Lake Management – Working with Mother Nature
When large, natural ponds suffer from a lack of suitable maintenance over a period of years, excessive and virulent weed growth this bound to take over. Of the most common are DUCKWEED (Lemna three species) and WATER-MEAL (Wolffia) and known to infest ponds aggressively. When this happens, the truth is that Mother Nature is entirely in charge and we have to work alongside her, rather than fight what is inevitable.
Because of this fact, it is imperative that the cause and not the effect of the weed growth is treated. With these type of aquatic weeds, prevention is key, in order to avoid ongoing and costly control measures. Aquatic weeds can be controlled with herbicides, although Wolffia is much more difficult to control with these than other forms of Duckweeds. This method can be effective if the herbicides are applied early on in the infestation, not once the pond is covered to any large extent.
External factors which can add to nutrients being available on which the weeds can thrive include Canada Geese droppings, lawn fertilisers, agricultural field run-offs, inefficient septic systems and land drainage. In addition to these contributors, large amounts of leaf fall during the Autumn season can cause sediment build up throughout successive years.
It may take several years for total control but reduction in the weed population in the majority of cases can be seen in a period of around 18 months. This timeline can be longer when there is a particularly dense accumulation of sediments – which is caused by the stratification and accompanying lack of oxygen in the deeper waters, and a reduction of the decomposed organic matter along the bottom.
Lake Management – Solutions and Actions
The first primary action to take is the manual removal of the majority of the floating Duckweed. The most beneficial course of action would be to leave the duckweed waste on the bank of the pond, this will act as a mulch around the margins and also any aquatic insects can make their way back into the pond safely. The regular manual removal of the recurring weed is time consuming and very costly.
The second step involves introducing a Duckweed Reduction Treatment plan and leave the body of water to sit for the winter months. Bio Lake should be introduced in order to reduce the nutrients which feed the unwanted plants. This treatment should be used throughout the year as, if left to its own devices the weed will grow again in a very explosive manner. Finally, the Pond should be treated with suitable doses of Bio Lake additive.
To prevent overgrowth of aquatic weeds going forward, aeration needs to be installed to promote water movement. There are a number of Aerators on the market that depends on your budget. We recommend either a more effective aeration system or the requisite size of fountain. After these additions, the pond’s weed growth should settle down, although there is always a chance that a little re-growth will appear from the historic spores which are currently sitting in the sludge and silt at the bottom.
Introducing Grass Carp or Rudd is beneficial in preventing bottom sludge but this will not deal with the existing problem. Also, ducks offer some benefit after treatment because they will indeed eat the Duckweed and Wolffia, thus preventing the nuisance populations of each. However, the ducks’ defecation can lead to serious nutrient issues and can cause a filamentous or planktonic algae blooms.