PARENT SESSION
Poster Session #22: Paleoecology.
Wednesday, August 8, 2001. Presentation from 10:30 AM to 12:00 PM. Exhibition Hall

Impact of European-American colonization on Horseshoe Lake, Alexander County, Illinois.

Brugam, Richard¹, Crenshaw, Michelle¹, ¹

ABSTRACT- Horseshoe Lake is an oxbow lake formed by the migration of the Mississippi River across its floodplain. The lake currently has one of the northernmost stands of bald cypress (Taxodium distichum) in the Midwest. Although the lake is currently protected from most flooding by levees constructed in the 1930's., it was heavily impacted by the 1993 Mississippi River flood. The levees have the effect of preventing the annual flooding that existed in pre-settlement times from influencing the lake. We took a 60 cm-long sediment core from a location in the lake that is accumulating sediment. Pollen analysis of the core shows that the appearance of abundant cypress pollen occurs at the time of the ragweed (Ambrosia) pollen increase that indicates the arrival of European-American settlers. Before that time, there is a low abundance of cypress pollen indicating that the tree was present, but as common in the area as it is currently. The coincidence of the ragweed rise and the increase of cypress may indicate that the arrival of European-Americans altered the hydrology of the lake enough to allow the tree to invade the lake. Alternatively, the great New Madrid earthquake of 1812 might have altered the hydrology of the lake sufficiently to allow cypress to grow. It is well known that the earthquake increased the size of Reelfoot Lake in Tennessee and created the St. Francis Sunk Lands in Arkansas. At the moment we cannot determine which of these competing hypotheses is correct for Horseshoe lake.

KEY WORDS: Taxodium distichum, Horseshoe Lake, Illinois, Paleoecology