by Hans Peterson, Saskatchewan Research Council
Before treating your dugout find out how much water it holds. A dugout that is 20 by 50 m (60 by150 feet) with an average depth of 2 m (6.6 feet) will hold around 2 million L (0.44 million gallons) when full. Cyanobacteria and some algae can be controlled fairly well with copper sulphate (bluestone). If you stock trout in your dugout you cannot use levels that are higher than 0.2 kg/million L (0.5 lb/250,000 gallons). In dugouts with no fish we recommend that you start with levels that are no higher than 0.5 kg/million L (1.25 lb/250,000 gallons).Should these relatively low applications fail, higher level treatments can be made a couple of days after the initial application. Apply no more than 1 kg/million L (2.5 lb/250,000 gallons). If this high level treatment will not work you likely have copper tolerant algae in your dugout. If the cyanobacteria have blown to one side of the dugout spot treatment may be attempted. Richard Pasquill (Manitoba Water Services Board) recommends spot treatments using 2.5 mL (´ teaspoon) of bluestone dissolved in 4.5 L (1 gallon) and then spray the affected area at the rate of 4.5 L (1 gallon) per 40 m 2 (440 ft2).
If the cyanobacteria were toxic, copper sulphate will release the toxins into the water, so that consumption of such water should be delayed for several days (2-7) if possible. Carbon filters in good condition can remove toxins and a delay may not be necessary.
Copper sulphate treatments can however, often trigger undesirable side-effects. These include the destruction of many of the "helpful" microbes in the dugout. Once these friendly microbes are killed, copper sulphate resistant green algae are able to grow rapidly and take control of the dugout because they have no more competition to deal with. This is an example of a "man-made bloom".
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Control of large algae blooms will, even if successful, result in poor quality water Algae control should be aimed at preventing a large biomass from being formed. Protecting your dugout from nutrient inputs (soil, dirty water, etc.) is the single most important step you can take to prevent this. Suggestions for protecting your water supply will appear in every issue of Prairie Water News.