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Understanding the influence of coastal ecosystems on the greenhouse effect


Oceans play a major part in regulating the carbon cycle in the terrestrial ecosystem. It appears, however, that this balance is increasingly threatened by human activities. Three teams of European researchers are the first to have studied the influence of coastal zones on this process.

Every living being comprises billions of atoms (the main ones being carbon, nitrogen and oxygen) which are released on death in the form of organic or inorganic molecules just like those which make up minerals, atmospheric gases, etc. This vital process, known as the cycle of matter, has been seriously disrupted since the industrial revolution. For example, by expelling CO2 into the atmosphere, transport systems and some industrial activities have upset the carbon cycle. This could in turn be contributing to the global warming which we seem to have been witnessing for several years.

From the oceans to their surroundings

The imbalance in the carbon cycle is a phenomenon which is not yet properly understood by scientists. They have studied the role of oceans, which are apparently capable of absorbing excess carbon from the atmosphere. But what about the areas alongside them? Michel Frankignoulle, a researcher at the Chemical Oceanography Unit of the University of Liège (Belgium), is exploring the role of sea coasts which are the site of considerable exchanges of matter between the earth and the sea. In 1989 he proposed studying the carbon cycle within coastal ecosystems. "We submitted an expression of interest to the European Commission specifying the topics on which we wanted to work," he explains. "The Commission put us in contact with other researchers with the same interests and that is how we were able to carry out a study with teams from the universities of Plymouth and Aveiro."

Variations in time and space

A year later, the Belgian, British and Portuguese researchers benefited from a grant under the European programme, MAST (Marine Science and Technology). Between 1990 and 1992, they studied three sites, visiting them four times a year: the Bay of Calvi (Corsica), the Tamar River Estuary at Plymouth (United Kingdom) and the Lagoon of Aveiro (Portugal).

Samples taken from these environments enabled them to measure various elements: substances containing carbon, CO2, phosphates, nitrates, oxygen, and so on. The comparisons they made between one site and another, and between different points in the same area, reveal interesting variations.

One example is CO2. This element can be found at very different degrees of concentration in the Aveiro Lagoon depending on whether one is in a spot near the coast - and hence rinsed by seawater - or in an industrial area. In Calvi, where there are no rivers or tides, the only factor which is likely to make the CO2 rate vary is the presence of posidonias, underwater sea plants whose growth varies according to the season. "We were able to observe the relative importance of the various processes, including photosynthesis, which is particularly impressive, as it can make the CO2 system vary over a period of 24 hours," explains Michel Frankignoulle. "In June, for example, we witnessed an important variation in the course of a day because the posidonias were photosynthesising a great deal. In the winter, on the other hand, they are at rest and practically nothing happens."

Extra estuaries

Ten stations were selected on the Tamar, in the river estuary, bay and lagoon. "We noticed that the estuary was the site of some quite significant imbalances and we wanted to establish comparisons. We began with the Thames and the Schelde. The results obtained for this latter site are so spectacular that we launched a new European project. This included twelve laboratories in order to study nine European estuaries, not just for the CO2 level, but also for methane, nitrogen oxides, etc.," clarifies Michel Frankignoulle.

In addition to these two estuaries, the new research project, named BIOGEST, will study those of the Elbe, the Ems, the Rhine, the Loire, the Gironde, the Douro and the Sado.

Apart from the purely scientific analyses, the work carried out under BIOGEST will have a socioeconomic impact. The conclusions drawn from it should make it possible to devise environmental management tools, particularly to deal with the worrying problem of the eutrophication of coastal areas.



Project Title:
Biochemical carbon cycling in coastal zones

Programme: Marine science and technology (MAST 3)
Contract Reference: MAST-0019

Cordis Database For more information on this project,
go to the CORDIS Database Record