Pond Fouling: Duckweed Danger (by Adrian R. Lawler, 2011)

Pond Fouling: Duckweed Danger (by Adrian R. Lawler, 2011)


Duckweed is a small floating freshwater plant that floats on the surface of ponds or slow moving bodies of water. The small leaves float on water with the roots (if any) hanging down. Under ideal conditions some species can reproduce every 30 hours; a doubling every 30 hours can quickly cover a pond. There are 38 species of 5 genera of Lemnaceae found around the world, especially in temperate and tropical regions.

Some fishes, turtles, and birds eat it. Some are eaten by humans, and "they contain about 40 percent protein (dry weight) and are equivalent to soybeans in their amino acid content (with high levels of all essential amino acids except methionine)." (Reference below)

If allowed to reproduce without control it can cover the surface of a pond, or a slow-moving body of water, and therein lies the danger.

Duckweed, left uncontrolled, can cover the surface of a pond, decreasing or blocking sunlight to submerged plants and plankton, and if they do not get enough sunlight they die. The decaying plants deplete the oxygen, and since there are no submerged plants left to produce oxygen below the pond surface, the fish, snails, plankton, etc. can die.

Animals that come to the surface to breathe may not be able to break through the mat of duckweed to get to air and they can die, too. This would include tadpoles, mosquito larvae, and various aquatic insects.

The pond owner is then left with a mostly dead pond below the surface and duckweed living on surface. And since the nutrients of the decaying dead plants and other organisms are still in the pond, the duckweed can then reproduce even better for a while, and it will take almost daily surface raking (use leaf rake) of duckweed to keep it harvested back.

Duckweed should cover no more than half of pond surface, better if less. Use floating barriers (booms) to prevent duckweed growing over all of pond surface. Or use floating circles (or other shapes) to contain duckweed inside.

If you want to clean out/control the duckweed with minimal labor, introduce one or more adult red-ear slider turtles. The adults have mostly a plant diet and will eat, and control, the duckweed.

Duckweed can be used as a food for livestock, rabbits, poultry, and fish, as a plant to clean up water, and as a mulch/organic fertilizer.

Other floating plants can block sunlight from pond submerged areas and cause problems, if not controlled: water hyacinth, water lettuce, parrot feather, water fern (as Salvinia), water lilies, etc.

A good reference: http://waynesword.palomar.edu/1wayindx.htm

Adrian R. Lawler,   (C)  2011 --