Duckweed; Friend or foe?
In 2023 we completed a project, jointly collaborating with Suffolk Wildlife Trust. A wet habitat at Police Station ditch, the ditch separating No Man’s Meadow and the Crankles, was created. The ditch was dug deeper and a pond was formed at the western end. To keep it wet all year, a lip or bund was built up at the Lark River confluence so that when the river is high, water flows into the ditch creating a backwater. This should provide the conditions needed for aquatic organisms and animals like the water vole, a critically endangered mammal in the UK. Suffolk is a water vole stronghold, so it was thought that creating more habitat for them would build on that status and secure their future.
The ditch stayed wet all 2024, achieving the desired effect, even when summer eventually arrived in July and August. But gradually over the year duckweed (Lemna minor one of 5 native species), began to dominate the surface. It could have been introduced from dog fur, dogs can’t resist a swim, (even though we have a handsome deterrent in the way of a dead hedge). It could just have come in on bird feet or duck feathers, as its name suggests.
For a tiny leaf floating on the surface of the water with a diminutive root not even anchored to the bottom of the ditch, it’s remarkably fast at reproducing; doubling in size in a couple of days. Before we knew it, the entire ditch was covered with what looked like a lush green lawn or cress you might sprinkle on your salad. Wind forward to this summer, with 3 heatwaves already under our belt (as you read, a fourth may have taken place too), even the backwater is waterless, but duckweed is still growing green and lush as the mud retains nutrients for the plant to feed on.
This is the rub. Nutrient rich water is just what it likes and our water bodies are getting nutrient-richer and richer. Nitrogen from various human activities such as agricultural runoff, pollution from roads and sewage and phosphorus from washing liquids and powders in wastewater treatments, all end up in our rivers and seas. It always has done; even Monks in their Abbey Church would have discharged their waste into the pristine chalk streams they lived alongside. But our climate is warmer and population has increased vastly, so the perfect conditions for duckweed (and others) to romp away are here to stay.
However it’s not all trouble, in fact it is a remarkable little plant in many ways. It’s high in protein containing more than soybeans (when grown in optimum conditions) so it’s an ideal food for waders, frogs and those water voles we are trying to attract. It also stops algal growth, another more sinister romper in nutrient-rich water, by using up that excess nitrogen and phosphorus which the algae would use. So it could be considered a water purifier too. Though many people in Asia already eat it, scientists are experimenting ways of making it an alternative food source to meat, due to its high protein content. Duckweed burgers on the BBQ this weekend?
Jillian Macready Bury Water Meadows Group Trustee
