Eutrophication of coastal waters: the case of Brittany’s green tides
By Nicolas ROLLO
L’Atlas Bleu / Protecting
Eutrophication, green algae, covered area, evolution, Brittany
After a contextualisation of the coastal waters eutrophication (world map), the article examines the case of Brittany, a French region strongly affected by this phenomenon. Graphical documents allow to assess its spatial impact in 2008 and its evolution from 1997 to 2011. Several elements of context on the fight against green tides are specified from an economic point of view.
In France, although strandings of green algae (Ulva) certainly occur elsewhere than Brittany, the media coverage they attract has led them to become associated with the Breton coastline. This association is such that the Brittany Region responded to the campaign carried out by France Nature Environment in 2011 by saying that ‘its image was damaged’, even though it was not explicitly mentioned in the offending posters. It should be said that since the early 1990s, Brittany has very often been singled out concerning deterioration in water quality, which has also resulted in the implementation of various wide-ranging intervention programs. Despite the fact that the situation is improving as a result of the actions taken, it is still a problem.
Poster of the campaign of the collective of associations France Nature Environnement, published in 2011
After having spread well beyond the historic sites of the bay of Saint-Brieuc and bay of Lannion in the 1990s, the green algae blooms seem to have peaked in 2009. The extent of the problem meant that the government had to take emergency measures integrating the implementation of the ‘green algae plan’. Specifically, the goal of this plan was to reduce by 40% the nitrogen fluxes that fed into the eight most affected bays, primarily located on the northern and western coastlines of the peninsula. Besides the imbalances caused within ecosystems, the eutrophication of coastal waters can have significant economic impacts. In the case of Brittany, it was estimated that it cost more than one million euros to collect and put to good use the 2009 green algae alone. The losses incurred, especially in terms of tourist activities, also need to be taken into account.
The mixed results of the actions taken can be partly explained by the inertia of the environment. As a result, given the slow response time of hydrosystems to changes in practices, the measures undertaken must be carried out over the long term in order to truly restore Breton aquatic environments.
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