In the Côtes-d’Armor, the long fight against green algae


For the visit of Annie Podeur, president of the second chamber of the Court of Auditors, the Lieue de Grève was adorned with its finest nuances. Blue sky, pristine white sand. A few bathers have come down from the granite houses which overlook the bay to go wading in a transparent sea. The uninformed tourist would find it hard to believe that the place is the second most affected by the tides of green algae, behind the bay of Saint-Brieuc.

→ TO (RE) READ. In Saint-Brieuc, green algae alert

You have to go down to the beach to see a thin stream of sea lettuce on the surface of the water. It will settle on the sand when the tide goes down, then will be immediately picked up. Here, as in the other green algae bays, the tractors rake the sand as soon as the algae appear. Sometimes daily. The aim is to prevent their putrefaction and the emanation of the dangerous gas that results, hydrogen sulphide.

“Uncertain” effects of policies

Annie Podeur traveled from Paris on July 20, 2021, to present her institution’s report on ten years of fight against green algae in Brittany. Several hundred pages and a harsh observation: at the level of the region, the objectives were “Ill-defined”, the effects of policies “Uncertain” and financial support, “Insufficient”.

The choice of the Lieue de Grève to present this report is no accident. Its watershed is not immune to criticism but would be “The most advanced in the fight against green algae”, recognized Annie Podeur in front of an audience of elected officials, agricultural representatives and environmental associations, gathered in the municipal hall of Saint-Michel-en-Grève. The goal of limiting the proliferation of algae by 2027 even seems “Attainable”.

Death of a jogger and a horse

The elected officials are enthusiastic about these words of encouragement. It must be said that the bay has come a long way. It was there that in 1989, a jogger had died, stuck in algae, raising the first concerns about their dangerousness. It was also there that in 2009, a horse had died from the fumes of green algae. His rider had been saved in extremis.

The political reaction had been swift. Prime Minister François Fillon went there and announced the first “government plan to fight against green algae” (Plav) across Brittany, for the period 2010-2015. A second will follow for 2017-2021.

→ INVESTIGATION. Death of an oyster farmer in Brittany: the green algae involved?

We must stop for a moment on the way in which these green algae proliferate. They find their source in the nitrates of the rivers which are rejected in the bays. In these places where water stagnates and currents are weak, the nitrate-heat-luminosity cocktail favors the appearance of these aquatic plants. The geological conditions are important: because it is shallow, the Lieue de Grève is more affected than other bays, even if the nitrate levels are sometimes lower than elsewhere.

Agricultural nitrogen

These excess nitrate are caused by the release of nitrogenous products into the water, 90% of which is of agricultural origin. Nitrogen is found in fertilizers for maize, which is the main food source in intensive livestock farming. It is also found in soybeans in animal feed, which then ends up in droppings spread on soils. It is a vicious circle: unlike grass, corn absorbs little excess nitrogen. This accentuates their flow in rivers.

This is where the political dilemma lies: the only lever for action lies in agricultural transformation. Which seems difficult in the first breeding region in France, which the policies of the 1960s pushed towards intensive agriculture.

In 1991, the European Commission adopted the nitrate directive to regulate their rate in European rivers. This regulation has led France to set up new standards for spreading and design of buildings to limit nitrogen leaks. Nitrate levels in Brittany and elsewhere have fallen significantly, but the Breton watersheds are still well above European targets.

Voluntary plan

Let us return to the year 2010. In the Lieue de Grève, the Lannion-Trégor Community agglomeration is entrusted with the responsibility of applying the green algae plan to the watershed scale. Controversial point: the policy is based on volunteering. Farmers are contacted one by one, diagnoses carried out on each farm to find out how to reduce their nitrogen leakage.

Of the 130 farmers in the watershed, 110 undertake to take more or less ambitious measures to reduce their nitrogen leakage (do not leave bare soils,limit spreading…). “It was still difficult, remembers Edwige Kerboriou, vice-president of the Côtes-d’Armor Chamber of Agriculture and breeder in the watershed. Some farmers lived very badly at being singled out. “.

Develop the meadows

However, the Lieue de Grève can play a card that the others do not have. Most of the herd is made up of dairy cows, partly fed on corn but also on grass. Local elected officials want to push farmers to further develop grazing systems, to partially replace corn and soybeans. Result after ten years: the Court of Auditors underlines a development “Notable” : in 2019, the area of ​​meadows increased by 7%, to reach 54% of the useful agricultural area of ​​the watershed.

Some farms have increased their meadow area by a handful of hectares. Others have switched to an almost exclusively grassland system. This is the case of Jean-Michel Perrot, breeder recently switched to organic after fifteen years of agriculture oriented towards productivism.

Milk strike

He welcomes us to the family farm, taken over from his parents in the 1990s. In the barn, around forty cows are wisely waiting to be taken to the pasture. When he took over the farm, there were only 25 cattle, mostly grass-fed. Then came the difficult years: “The cooperative told us, we must produce! So we went up to 45 dairy cows ”. At the time, its surfaces were not enough to feed the animals. He switches to corn.

It costs him dear in seeds and fertilizer. In 2009, Jean-Michel Perrot went on a milk strike to protest against ever heavier charges and a stagnant milk price. His throat is tight when he says: “One morning, I milked my cows and then I drove to Morbihan to throw in my milk. “. The same evening, he decides to go organic. He does not have the issue of green algae in mind, he just wants to reconnect with a more extensive and profitable system.

Psychological brakes

Where its history meets that of the bay, it is when it brings in a technician from Cedapa, an association of farmers, whose intervention is subsidized by the green algae plan. This advisor suggests that he switch to an almost totally grassland system. This is not a requirement of the organic specifications, but it helps reduce costs. It will take him seven years to bring the project to fruition.

“There are psychological brakes, recognizes Jean-Michel Perrot. The day I replaced my last piece of corn, it was very hard. I wondered if the cows were going to have enough to eat ”. The techniques are different, you have to invest in equipment, in short, he says, “ it is not enough to plant grass ”.

The land issue

Then there is the problem of land. The land must be grouped together so that the cows can graze. However, part of his property is on the other side of the departmental road. The place is dangerous: cars come out of a bend at 80 km / h. However, the Cedapa technician convinced Jean-Michel Perrot to transform these lands into meadows and to cross the road with his cows, morning and evening.

He is half-amused, half-bitter when he mimics his new routine: “I run across the road and pray that the cows will follow and the cars will stop”. He would have preferred a boviduc, a sort of underground passage, but had to do without it, for lack of financial assistance.

The current green algae plan will end in 2021. In the rivers of the Lieue de Grève, the nitrate levels have fallen from 40 mg / l in 2000, to 28 mg / l in 2019. The tonnages of green algae have decreased slightly but experience peaks in some years. The process is long because nitrates stay more than five years in their environment.

Third plane green algae

At the national level, a third plan is being prepared. In June, the Rennes administrative court ordered the state to take new regulatory measures against green algae within four months. ” The main challenges will be to convince – or coerce – the last farmers who have not made an effort », Underlines Annie Bras Denis, vice-president of the Lannion-Trégor-Communauté agglomeration.

The other brake is that of land: half of Breton farms will change hands within ten years. The Court of Auditors suggests that they be primarily intended for projects limiting nitrogen leaks.

If the Lieue de Grève held up rather well thanks to the meadows, the question of intensive pig and poultry farming arises elsewhere. There are ways to improve spreading techniques and crop rotation to limit nitrogen leaks., notes Patrick Durand, agronomy researcher at INRA. But it is essential to one day have to reduce the herds.

This is also a long-standing request from the Eau & Rivière de Bretagne environmental association. But it’s a red line for the local Chamber of Agriculture.

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Ten years of “green algae” plans

►Between 2010 and 2021, the two Green Algae Plans (Plav) focused oneight Breton bays and their watershed.

►109 million euros were injected into the Plav, of which more than 60% devoted to curative (collection of algae) and sanitation.

►The average concentration of nitrates in Breton rivers went from 47 to 35 mg / l between 1995 and 2013, then to 31.7 mg / l in 2019. For the Court of Auditors, these figures show that the decrease is ” largely “ due to previous measurements to green algae plans.

►Algae stranding increased from 1,200 to 1,192 hectares between 2010 and 2020.

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