PARENT SESSION
Oral Session #10: Paleoecology. Presiding: S. Hotchkiss.
Monday, August 6, 2001. 8:00 AM to 12:00 PM. Hall of Ideas J.

A Diatom and pollen record from Catfish Pond, Illinois.

Teed, Rebecca¹, ¹

ABSTRACT- Fossil pollen and diatom samples from a lake sediment core from Catfish Pond, Illinois, provide a nearly continuous record of vegetation and water chemistry > 22,000 years long. Diatom assemblages of the deepest, presumably oldest, levels contain mostly Eunotia monodon and large (80 m+) Pinnularia, including P. maior and P. viridis. These levels are also rich in pine, oak, ash, and sedge pollen. Sediments dated to the late Wisconsinan glacial period, > 22,000 ¹⁴C years ago, also contain a lot of spruce pollen, indicating a cooler climate. Eunotia monodon accounts for > 60% of the diatom valves counted, up from 20% in older levels. Between 6,000 and 200 years ago, the pollen assemblages indicate that the landscape was a mosaic of oak-hickory forest and prairie. Eunotia monodon decreases to < 10% of valves counted and the diatom flora becomes more diverse, including substantial amounts of Stauroneis phoenicenteron and Neidium affine. After 200 years ago, sedimentation rate and ragweed pollen percentages increased, indicating homesteading and associated intense agriculture in central Illinois. The diatom assemblages have become even more diverse, dominated in the upper levels by Aulacoseira italica. Throughout the record, there is a tight correlation between Eunotia monodon as a percentage of diatom valves counted and coniferous tree pollen as a percentage of terrestrial pollen types (r² = 0.7924, p > 0.0000). Perhaps both the diatom flora and tree taxa are responding synchronously to climate change or perhaps there is a more direct link. Coniferous tree litter tends to decompose slowly and to acidify the soil of the catchment, which would in turn decrease the pH and increase the DOC content of the lake, which might favor Eunotia monodon over its competitors.

KEY WORDS: paleolimnology, diatoms, pollen, soil development