DHI Water and Environment THE 2002 OXYGEN DEFICIENCY UNDER DIFFERENT METEOROLOGICAL AND LOADING SCENARIOS Ian Sehested Hansen DHI Water and Environment

Agenda Modelling approach for oxygen assessments Model description 2002 hydrodynamics 2002 oxygen conditions Sensitivity to meteorological conditions Sensitivity to load conditions

Model description MIKE3 3D model Bathymetry (9/3 nautical miles, 2 m)

Modules Hydrodynamic (HD) Governing equations: continuity, momentum, turbulence, (S, T) Forcing data: Wind, pressure, precipitation, air temperature, cloudiness Run-off Tide and S/T on open boundaries HD results: water level current salinity water temperature

Modules Advection-dispersion (AD) Eutrophication (EU) N mass budget P mass budget Oxygen mass budget Carbon mass budget (open)

Modules Eutrophication (EU) 12(+) state variables Forcing data: Light Load (land and atmospheric) Concentrations on open boundary EU results: Concentrations Process rates (primary production, denitrification, etc.) Mich. (Secchi depth, etc)

2002 hydrodynamics Surface salinity

Accumulated water flux Great Belt

Accumulated water flux The Sound

Validation by monitoring results from Great Belt

2002 N-S transect of salinity and oxygen stratification Kattegat  Great Belt FemerbæltDarss Arkona Basin

Oxygen in 2002 Oxygen concentration at bottom level

Oxygen in 2002 Oxygen depletion area within Kattegat to Darss (including Swedish and German areas)

Sensitivity to meteorology Wind conditions 11 September to 20 October 2002 Wind conditions 11 September to 20 October 2000

Sensitivity to meteorology

Sensitivity to loading Kattegat to Darss (year 2000): DK: ~ 60.000 t TN S: ~ 24.000 t TN GE: ~ 10.000 t TN Atm: ~ 39.000 t TN Total: ~130.000 t TN No Danish loading (45% reduction in local N load)

Sensitivity for annual mean of IN at surface level (year 2000)

Sensitivity for oxygen depletion area (year 2000) Iltsvindaareal

Total area affected by oxygen depletion km2 < 4 mg/l <2 mg/l <0.5 mg/l Year 2000 Present 17100 8100 3500 No DK Loads 15700 7300 2800 (-8%) (-10%) (-18%) Year 2002 (medio okt.) Present 27200 16200 7800 Sep-oct 2000 meteo 24200 13200 5800 (-11%) (-18%) (-25%)

Sensitivity to loading NMR project NOCOMMENTS: Year 2000 -30% N run-off -30% atm. N-load

Sensitivity to loading Ongoing IMV project on VMP3 initatives with at further developed model setup: actual 2000 conditions reduction scenarios, including: further Danish reductions general reductions in North Sea/Baltic Sea catchment area ??