A multivariate assessment of coastal eutrophication. Examples from the Gulf of Finland, northern Baltic Sea

The Gulf of Finland is the sub-basin of the Baltic Sea that is most seriously affected by the effects and consequences of eutrophication. In this study, physical, chemical and biological long-term data (1980–2002) from the Finnish environmental monitoring programme is used to detect possible gradients of eutrophication in the Gulf. The Finnish coastal area of the Gulf of Finland is divided into three parts in an east–west direction, and into three zones (inner, middle, outer) according to differences in descriptive parameters. We use principal component analysis (PCA) to study spatial and temporal differences in relation to eutrophication. Clear differences between coastal and offshore areas are seen. Differences between eastern and western Gulf are not as evident. The changes due to eutrophication are larger for the inner archipelago, whereas the outer areas have been more stable over time. The concentration of oxygen is the strongest driving factor for eutrophication in the region.