, turbidity, nitrates, phosphates, metalsSyllabus objective4.4.4Biochemical oxygen demand (BOD)• Dissolved oxygen required by microorganisms for decomposition• mg O₂ per litre in 5 days at 20°CSyllabus objective4.4.5Eutrophication• Mineral nutrient inputs (nitrates, phosphates)• Excessive phytoplankton growth (algal blooms)Syllabus objective4.4.6Eutrophication sequence• Impacts and changes to aquatic systemSyllabus objective4.4.7Eutrophication and ecosystem services• Eutrophication can substantially impact ecosystem services• Eutrophication can affect services associated with fisheries, recreation, aesthetics and healthSyllabus objective4.4.8Eutrophication management levels• Eutrophication can be addressed at three different levels of management• These three levels of management are:• the reduction of human activities that produce pollutants—e.g., alternatives to current fertilizers and detergents• the reduction of the release of pollution into the environment—e.g., treatment of wastewater to remove nitrates and phosphatesSyllabus objective4.4.9(HL)—Water pollutants• There is a wide range of pollutants that can be found in water• These pollutants may include organic matter (e.g., sewage), dissolved substances (e.g., tributyltin, an endocrine-disrupting chemical), persistent chemicalsSyllabus objective4.4.10(HL)—Harmful algal blooms• Algal blooms may produce toxins that threaten the health of humans and other animals• Harmful algal blooms (HABs) contain a variety of organisms, including cyanobacteria, protists, algae and dinoflagellates• A small number of these organisms produce potentially fatal toxins• In freshwater, cyanotoxins are the most common toxinsSyllabus objective4.4.11(HL)—Anoxic and hypoxic waters• The frequency of anoxic/hypoxic waters is likely to increase due to the combined effects of global warming, freshwater stratification, sewage disposal and eutrophication• Hypoxic conditions can arise from a variety of causes, resulting in aquatic dead zonesSyllabus objective4.4.12(HL)—Sewage treatment stages• Sewage is treated to allow safe release of effluent by primary, secondary and tertiary water treatment stages• Consider: what is achieved in each of the sewage treatment stages, including both biological and chemical processes• Also consider the challenges of implementing sewage treatment equitably in all societiesSyllabus objective4.4.13(HL)—Indicator species• Some species are sensitive to pollutants or are adapted to polluted waters, so these can be used as indicator speciesSyllabus objective4.4.14(HL)—Biotic index• Indirect water quality measure• Based on species tolerance, abundance, diversity• Example: Trent biotic indexSyllabus objective4.4.15(HL)—Water Quality Index (WQI)• Single weighted average of multiple test parameters• Represents contamination degreeSyllabus objective4.4.16(HL)—Water quality guidelines• WHO drinking water quality guidelines• Local government statutory standardsSyllabus objective4.4.17(HL)—Citizen action• Reduce water pollution• Consumption changes, protest, data collection, lobbyingSyllabus objective
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