The Importance of Silicon in Coastal Ecosystems

Although nitrogen is the element primarily controlling eutrophication in estuaries and coastal seas, and phosphorus is the element primarily controlling eutrophication in lakes, other elements can have a major influence on the community structure of aquatic ecosystems and can influence the nature of the response to eutrophication. A key element in this regard is silica (silicon), an element required by diatoms. The availability of silica in a water body has little or no influence on the overall rate of primary production, but when silica is abundant, diatoms are one of the major components of the phytoplankton. When silica is in low supply other classes of algae dominate the phytoplankton composition. 

Eutrophication in a system can further decrease silica availability as it is deposited with diatoms and stored in bottom sediments, as demonstrated in the Baltic Sea. The decrease in silica availability, particularly if accompanied by increases in nitrogen, may encourage the formation of some blooms of harmful algae as competition with diatoms is decreased (NRC, 1993). For all cases where long term data sets are available on silica availability in coastal waters, a decrease in silica availability relative to nitrogen or phosphorus has been correlated with an increase in harmful algal blooms. 

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