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Conduct ESE Interpretive Analyses

Subtask Description: Conduct ESE interpretive analyses
Functionality of the Ecological Component model: results, limits, ecosystem stability, restorative potential.

Action points of the implementation:
Each of the ESE component models need to be fully checked to ensure that they represent the part of the system that they are designed to represent. A series of runs will be carried out on each of the component models to identify any problems prior to their inclusion in the full simulation model. These analyses and descriptions interpret the simulation results of the NC model and its objectives.

Result: Documentation showing the interpretive analysis of the ecological component model.

Area:
Himmerfjärden , Sweden

Policy Issue:
Eutrophication status and reduction.

Human Activities:
Urban sewage discharge, agriculture and industrial activity, tourism.

General Information:
Nutrient loading has caused increased turbidity, loss of biodiversity, including submerged aquatic vegetation, deep water oxygen def iciency, phytoplankton blooms and biodiversity loss. The main stakeholder concerns are connected with tourism, recreational activities and nature enjoyment, and the sustainable implementation of WFD that poses economic challenges for several activities in the area.

Example of Implementation:
The objective of the ecological model is to simulate the response in terms of water transparency (Secchi depth) of the coastal ecosystem of the Himmerfjärden area to changes in nutrient loads in terms of nitrogen concentrations. The study area consists of three sub-basins (HA, NA and HI), differing in size, sill depths, and dominant nutrient sources. Several policy options for nutrient load reductions are combined into four (preliminary) scenarios of management of nutrient loads.

The results of the scenario simulations are shown in the table below. For model basin HI, the hindcast showed fairly good agreement between nitrogen concentrations and Secchi depth from the data and model. Agreement was not as good for the other basins. The Secchi depth improvement in the scenarios does, however, give a reasonable indication of the improvement that could be expected.

The model hindcast showed a relatively good fit between modelled and measured total nitrogen in the Näslandsfärden (NA) and Himmerfjärden (HI) model basins. For two of the years, there was a good fit for the winter concentration of nitrogen in the inner basin Hallsfjärden (HA), but for two years the model clearly underestimated concentrations. This may reflect the limited data on nutrients in local runoff, but may also be an effect of over-estimated water turn-over rates, i.e. two large inflows of deep water leading to short residence time.

Comments:
Scope and Limitations of the implementation: For the NA and HI model basins, the empirical relationship with total nitrogen was quite successful in predicting the Secchi depth of the individual hindcast years. Any discrepancy mostly resulted from over- or underestimates of the nitrogen concentration. The current empirical relationship between tot-N and Secchi depth seemed to underestimate Secchi depth in basin HA. Adding more data to the empirical relationship, covering a greater range may improve these results. In addition, the inclusion of phytoplankton and chlorophyll in the model, and empirical relationships between chlorophyll and Secchi depth, may shed light on the reason for the discrepancy.

Contact: Jakob Walve jakob.walve@ecology.su.se