France Under a Deadly Green Wave
On the west coast of France, in the region of Brittany, green waves are threatening the people. 36 boars died, one horse died, a jogger died… The green waves come back every year, spread on the beach and exhale a deadly scent.
The culprit is an alga of the Ulva type, also called “sea lettuce”. It’s a very efficient reproducers since each independent cell can create a new organism. That’s why it’s very hard to get rid of it. This alga is blooming from May to October, in warm and low water depth bays protected from any swell perturbation. These green algae then deposit on the coast and rot quickly. After 48h, it starts emitting a dangerous gas: the hydrogen sulfide. At a concentration of 1700 ppm, this gas smells like a rotten egg and can kill an adult in one minute. Concentration reaching 1000 ppm was measured on the coast, this explains the worry of the local authorities for people safety. Moreover the green waves were calculated to create a 1-billion-euros loss a year for the local economy especially in the tourism sector.
However algae are not to blame, they are only opportunistic organisms growing and reproducing in a friendly environment created by human.
In the 60s, the French government started a national policy of agriculture intensification with the cut of hedgerows between fields and the increase of fertilizer and pesticide use. This intensification policy created larger agricultural fields which decreased the cost of production, optimized the farmer movement and increased the efficiency of mechanization.
This change in agricultural practices disturbed the ecosystem. The soil eroded and the rivers received chemicals such as phosphates and nitrates which were then fertilizing the sea.
The livestock industry is also a cause of water pollution since the million of pigs and cows raised in Brittany poop a lot. The manure used to be spread on the field as a fertilizer and was adding its nitrate to the agricultural pollution.
A new policy to solve the problem of green algae has been implemented for the period of 2017–2021 with an investment of 55 millions euros. The plan will mainly identify the sensible agricultural fields next to the sea which need to be managed more organically to reduce chemical leaching. The plan will also support experimentation and innovation to find a way to decrease the quantity of phosphate and nitrate going to the sea.
For example, to reduce the leaching of phosphates and nitrates; hedgerows, catch crops, strip of wild plants and flowers are regrown like in the past agricultural landscape. These organic practices absorb the nitrate and other fertilizers when they are still in the soil and therefore decrease their negative effect in the ocean. Nitrate content is already decreasing thanks to the evolving agricultural practices. A part of the funding supports the collect of the dead green algae on the beach to avoid further accidents.
The scientific community is also involved to create new knowledge about the phenomenon and help decision makers to take action and measure their impact. Several indicators are used to measure the efficiency of this plan, for example the quality of water and its chemical content, and the quantity of algae collected on the beach. (currently 50 000 tons a year)
To use the algae which are blooming despite the effort to decrease fertilizer inputs, they are collected and directly put on agricultural field. 80% of algae are used this way because it’s cheap and quick. However algae can only be transported on a short distance (under 40 km) because of the cost of transportation, and a field can be fertilized with algae only once every 5 years to avoid soil pH increase.
When algae are composted, they can be collected few days after depositing on the beach, but then need to be dried for an easier transportation. For this reason a source of heat like fuel or factories is needed next to the beach. On the compost plant, algae are mixed with chipped wood. This process has to be far from human activities because their rotting smell is terrible. After two weeks of aerobic decomposition the compost is sieved at 0.3 cm and stored during one year to avoid any hydrogen sulfide emissions. Afterward, it can be used as a fertilizer on organic fields.
The important algal biomass arriving on the coast created a business opportunity. The consortium ULVANS made of private companies and public research centers are innovating to synthesize new products out of green algae. ULVANS is led by Olmix, a world leader in algae based biotechnology. The company manages all the transformation process, from the collection, cleaning and valorization of these underrated algae.
The initiative is encouraged and co-financed by the local government, however it’s not welcomed by everybody. A study of impact on the alga collection showed a 30% mortality of cockles (Tellina sp, Donax sp) under the vehicle tracks. Moreover the collection of fresh algae is a difficult task which is even harder with the French administration and rules about environmental protection. The company needs a special authorization to harvest green algae in protected area.
The sustainability of the business is also questioned since it is based on a resource everybody wants to get rid of. What would be the future of the industry if the pollution decreases and the algae disappear? This business may also be an excuse to not reduce the fertilizer input in agriculture and keep polluting the environment. The algae blooming won’t be seen as a burden anymore because ULVANS will use it and create economic value out of it. However the pollution will still be there.
Using the excess of green algae to enhance the local economy is not a panacea. ULVANS business may decrease the amount of algae on the beach, it may erase the symptoms. However the ecosystem will still be sick, unable to digest the chemicals of productivity injected by human. Let’s hope we could still live a long and happy life with this sickness.
