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Wetlands
Algae & Algal Blooms found in NSW Wetlands
Introduction
What Are
Algae?
Growth
Forms of Algae
Types of
Algae
Green Algae
Diatoms
Euglenoids
Blue-Green
Algae
Blue-Green
Algal Blooms
Problems
associated with Blue-Green Algae
Causes of Blooms
Management
Responses
Other
Prolific Algal Growth
Healthy
Situations
A Key to
Blooms
What do you do
if you believe you have a bloom?
References
& Further Reading
Introduction
Algae are generally microscopic organisms. They live in a wide range of aquatic environments and are a natural component of most aquatic ecosystems. The types of algae and algal blooms that you may encounter in the wetlands of NSW are described in the following pages. Details of management responses and a key to blooms are also provided.
What Are Algae?
There is no easy definition of an alga. Algae are generally thought of as simple aquatic plants which do not have roots, stems or leaves and have primitive methods of reproduction. However some algae display primitive animal features such as motility, while blue-green algae differ markedly from plants and all other algae, in that they have a cellular structure and function that is more common to bacteria than to the plant kingdom. Additionally, algae grow in almost every habitat imaginable, and while many do live in water, a great many are also terrestrial, living in soil, snow, or in association with other organisms, especially fungi (as lichens), and animals. Aquatic algae are found in both fresh and marine waters. They range in size from large kelps (metres in length) to those visible only under a microscope1.
Growth Forms of Algae
Algae vary considerably in size, shape, and growth form.
Depending on species, they can be:
- Single celled;
- Many celled - either colonially or as filaments of cells; or
- Elaborate plant bodies with differentiated cell types
Growth form in many ways determines the habitat preference of an algal species. Main habitat preferences are:
- Free floating in the water column (planktonic). These comprise the microscopic unicellular algae and colonial and filamentous algae, known as "phytoplankton".
- Growing as a film on rocks on the bottom (benthic) or on plants growing in the water (epiphytic). These may be single celled or small colonial and filamentous species.
- Growing out into the water column but attached to a substrate at one point. These comprise the larger filamentous algae, and macroalgae (eg. seaweeds).1
Types of Algae
The main groups of algae found in Australian freshwater are the:
- Green algae (Chlorophyceae)
- Diatoms (Bacillariophyceae)
- Euglenoids (Euglenineae)
- Blue-green algae (Cyanophyceae)
However there are also other less common groups of algae that do occur in freshwaters as well.2
Green Algae
Green algae range in size from microscopic to large plants, and can be single celled, colonial, or filamentous. Some of the single celled and colonial green algae have small tails or "flagella" attached to each cell, which they use to swim with. However many green algae are non-motile. Green algae may be either planktonic or attached. They show the greatest diversity of shapes, sizes and species of any group of freshwater algae. Green chloroplasts are frequently observable within the cells of green algae when looked at under a microscope. Other structures within the cell may also be seen at times, especially starch granules which stain dark with a preservative know as Lugols iodine solution.1
What do Green Algae look like?
Figure 1. The filamentous green alga Cladophora in a creek. Photo taken by Simon Mitrovic.
Diatoms
Most freshwater diatoms are microscopic, and the most marked distinguishing feature of diatoms under a microscope is that they have thick outer cell walls composed of silica. They have green, yellow, or brownish coloured chloroplasts. All are non-flagellated, meaning that they are unable to swim. They may be planktonic, although many are benthic or grow on other submerged objects. Many are single celled, although some are colonial or filamentous.
There are two main forms of diatoms - centric and pennate. Centric diatoms appear circular, pennate diatoms are long and narrow. The siliceous cell walls are composed of two overlapping halves, with a central girdle band between them. The siliceous cell walls are often decorated by small holes, forming patterns. Many pennate diatoms also have an opening (raphe) running down one side of them.1
What do the Diatoms look like?
Figure 2. Cyclotella at 20x magnification. Photo taken by Justine Moore.
Figure 3. Navicula at 20x magnification. Photo taken by Justine Moore.
Euglenoids
Euglenoids are microscopic unicellular planktonic algae that are motile. They swim with the aid of one, or sometimes two, emergent flagella. Euglenoids generally appear green under the microscope, although some have a hard external covering (lorica) which makes them appear brown or black. The cell wall of euglenoids is composed of overlapping ) spiral layers that wind around the cell. Some internal structure is sometimes visible within the cell, when observed under a microscope. The flagella emerge from a canal at the anterior (front) end of the cell, or from a pore in the lorica. Many euglenoids can change their shape, from cigar shaped to circular, and withdraw their flagella, under the bright light of a microscope. They can also move in a gliding manner once they have done this.1
What do the Euglenoids look like?
Figure 4. Trachlemonas. Photo taken by Justine Moore.
Figure 5. Euglena. Photo taken by Justine Moore.
Blue-Green Algae
Blue-green algae or Cyanobacteria are microscopic cells that grow naturally in Australian fresh and salt waters. They are a type of bacteria, but in some ways act like plants by using sunlight to manufacture carbohydrates from carbon dioxide and water, a process know as photosynthesis. In doing do, they release oxygen. They grow in dams, rivers, creeks, reservoirs, lakes and even hot springs.1
What do Blue-Green Algae Look Like?
Blue-green algal cells are microscopic and are grouped in colonies and chains. Two examples of blue-green algae as they appear under a microscope are given below.
Figure 6. The blue-green alga Anabaena at 400X magnification. The larger cells in the chains are heterocysts that fix nitrogen. Photo taken by Simon Mitrovic.
Figure 7. The blue-green alga Microcystis in large colonies of cells at 400X magnification. Photo taken by Sean Hardiman.
Blue-Green Algal Blooms
When blue-green algae bloom, that is, grow to large numbers, they can form thick accumulations on the surface of the water. These accumulations are commonly known as scums. Blue-green algal scums form when large numbers of the algae float to the water surface using vesicles within their cells that they inflate with gas. Coming close to the surface enables them to gain maximum sunlight. Wind pushes the floating algae across the water, concentrating scums against leeward shores. Scums can vary from small dots (blue-green algal colonies) resembling green dust floating on the water at the beginning of a bloom, to thick paint-like accumulations on the surface during the height of a bloom. Blooms are often green or blue-green but can also be white, brown, blue, yellow-brown or red. Swirling patterns of a mixture of these colours in scums can be caused by wind movement, bleaching by sunlight, and other blooming algae.2
Blue-green algal blooms were recorded by explorers of the Murray-Darling Basin as early as last century. While the problem is not new, it has increased in recent times because of our land and water management practices and seasonal droughts.1
Blue-green algal blooms happen when growth conditions are favourable. These conditions include high nutrient levels, low flows in rivers, low wind and high temperatures. There was a severe blue-green algal bloom over 1000 km long in the Barwon-Darling River system in October and November of 1991. This bloom impacted greatly on water supplies, agriculture, fish and aquatic animals, tourism and recreation.2
Figure 8: Part of a blue-green algal bloom in the Barwon-Darling River system in NSW during November 1991. This section at Bourke is near where the bloom first developed (Lee Bowling).2
Problems associated with Blue-Green Algae
Odours & Tastes
Blue-green algae can cause unpleasant odours and tastes in water and they can also clog filters and cause large fluctuations in pH. Such problems increase the cost of operating water treatment plants. The poor aesthetics of the scums and the smells produced during a blue-green algal bloom affect recreation and tourism.2
Toxins
While blue-green algal blooms can cause water quality problems such as a deterioration in taste and odour, filter clogging, and deoxygenation associated with their decomposition, the main cause of concern is the ability of some to produce highly potent toxins.1
There are four different forms of toxins that can be produced:
Hepatotoxins
These attack the liver and other internal organs of the poisoned victim. Some have also been identified as cancer promoting substances.1
Neurotoxins
These act as neuromuscular blocking agents, leading to respiratory arrest. The main neurotoxins found in Australian blue-green algae are the same as those produced by marine dinoflagellates and which cause paralytic shellfish poisoning in humans.1
Endotoxins (Lipopolysaccharides)
These are contact irritants, and can cause severe dermatitis and conjunctivitis in people coming into contact with the algae through swimming or showering. They may also cause stomach cramps, nausea, fever and headaches if consumed. Their presence in aerosols can cause asthma. Some are also thought to be possible tumour promoters, although this has yet to be shown.1
Non-specific toxins
These are relatively slow acting general toxins which progressively damage most organs, including the liver.
In Australia no recorded human deaths have been attributed to blue-green algal toxins. However, many stock deaths have been documented. The toxins produced can persist in water for weeks. The toxins can also be concentrated by shellfish, which poses a potential health risk if they are consumed.1
Species from the following genera of blue-green algae have been shown to be either hepatotoxic or neurotoxic in Australia
- Microcystis
- Anabaena
- Cylindrospermopsis
- Nostoc
- Nodularia
- Aphanizomenon
- Trichodesmium
Most of these blue-green algae occur in freshwaters. Nodularia is more common in brackish waters, while Trichodesmium is a marine blue-green alga.
There have also been unconfirmed reports of possibly toxic Oscillatoria or Planktothrix in aquaculture.1
Not all blue-green algal species are toxic, and even different strains of the same species may differ, with some being highly toxic and others non-toxic. Even a single bloom may be toxic at some times and non-toxic at others (or have toxicity too low to be detected). Variation in toxicity may result from differing strains of blue-green algae being present at different times during the period of the bloom, or blue-green algae may possibly be able to vary toxin production over time, or depending on their physiological condition. The reasons why blue-green algae produce toxins, and the environmental and physiological conditions that stimulate toxin production are pooly understood.
All blue-green algae however, contain lipopolysaccharides, which act as contact irritants, as these are an integral constituent of the cell walls of all blue-green algae. Even if the other more potent blue-green algal toxins are not present, the presence of these contact irritants may make the water unsuitable for body contact or recreation if the blue-green algae are present in bloom proportions.1
A number of other blue-green algae have been shown to be toxic overseas, but not yet so in Australia. Therefore these too should be treated with caution when present in bloom proportions. They include, Anabaenopsis, Phormidium and Pseudanabaena.1
The four main toxic blue-green algae in Australia are Anabaena, Microcystis, Cylindrospermopsis and Nodularia. Anabaena and Microcystis are the two main bloom forming genera in NSW waters.1
Anabaena circinalis was the main bloom forming algae in the famous Barwon-Darling blooms of 1991. Anabaena forms long chains of cells, called a trichome, which sometimes grows in a spiral, depending on the species.1
Microsystis aeruginosa is most common in lakes and reservoirs. It forms irregularly shaped colonies of cells up to 1 to 2 mm wide that can be visible to the naked eye. Microsystis blooms can be quite persistent lasting for months, or even years in some cases.1
Nodularia often forms thinner scums than those of Anabaena and Microcystis blooms. Nodularia, like Anabaena, forms chains of cells or trichomes. Although it occurs in fresh waters, it is more common in brackish waters, and causes real problems in Lake Alexandrina and the lower Murray River in South Australia, and in the Gippsland lakes in Victoria.1
Cylindrospermposis is commonly thought of a subtropical blue-green algae, but it also occurs in more temperate regions during the summer, including parts of New South Wales. It has very tiny cells that form chains or trichomes. It is a freshwater species, and causes problems in town water supply systems in Queensland due to its highly potent toxins.1
Causes of Blooms
Blue-green algal blooms are a natural phenomena and while it is not exactly clear what triggers a bloom, excess nutrients certainly can increase the intensity of blooms (ie. greater number of algae). The natural nutrient load of a water body is increased with human sources of nutrients such as fertilisers and sewage.2
One of the most important factors triggering blue-green algal blooms appears to be a lack of mixing of surface and deeper water layers in a river or reservoir. In lakes and reservoirs mixing is mainly controlled by wind and temperature. Through the summer months, and during periods of hot weather, ambient temperatures increase and if winds die down, the surface waters heat up. This can result in two distinct layers of water (thermal stratification), a warmer top layer and cooler bottom layer which do not mix. In rivers, mixing is mainly caused by flow. Flows from headwaters can decrease or stop during drought conditions allowing thermal stratification to develop. Weirs and extraction of water for irrigation and stock watering also reduce flow in rivers.2
Figure 9: Weirs reduce the flow and hence mixing of water thus allowing the river to act as a series of pools under low flow conditions. Thermal stratification can then occur, providing conditions conducive to a blue-green algal bloom (Simon Mitrovic).
Many algae rely on mixing to move them toward surface waters to gain light for photosynthesis, hence growth. Under stratified conditions, mixing of water is minimised and these algae may sink lower in the water column and away from the light. Some blue-green algae have the ability to regulate buoyancy, and can float to the surface under these conditions having access to all the light in the top waters (photic region) and nutrients in the top and bottom waters. This allows the algae to flourish and bloom. Some other algae such as euglenoids are motile and can swim to the photic region under these conditions.2
Many other factors play a role in the dominance and ecology of blue-green algal species such as temperature, salinity, zooplankton grazing, pH and turbidity.2
Management Responses
Ways of Controlling Blooms
Once a blue-green algal bloom occurs, very little can be done to stop it. Unfortunately, there is no easy way of detecting if a bloom is toxic. The only way is to take samples. These samples should then be sent to a laboratory for examination under a microscope. If the sample has been taken correctly, this will give information on what type of algae is present, and the cell density at which it is present within the sample. Additional samples can be sent to test for the presence of hepatotoxins or neurotoxins, either by chemical analyses, or by mouse bioassays. Frequent testing to see if the bloom is toxic can help in the management of water use. If the bloom is toxic, alternative water supplies must be found for stock watering and domestic uses.2
Toxins in water infested with a bloom can be removed in water treatment plants by powdered activated carbon (PAC) or granular activated carbon (GAC), but both can be very expensive. PAC is generally used in water treatment plants when the problem is infrequent and is of short duration, and GAC for frequent and more persistent occurrences. If a bloom that is not toxic is used for stock watering, frequent testing must be done to ensure the bloom does not become toxic. Toxicity testing is expensive and it can take several days for a result to be confirmed.2 It is recommended that the Department of Land and Water Conservation is consulted prior to the application of any treatment.
Flushing rivers with large quantities of water can disperse blooms and remove stratification. This is rarely an option, as there is often a lack of water in headwaters as blooms often grow in dry periods. Unless sufficient water is released, the result may be to just move the problem downstream.2
The most practical way of controlling blooms is to prevent them. Stratification in a water body can be stopped or reduced by several means. In rivers, maintaining a sufficient flow of water will keep the water mixed and prevent stratification. This is only viable if the water volume in headwaters is sufficient, and it may not be practical or possible in times of drought. In fact, it is during droughts that blooms would have occurred naturally in our inland waters before European settlement. Stratification in lakes and reservoirs can be mechanically prevented using artificial de-stratifiers. The use of air bubblers placed at the bottom of a reservoir, can prevent stratification. These can be effective if installed and used appropriately. Reducing the amount of phosphorous entering waterways through the application of catchment management activities may also decrease the severity of blue-green algal blooms in the long-term. To be most effective, a combination of methods, including catchment management, in-storage management, and water treatment management, may be the best and ultimately the cheapest way of controlling blue-green algal blooms.2
Algal Alert Levels
Because of the toxic nature of a number of commonly occurring blue-green algae, guidelines for their presence in waters have been set.2
There are three algal alert levels.
- Low.
500 cells per mL to 2,000 cells per mL.
These numbers are typical of non-bloom conditions in nutrient enriched waters. The water should be free of visible colour, but some blue-greens may impart tastes and odours to the water.1
- Medium.
2,000 to 15,000 cells per mL. These cell numbers tend to indicate that blue-green algae are multiplying. The water may exhibit a green tinge, and musty or organic tastes and odours. Scums may form at cell numbers exceeding 5,000 cells per mL. Alternative drinking water supplies or water treatment must be considered.1
- High.
> 15,000 cells per mL. These numbers represent bloom conditions. The water should be distinctively green and have a strong musty or organically polluted taste and odour. Toxicity must be presumed and the water considered unsafe for human consumption and contact, and unsafe for stock water supply. Scums are most likely present.1
These Algal Alert Levels are applied to all water bodies (drinking and recreational) in NSW. They vary depending on the type of water use.
Warning signs are usually erected at recreational venues such as dams, lakes and rivers if toxic blue-green algae are present. Warnings are also issued through the local media.
Other Prolific Algal Growth
Other algae, such as the flagellated green algae and the euglenoids also bloom and may form scums. Other algal blooms will discolour the water without forming surface scums.2 For example, diatom, dinoflagellate or yellow-brown algal blooms would appear brownish; while green algal, blue-green algal or euglenoid blooms may make it appear greenish. Some cryptomonad and other algal blooms appear brick reddish.1
Some free-floating aquatic plants are sometimes also wrongly confused with blue-green algal blooms.2
Figures 10a to d show some of the types of scums and plant growth found in Australian waters.
Figure 10a shows the scum of organic debris and some algae near Nyngan
(Simon Mitrovic).
Figure 10b shows a Euglena bloom in the Bogan River (Simon
Mitrovic).
Figure 10c excessive growth of the green alga Chara in a creek
(Bruce Cooper).
|
Figure 10d the green alga Cladophora in a creek (Simon Mitrovic).
Identification of the algal species causing a bloom or scum (blue-green algae or otherwise) requires looking at the organism under a microscope. However a simple key can be used to determine those scums which are potentially dangerous and where professional advice needs to be sought. This is essential so that measures can be taken to safeguard water for drinking, domestic and stock watering uses.2
Healthy Situations
Figure 11. An example of a healthy mix of aquatic plants. The large round leaf is Nymphoides, the medium sized leaves are Ludwigia and the small plants are floating duckweeds. Photograph is taken at Toonumbar Reservoir by Peter Bek.
Figure 12. Another example of a healthy situation. Winter sunset over the Darling River at Rose Isle with no algal blooms visible. Photograph taken by Simon Mitrovic.
Key to Blooms
To help in the identification of scums, a simple key can be used. Follow the steps using the pictures to find if the scum is possibly caused by a blue-green alga, another alga or by an aquatic plant. It is necessary to go to the surface of the scum to do some simple tests. However do not touch the scum with your bare hands, because of the possibility of the presence of toxins or contact irritants.2
How to use the key
When using a dichotomous key make a choice based on the characters involved, then move to the number indicated at the end of that choice. When no numbers are left and a name to the scum is given, you have identified the scum, provided the correct choices were made.2
Start
1. Use a stick to break the scum surface where present and look at the texture. If the scum is composed of many small free-floating plants with or without roots, floating attached plants with roots or algae similar to a flowering plant. Go to 2.
1a. Bloom otherwise. Go to 6.
2. Plant fern like, free floating with roots. Azolla (Figure 13 and 14).
Figure 13.
Figure 14.2b. Plant / algae otherwise. Go to 3.
3. Algae superficially like plant: roots absent and has whorled branches. Go to 4.
3b. Free-floating plant with or without hair like roots. Go to 5.
4. Algae grey-green and secondary branches without whorls of branches. A stonewort (Characeae) of the genus Chara (Muskgrass). Figure 15.
Figure 15.4b. Algae greener in colour and secondary branches with whorls of branches. A stonewort (Characeae) of the genus Nitella. Figure 15.
5. Free-floating plant with or without hair-like roots. Plant small, less than 2 cm long. A Duckweed being the genera Lemna, Wolffia, or Spirodela (Figure 16). The small leaved Wolffia does not have roots but is a small plant c. 1 mm in diameter.
Figure 16.5b. Free-floating and differentiated into leaves and stem but not radially symmetrical up to 5 cm in diameter with no roots present. Liverwort (Bryophyte); Riccia or Ricciocarpus. (Figures 17 & 18).
Figure 17.
Figure 18.6. Scum composed of strands (filaments) either straight or branched. Go to 7.
6a. Scum otherwise. Go to 9.
7. Filaments green or brown, straight or branched. Go to 8.
7a. Filaments arranged into a hair-net type pattern, possibly the green alga Hydrodictyon (Figure 19 & 20).
Figure 19.
Figure 20.8. Filaments in a thick mat, green or brown usually branched. Possibly the green alga Cladophora (Figure 21) or Enteromorpha (Figure 22).
Figure 21.
Figure 22.8a. Filaments green and feel like wet soapy hair, possibly the green alga Spirogyra (Figure 23).
Figure 23.9. Algae one discrete unit, either globular or leaf like: green or brown and not composed of fine filaments or colonies and not paint like. If the broken it will not reform. A macro algae (Figure 24).
Figure 24.9a. Bloom otherwise. Go to 10.
10. Bloom with a thick paint-like surface or strong colour to water surface. May be green cloudiness or colour to the water. It is not composed of strands or filaments of algae. Go to 11.
10a. Bloom composed of small green, red or brown flecks. May be well spaced or form a thick scum. Go to 13.
11. Bloom blue-green or strong green, possibly a blue-green algae, Anabaena or Microcystis (Figures 25 - 30).
Figure 25.
Figure 26.
Figure 27.
Figure 28.
Figure 29.
Figure 30.11a. Scum otherwise. Go to 12.
12. Bloom khaki, or reddish. May be the green alga Chlamydomonas or the Euglenoid Euglena. Clamydomonas is usually khaki. Euglena can be khaki or reddish and this may change during the day. This should still be checked microscopically as it may be a blue-green algae. (Figures 31 -33).
Figure 31.
Figure 32.
Figure 33.12a. Bloom white, grey, yellow-brown, red or blue. May be a mixture of these colours with some green and/or dark humus-type substances included. Possibly a blue-green algal scum after photo-oxidation (Figures 26, 27 & 29). If there is a brown colour to the water it may be a Diatom bloom (Figure 34).
Figure 34.13. Small flecks on the water surface not uniform in size. May be aggregated to cover a large area or well dispersed. Possibly the blue-green alga Microcystis (Figures 35 - 36).
Figure 35.
Figure 36.13a. Small green flecks uniform in size. May be aggregated to make thick scum or well dispersed. Possibly the green alga Pediastrum. This should be checked microscopically as it may be a blue-green algae (Figure 37).
Figure 37.
This key is by no means exhaustive, but includes many blooms likely to be confused as blue-green algae. The algae here are generally found in freshwater systems such as lakes, rivers, reservoirs, creeks and ponds.
What do you do if you believe you have a bloom?
- Stop using the water if an alternative source is available.
Do not drink or swim or allow your pets or stock to drink or swim in the
water.
- Contact the your local Council, who will notify the
Regional Algal Co-ordinating Committee (RACC), who in turn will notify
relevant State authorities such as DLWC.
- Do not use the water until informed it is safe.
- Prior to treatment contact the Department of Land and Water Conservation.
References & Further Reading
1Bowling, L. (not published). Notes on Algal Identification and Enumeration, and Sampling. Internal DLWC Document.
Entwisle, T.J., Sonneman, J.A. and Lewis, S.H. (1997) Freshwater Algae in Australia. Sainty and Associates Pty Ltd, Sydney
Jacobs, S. W. L. (1983). Vegetation. In "Wetlands in New South Wales". (Ed C. Haigh). National Parks and Wildlife Service, NSW
Jones, G. J. (1994). "Cyanobacterial Research in Australia". CSIRO, Australia.
2Mitrovic, S. (1997). What Scum is that? Algal Blooms and Other Prolific Plant Growth. Water Quality Services Unit, Centre for Natural Resources, Department of Land & Water Conservation, Parramatta.
Mitrovic, S., Bowling, L. (1995). "Algalwatch", Field Kits for Blue-Green Algae Monitoring, (Report No. TS95.153 of the Technical Services Directorate, Department of Land & Water Conservation, Parramatta).
NSW Blue-Green Algae Task Force. (1992). "Final Report – Summary". NSW Department of Water Resources.
Prescott, G. W. (1964). "How to know freshwater algae". W. C. Brown, Dubuque, Iowa.
Sainty, G. R. and Jacobs, S.W.L. (1981) Waterplants of New South Wales. Water Resources Commission, Sydney.
Sainty, G. R. and Jacobs, S.W.L. (1994) Waterplants in Australia. Edn. 3. Sainty and Associates, Sydney.
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