Abstract
The protection of the underwater ecosystems is essential both
for the equilibrium of water species and a healthy feeding of the local
population. Lake Nokoué located in the south of Benin, is affected by
several forms of pollution originated mostly by anthropic activities. This
research work is aiming at making reliable contributions as regards fighting
diverse forms of pollution on this lake today. In so doing, we'll find it
easier to fight against all sorts of ecotoxicologic risks and dangers run by
it. To reach this goal, we had to go through some research strategies including
mostly field work, interviewing resource people and local population. The
results from the physical chemical and bacteriological analyses of water from
the lake have let us discover that the sources of the different noticeable
polluting agents of Lake Nokoué are the following:
- petrol products poured in the lake;
- «acadja» branches daily abandoned in the lake;
- house and biomedical garbage poured down on the lake's
banks;
- unclean rain water from Cotonou evacuating collectors
without any former treatment;
- residues and pesticides carried by the
Ouémé;
- refusals of human and animal faeces;
- the throwing out of house garbage in the lake by local
populations.
The different polluting agents found in the lake really
influence the quality of the lake water. Regarding the results of the research,
some parameters critical values are out passed. As a result, the dissolved
oxygen content vary from 2.76 mg/L to 3.62 mg/L, the DBO5 from 10 mg/L to 29 mg
and the DCO from 252 mg/L to 253 mg/L. As far as the ammonium content, it goes
beyond 8 mg/L whereas the nitrite content is about 0.7 mg/L in places. As
regards the total coliforms content, it is between 4,000/100 ml and 6,000/100
ml; the faecal streptococcus content varies between 500/100ml and 4,000/100 ml.
These data show that the lake is polluted. Depolluting strategies need carrying
out by every authority in order to avoid ecohealth problems connected with
water products from the lake.
Key words: Pollution, lake Nokoué, south of
Bénin, écotoxicologic risks.
INTRODUCTION
1 - Contexte scientifique de l'étude
De jour en jour, les problèmes environnementaux
prennent une place importante dans les différents débats qui
concernent le développement durable.
Au départ, le terme " environnement " était
considéré comme une nouvelle spéculation, mais avec la
conférence de Stockholm en 1972 et celle de Rio de Janeiro en 1992, il
est indéniable que la question se pose et ce, avec une importante
acuité selon l'état de développement de chaque pays. De
façon générale, les problèmes environnementaux font
penser à la pollution de l'air, du sol, de l'eau, aux changements
climatiques etc. La République du Bénin n'est pas
épargnée par ces problèmes, notamment la pollution
liée aux mauvaises pratiques de gestion des plans d'eau en
général et du lac Nokoué en particulier.
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