Studies in aquatic environments

...and was rewarded in December 2004 with certification in the ISO 14001 Environment Management Standard, which imposes regulatory obligations. After results announced at the last Regional Air Observatory seminar showing that the quality of our air is good, CSG has decided to pursue its environmental studies, this time in aquatic environments. Since the meeting of the Secrétariat Permanent de Prévention des Pollutions Industrielles (Permanent Secretariat for the Prevention of Industrial Pollution) in December 2005, CNES CSG has decided to reinforce monitoring of waterways and to include aquatic invertebrates as biological indicators of water quality. Hydréco, an environmental studies bureau certified by the Ministry of Research, is responsible for taking and analysing samples in the three rivers running through the Space Base: the Karouabo, the Crique des Pères (a pilot site) and the Malmanoury.

On the bridge over the River Karouabo, the team from Hydréco prepares to raise the nets placed the previous day 2 km downstream and 1 km upstream from the bridge, two batteries of ten nets each, taking the measure of the Karouabo. In the labyrinth of vegetation, the ichthyologist Régis Vigouroux steers between the moucou-moucous and the moriche palms. To the sound of iguanas dropping unexpectedly from the trees like ripe fruit, he explains that CSG is monitoring fish populations by taking samples along the rivers. Hydréco has adopted a quality approach to equipment, communication procedures and appropriate sampling techniques. They use a battery of nets with different meshes, from 10 to 70 mm. Studies carried out at Petit-Saut have proven that this method works well for obtaining a good picture of the diversity and structure of fish populations. Regular use of this passive but selective technique can reveal changes in the aquatic environment relative to its normal state or changes in the climate, or show the impact of launches. From now on, the rivers will be sampled twice a year instead of once, in the rainy season as now and also in the dry season. This means that sampling can be less intensive, as there is always the danger of rapidly exhausting the environments tested. The nets are 25 m long and 2 m wide and are strung at the surface along the banks, where the fish find their food, their hiding places and the calm conditions necessary for reproduction. Whatever the height of the water, these 2 m at the surface do not change and provide a random selection of the fish population, depending on hydrological features such as the tides or the strength and direction of the current. A characteristic of the Karouabo is that there is a loss of oxygen in its water column, which drives the fish to find refuge in flooded areas or at the surface. A strange little fish, a dark, slimy torpedo with a soft body called a bla-bla “Blahs” its objections to the fingers trying to extract it from the net (which explains its name).

The small fry may manage to wriggle out of the nets, but the researchers can still count them. Much smaller sizes, however, that cannot be distinguished with the naked eye, are of great interest to the scientists. Aquatic invertebrates, known as ephemera, such as the larvae of various insects or tricoptera, are the first organisms to be affected by any pollution of the aquatic environment, whether caused by human agency or not. They provide a reliable measurement of water quality, the SMEG, Score Moyen des Ephémères de Guyane (average score of Guianese ephemera).

Although all waterways on the French mainland have been closely monitored using this measurement for over 20 years, it is not possible to use the same data here. A special scoring system was created for French Guiana in 1998 by the DIREN and has been applied since 2006 at CSG. With this index a waterway can be given a score and placed in one of five classes, by identifying and analysing the aquatic vertebrae found there. Some of these organisms, called ephemera, are at the beginning of the food chain and are affected very rapidly and their lifespan of between two days and a few months does not allow them to escape from pollution as fish can. In parallel with the fish analyses, the SMEG gives a rapid and reliable overall view of the aquatic environment. The ephemera are collected both from the river bed and from banks, for a specific period laid down for each environment. In accessible places, they can also be processed in artificial substrates, as the scientists plan to do for the next Hydréco operation.

Like the specimens collected, it’s a thin catch: 13 fish compared to 69 the day before on the Crique des Pères and over 200 on the Sinnamary in equivalent conditions. Does all this prove some impact by the nearby Space activity? Régis answers frankly that fish sampling since 1998 has shown little change, as there has been little monitoring of the environment. Analyses have shown no aluminium in the fish, so we cannot conclude that Space activities have had any direct impact, but we have no ‘Point 0’ from when CSG was built and therefore no reference. The researchers busy themselves with counting the catch, weighing and measuring the fish and entering the results in their database. Lined up on the table, patagaïs, pacoussis and bla-bla await interrogation to reveal their stage of growth, health and sex, before having a sliver of flesh removed for analysis. Régis recalls that at the time of his first visit in 1998, the Karouabo showed signs of having suffered earlier, visible even in the vegetation. Since then, it has improved considerably and seems to be on its way to a full recovery. Laurent Guillemet, head of Hydréco’s invertebrates unit, tells us that the results of the first catch of invertebrates in 2005 largely corroborate the fish results. It is true that the analyses show signs of the impact of external factors, but these are unfortunately too uncertain to reveal the cause, because of the lack of long-term data.

Now we await the next catch, the first where we shall see the state of the waterways in the dry season. We shall be able to compile comparative data, particularly with the Malmanoury, the most distant from the launch areas. We shall also be able to identify refuge areas and decide whether to retain or adapt our sampling methods. As for the aquatic invertebrates, at least three years of results will be necessary to reveal significant changes and start to provide explanations.