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A 700 year record of temperature and nutrient changes in a small eutrophied lake in southern Finland

Department of Geology, P.O. Box 64, FIN-00014 University of Helsinki, Finland, tomi.luoto{at}helsinki.fi

Kaarina Sarmaja-Korjonen

Department of Geology, P.O. Box 64, FIN-00014 University of Helsinki, Finland

Liisa Nevalainen

Department of Geology, P.O. Box 64, FIN-00014 University of Helsinki, Finland

Tommi Kauppila

Geological Survey of Finland, P.O. Box 1237, FIN-70211 Kuopio, Finland

This study aimed to distinguish natural and anthropogenic environmental changes, mainly in climate and nutrient conditions, during the past c. 700 years in Lake Hampträsk, southern Finland. We used sedimentary assemblages of aquatic organisms and physical properties of the sediment as proxies for the past environmental conditions. The results of diatom-inferred phosphorus reconstruction indicated that the lake was already meso-eutrophic at c. AD 1400, possibly because the preceding cultivation of the area had increased the lake’s nutrient condition. Chironomid-inferred temperatures indicated favourable climatic conditions at the end of the ‘Medieval Warm Period’, but the temperatures steadily decreased until a significant drop in the values occurred at c. AD 1700, representing the coldest period of the ‘Little Ice Age’ (LIA) in southern Finland. This cold period was illustrated by major changes in the lake’s ecosystem and physical environment. After the LIA, the chironomid-inferred temperatures increased, as expected in the light of modern observations. However, the diatom-inferred phosphorus showed a decreasing trend, which is in contrast to the measured phosphorus values that imply a currently eutrophic condition. The reason for the underestimation may be the predominance of periphytic taxa that are assigned low TP optima in the inference model.

Key Words: Chironomids • diatoms • zoological macro-remains • transfer functions • lake sediments • late Holocene.

The Holocene, Vol. 19, No. 7, 1063-1072 (2009)
DOI: 10.1177/0959683609341002


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