THE PLANT-MACROFOSSIL RECORD OF PAST LAKE-LEVEL CHANGES

Plant-macrofossil analysis is one of the most useful biostratigraphica l methods for the reconstruction of former lake-level changes. The dis tribution of submerged, floating-leaved and emergent lake-shore vegeta tion is mainly dependant on water depth, but water chemistry and nutri ent status must also be taken into account when interpreting water-lev el changes. Lake-level studies should be based on the investigation of several littoral cores along a transect perpendicular to the lake-sho re. Multiple cores are essential for separating genuine lake-level cha nges from other processes influencing the plant-macrofossil record. Ph ysical analyses of sediment stratigraphy provide important additional information to the plant-fossil record, because natural infilling proc esses and erosion from the catchment must be distinguished from climat ic events causing a change in the water level. Here we review several important concepts, including suitability of lakes for lake-level stud y, the degree of detail required in the analysis, and macrofossil reco rds of lake-level changes, and illustrate those concepts by examples f rom southern Sweden and Minnesota. We discuss how to reconcile alterna tive hypotheses for the stratigraphic changes seen in the macrofossil assemblages.