|Impact of pollution on the ecosystem
c-Fauna and Flora
a-Sediment contamination :
Much of the particulate
material and associated contaminants do not dissolve into
the water column, instead, they settle to the bottom to
become part of the sediments.
- It's a contamination by
PTE's( Potential Toxic Elements). It is possibly caused by
the migration from the solid waste landfill in ML B. through
run off and atmospheric transport.
-Contamination by Hg is
caused by untreated waste water discharged in the lagoon
basin prior to 1999 and landfills.
sediments have been identified as contaminated with several
pollutants such as Polyclic Aromatic Hydrocarbons (PAH),
PTEs: heavy metals and metal like components.
- HLB and DDT. (DDT and
DDD) were detected mainly in the north area near ML
Abderrahman and the northwest.
pesticides pollution source in these areas can be from the
use of pesticides in the past (now forbidden) in
agricultural areas surrounding the lagoon, domestic sewage,
and atmospheric transport.
- Organic matter contents
of sediments appear high (>19% of dry weight.)
- The sediments of
ML.Bourguiba area seem to be rich in organic matters (>28%)
- This is true for 2 other
adjacent cities to the lagoon: ML.JMIL and ML Abd., due to
the massive discharge of raw municipal or industrial waste
water before 1999.
- This massive discharge
of loaded waters explains that the superficial sediments of
the lagoon are the seat of an intense and various biological
activities, such as nitrification, sulphato reduction .
- The sediments bordering
the zone of ML.Bourguiba were especially rich in N(nitrogen)
biomass (>23.4mg-1dry wt.)
-This result indicates an
intense microbial activity in the sediments.
- The C(carbon) biomass
appeared very important particularly in the agricultural
area, near the city of ML.Bourguiba and the center of
the lagoon. (>723 mg-1dry wt.)
- This contamination has
been associated with impacts on animals living in the
sediments mainly bottom--dwelling fish and shellfish that
can accumulate contaminants, hence the threat that they pose
to humans who consume them (the food chain.)
Total Coliforms :(Bacteria) Concentrated in the shallow zones of the lagoon
near the urban agglomerations of ML. Abderrahman, ML.
Bourguiba, the zone of shellfish activities and mainly near
the wild landfill of Bizerte. They aren't indicators of
Faecal Coliforms : They are largely distributed in the neighbouring urban
communities surrounding the lagoon and shellfish and
aquaculture zone. (>198 bacteria g1 dry wt)
They are directly related
to the presence of faecal contamination or pathogens in
water, soil, sediments.
Clostridia : They are anaerobic, spore-forming
organisms. They are regarded as indicators of intermittent
or remote sediment contamination. They are found in
sediments near ML Abd. And around all agricultural zones (>
270 bac g-1 dry wt.)
Enteroviruses : They were detected by means of
RT-PCR (reverse transcription) in 6 of 15 samples taken from
various repository sediments. (These viruses are the most
important viral pathogens of humans. They can cause
different diseases affecting a variety of targets:
neurologic, respiratory, cardiovascular…)
b- Water :
- The well-protected basin
of the lagoon and its shallowness make it a closed space
with very weak currents.
-The marine currents
penetrating the lagoon move in the opposite direction of a
watch, moving along the western coasts until ML
Bourguiba then settle on the coast of Menzel Abderrahman.
-The lowest Ph is found in
ML Abd: can be related to the importance of domestic
disposals. ( 7.82 in summer and 7.95 in winter.)
-High concentrations of
nutritional salts (nitrogen and phosphorus) were observed
near urban and industrial waste water disposal points.
constructions on lake Ishkeul may affect dangerously the
quality of the lagoon waters, reducing its richness.
- An eutrophication
process threatens the lagoon because of urban and industrial
sewage disposals which increase the rate of nitrogen and
c-The Fauna and flora
Pelagic fauna and flora
haven't been deeply studied yet.
27 species of zooplankton
and 58 species of phytoplankton have been counted.
- Sea phanerogams are
present near the coast . There are 4 species: zosteranoltii,
Zostera marina, Cymodeea nodosa andRuppia maritime. Their
respective distribution is very low depending on the water
-50% of the lake's total
area is dominated by algae from -3m deep to -10m deep.
- Red algae: Gracilaria
verrucosa and Gracilaria bursa pastoris are
situated between ML Abd.
And the south of the conchylical station in ML Jmil. Their
presence is related to the shallowness of the waters, to the
tide and especially to the dominant winds: North West 200
days/year with a speed of 5 to 8 m/ second.
-Detergents have a toxic
effect on cell membranes of certain micro-organisms which
ensure bacterial auto-purification, or by the formation of
foams which can concentrate other pollutants and thus
prevent light from penetrating the water causing a decrease
of photosynthesis and consequently the primary production.
- Thermal waters
discharged by El Fouledh, having a temperature of 40°C may
cause an increase in the turbidity of the water, less
dissolved oxygen and less light penetration which may cause
in turn perturbation of algae reproduction.
-Physical pollution caused
by the fumes and dust discharged by the cement works and El
Fouledh, causes the increase of water turbidity and prevents
the penetration of sunlight and consequently decreases
primary production and the biomass.
This may present a danger
to fish: toxicity and death.
Studies on the fauna have
shown that from 1990 the production has been decreasing for
many reasons especially the imbalance in the flow of fresh
water from Lake Ishkeul caused by the setting up of the
sluice and dams on effluent resources.
- Benthic Fauna:
nematodes are biological indicators of pollution from a
natural fragile ecosystem.
were observed between the sediment content of fine fraction
and those of TOC (Total Organic Carbon)
-This association is due
to a common phenomenon: flocculation.
phenomenon is very important for trapping heavy metals which
can be fatal for benthic meiofauna and particularly
free-living nematodes.(Essid 1999: nematofauna)
were observed between heavy metals concentrations (Pb, Mn,
and Zn) and nematode densities (nematodes are very sensitive
to the change in the biological environment.)
-The density of the
nematode community (meiofauna) decreased, a species(52)
impoverishment whereas the mean individual weight increased.
-The sensitive nematode
species: Sabateria punctata was replaced by the more
tolerant and opportunist species: Sabateria granulosa (East)
or Terschellingia longicaudata (North near the centre and in
Most of the aquaculture
activity is concentrated in near shore areas. To prevent
contamination risk by Hg, oyster farming is forbidden in
summertime since high temperatures enhance the
bioavailability of contaminants.
There are 94 species
distributed in 4 classes and 41 families.
-The bivalves are
represented by 47 species.
-The gasteropodes are
represented by 45 species.
-The scaphopodes and
“placophores” are represented by only one species each.
A decrease has been
noticed in the quality of some species (e.g. Hydrobia
ventrosa, Fusinus rostatus, Cerastoderma edule, Arca noae)
and a decrease of the quantity of some species (e.g.
Phyllontus trunculus of the gasteropodes which were present
in 70% of the stations, it has been found only in 20% of the
-This decrease is caused
by the increase of pollution in the lagoon and exploitation
of certain species.
-The central depression,
characterized by a maximum depth and a muddy faces, is poor
in species and photophile seaweed.
-The north of the lagoon
isn't very rich because it is a confined area and the waters
don't change. It is a little deep, deteriorated zone.
- The exchange area with
the sea is characterized by a significant species diversity
because of a permanent passage, a homogeneous sediment and
low concentration of organic matter, of currents TOC and
-There is a great
imbalance at the populations level.
Some techniques of
traditional ways of fishing were used to capture fish and
have samples of fish in the Bouheira.
Using a v-shaped boat with
rows, these are the fish caught:
Anguilla Anguilla Mugil
auratus Solea vulgaris vulgaris
Atherina boyeri Mugil
saliens Sparus auratus
Dicentarchus Labrax Mullus
barbatus Trachinus draco
Gobius nigh jizo Nerophis
ophidian Liza ramada
Gymnamodytes Cicerellus Nerophis ophidian
-The amounts of Cd and Hg
in the muscles of certain fishes as Mugul aurata (Cd) and
Sparus aurata (Hg) and in the coat of Sepia officinalis
(Hg), are relatively low and are below the tolerated limit(from
0.032 to 0.280ppm and from 0.10 to 0.210ppm.
(concentration) of heavy metals in species depends on the
diet and the habitat.
-Mugil aurata is a
limivorous and detrivorous living near muddy areas,
accumulates more Cadimium than fish and Sepia officinalis.
These are carnivores and live in deep areas.
aurata feed on sea urchins and shellfish which accumulates
mostly heavy metals.
-Fish die when the Ph is
<45. Ph equal to 3.3 was recorded. It prevents
photosynthesis and the death of algae.