Bioremediation is an effective lake maintenance method

Swimming spots, biodiversity reservoirs, ponds and lakes used for sports and fun are all important in our lives. But with global warming, the fragile balance of these ecosystems is threatened and many public authorities are wondering how to clean the ponds beds before it is too late. To learn more about the challenges and techniques involved, we talked to Laurent-Pierre Castagnera, Director of Taso, a French company that bioremediates ponds, lakes and gravel pits.

Healthy water is not always natural

You might think it is enough to add a few fish, ducks and plants in a water-based ecosystem to create a natural balance. In practice, it is more complicated, as Laurent-Pierre Castagnera explains.

“Fish, just like algae, live and then die, producing organic matter which settles to the bottom of aquatic water systems. Without regulation, this layer of silt builds up, causing an excess of nutrients leading to excessive growth of plants and algae which consume all the free oxygen in the water. Called eutrophication, this premature ageing is what causes the well-known green algae problem. Over time, the water lacks oxygen and the whole ecosystem suffocates.”

To check if the water level is imbalanced, trust your senses. First of all, it is a bad sign if the water is green or smells like a rotten egg. If algae have collected all the free oxygen, the fish die in the spring. You have to act quickly!

Lakes maintenance is essential – but often forgotten

With global warming, ponds and lakes warm up. This rise in temperature causes the multiplication of cyanobacteria, some of which are harmful to people and animals.

Cyanobacteria and filamentous algae in a pond © Taso

However, for many small towns and villages without municipal swimming pools, natural ponds and lakes are the only chance local inhabitants who do not live near the coast have to cool off during heat waves. These social spaces and all the economic ecosystems which depend on them (life guards, ice cream kiosks, campsites, etc.) can quickly go bankrupt when the cyanobacteria attack due to lack of preventive maintenance of these fragile green spaces. Every summer, more and more public authorities have to close their ponds and lakes. “Swimming is not just canceled for the current year but it should not be forgotten that after an event like that, people tend to go somewhere else the following year, even if everything has been done to clean up the water meanwhile. Laurent-Pierre Castagnera emphasizes that “the tourist trade can really lose out”.

Overview of major challenges to ensure public parks safety

Ponds and lakes are also reservoirs for biodiversity. It is essential to protect them and this will become increasingly important as, to ensure a better future for all, public authorities adopt a sustainable approach to town planning.

Prevention rather than cure: bioremediation techniques to the rescue of lakes

In some cases, water eutrophication is so complete that only invasive techniques like dredging or weeding can clean the pond bed. As Laurent-Pierre Castagnera explains, “these remedies are expensive in France, as you need to get permission from the Préfecture, prepare a silt disposal plan, etc. Overall the administrative costs are very high. Many town halls cannot afford them and abandon their ponds and lakes. So while there is still time, it is better to adopt preventive measures which save money in the long run”.

“Soft” bioremediation methods are now available. Several techniques can be used to rebalance the water chemistry:

• adjust the pH to fight acidification;
• reoxygenate the water to facilitate the destruction of organic matter by bacteria;
• block photosynthesis to stop plant growth;
• boost mineralization of the organic matter.

Even very big lakes are at risk. “There are fewer problems in big lakes because it takes longer to imbalance these parameters. But as algae growth is exponential, the day it becomes a problem it is already too late to take preventive measures” says Laurent-Pierre Castagnera.

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Ultrasounds, a new pond and lake bioremediation maintenance method

For the last 12 years, the Taso company, already well-known for its natural calcium carbonate Nautex, has been marketing a new, ideal and original solution to public authorities having adopted a water maintenance plan - ultrasounds, with its innovation Ultrason Quattro Pro50 360°.

Ultrasounds platform from Taso © Taso

“Cyanobacteria have gas-filled vacuoles with lift the algae to the surface of the water to collect the rays of the sun and then deflate to sink them down to the bottom again during the night. Ultrasounds vibrate these vacuoles until they burst. Unable to manage their buoyancy, the algae fall into the mud, are eaten by bacteria and can no longer leach toxins into the water. This technology works just as well on the membranes of the filamentous algae” explains Laurent-Pierre Castagnera.

This preventive method is risk-free for humans and animals and can be used to restore chemical balance for all waters, from small ponds to big lakes, with minimum maintenance. The Taso stand-alone version which can treat up to 50 hectares with a single appliance is powered by solar panels. Meeting all the requirements for sustainable development, it is already at work in many cities in France, including Saint-Etienne, Orleans and Roanne.

Global warming makes the bioremediation of ponds and lakes an essential challenge to face up to and include in a more global, reasoned green space maintenance solution. Technologies to deal with the problem exist, but to maximize effectiveness the watchword must become prevention, not cure.

Our thanks to Laurent-Pierre Castagnera for sharing his expertise.

© Photo credit: yk_stock / Adobe Stock