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thomas.neumann@io-warnemuende.de
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Thomas Neumann and Gerald Schernewski
Baltic Sea Research Institute
Different abatement strategies are under discussion
Ecosystem models are appropriate tools for testing different measures
What are the ecological consequences of different abatement strategies?
Thomas Neumann
Basin-wide gradient in salinity
No tides
Ice coverage
South-north-spread: ca. 1300 km
West-east-spread: ca. 1000 km
Average depth: 52 m
Maximum depth: 460 m
Population (catchment) 85 millions
The Problem
In the last century the phosphorus input has increased eightfold and the nitrogen input fourfold
Baltic Sea ecosystem has changed from an oligotrophic state into a mesotrophic state
Sensitivity of the public to environmental issues of the Baltic Sea has increased
Thomas Neumann
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Ministerial declaration (riparian states) of 1988 set reduction of the nitrogen and phosphorus loads by 50% as a goal. (proportional approach)
Because of different anthropogenic loading of the Baltic Sea rivers from an economic point of view this is not an optimal solution.
=> An alternative approach suggested by Gren (2000), is to achieve the 50% nutrient load reduction goal at minimum total costs. This implies that nutrient load reduction takes place in countries and drainage basins where it is most cost-efficient. (cost-effective approach)
Solution?
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After Gren in Gren, Turner & Wulff (eds.) (2000): Managing a Sea
Total annual costs (million €)
Thomas Neumann
MOM3 application to the Baltic Sea
3 nm … 9 nm horizontal resolution
77 vertical layers 3 m … 6 m
Open boundary condition towards the North Sea
ERA-15 / ERA-40 meteorological forcing
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Solar
Radiation
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Example for a 3D simulation
Thomas Neumann
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Reduction after 12 years of simulation time based on an annual mean.
Phytoplankton biomass is reduced especially near the river outlets
Strong reduction for Diatoms
Quicker response of nitrogen compared to phosphorus concentrations
Thomas Neumann
Reduction along an offshore section
Reduced phytoplankton biomass in the Gdansk Bay due to Diatoms and Flagellates reduction
Enhanced phytoplankton biomass in the central part during summer due to cyanobacteria
Thomas Neumann
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Relative decrease of the inventories for the two load reduction scenarios
black line: proportional reduction
green line: cost-effective reduction
Quick response of N compared to P
Reduced N to P ratio and in turn enhanced Cyanobacteria blooms
Thomas Neumann
In general the cost-effective approach produces lower concentrations in the southern part and higher concentrations in the northern part of the Baltic Sea.
This is as expected because of the stronger load reduction in the southeastern drainage area. However, the differences are comparable small. Cyanobacteria are most sensitive.
Cost-effective approach minus proportional approach compared to the control run
Thomas Neumann
Further nutrient reduction with the cost-effective approach
Thomas Neumann
With the cost-effective approach especially the phosphate reduction is less compared to the proportional approach.
Thomas Neumann
Thomas Neumann
Riverborne nutrient load reduction yields lower nutrient concentrations and phytoplankton biomass. However, for at least a transition period enhanced cyanobacteria blooms can be expected.
The offshore regions are more affected than the central regions.
A cost-effective abatement strategy does not restrict the overall response of the Baltic Sea ecosystem.
The uneven load reduction to different areas produce stronger effects in the southeastern part of the Baltic Proper compared to the proportional reduction.
Spatial differences in the achieved reduction effect are less then 10% related to the control simulation.
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