Algal blooms only occur if phytoplankton growth had previously been limited by lower concentrations of phosphate and/or nitrate. Humans cause eutrophication when releasing detergents, sewage or agricultural fertilizers into water bodies.

Excessive growth of phytoplankton is typically followed by their death and, therefore, high rates of decomposition, rapid consumption of dissolved oxygen leading to hypoxia or anoxia in the water, and death of aquatic life that depends on dissolved oxygen occur.

Application of skills: Create a systems model to show the impacts and changes eutrophication produces in an aquatic system. This model should include examples of positive feedback (for example, increase in nutrients>increase in death of organisms>increase in decomposition>increase in nutrients).

EdPuzzle Videos

These three levels of management are:

• the reduction of human activities that produce pollutants—for example, alternatives to current fertilizers and detergents

• the reduction of the release of pollution into the environment—for example, treatment of wastewater to remove nitrates and phosphates

• the removal of pollutants from the environment and restoration of ecosystems—for example, removal of mud from eutrophic lakes and reintroduction of plant and fish species.

These methods can also apply to other examples of pollution.

The usual measure is milligrams of oxygen consumed per litre of sample in five days at 20°C. BOD provides an indirect measure of the amount of organic matter within a sample.

On Canva create information posters about:

• PCBs (a persistent pollutant)

• Tributyltin (a dissolved substance)

• Plastics

• Heat as a pollutant

Produce a TV news clip about a specific Harmful Algal Bloom event.

Extension: https://youtu.be/Y7tRFdoGS14?si=-AizNLiNIMgTUslF

CAS: Arrange a school visit to a STW

A WQI is a single, weighted average, consisting of the combined results of several individual water quality test parameters, representing the degree of contamination in a given water sample. Vernier’s WQI is one example.

Make sketch notes about the following information:

• The World Health Organization (WHO) provides guidelines for what counts as safe drinking water — for example, limits on bacteria, heavy metals, or nitrates.

• However, it's local governments (like Zambia's Ministry of Health or Costa Rica's water regulator, AyA) that decide the legal standards — these can be stricter or weaker than WHO's guidelines.

• These standards become especially important when:

  • A company wants to extract water, build a bottling plant, or affect local water sources.

  • An Environmental Impact Assessment (EIA) is required.

  • The company is international and might follow different rules in its home country.

The best example of this comes from outside of our case study countries, in the USA.

Nestlé has been extracting millions of gallons of spring water from U.S. sites like California’s Strawberry Creek and bottling it for profit, paying little in return. Critics say this has dried up local ecosystems and accuse Nestlé of exploiting weak regulations, lobbying governments, and cozying up to officials to secure permits—sometimes even influencing environmental rulings. Despite being ordered to stop unauthorized withdrawals, Nestlé has continued under renewed permits. Opponents argue water is a human right, not a commodity, while Nestlé defends its actions as sustainable and community-focused. The broader battle highlights concerns over water privatization and environmental harm.

You can learn about this in case study countries here. 

Activities

• Litter pick in Hyde Park, with story map

• Microplastic netting in Serpentine