Are your dams turning blue?

Algal blooms can be common during the summer months as the onset of warm weather provides ideal conditions for algal growth. Algal growth can cause problems as it can taint the taste and smell of the water. The algae can clog filters and irrigation lines and lead to corrosion of metal pipes and fittings.

In some cases the release of toxins from some algaes (the blue-green algae) can be toxic to animals.

Algae are a normal part of the aquatic ecosystem and require sunlight, water and nutrients (particularly phosphorous and nitrogen) to grow.

There are many different types of algae found in dams and not all cause problems with farm water supplies. The main one to be concerned with is the blue-green algae which can form as thick scums on the down-wind surface of a water body.

Often these scums look like a suspension of greenish paint, though color can range from pale green through blue green, dark green to brown.

Often there is a very foul odour. Some species of blue-green algae produce poisons harmful to humans and possibly fatal to animals and fish.

There are no simple tests you can do to identify algal toxins and while the chance of it being a toxic algae is low, it’s best to play safe and prevent stock from having access to the dam until it’s treated.

There are a number of treatment options for algae, so contact Lyn Dohle at the Government of South Australia PIRSA office (0419 846 204) for the best option for your particular dam.

The best option is to prevent the algal blooms in the first instance.

As mentioned above, the triggers for algal growth are high levels of nutrients (nitrogen, carbonates and particularly phosphorus); warm temperatures; still shallow water, or a dam where the surface water is strongly stratified relative to the lower waters (ie no mixing); high levels of organic matter; and direct exposure to sunlight.

So long term management involves addressing the above issues, particularly nutrient availability which is the key driver for algal growth.

Try where possible to adhere to the following:

  • Fence off dams to prevent stock physically disturbing dam sides and sediments, or defecating and urinating in the water.
  • If that’s not possible then try and keep a good level of ground cover above the dam to act as a filter for manures and nutrients.
  • Keep soil erosion to a minimum above dams (consider a silt trap or drains to divert early flows past the dam).
  • Don’t spread fertiliser close to dams and drainage lines
  • Keep drainage/creek lines well vegetated (and ideally have creek lines fenced off) and use properly constructed creek crossings
  • Occasionally desludge dam to avoid excessive buildup of sediments and organic material.

If you have any concerns about your dam and water quality for livestock contact the PIRSA Office Kingscote on 8553 4949 (remember the office does provide a water salinity testing service).

 

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