K. Kalbitz et W. Geyer, Humification indices of water-soluble fulvic acids derived from synchronous fluorescence spectra - effects of spectrometer type and concentration, J PLANT NU, 164(3), 2001, pp. 259-265
Citations number
38
Categorie Soggetti
Agriculture/Agronomy
Journal title
JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE-ZEITSCHRIFT FUR PFLANZENERNAHRUNG UND BODENKUNDE
The high variability of dissolved organic matter (DOM) in natural systems (
concentration, composition) means rapid methods are required for its charac
terization so that a high number of samples can be analyzed. The objective
of the present study was to quantify the effects of spectrometer type and d
issolved organic carbon (DOC) concentration on the humification indices of
water-soluble fulvic acids (FAs) derived from synchronous fluorescence spec
tra, and thus enable the broader application of this method for DOM charact
erization. We used three standard FAs from the International Humic Substanc
es Society, 24 water-soluble FAs isolated from topsoil, groundwater and sur
face water in a fen area, and two different spectrometers. The wavelengths
at which bands occurred were similar for all the FAs. Therefore, the differ
ences between the spectra of the FAs studied could be described by humifica
tion indices (band ratios). The humification indices calculated correlated
very well between spectrometers despite small differences in the wavelength
s of bands and shoulders. The absolute values of these indices deduced from
two spectrometers can only be directly compared if the spectra are correct
ed using a standard substance. Increasing DOC concentration resulted in a l
inear increase in humification indices with a sample specific slope. Theref
ore, we recommend using an uniformly low DOC concentration of about 10 mg C
l(-1) for recording the spectra of samples with typically low DOC concentr
ations (aquatic samples, soil solutions). This value is a compromise betwee
n relatively low absorption to minimize inner filter effects and a sufficie
nt signal-to-noise ratio.