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Potable water treatment

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3.5.1 Algae

Algae are photosynthetic organisms that are generally aquatic; they are primary producers. Many freshwater algae are of microscopic size, but when amassed can be seen as a green, brown or blue-green scum. Blue-green algae are capable of producing toxins and these have caused the death of wild animals, farm livestock and domestic pets which have consumed the contaminated water. The toxins can produce a painful rash on human skin. The extract below shows what happened off the west coast of Scotland in 2000 when algal blooms appeared there.

WWF blames fish farms for poison algae

By Rob Edwards, Environment Correspondent

Dramatic new evidence blames pollution from fish farms for causing the poisonous algae that is devastating Scotland's £50 million shellfish industry.

A report to be published tomorrow by the World Wide Fund for Nature, one of the country's most respected environmental groups, will conclude that the vast amount of waste excreted by the millions of salmon penned in 350 cages along the west coast is linked to toxic algal blooms. Scottish ministers have always denied such a link, and the results of the study will come as a blow to the Executive.

The accusation, made by a leading international marine scientist commissioned by the WWF, could hardly have come at a more embarrassing time. For the last month shellfish farmers have been banned from taking scallops from virtually all of the west coast waters from the Mull of Kintyre in the south to the Orkney Isles in the North. Sampling by Scottish Executive scientists showed that scallops in most western areas now contain dangerous levels of the algal toxin that causes Amnesiac Shellfish Poisoning (ASP) in humans. Symptoms of ASP include vomiting, diarrhoea, memory loss, seizures and comas.

On Tuesday, the Rural Affairs Committee of the Scottish parliament is due to hear a petition from a former shellfish farmer calling for an independent inquiry into the environmental impact of fish farming. Allan Berry, who is also a marine toxicologist, will argue that the discharges from fish farms are implicated in the recent 'epidemic' of toxic blooms.

Tomorrow's WWF report will give Berry powerful new evidence on the enormous amount of waste nutrients that comes from caged fish. Its author, Scottish-based environmental consultant Malcolm MacGarvin, is very critical of the Executive's refusal to acknowledge a connection between waste and the floating algal blooms.

'On the balance of probabilities you cannot rule out nutrients from fish farms as a factor', he told the Sunday Herald. 'If you put in more nutrients, you get more blooms and they last longer and affect a larger geographical area'.

The Executive fails to take account of the complex three-dimensional movement of the coastal waters, which could mean that a lot of fish farm waste remains in the top 10 metres of water where blooms are formed, he argued. It also dismisses laboratory evidence which suggests that nutrients can help the growth of algal toxins.

MacGarvin, who has advised governments, industry and environmental groups around the world on the marine environment, agreed that the absence of absolute proof should not be used as an excuse for inaction. The vast majority of studies in scientific journals were about how emissions of nutrients were linked to toxic blooms, not about whether they were.

'There is a lot of evidence saying that there is relationship between nutrients and blooms', he said. 'This is something we should be worrying about'.

The WWF itself declined to comment on the report until it has been published. The Scottish Executive, however, continues to insist that toxic blooms are naturally occurring and unrelated to the fish farming industry. In a detailed 40-page response to Allan Berry's petition released on the Executive's website last week, it attempted to undermine his arguments.

Executive scientists pointed out that the toxins which cause ASP and other hazardous shellfish diseases occur worldwide in areas where there are no fish farms. 'There is no evidence to support the case that such emissions from fish farms have ever actually been responsible for an algal bloom or shellfish poisoning event in Scotland', they stated.

But Berry claims that 57 of the 60 sites closed due to ASP or other toxins in August are in areas used for fish farming. 'None of these 57 sites had any record of toxicity previous to 1988', he said.

His petition to the Scottish parliament accuses government bodies meant to regulate the fish farming industry of being biased in its favour. 'There are many good reasons to question the propriety and prudence of regulators who have so consistently declined to face up to the damage caused by 'their' industry', it alleges.

'Discharges from the farms are implicated in the epidemic of biotoxin production and contamination of shellfish now regularly occurring in water subject to discharges from sea cage fish farms'.

In February the Sunday Herald disclosed new scientific studies suggesting that waste and pollution from fish farms helped the growth of algal toxins. And in June we reported predictions that there would be widespread bans of shellfishing due to toxic blooms. But whatever the rights and wrongs, it is the shellfishing industry which suffers from the bans. 'It's very tough', said John Holmyard, who farms mussels in Loch Etive, north of Oban. 'It puts you out of business while it carries on and if it goes on for long enough it can put you out of business permanently'.

(Source: The Sunday Herald, 17 September 2000, p.7. Copyright © 2000 Scottish Media Newspapers Limited)

Algae may be attached to rocks or be floating, in which case they are usually referred to as phytoplankton. There are also some macroscopic ones which are branched and attached to stones and rocks. In the seas and oceans, algae are more commonly called seaweeds; they are of various colours, and are large and branching.

In contrast to the large green plants which are rooted in the river bed or banks, algae take their nutrients directly from the surrounding water. For the process of photosynthesis, both carbon dioxide and water are needed. (As mentioned in Section 2.4, blue-green algae have the ability to use bicarbonate as the carbon source.) The carbon dioxide entering the cells of the plants is that dissolved in the water.

Some of the common algae found in waters (illustrated in Figure 14) are:

  • Diatoms (e.g. Asterionella species (spp.)

  • Blue-green algae (e.g. Anabaena spp.)

  • Green algae (e.g. Spirogyra spp.)

  • (note: spp. stands for species pluralis, Latin for ‘multiple species’)

In an aquatic environment there are also decomposers and scavengers. These organisms utilise dead plants or animals as sources of food, and in so doing release minerals and nutrients which can then be reassimilated by plant and animal life. The decomposers which are important in the life of aquatic ecosystems are the fungi, bacteria and protozoa.

Figure 14
Figure 14 Some common algae