PLANT PIGMENT RATIOS FROM LAKE-SEDIMENTS AS INDICATORS OF RECENT ACIDIFICATION IN ALPINE LAKES

Chromatographic and spectrophotometric analyses of plant pigments from sediment cores have long been used to assess the developmental history of trophic status and plant productivity of lakes. We explore the possibility of using an acetone extract ratio of absorbance at two wavelengths (430 and 410 nm) in sediment to reconstruct the time-course of acidification in alpine lakes. Our data demonstrate that this easily measured ratio is closely correlated to lake-water pH and that it can be used stratigraphically to describe past changes in lake acidity. Thus, the easily determined 430:410 ratio can complement stratigraphic studies of fossil diatoms, chrysophycean scales, and carbonaceous particles now used to provide important insights into the responses of sensitive lake systems to acid deposition.