Southeastern Section–55th Annual Meeting (23–24 March 2006)

Paper No. 5
Presentation Time: 1:30 PM-5:30 PM


LANE, Chad S.1, TAYLOR, Zachary P.1, MORA, Claudia I.2, HORN, Sally P.1 and ORVIS, Kenneth H.1, (1)Department of Geography, University of Tennessee, Knoxville, TN 37996-0925, (2)Earth and Planetary Sciences, Univ of Tennessee, Knoxville, TN 37996-1410,

Variation in the stable carbon isotope composition (d13C) of lake sediments is often interpreted to reflect natural changes in watershed vegetation and/or changes in carbon cycling within the lake itself.  However, with increased recognition that prehistoric human populations may have had far more drastic impacts on landscape composition and disturbance regimes than once thought, it is important to differentiate naturally- and anthropogenically- driven vegetation and limnological change.  Here we present data from six tropical lakes documenting drastic changes in the d13C value of lake sediments as a result of prehistoric forest clearance and maize agriculture during the late Holocene.  We hypothesize that these changes are due to the fact that most trees and understory herbs in tropical forests utilize the C3 photosynthetic pathway (d13C = ~ -31‰ to -23‰ V-PDB), while many shade intolerant cultigens and crops, including maize, utilize the C4 photosynthetic pathway (d13C = ~ -16‰ to -10‰ V-PDB).  A shift in the relative dominance of these two photosynthetic pathways, and therefore the average d13C value of biomass, can be expected following human forest clearance and agriculture.  In addition to using these data as a warning to researchers interpreting the d13C value of lake sediments, we also propose that the d13C value of lake sediments during periods of documented forest clearance and agriculture may be a very useful tool.  Based on the existing assumptions of isotopic mixing models, it may actually be possible to reconstruct the areal extent of forest clearance and maize agriculture in archaeological study sites, which would otherwise require extensive excavation.  Also, we suggest that the d13C value of lake sediments may be a useful proxy of forest clearance and maize agriculture in sedimentary archives where preservation of other organic proxies, such as pollen, is poor.