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Modeling of the primary production in the Bizerte Lagoon Modeling of the primary production in the Bizerte Lagoon ––Description of climatic change effects by an hydroDescription of climatic change effects by an hydro--ecological ecological
threethree--dimensional modeldimensional model
by : by :
Béchir BEJAOUI, Ali HARZALLAH & Mahmoud MOUSSA
Email: [email protected]
10/12/2007
Several methods have been used to resolve this problematic. Thecoupled dynamic-ecology modeling is actually a very interesting tool for studying the marine ecosystems under the effect of anthropogenicinterventions. This technique is also used to predict the future evolution of the ecosystems under climate change.
The model developed at our institute is used to study the impact of climate change on the Bizerte Lagoon ecosystem.
How can we predict the effects of external forcing on marine ecosystems ?
What is the problematic ?What is the problematic ?
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Presentation of Bizerte LagoonPresentation of Bizerte Lagoon
Situation:Latitude : 37°8' - 37°14' NLongitude: 9°46' - 9°56' E
Characteristics: An area of about 128 km2 (11 km and a maximum length of 13 km) with a mean depth of 7 m.
Connection: The lagoon is connected to the Mediterranean sea by 6 km inlet (12 m depth and 0.8 km width). and to the Ichkeul Lake through the Tinja channel of approximately 5 km length.
Continental Hydrology: The catchment's area is about 380 km2 with total amount of fresh water discharge of 125 Mm3/year (ANPE, 1990) .
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- The Bizerte lagoon model is 3D sigma coordinate system (σ) (Based on Princeton Ocean Model).
- The lagoon is discretized into 61x52 grid-points.
The dynamicgrid model
Hydrodynamic modelHydrodynamic model
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EcosystemEcosystem ModelModelConceptual diagram of the Bizerte Lagoon ecosystem modelConceptual diagram of the Bizerte Lagoon ecosystem model
ZOO
NH4E
NDETO2E
NDETSNH4S NO3S Mineralization
NO3E
Diff
Diff
Diff
PHYT
Sedi
me n
tatio
n
Uptake
Uptake
Nitrification
Grazing
Mineralization
Death
Denitrification
Death
Faeces
Excr
eti o
nTE
O2E O2E
Phot
osyn
thes
is
Respiration
Resp
iratio
n
Rea
erat
ion
Light WindRiver
O2E
TE
TS O2S O2STS O2STS
O2ETE
Sola
r ra d
iati o
nD
iff
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Ammonia and OxygenAmmonia and Oxygen EvolutionEvolution
Season variation: Ammonia - Oxygen
0 2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 00
1 0
2 0
3 0
4 0
5 0
6 0E v o lu tio n d e la c o n c e n tra tio n d e N H 4
jo u r
C(m
gN/m
3)
N H 4 mN H 4 s
0 2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 03
4
5
6
7
8
9E vo l u t io n d e la co n c e n t ra ti o n d e O 2
jo u r
C(g
/m3)
O 2 mO 2 s
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Interrelation between Current Temperature Interrelation between Current Temperature and Chlorophylland Chlorophyll--aa
2
3
4
5
6
7
8
9.78 9.8 9.82 9.84 9.86 9.88 9.9 9.92
37.14
37.16
37.18
37.2
37.22
37.24
37.26
P hyt. s imulé à la s urface en é té 2003 : mg/m3
Phytoplankton
30
30.5
31
31.5
32
32.5
33
33.5
34
34.5
35
9.78 9.8 9.82 9.84 9.86 9.88 9.9 9.92
37.14
37.16
37.18
37.2
37.22
37.24
37.26
Temp. s imulée à la s urface en été 2003 : °C
Temperature
9.78 9.8 9.82 9.84 9.86 9.88 9.9 9.92
37.14
37.16
37.18
37.2
37.22
37.24
37.26
Vitesse s imulée à la surface en été 2003 : m/s
Surface Current
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Study of climate scenariosStudy of climate scenarios
Case study I: Extreme Case study I: Extreme heatwaveheatwave, ,
Case study II: Global warming,Case study II: Global warming,
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Case study ICase study I:: Extreme heatwaveExtreme heatwave MarchMarch--AprilApril--MayMay
Wind*0.2, LH (-5W/m2), SW (+50W/m2),SH (+7 W/m2), Prec*0.2, Rivers*0.2
3 6 5 7 3 0 7 8 9 8 8 0 1 0 9 50
1
2
3
4
5
6
7
8
9
1 0
1 1P h y t . C O N TR O LE (B ), V A G U E C H A LE U R m a rs -m a i (R )
jo u rs
mg/
m3
2 0 0 2 2 0 0 3 2 0 0 4
Chla: Controle (B). Heatwave (R)
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Case study ICase study I:: Extreme heatwaveExtreme heatwave MarchMarch--AprilApril--MayMay
Wind*0.2, LH (-5W/m2), SW (+50W/m2),SH (+7 W/m2), Prec*0.2, Rivers*0.2
3 6 5 7 3 0 7 8 9 8 8 0 1 0 9 50
1
2
3
4
5
6
7
8
9
1 0
1 1Z o o . C O N T R O L E (B ), V A G U E C H A L E U R m a rs -m a i (R )
jo u rs
mm
olN
/m3
2 0 0 2 2 0 0 3 2 0 0 4
Zoo: Controle (B). Heatwave (R)
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Case study IICase study II:: Global Global warmingwarming
Heat (+7W/m2), Prec *0.7, Rivers *0.7, + evap*1.
3 6 5 7 3 0 1 0 9 5 1 4 6 1 1 8 2 6 2 1 9 1-0 . 8
-0 . 6
-0 . 4
-0 . 2
0
0 . 2
0 . 4
0 . 6
0 . 8O 2 : F U T U R -A C T U E L ~ -3 %
jo u rs
g/m
3
2 0 0 1 2 0 0 2 2 0 0 3 2 0 0 4 2 0 0 5 2 0 0 6
O2: Future-Actual ~ -3%
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Case study IICase study II:: Global Global warmingwarming
Heat (+7W/m2), Prec *0.7, Rivers *0.7, + evap*1.
-8
-7
-6
-5
-4
-3
-2
-1
9.78 9.8 9.82 9.84 9.86 9.88 9.9 9.92
37.14
37.16
37.18
37.2
37.22
37.24
37.26
Phyt. FUTUR - PRESENT (été 2003) : mg/m3Chla: Future-Actual Summer 2003 (mg/m3)
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Case study IICase study II:: Global Global warmingwarming
Heat (+7W/m2), Prec *0.7, Rivers *0.7, + evap*1.
3 6 5 7 3 0 1 0 9 5 1 4 6 1 1 8 2 6 2 1 9 1-4
-2
0
2
4
6
8
1 0F LU X E N TR A N T C A N A L : F U TU R -A C TU E L ~ 5 1 0 %
jo u rs
mm
/jour
2 0 0 1 2 0 0 2 2 0 0 3 2 0 0 4 2 0 0 5 2 0 0 6
Water input from inlet: Future-Actual ~ 5-10 %
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The possible evolution of the Lagoon under future global heat
The lagoon will behave The lagoon will behave like (as) a concentration basinlike (as) a concentration basin.
LagoonInlet
A thermoA thermo--halinehaline ventilation ventilation in the inlet could save itin the inlet could save it
Harzallah A.
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Conclusions & PerspectivesConclusions & Perspectives
ConclusionsConclusions
The model allowed to reproduce the Bizerte Lagoon ecosystem The model allowed to reproduce the Bizerte Lagoon ecosystem variables,variables,The model could be used as a tool to simulate the effect of climThe model could be used as a tool to simulate the effect of climate ate changes on ecosystems evolutionchanges on ecosystems evolution..
PerspectivesPerspectives
Distinguish micro and Distinguish micro and mesomeso--plankton in phytoplankton and plankton in phytoplankton and zooplankton, zooplankton, Develop an operational version of the model.Develop an operational version of the model.
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Thank you for your attentionThank you for your attention
Grazie per il vostro ascolto.Grazie per il vostro ascolto.
