A HOLOCENE DIATOM RECORD FROM WALDEN POND, MA (USA) (Invited Presentation)

Walden Pond is best known as an icon of wild Nature through the writings of Henry David Thoreau, but the history of the pond began long before the days of Thoreau. We present here an overview of diatom assemblages in an 8 m long sediment core that represent the last 13,000 years of limnological history in Walden Pond. An abundance of benthic pennate taxa in the basal section of the core indicate shallow conditions in the lacustrine kettle depression following regional deglaciation. Deep-water planktonic diatoms dominated the assemblages after ca. 11,000 cal yr BP, particularly members of the genera Discostella, Lindavia, and Tabellaria. A prominent peak in the percentages of long, slender taxa (Synedra spp.) and chrysophyte scales coincided with the 8200 cal yr BP cooling event in the North Atlantic region. A dramatic shift in the composition of the planktonic diatom community ca. A.D. 1930 marked the onset of cultural eutrophication due to human activity in the watershed and represented the most extreme ecological change in the Holocene history of the pond. Multiple signs of global- to local-scale impacts in the post-19^th century sediments reflect an increasingly powerful human presence during the Anthropocene epoch, making Walden Pond a mirror in which, to paraphrase Thoreau, we can see the depths of our own nature.