THE IMPACT OF LAKE-LEVEL FLUCTUATIONS ON THE SEDIMENT COMPOSITION JAAN-MATI PUNNING * , JAANUS TERASMAA and TIIT VAASMA Institute of Ecology, Tallinn University, Uus-Sadama 5, Tallinn 10120, Estonia ( * author for correspondence, e-mail: mati@eco.tlu.ee; phone: +372-61-99833; fax: +372-61-99801) Abstract. Lithological and granulometric investigations of the surface and short core sediments in L. Martiska (northeastern Estonia) showed that variations in the grain-size parameters and LOI content were influenced by the changes in deposition conditions during the regression and transgression phases monitored in the lake since the 1960s. During the regression and transgression phases displacement of the erosion-transport-accumulation zones in the lake took place depending on the bottom topography. The water level fluctuations are especially clearly reflected in grain-size variations in cores from peripherial area. Keywords: lake-level fluctuations, palaeolimnology, resedimentation, sediment grain size 1. Introduction Numerous sediment studies are focused on describing direct responses of various bioindicators, geochemical records and hydrological changes to the trophic state of a lake (Dearing, 1983; Engstrom, Swain, & Kingston, 1985). Less attention has been paid to sedimentary processes, especially to the grain size of lake sediments; however, these studies have been promising in investigating lake-level variations in small temperate lakes (Digerfeldt, 1986; Punning, Alliksaar, Terasmaa, & Jevrejeva, 2004). The fluctuations of water level alter the lake morphometry and transform the characteristics of the sedimentation zones (erosion, transportation, accumulation; Håkanson, 1977) of the lake bed, thereby directly influencing sedimentation, resuspension as well as biogeochemical dynamics in the lake. Several studies have been successful in investigating water level variations in small temperate lakes (Dearing, 1997; Digerfeldt, 1986). Recent studies in palaeolimnology (Beierle, Lamoreux, Cockburn, & Spooner, 2002) have shown that the quantitative and qualitative analyses enable to describe sedimentological processes and distinguish the changes of the past environment. The main aim of this research was to study the lithological composition and grain-size parameters of sediments accumulated in a small lake and to compare the data with the historical evidences about its water level fluctuations. Water, Air, and Soil Pollution: Focus (2006) 6: 515–521 DOI: 10.1007/s11267-006-9035-4 © Springer Science + Business Media B.V. 2006