High concentrations of amorphous, biogenic Si (BSi) in the sediment of a small high-latitude lake: implications for biogeochemical Si cycling and for the use of BSi as a paleoproxy

Abstract

The concentration of biogenic silica (BSi) in soils and sediments may be studied for several purposes, most notably either as a paleo-environmental proxy or to clarify the transport of weathering-derived Si within the biogeosphere. With this in mind, we explored the reasons behind the very high BSi concentration (average 250 mg Si g−1 dry mass) in the sediment of a small, high-latitude lake in Finnish Lapland, Lake Kuutsjärvi, using bulk BSi and stable Si isotope analysis of major Si pools in the lake and its drainage area. The high BSi content of the sediment was relatively stable over the past few hundred years and recent changes in the food web of the lake were not clearly reflected in the data. The origin of the sedimentary BSi was not solely autochthonous diatom production: extraneous sources accounted for possibly as much as 54–88 % (isotope analysis). A main reason for the high BSi content appeared to be the transport of older deposits of diatom material from the drainage area into the current lake basin, although other factors such as good preservation conditions may have contributed. Although our results indicate that small high-latitude lakes may be hot-spots in the burial of BSi, more information is needed on the processes that affect the translocation of BSi from the drainage area to the aquatic system. Caution is advisable when past lake conditions are inferred from sedimentary BSi only.