Run Scenario Simulations

Subtask Description:
Prepare, conduct, and test scenario versions of the simulation model.

Action points of the implementation:
Scenarios should then be applied to the model in a simulation run. This represents outputs of your model and is the data which will be used in the output step to inform the stakeholder group of your findings.

Result: Simulation output values from the simulation model that reflect changes caused by applying the scenarios.

Area:
Limfjorden, Denmark

Policy Issue:
Interaction between eutrophication and mussel production.

Human Activities:
Fisheries, aquaculture, agriculture, water based recreational activities, transport.

General Information:
In the early 1990’s a regime shift took place in the area, and there was an activity transition from demersal fishery to mussel fishery. Eutrophication, caused by nitrogen and phosphate loadings, is still causing periodical hypoxia, sometimes resulting in major death of mussels, and Harmful Algal Blooms, resulting in periodical commercial bans of the product. In 2006 the mussel landings fell to exceptionally low level and there is high risk of a total collapse of the mussel production. Mussel culture in lines is introduced to the area to replace the fishing activity, but this new venture is not economically viable. The main stakeholder concerns are connected to the impacts of hypoxia, mussel fishery and the lack of finfish and a understanding of their ecosystem functioning.

Example of Implementation:
The first series of scenarios reduced nitrogen loading (keeping the phosphorous loading constant at the year 2007 level of 486 Tons/year.The ESE model predicted that a reduction of the Limfjord nitrogen loading from 19,800 Tons/year (mean of loading from 1985-2007) with 50 % (WFD target loading of 10,000 Tons/year) could reduce the maximum landings of mussels (figure below). The ESE model scenarios showed that with a reduction of nitrogen loading to a level (50 % of today) that meets the goals of the WFD, the mussel fishery would be reduced by ~35 % in possible landings of mussels, from 7,200 to 5.000 Tons/year.

 

 


Scenarios changing nitrogen loadings from present day level (100 %) to the target of the FWD (50 %) and to zero.

The second series of scenarios reduced phosphorous loading (keeping the nitrogen loading constant at the year 2007 level of 13,900 Tons/year). The ESE model predicts that a reduction of the Limfjord phosphorus loading from 581 Tons/year (mean of loading from 1985-2007) with ~50 % (WFD target loading of 300 Tons/year) could reduce the maximum landings of mussels (Figure below). The ESE model scenarios showed that with a reduction of nitrogen loading to a level (50 % of today) that meets the goals of the WFD, the mussel fishery would be reduced by ~50 % in possible landings of mussels, from 7,200 to <4,000 Tons/year. The scenario results show that the Limfjord system is a phosphorous controlled or limited system.


Scenarios changing phosphorous loadings from present day level (100%) to the target of the FWD (50%) and to zero.

Two other series of scenarios are also run: Scenarios simultaneously changing both the nitrogen and phosphorous loadings and Scenarios changing nitrogen, phosphorous and both nutrients simultaneously.

Contact: Grete E. Dinesen gdi@aqua.dtu.dk