AN 850-YEAR RECORD OF HUMAN AND ENVIRONMENTAL CHANGE NEAR THE MISSISSIPPIAN-ERA CITY OF MOUNDVILLE (ALABAMA) FROM LAKE SEDIMENT GEOCHEMISTRY

Touson Lake (33.0070 N, 87.6623 W) is a small monomictic, oxbow lake located in west-central Alabama, USA. The lake has a large catchment to surface area ratio and receives inflow from two small streams, with an outflow stream draining to the nearby Black Warrior River. The prehistoric Mississippian city, Moundville, is located 3.2 km east of the lake. The close proximity of Touson Lake to Moundville places it within a region that would have been impacted by this settlement. Human-induced land-use changes in the area are known to have taken place during the Mississippian Period from 1000 to 1450 AD, when up to 10,000 people lived in the area, and 29 large earthen mounds were constructed within the city. We hypothesized that these human activities would be recorded in Touson Lake sediments.

We retrieved a 1.8-m long sediment core from the 6.2-m deep anoxic basin of Touson Lake to identify past sedimentary changes related to environmental and human disturbance. The sediments were dated using ²¹⁰Pb, ¹³⁷Cs, and ¹⁴C dating techniques. We measured weight percent organic matter, sorbed metal concentrations, and magnetic susceptibility. Lead (Pb) and zinc (Zn) concentrations were measured because their concentrations in sediments are commonly influenced by human activities (Cohen, 2003). Increases in Pb concentrations around 1400 and 1700 AD suggest that emissions from Mississippian settlements and European settlement are preserved in Touson Lake. Corresponding increases in Zn from 1650 to 1800 AD suggest that other metals, such as zinc and copper, could potentially be used to track inputs from metalworking. In addition, magnetic susceptibility and organic matter measurements record large fluctuations during intervals of mound-building and settlement reorganization in the region, suggesting changes in the amount of erosion during these periods. The Touson Lake record demonstrates that sediments recovered from oxbow lakes in southeast North America could be used to measure past human and environmental changes, which may hold implications for improving both archaeological and paleoenvironmental interpretations.

Resources

Cohen, Andrew S. "Geochemical Archives in Lake Deposits." Paleolimnology: The History and Evolution of Lake Systems. Oxford: New York, 2003. 241-55. Print.