Topic 4: Water

• Solar radiation and gravity • Heat for evaporation, gravity for drainage

• System with stores and flows • Stores: boxes; flows: arrows

• Oceans (96.5%), glaciers/ice caps (1.7%), groundwater (1.7%) • Surface freshwater (0.02%), atmosphere (0.001%), organisms (0.0001%)

• Transpiration, sublimation, evaporation, condensation, advection, precipitation • Melting, freezing, run-off, infiltration, percolation, streamflow, groundwater flow

• Agriculture, deforestation, urbanization alter flows and stores • Reduced evapotranspiration, increased run-off → flash floods

• Flow diagrams of inputs and outputs • Calculate sustainable harvesting rates

• Polarity, cohesion, adhesion, solvent properties • Transparency, high specific heat capacity • Density variations with temperature • Gas solubility variations

• Absorb atmospheric CO₂ and sequester it • Moderates atmospheric CO₂ increases • Saturation point may be reached

• Short-term: dissolved CO₂ → ocean acidification • Long-term: biomass accumulates on seabed → fossil fuels

• Cold water below, warmer above • Density differences restrict mixing → stratification • Water densest at 4°C → freezing from surface down

• Occurs in deeper lakes, coastal areas, seas, ocean • Thermocline: transition layer between warm surface and cold deep water • Differences in dissolved oxygen and mineral nutrients

• Global warming and salinity changes • Most pronounced in upper 200m

• Bring cold, nutrient-rich waters to surface • Mass vertical movement from depths • Seasonal cycles in stratified lakes and ENSO

• Driven by temperature and salinity differences • Ocean conveyor belt distributes heat globally • Affects climate

4.2.1Water security definition

• Access to sufficient safe drinking water • Component of sustainable societies

4.2.2Factors affecting water availability

• Social, cultural, economic, political factors • Impact availability and equitable access

4.2.3Water supply increase needs

• Population growth or economic development • Uses: domestic, irrigation, livestock, industry

4.2.4Increasing water supplies

• Dams, reservoirs, rainwater catchment, desalination plants • Natural wetland enhancement

4.2.5Water scarcity types

• Physical scarcity: limited abundance • Economic scarcity: limited storage/transport systems

4.2.6Domestic water conservation

• Metering, rationing, grey-water recycling • Low-flush toilets, rainwater harvesting

4.2.7Industrial water conservation

• Food production systems • Greenhouses, aquaponics, drip irrigation, drought-resistant crops

4.2.8Water scarcity mitigation strategies

• Country-specific management strategies

4.2.9(HL)—Freshwater planetary boundary

• Increasing demand causing water stress • Risk of abrupt/irreversible hydrological system changes

4.2.10(HL)—Governance for sustainability

• Local and global governance needed • Examples: local regulations, international agreements

4.2.11(HL)—Water footprints

• Measure of water use by individuals/nations/products • Informs decision-making about water security

4.2.12(HL)—Citizen science role

• Monitoring and managing water resources

4.2.13(HL)—Water stress definition

• Considers scarcity, quality, environmental flows, accessibility

4.2.14(HL)—Water stress threshold

• < 1,700 m³ per year per capita

4.2.15(HL)—Water stress causes

• Depend on socio-economic context

4.2.16(HL)—Transboundary disputes

• Water sources crossing regional boundaries

4.2.17(HL)—Industrial-level water stress solutions

• Dams, pipelines, desalination, water treatment plants • Aquifer storage and recovery (ASR)

4.2.18(HL)—Freshwater production impacts

• Negative environmental impacts • Brine discharges, noise, air pollution, aquifer impacts

4.2.19(HL)—Inequitable access impacts

• Negatively impacts health and sustainable development • Affects marginalized groups

• Phytoplankton: microscopic photosynthetic plankton • Macrophytes: visible aquatic plants

• Organisms from freshwater and marine environments

• Human population growth, dietary preference changes

• Bottom trawling, ghost fishing, poisons, explosives

• Dramatic, lasting stock decrease • Example: Newfoundland cod

• Highest annual catch sustainable over time • Used to set fishing quotas

• Ocean acidification • May cause population collapse in aquatic ecosystems • Example: coral bleaching

• Policy legislation for fishing industry • Consumer behaviour changes • Permits, quotas, seasons, mesh size, zones, labelling

• Support food chains, maintain sustainable yields • Provide shelter and spawning grounds

• Farming of aquatic organisms • Expanding for food supply and economic development • Impacts: habitat loss, pollution, disease spread, escapees

• Productivity, thermal stratification, nutrient mixing/loading • Highest productivity near coastlines and shallow seas

• Required for conservation and sustainable use • Monitoring harvest rates

• Estimated value, inevitably inaccurate • Exceeding rate → positive feedback → rapid decline

• Requires cooperation: governments, industry, consumers, NGOs • Measures: fishing bans, license limits, bycatch prevention

• Exclusive economic zone: 370 km from coast • High seas (60% of ocean): limited regulation • Equity issues when countries sell fishing access

• Seals, whales, dolphins • Animal rights vs. indigenous group rights

• Sewage, agricultural run-off, industrial effluent • Urban run-off, solid waste disposal, oil spills

• Marine environments • Oceanic gyres, microplastics enter food chain

• Chemical, physical, biological characteristics • Water quality index (WQI) • Parameters: dissolved O₂, pH, temperature, turbidity, nitrates, phosphates, metals

• Dissolved oxygen required by microorganisms for decomposition • mg O₂ per litre in 5 days at 20°C

• Mineral nutrient inputs (nitrates, phosphates) • Excessive phytoplankton growth (algal blooms)

• Impacts and changes to aquatic system

• Eutrophication can substantially impact ecosystem services • Eutrophication can affect services associated with fisheries, recreation, aesthetics and health

• 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 phosphates

• 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 chemicals

• 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 toxins

• 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 zones

• 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 societies

• Some species are sensitive to pollutants or are adapted to polluted waters, so these can be used as indicator species

• Indirect water quality measure • Based on species tolerance, abundance, diversity • Example: Trent biotic index

• Single weighted average of multiple test parameters • Represents contamination degree

• WHO drinking water quality guidelines • Local government statutory standards

• Reduce water pollution • Consumption changes, protest, data collection, lobbying