Trends in heavy metal concentrations in the Western and Central Baltic Sea waters detected by using empirical orthogonal functions analysis

Heavy metal concentrations from annual sampling in the period 1993–2000 at the monitoring stations in the Baltic Sea were analysed using empirical orthogonal functions. If all monitoring data from the upper layer are used, no significant trend exists except a decrease in cadmium suspended particulate material (SPM) and an increase in dissolved copper. If the data are separated into different regions, significant trends can be identified in the Baltic Proper. In the surface water, negative trends appear in cadmium SPM, lead SPM, and zinc SPM. However, positive trends can be identified in dissolved cadmium and copper. The increase is in the order of one third standard deviation per year. In contrast, in deeper parts (below 80 m), dissolved cadmium and lead SPM decrease whereas dissolved copper increase.