The magnitude of Si dissolution from diatoms at the sediment surface and its potential impact on P mobilization

The magnitude of the influence of diatom-derived dissolved Si on the mobili ty of P at the sediment-water interface was investigated in eutrophic Lake Vesijarvi, southern Finland. The spring bloom, which consisted of small cen tric diatoms, depleted the Si from the water column (<100 mu g l(-1)) and w as followed by a sharp increase in the diatom numbers at the sediment surfa ce and by a peak of dissolved Si in the sediment interstitial water. The di atom cells disappeared from the surface sediment on a time scale of weeks ( 5 % d(-1)). Calculations based on the cell numbers and on the Si deficit in the water column indicated that the dissolution of diatoms in the sediment surface layer may produce Si pulses high enough to influence the mobility of P.