Thau Watershed Lagoon model coupling' Scenario analysis eutrophication Last developments

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ThauWatershed Lagoon model coupling. Scenario
analysis eutrophication Last developments
C. Aliaume, C. Soulage, A. Fiandrino, T. Laugier,
M. Plus
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Water Framework Directive
France convicted by EU for not having declared
Thau lagoon as  sensitive zone to
eutrophication  ? Being a sensitive zone
imposes a new regulation for treated water quality
Three WWTPs are concerned on the Thau watershed
Mèze, Marseillan Poussan
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Nutrient sources
Mainly from - wastewater treatment plant -
industrial plants - soil drainage
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Scenario definition
1 REF Baseline scenario. 2 ZON Thau under
sensitive zone regulation Meze, Marseillan,
Poussan. 3 DEV Deviation of Poussan-Bouzigues
WWT plant discharge directly to the sea 4 ZDE
scenarios 2 and 3 combined All scenarios are
considered with dry year (1998) and wet year
(1999) conditions
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Model system for the Thau lagoon
3D hydrodynamical Model
DIN Water flux
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1999    Qr 5 439 MJ/m2 Mean temp 15.3
C Precipitation 967 mm
1998    Qr 5 699 MJ/m2 Mean temp 14.9
C Precipitation 279 mm
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1998
1999
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Watershed Thau lagoon model coupling.Main
conclusions

• Phytoplankton important annual net production
• Macrophytes respiration roughly balances the
  production.
• Important nitrogen watershed inputs does not
  imply systematically important primary production
  ? light temperature inter-annual variations can
  also impact sensibly the primary production.
• Riverine inputs can only meet for 1-10 of
  annual phytoplankton nitrogen requirements ?
  lagoon production might be largely supported by
  regenerated nutrients.
• Reduction of DIN discharges has a greater impact
  on macrophyte net production than on phytopk
  production ZDE ? - 50 mac. net production -
  1 phytopk. net production
• further development are needed on larger times
  scales with macrophytes as real states
  variables in order to simulate eventual
  modifications of the lagoon primary producers
  structuration.