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Ag News - 7th March 2006

Ag News - 7th March 2006

By Department of Primary Industries - 7th March 2006 - Back to News

Have you got a dam(n) algae problem?

By Colin Waters, DPI Ellinbank

Now is the time of the year when it is not uncommon to see algae growing in dams, reuse systems and streams. Algae can block pumps and contaminate water with algal toxins, poisoning stock and making the water generally unusable.

Understanding algae

Algae are a normal part of any healthy body of water, but when conditions favour algal growth they can often bloom and it is the blooms that cause the problems. Algal blooms are, however a problem that will go away naturally and intervening may delay the return to a natural balance in the dam.

Algal growth is favoured by abundant phosphorus and nitrogen, long periods of sunlight providing warmer temperatures and energy for growth, and relatively calm conditions. All of these are common in most dams during summer.

There are many types of algae. Some are just annoying, blocking pumps and channels and creating unpleasant tastes and odours. However, some blue-green algae produce toxins that can poison humans, animals and birds contacting or drinking the contaminated water. When in bloom, blue-green algae often appear as a thick, smelly, green paint-like scum on the surface, especially on the downwind end of the dam and tiny green flecks in the water. The toxins produced by blue-green algae can cause liver and gut damage or cause muscle tremor, staggering, paralysis and breathing difficulties in animals. The effects on individual animals that drink contaminated water can range from a slight decline in milk yield to death.

What to do if you have an algal bloom on your dam?

Isolate stock from the dam and provide an alternative water supply. If you do not have an easily accessible alternative water supply try to arrange a short-term supply while you quickly get the water tested. Contact your local DPI office for advice.

Get a sample of water tested to identify the algae and determine if it is potentially toxic. This will help identify the most appropriate course of action. Contact your local DPI office for the names of laboratories that can test water samples for algae. The DPI Ellinbank number is 5624 2222.

Contact your vet if you notice any symptoms in stock or have concerns about your stock being exposed to algal toxins.

Should I use chemical algicides?

Using chemicals to control algae is not generally recommended and should only be contemplated in exceptional circumstances. You first need to identify the type of algae and its potential toxicity. Before using chemicals consider whether you can afford to not use that water for up to 4 weeks. If toxic algae are killed with chemicals, the toxins are released and may take up to 4 weeks to break down. Remember also that most chemicals will have a withholding period, which will be stated on the product label.

If you do use chemicals, only use those registered for that purpose (eg. to kill certain species of blue-green algae in a dam).

Let nature take its course

There is no quick fix for an algal bloom. Algal blooms are a natural occurrence and over time the algae and their toxins will decompose. Using chemicals may delay this process by killing useful organisms.

Long-term prevention

You can’t completely prevent all algal blooms on your dams. However you can affect how often they occur. Measures include:

• preventing the run-off of nutrients from dairy sheds, tracks and feedpads into the dam;
• fertilising pastures to avoid periods of run-off and leaving an unfertilised strip around the dam;
• fencing stock out of dams;
• establishing vegetation around dams to trap soil particles that are eroded from the dam catchment;
• utilise and turnover water held reuse systems before the warmer months;
• if you only have one main water supply, consider establishing alternative storage or supplies on the farm.

Blue-green algae in irrigation water reuse systems

Source: http://gippsland.com/

Published by: news@gippsland.com