4.4 Water pollution

• 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