The SCOBI model (Swedish Coastal and Ocean BIogeochemical model) developed by SMHI is used to study the influence of climate changes and human activities on biological and chemical processes and the cycling of nutrients in the seas surrounding Sweden. The aim is to develop a model system tool to support decision makers for the marine environmental conservation.

The SCOBI model may provide information of for example:

  • Nutrients, oxygen conditions and production of biomass.
  • Fluxes, transports, sources and sinks.
  • Water quality and sedimentation of organic matter.
  • Development and spreading of algal blooms.
  • Occurrence of harmful algal blooms (e.g. cyanobacteria).

In the Swedish decision support system HOME Vatten SCOBI is used in combination with the PROBE-model. HOME Vatten is developed for the Swedish water administration and includes lakes, watercourses, and all coastal waters from Haparanda in the north to the Norwegian border in Skagerrak.

The model system is also a part of the Baltic HOME expert system that is an operational marine cores service that handles flows of water, energy and substances in the Baltic Sea, the North Sea, and the corresponding catchment areas.

SCOBI is one of the main components of an operational 3-D ecological model based on the ocean circulation model HIROMB coupled with atmospheric and hydrological models calculating the nutrient supplies from land and atmosphere.

SCOBI is also coupled to a high resolution 3-D ocean circulation climate model (Rossby Centre Ocean model, RCO). The aim is to perform experiments with a high spatial resolution ecological model on long time scales. The RCO-SCOBI model is used to study for example:

  • the influence of climate changes on nutrient dynamics and biogeochemical cycles in the Baltic Sea.
  • the influence of human activities on eutrophication related problems.
  • transports of nutrients from sources to sinks
  • the influence of natural events like deepwater inflows.
Figure of the SCOBI models processes
Figure 1. Sediment variables and processes are shown in the lower left box. Note that the process descriptions oxygen and hydrogen sulphide in the figure are much simplified for clarity
Enlarge Image

The SCOBI model handle dynamics of nitrogen- (N), oxygen- (O2) and phosphorus- (P), including inorganic nutrients, nitrate (NO3), ammonia (NH4) and phosphate (PO4) and particulate organic matter consisting of phytoplankton (autotrophs), dead organic matter detritus (DET) and zooplankton (ZOO). Primary production assimilates the inorganic nutrients by three functional groups of phytoplankton, diatoms (A1), flagellates and others (A2) and cyanobacteria (A3).

Besides the possibility to assimilate inorganic nutrients the modelled cyanobacteria also has the ability to fix molecular nitrogen (N2) which may constitute an external nitrogen source for the model system. Organic material may sink and accumulate in the model sediment as nitrogen (NBT) and phosphorus (PBT). In periods with strong currents and waves sediments in shallow areas may be lifted up into the overlying water again and become transported to deeper parts.

Decomposition of organic matter in the water and sediments consumes oxygen and may return the nutrients to inorganic forms (NH4 and PO4) again. When oxygen is almost completely consumed anoxic decomposition takes place. Anoxic decomposition processes utilize oxygen from nitrate reduction (denitrifikation) and thereafter from sulphate reduction (SO42-).

Sulphate reduction produces poisonous hydrogen sulphide (H2S) that is included as negative oxygen in the model and may be removed when oxygen is supplied e.g. by inflowing water. A fraction of the sediment nutrients are continuously buried while the nutrient flux to the overlying water is controlled by the water temperature and oxygen concentrations.


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