K. Kalbitz et al., Spectroscopic properties of dissolved humic substances - a reflection of land use history in a fen area, BIOGEOCHEMI, 47(2), 1999, pp. 219-238
The elemental composition and spectroscopic properties of dissolved fulvic
acids isolated from different sampling media (topsoil, ground and surface w
ater) of a natural fen area (high portion of organic soils) were examined t
o reveal the effects of land use history. These effects need to be known if
dissolved humic substances are to be a major factor in identifying the imp
act of present and future changes in land use. Dissolved fulvic acids (tops
oil, groundwater) from highly degraded peatlands (due to a long-term agricu
ltural use) exhibit lower C/N ratios, higher absorption in the UV spectra,
and higher absorption at 1,620 cm(-1) in the FTIR spectra compared with ful
vic acids from relatively intact peatlands. These properties illustrate tha
t long-term agricultural use with high inputs results in increased aromatic
structures and a further humification of dissolved fulvic acids due to ver
y strong peat decomposition compared with relatively intact peatlands. Sync
hronous fluorescence spectra also indicate the higher level of aromatic str
uctures within fulvic acids isolated from sites with long-term agricultural
use (high peat decomposition) compared with a land use history resulting i
n a lower peat decomposition. The different sources of fulvic acids in surf
ace water (precipitation, runoff, interflow, groundwater) are the main reas
on for these effects not being detected in fulvic acids isolated from surfa
ce water. Short-term changes in land use characterized by a transition from
crop farming to an unimproved grassland were found not to affect the spect
roscopic properties of dissolved fulvic acids. A humification index deduced
from the synchronous fluorescence spectra is proposed. We have strong evid
ence that dissolved humic substances indicate changes in the environmental
conditions (both anthropogenic and natural) of wetlands with a high proport
ion of organic soils.