Modern pollen rain and diatom assemblages in a Lake Erie coastal marsh

Abstract

We present an analysis of modern pollen and diatom assemblages in surficial sediments in a coastal marsh at Rondeau Provincial Park, on the northern shore of Lake Erie in southwestern Ontario, Canada. The objectives of the study were (1) to determine how pollen and diatom assemblages in surface sediments vary as a function of the dominant vegetation community and moisture availability at the sampling site and (2) to analyze pollen-vegetation relationships of four dominant wetland plants: Cephalanthus occidentalis, Phragmites australis, Typha spp., and Zizania aquatica, in order to improve interpretations of fossil sequences. Canonical variate analysis (CVA) was used to compare pollen and diatom spectra from sampling sites in three marsh zones delineated on the basis of moisture availability. Using the pollen or the diatom datasets, the resulting discriminant functions correctly classified 86% of the wettest sites, 72% of those with intermediate moisture availability, and only 25% of the sites in the driest parts of the wetland. Since 35% of the sampling sites were misclassified by the CVA on the basis of pollen assemblages, a representation factor approach is needed to complement the comparative approach when analyzing pollen datasets from wetland contexts. Percent cover vegetation data at sediment sampling sites are used to illustrate pollen-vegetation relationships for the ecologically important wetland plants at the site. Phragmites australis and Typha spp. produce small amounts of pollen relative to their abundance, while Cephalanthus occidentalis and Zizania aquatica produce abundant pollen, which is deposited highly locally in the case of Cephalanthus. These data will enable improved interpretations of fossil pollen and diatom sequences from wetland contexts.