Silicate Release from Sand-Manipulated Sediment Cores: Biogenic or Adsorbed Si?

The influence of an addition of either sand and/or spring-bloom algae on the efflux of nutrients from intact sediment cores from the Baltic Sea was studied in a flow-through experiment. The addition of sand significantly increased the efflux of silicon (Si) from sediment, but the algal addition did not. The effects on phosphorus (P) were not as clear, and fluxes of nitrogen (NH4 and NO2 + 3) remained relatively unaffected by the additions. The small effect of the algal addition was caused by the short time-period covered by the experiment and possibly by adsorption of released Si by the sediment. A follow-up bottle experiment showed that despite the apparently lower content of easily available Si and biogenic silica, BSi, in the sand, the sand-induced Si efflux was caused by release of Si from the sand itself, rather than by indirectly increasing the dissolution of BSi present in the sediment.