By Obioha Durunna, Regional Livestock Specialist, Prince Albert
Several dugouts are filled with duckweed or algal blooms during the summer months. Even though their presence doesn’t necessarily signify poor water quality, it may indicate areas that need your attention.
Presence of excess nutrients such as nitrogen and phosphorus in dugouts encourage growth of aquatic plants. We need to be aware of potential recharging sources of these nutrients, such as runoffs containing fertilizers, pesticides or animal waste. Doing nothing to control these blooms can cost you.
We should remember that a chemical analysis on the water sample will provide us with better information, leading us to take appropriate action.
Identify the bloom
Knowing what is growing in your dugout is the first step toward addressing the issue. Algal blooms thrive in warm water that receives lots of sunlight. It’s important for you to know whether it’s a filamentous or planktonic type of algae.
Filamentous algae can have colours ranging from green to orange. When scooped with the hand, they look like a mesh. Some may even feel silky or slippery and, when squeezed, may look like cotton. This type of algae may have a septic or pigpen odour.
Planktonic algae generally look like pea soup or grass/fingernail clippings with colours ranging from bright-green to black. When you scoop it with your hand, planktonic algae usually drains from the fingers, leaving some smudges. We are more concerned with cyanobacteria, commonly referred to as blue-green algae. They are of concern because they produce toxins that may cause liver damage (hepatotoxins), paralysis (neurotoxins) or death to humans and livestock.
Duckweed is an aquatic plant that we can easily misidentify as algae because they look similar from a distance. Each duckweed has an oval-shaped body called a frond and a small, root-like structure. The fronds tend to grab each other, forming a thick mat on the water surface. Duckweeds proliferate in slow-moving or stagnant water bodies and are easily spread by aquatic birds or floods.
Having duckweed in your dugout could be beneficial. Besides removing excess nutrients from dugouts, they shade the water, thereby reducing evaporative losses. By so doing, they make the water cooler and keep algae away.
Managing the blooms
We can control these blooms by mechanical, biological and chemical methods.
The mechanical method is accomplished by skimming the blooms with rakes/floating booms, by aeration or both. Skimming works well with filamentous algae and duckweed, while aeration works better on planktonic algae. Regular skimming (especially for duckweed) ensures that the nutrients are not recycled back to the dugout.
We can also use fish, barley straw or additives as biological methods of controlling the blooms. Fish such as grass carp or tilapia can be used but you need to be cognizant of the aquatic regulations in your area. Anchoring nets of loose barley straw at 2-3 bales per surface acre may inhibit growth of new algae, but results may be inconsistent. Dugout additives that contain bacteria or enzymes or both may reduce the levels of nutrients in the water thereby depriving algae of those nutrients. This method may not be economical in larger ponds and the results may vary.
Most of us are aware of some chemical methods. Dugouts with blue-green algae can be treated with copper sulphates or bluestone. The toxins these algae release when they die can be fatal. Therefore, you should wait at least 14 days before supplying the water livestock. Herbicides like diquat can be used to control duckweed.
It is recommended that you develop off-site or remote watering systems for your livestock. This will reduce contamination of the water as a result of direct access to animals. As a Saskatchewan producer, you may be eligible for some funding under the Farm and Ranch Water Infrastructure Program. Contact your Agriculture Regional Office for more information.