ENVIRONMENTAL CHANGES ASSOCIATED WITH NATIVE AMERICAN LAND USE PRACTICES: A GEOARCHAEOLOGICAL INVESTIGATION OF AN APPALACHIAN WATERSHED

Stable isotopes of carbon (δ¹³C_calc) in calcite stalagmites reflect past climatic and land use changes. Anomalous increases are present in δ¹³C_calc and δ¹³C of stream sediments from Buckeye Creek Cave (BCC), West Virginia beginning around 2,100 (cal.) years B.P. This implies sudden aridity, changes in the soil C cycle, an increase in C₄ vegetation, or a combination of above. However, regional pollen records do not show a rise in dry-adapted vegetation nor does δ¹³C_org time series from contemporaneous slackwater sediments in a nearby cave. Archaeological evidence supports the presence of Native Americans (NA) in the BCC system contemporary with the C anomalies and the latter could possibly be attributable to NA land use practices.

To test this hypothesis, charcoal abundances (CA) were measured for the stream sediments using organic bleaching method. In order to understand the response of vegetation to climate and disturbance by fire, published pollen data were compared to CA and δ¹³C values by means of cross correlation of time series. According to the calculated CA, peak fire events were recorded following 4,000 years B.P. and correlate with mid-successional mast tree pollen abundance. This observation is consistent with published studies claiming that NA used fire as a forest management tool. Late Holocene δ¹³C_calc values coincide with the highest sediment CA. Grain size analyses of stream sediments also suggest landscape alterations associated with forest fires.

Notably, stalagmite Sr/Ca ratios, a wet/dry proxy, are correlated with δ¹³C_calc until 2,100 years B.P., after which Sr/Ca remained correlated with marine climate proxies but not δ¹³C_calc. δ¹³C_calc values were extrapolated for the anomalous period based on the assumption that stalagmite Sr/Ca ratios correlate with δ¹³C_calc when drip water residence times and CO₂ degassing rates depend on local climate. Calculated values resembled observed values prior to 2,100 years B.P., but subsequent values deviate markedly from the observed trend, suggesting the effect of factors other than climate on δ¹³C_calc. Collectively, this and the other available data support the hypothesis that the local environment and C cycle were significantly disturbed prior to the arrival of Europeans and that NA played a major role in shaping this local pre-Columbian ecosystem.