Analysis of multiple depth profiles in sediment cores: an application to pollen and diatom data from lakes sensitive to acidification

The methods of clustering and ordination were compared with polynomial and segmented regression methods by application to the pollen and diatom profiles from two sediment cores obtained from lakes susceptible to acid precipitation. Clustering and ordination methods have previously been used to determine zones in sediment profiles, but regression methods which summarize the changes with depth in terms of one or more smooth curves, explicitly use the depth information. Plots of running means were also used to characterize profile shapes. The latter two methods provided a clearer understanding of the changes in diatom and pollen levels in the cores. For low diatom concentrations, non-parametric methods were used to test for a change in concentration with depth. Changes in dry weight of sediment, different bases for concentration and depth, and the effect of poor represententation of an extreme group on the pH spectrum were also considered. The regression procedures were shown to provide summaries useful for comparison of different species or of the same species in different cores. Finally, a summary is given of the similarity of the patterns in the depth profiles of eight pollen types and the non-rare diatom species in one core from each of Kejimkujik and Beaverskin Lakes, respectively.