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."
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
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.