Linköping Studies in Art and Science • No. 535 Linköping University,
Department of Thematic Studies – Water and Environmental Studies Linköping 2011
Silicon cycling in the Baltic Sea:
Trends and budget of dissolved silica
The dissolved silicon (DSi) has a crucial role for growth of a large group of primary producers – diatoms and, hence, impact on functioning of the aquatic food web. This thesis contributes to an increased understanding of the modifications of the DSi cycling in the Baltic Sea. The results provide new information about spatial and temporal changes in DSi concentrations and nutrient ratios for the period 1970–2001 as well as during the 20th century.
For the period 1970–2001, the declining DSi trends were found at the ma-jority of monitoring stations all over the Baltic Sea. This decrease is as-sumed to be mainly due to the ongoing eutrophication. It is supported by the increasing trends of inorganic nitrogen and phosphorus. The trends have implications for the nutrient ratios, DSi:DIN and DSi:DIP, which are important indicators of the state of an ecosystem. The long-term retrospec-tive DSi budget has shown that the DSi concentrations before major hydro-logical alterations and eutrophication were about twice the present ones. This decrease is related to both eutrophication and anthropogenic pertur-bations in the catchment.
The occurrence of DSi concentrations close to the potentially limiting lev-els has been also analysed. While DSi concentrations are still high in the northern regions of the Baltic, other areas may be at risk of developing Si limitation if the decrease in DSi concentrations persists. The results depict the Baltic Sea journey from being water body with DSi levels sufficient to support diatom production to one that may experience Si limitation and its adverse ecological consequences.
