Journal of Paleolimnology 18: 15–28, 1997. 15 c 1997 Kluwer Academic Publishers. Printed in Belgium. The plant-macrofossil record of past lake-level changes Gina E. Hannon & Marie-Jos´ e Gaillard Department of Quaternary Geology, Lund University, T¨ ornav¨ agen 13, 22363 Lund, Sweden (email: Gina.Hannon@geol.lu.se; Marie-Jose.Gaillard-Lemdahl@geol.lu.se) Received 11 January 1996; accepted 6 June 1996 Key words: plant-macrofossils, palaeoecology, water-chemistry, trophic-status, water-depth, lake-level changes, Holocene Abstract Plant-macrofossil analysis is one of the most useful biostratigraphical methods for the reconstruction of former lake-level changes. The distribution of submerged, floating-leaved and emergent lake-shore vegetation is mainly dependant on water depth, but water chemistry and nutrient status must also be taken into account when interpreting water-level changes. Lake-level studies should be based on the investigation of several littoral cores along a transect perpendicular to the lake-shore. Multiple cores are essential for separating genuine lake-level changes from other processes influencing the plant-macrofossil record. Physical analyses of sediment stratigraphy provide important additional information to the plant-fossil record, because natural infilling processes and erosion from the catchment must be distinguished from climatic events causing a change in the water level. Here we review several important concepts, including suitability of lakes for lake-level study, the degree of detail required in the analysis, and macrofossil records of lake-level changes, and illustrate those concepts by examples from southern Sweden and Minnesota. We discuss how to reconcile alternative hypotheses for the stratigraphic changes seen in the macrofossil assemblages. Introduction The reconstruction of past lake-level changes can best be achieved by the examination of several types of complementary litho- and biostratigraphical evi- dence (Digerfeldt, 1986, submitted; Gaillard & Diger- feldt, 1991; Harrison & Digerfeldt, 1993). Plant- macrofossils are one of the biological archives well suited to the reconstruction of former lake-level changes, and hence former climates. The use of plant-macrofossils to reconstruct lake- level changes assumes that distinctive zones of aquat- ic vegetation are associated with particular water- depths, giving rise to the characteristic zonation of emergent, floating-leaved and submerged vegetation outwards from the shore (Digerfeldt, 1986; Harrison This paper is one in a series of papers to be published in the Journal of Palaeolimnology that resulted from a European Science Foundation Workshop, convened in Sweden by Dr S. Harrison and Prof. B. Frenzel, entitled ‘Palaeohydrology as Reflected in Lake Level Changes as Climatic Evidence for Holocene Times’. & Digerfelt, 1993). Complicating factors are, first, that many different environmental changes can lead to changes in aquatic vegetation (Hutchinson, 1975; Jack- son & Charles, 1987; Jackson et al., 1988; Jackson & Whitehead, 1991), and second, that aquatic vegetation is imperfectly represented in the macrofossil record (Birks, 1973, 1980). A further complication is that lake-levels may be controlled by both local and region- al factors (Gaillard & Digerfeldt, 1991; Harrison et al., 1993). Local changes resulting from natural hydroser- al succession or local environmental changes such as erosion, deforestation or changes in land use should be separated from changes expressed over a large region that probably result from climatic change. Digerfeldt (1986) has developed a method to address these prob- lems. This involves the study of transects of mar- ginal sediment cores, incorporating plant-macrofossil and pollen stratigraphy, sediment composition, and changes in the level of the sediment limit (Lundqvist,