Theme 3: Human Impacts on Catchments

Topic: Algal Blooms

What is an algal bloom?

Algae are present in creeks, rivers and wetlands at all times. However, when the environmental conditions for the algae become optimal, the algae grows rapidly and blooms form on the water's surface. Freshwater algal blooms range in colour from dark green, to yellow, or blue-green in colour and look like scum on the surface of the water.

Marine or estuarine blooms are called 'red tides'. These are a red-brown colour. Not all algal blooms are harmful.

What causes a bloom?

Algal blooms are believed to be caused by three main factors:

• stagnant or slow flowing water
• high levels of nutrients, and
• the weather being sunny and hot for long periods.

High levels of nutrients

Most freshwater systems require some level of phosphorus in the water to enable plants to grow. This includes algae. However, major increases in the amount of phosphorus entering the river or creek can cause rapid increases in algal growth rates that can lead to an algal bloom forming. Phosphorus is contained in many products such as fertilisers, detergents, faeces and even winery wastes. They are able to enter the water through stormwater, land runoff or are directly disposed of into the river.

Stagnant or slow flowing water

During summer, periods of limited rainfall, or when river flows are reduced, conditions are ideal for algal blooms to form. This commonly occurs in wetlands, or dams or regulated rivers. Algae do not like fast flowing or turbulent water as they are not able to maintain their position at the water's surface. Flowing water also helps to stop water becoming stratified, allowing a warm layer of water to form at the water's surface, which provides ideal conditions for the algae to grow. Algae like to live near the water's surface so that they can receive as much sunlight as possible to help them to grow.

Types of algal blooms

There are several types of algal blooms.

Two of the main types are:

• Blue-green algal blooms - Blue-green algal blooms are a major national problem. Blue green algae are not actually algae at all. They are a form of bacteria that rely on the sunlight for energy. Blue-green algae are present in almost all aquatic ecosystems, including creeks, rivers and wetlands. Blue-green algal blooms are a result of excessive nutrients (especially phosphorus) becoming available in the water body, as well as increased sunlight and slow moving water. The bloom ranges in colour from dark green to yellowish brown. As they dry out around the water's edge, a blue pigment can also been seen and it can appear like dried-out paint.
• Red tides - Red tides rarely occur in Australia, but have been know to occur in the Port River in the Torrens Catchment. Red tides occur when tiny marine algae cells called dinoflagellates receive just the right conditions to grow. Dinoflagellates populations grow fast in the right conditions to form a bloom which turns bodies of water red, brown or even luminous at night. Excessive levels of nutrients from industries, entering the estuary or ocean via stormwater, can cause red tides to occur. Red tides can be quite dangerous as they use up available oxygen in salty water. They also produce toxins which are ingested by shellfish and can then be eaten by humans. These toxins are very poisonous to humans.

Impacts of algal blooms

Algal blooms have many impacts on the ecosystem.

In the fresh water environment, algal blooms can cause the following threats:

• To recreation and tourism - Algal blooms often lead to the closure of local waterways for swimming, fishing and boating. They can cause major fish deaths and reduce the agricultural and tourism of the affected area. It has been estimated that algal blooms cost Australia $150 million a year.
• To human and livestock health - Toxins produced by the algae make drinking water dangerous for humans and animals. They can also cause unpleasant odours and tastes in the water that make recreational activities such as swimming, boating or fishing impossible. Water that becomes affected by a bloom is also unsuitable for agricultural use.
• To water supply - When blooms form in drinking water storages, such as reservoirs or dams, they can cause serious problems for drinking water suppliers. Some species of blue-green algae produce chemicals that cause musty or earthy tastes and odours in the drinking water. Removing these chemicals requires extensive treatment and, in severe cases, the water becomes undrinkable. Other species of blue-green algae can also produce toxins that are very dangerous to humans and animals if they are consumed, inhaled or even touch the skin.

Red tides have two main impacts:

• Reducing the amount of oxygen in the water - This can suffocate organisms living in the water causing them to die.
• Shellfish poisoning - During red tide events shellfish continue to feed on the toxic algae. The algae do not affect the health of the shellfish. However some of these shellfish are consumed by humans and can cause severe illness, even death. There are three types of shellfish poisoning, each having differing effects from short term memory loss to diarrhea to cramps or even death. Luckily, shellfish poisoning is rare in Australia. However, overseas countries are not so lucky with more than 100 deaths and nearly 1500 cases of poisoning being reported every year.

Student Activity Ideas

• Students to conduct an audit of their homes to discover how many products they have at home contain phosphate. How do they dispose of these at home?
• Making algae bloom - See if you can grow algae in a container on a window sill in your classroom. Add different nutrients to see what happens. Look at the growth rates over a few weeks.
• Collect some algae from your local creek. Use microscopes to see what structure it has.
• Students can research algal blooms in SA, including when they occurred. What effects did they have on the environment?

Enquiry Learning

• What factors lead to algal blooms?
• How do changed flow conditions in waterways, combined with nutrient pollution loads, establish the conditions in which algal blooms can occur?
• How has the deterioration of natural ecosystems exacerbated the problem?
• What do algal blooms tell us about the overall health of a catchment?

Internet Resources

Type	Description	Resources Covering the Topic
Easy	Algal bloom water facts. A comprehensive site with photos and succinct descriptions of the important issues.	Water and Rivers Commission WA www.wrc.wa.gov.au/public/ waterfacts/6_algal_blooms/ index.html
	Facts about blue green algae.	Water Resources in South Australia: Regional Net www.regional.net.au/water/infor/ algae/default.htm
	Toxic algal blooms. Thorough review of the main issues.	Australian Academy of Science www.science.org.au/nova/017/ 017key.htm
More Comprehensive	Explains different types of algal blooms in marine, estuarine and freshwater ecosystems.	CSIRO www.csiro.au/index.asp?type=faq&id=AlgalBlooms

Activities

Band	Activity	Contact
Early Years	Algal Bloom. Student activity worksheet.	Onkaparinga Catchment Water Management Board www.onkaparinga.net/education/ downloads/folder_3/10a_slime.pdf

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