Biological Utilization and Regeneration of Silicon in Lake Michigan

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Abstract
Depth profiles of dissolved reactive silicon and amorphous particulate silicon were made at monthly intervals (April–November 1975) at stations along a southwest transect from Grand Haven, Michigan, to a point approximately in the center of the southern basin of Lake Michigan Biological utilization of reactive silicon occurred prior to stratification in late May or early June. A shift from a 100% diatom-dominated phytoplankton community in spring to ~ 12% diatoms in August was attributed to the low dissolved silicon values observed in the surface water (< 2 μmol/ℓ) during summer. The total amount of biologically active silicon (TBAS) for the lake was found to be approximately 19 μmol/ℓ. Winter values were ~ 2 mol/ℓ amorphous silicon and ~ 17 μmol/ℓ reactive silicon. During the period June–August 80% of TBAS had been utilized by the diatom community, with only 20% remaining as reactive silicon. Greater than 50% of TBAS was lost from the water column during spring and early summer, which was attributed to settling of diatom frustules and the sinking of zooplankton fecal pellets containing frustules. This silicon was subsequently returned, in a soluble form, to the deep water during the fall. The amount of TBAS that was recycled was estimated to be 80–100%. Key words: Lake Michigan, diatoms, recycling, dissolution, limitation, silicon