Interpreting δ13C Values Obtained on SOM from Ancient Maya Reservoirs and Depressions

elemental analyzer (EA) Isotope Ratio Mass Spectrometry was used to measure ∂13C values on soil organic matter from reservoirs and depressions at the ancient Maya urban centers of Tikal, Guatemala and Yaxnohcah, Mexico. Variation in δ13C values on soil organic matter were > −2.0‰, which suggests enrichment from C4 plants including maize, other tropical grasses (Poaceae), and tropical sedges (Cyperaceae), CAM plants (Clusia sp.), and cyanobacteria (blue-green algae). Cyanobacteria were likely a major contributor to the 13C enrichment of soil organic matter in Maya reservoirs and depressions, which has obfuscated our understanding of ancient Maya maize production. It is possible that the Maya used cyanobacteria as a fertilizer, which enriched agricultural field soil organic matter.