Historical Development of Laminated Sediments – an Approach to Detect Soft Sediment Ecosystem Changes in the Baltic Sea

In this study, we attempt to use laminated sediments as a tool for establishing effect-related water quality criteria for the eutrophicated Baltic Sea. After initial sediment mapping in the St. Anna archipelago, 47 sediment cores were taken. From analyses and lamina counting, spatial and temporal trends in distribution of laminated sediments were calculated. The expansion in the archipelago started in the 1960s, rapidly increasing during the 1970–1980s, reaching a maximum in the mid 1980s. Thereafter, the area has decreased. The possible reasons for the changes are discussed in relation to trends in the offshore Baltic proper. This study indicates that acceptable environmental conditions were prevalent in the 1950s in the archipelago and in the late 1920s in the offshore Baltic proper. Thus, the nutrient discharges have to be reduced to what they were in the 1950s and the 1920s, respectively.