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The effects of natural environmental changes on sedimentation in Lake Kuttanen, a small closed lake in Finnish Lapland

Laboratory of Physical Geography, PO Box 9, Fin-00014 University of Helsinki, Finland

A sediment core from Lake Kuttanen, a small closed lake in Finnish Lapland, was investigated to determine the effects of Holocene water-table changes, aeolian activity and forest fires on sediment physical properties and sediment geochemistry. Sediment properties were examined by water content, loss-on-ignition (LOI) and dry matter sedimentation rate analyses. Sediment geochemistry was studied by determining the acid-soluble accumulation rates of Al, Ca, Cu, Fe, K, Mg, Mn, Na, P and Zn. The Fe/Mn ratio was calculated to study changes in the redox potential and charcoal concentrations were measured to determine the occurrence of local and regional fires. The sediment accumulation rate was determined using ¹⁴C and b-activity measurements. Principal components analysis (PCA) was used to examine variations within the data and intercorrelations among the variables. After the isolation of the basin, all the element accumulation values were high because of the erosional supply from the catchment before stable soil formation. During the supposed termination of the early Holocene dry and warm period (6000–4000 cal. BP) the element and dry matter accumulation values decreased and LOI increased rapidly. The sedimentation rate increased gradually and the element accumulation values began to increase after 4000 cal. BP along with the increase in dry matter accumulation. The accumulation of Fe was affected also by chemical mobilization from the soils. The LOI values decrease gradually towards the sediment surface, suggesting higher water levels, increasing aeolian activity on a regional scale and dilution by Fe supply from the catchment soils. About 900 cal. BP this activity began locally very near the lake. Charcoal analysis shows that forest fires were a common feature on a regional scale. Their geochemical impact is somewhat unclear; perhaps because most were of little or no geochemical significance, which may have been related to the properties of the permeable soil of the catchment. The fires around 1600 and 900 cal. BP probably triggered the aeolian activity near the lake, which has led to the mobilization of Fe from the catchment, and reverse datings in the ¹⁴C analysis. Thus, natural environmental changes can cause rapid sedimentological and geochemical changes. The main force behind the changes appears to be climatic.

Key Words: Sediment geochemistry • lake sedimentology • charcoal • forest fires • aeolian activity • climatic change • Holocene • Finnish Lapland.

The Holocene, Vol. 10, No. 3, 377-386 (2000)
DOI: 10.1191/095968300677636627


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