Infrared absorption spectra were run on humic substances from Lake Apopka sediment samples and compared with spectra from citrus and muck farm humic substances from sediment in the surrounding drainage basin, and also with spectra from autochthonous plankton humic substances. The 1540 cm'1 and 1650 cm' 1 peaks in the plankton and lake sediment samples, in addition to other spectra similarities, indicate that plankton is the probable precursor of lake sediment humic substances. The absorption bands at 1650 cm 1 and 1540 cm 1 are thought to be due to peptide bonds in protein, with amide I absorption occurring at 1650 cm 1 and amide II absorption at 1540 cm 1 . The spectra from the muck farm soil and citrus soil differ to a greater extent from the spectrum of the lake sediment than do the plankton spectra.
Belanger, Thomas V., "Infrared Absorption Study Of Humic Substances From Lake Apopka Sediment, Plankton And The Surrounding Drainage Basin" (1981). Ocean Engineering and Marine Sciences Faculty Publications. 139.