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What is Duckweed?

Posted on March 25 2019

What is Duckweed?

Duckweed which is often misidentified as algae is a free-floating aquatic plant that grows in both still and running fresh water. However, it prefers nutrient-rich, stagnant, slow-moving water such as in retention ponds or dugouts. Contrary to what one might expect from the name, no ducks are involved in the growth habits of the plant, although ducks undoubtedly feed on it when they find it growing. Ducks and other waterfowl help spread these plants, as the little leaflets will get stuck on the legs and feathers of the birds and travel on them from pond to pond, therefore dispersing themselves to many waterbody locations.

Depending on the circumstances, Duckweed can be an extremely invasive species or a welcomed aquatic plant. Duckweed proliferates and is capable of doubling its biomass over 16 hours. Therefore, this plant can quickly turn into a significant problem, especially in areas where water is polluted with excessive nutrients, such as fertilizer runoff from farms, or spills from manure pits at confined animal feeding operations. Well-nourished Duckweed can spread rapidly across a body of water, and if the Duckweed completely covers the surface of a pond for an extended period, it will cause oxygen depletion which in turn threatens fish and other aquatic organisms. These colonies will also eliminate submerged plants by blocking sunlight penetration. The plant can also clog propellers and filtration systems, making it a nuisance to humans as well as animals.

If Duckweed suddenly appears in an area where it has not been present before, this can be a sign that something about the environment has changed. Droughts, nutrient pollution, and unusual weather patterns can all create blooms. Some gardeners like to use Duckweed as an ornamental for their water features, but they should think carefully before doing this, as it can get out of control or spread to local bodies of water.

Where Does it Grow?

Duckweed tends to grow in dense colonies in quiet water, undisturbed by wave action. Often more than one species of Duckweed will be associated together in these colonies.

Is it Invasive?

Although Duckweed is native, it can be aggressive invaders of ponds and are often found mixed in with mosquito fern, watermeal and multiple types of Duckweed species. If colonies cover the surface of the water, then oxygen depletion and fish kills can occur. These plants should be controlled before they cover the entire surface of the pond.

There are many different species of Duckweed in Canada; however the most common are Common Duckweed, Forked Duckweed and Giant Duckweed.

Common Duckweed-This is the most common species of Duckweed. It has tiny light green leaves, approximately 1/16 to 1/8 inch in length. A single root protrudes from each frond. This species floats directly on the surface of the water.

Forked Duckweed- Forked Duckweed has a simple, flattened leaf body or frond that is long-stalked with three faint nerves and a single root. Lateral fronds often remain attached to the parent frond, creating a “rowboat and oars” shape. Forked Duckweed is usually found just under the water surface. Because it is free floating, it drifts with the wind and current and is not dependent on depth, sediment type, or water clarity. However, there must be adequate nutrients in the water to sustain its growth — it overwinters by producing winter buds that rest on the sediment. In spring the buds become buoyant and float to the surface.

Giant Duckweed- This species is still relatively small (1/16 to 1/4 inch) with 1 to 4 leaves or fronds, and is light green in colour. Three or more roots protrude from each frond. Giant Duckweed floats directly on the surface of the water and looks very similar to Common Duckweed. However, the primary way to tell them apart is that the leaves of the Giant Duckweed are much larger.

Another aquatic species that is often found within the Duckweed colonies is Watermeal.

Watermeal- is known as one of the smallest flowering plants in the world. It is less than 1 millimetre in size; it can be dark to light green in colour and resembles tiny grains of sand or cornmeal. It looks like tiny dots covering the pond. Reproduction occurs by splitting, so this plant can completely cover an entire pond very quickly. This plant also prefers nutrient rich slow-moving water bodies.

How do I prevent or reduce the Duckweed in my water body?

Since all Duckweed species prefer slow-moving nutrient-rich water,  the best way to prevent it from forming in your water body is to install aeration and reduce the nutrients present in the water column. Aeration will help circulate the water within your pond which will create a non-desirable habitat for the Duckweed to grow, but it will also increase your dissolved oxygen levels which will create a healthier environment for the aquatic organisms living in your water body. You can reduce the nutrients in your water column by applying MuckAway, which will breakdown the organic material that is along the bottom of your water body that releases nutrients into the water column. You can also apply Pond Clear which is a dissolvable packet of bacteria that consumes the nutrients that are floating within the water column. However, we highly recommend using these products and systems before Duckweed enters your pond or when you first notice it, because once it takes over the water body, it is much more difficult to completely rid of it!

If you have any other questions about Duckweed, please feel free to contact us at 204-745-6898.

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