Modelling of eutrophication effects on coastal ecosystems with eelgrass as the dominating macrophyte

In shallow areas eelgrass (Zostera sp.) has a major influence on the biological structure. The presence of eelgrass affects the nutrient cycling, sedimentation/resuspension, and is necessary for natural populations of fish and zoobenthos acting as part of the total coastal ecosystem. In Denmark and in other countries increasing eutrophication has caused a reduction in water transparency and increased growth of epiphytes on the eelgrass in many coastal areas leading to a severe suppression of the natural extension of eelgrass, mainly reducing their extension depth from several meters to 1-2 meters. A model describing eelgrass (Zostera marina) growth has been developed as a sub-module to an existing general eutrophication model for coastal marine areas which describes phytoplankton growth depending mainly on nutrient availability. The eelgrass submodel describes seasonal variations in production and biomass of leaves and roots and how this is affected by eutrophication processes related to nutrient loadings and other environmental impacts such as outlet of cooling water. The model has been used as a tool to evaluate the impact of eutrophication caused by nutrient loadings in combination with an expansion of a power plant on the island of Masnedø. The results of consequence calculations have been used to evaluate the impact of eutrophication on the eelgrass community as a vital part of the ecosystem in the area investigated which is of great tourist, recreational and natural value.