Fig. 1. Liquid-state ¹³C nuclear magnetic resonance (NMR) spectra of HA, FA, LMA, HON, and LMN derived from alkali extracts of the Oa1 horizon in Site 1 soil. HA, humic acids (14700 scans); FA, fulvic acids (13801 scans); LMA, low-molecular-weight acids (17000 scans); HON, hydrophobic neutrals (14001 scans); LMN, low-molecular-weight neutrals (14220 scans)