『Abstract
Although several studies have used bogs in order to reconstruct
paleoclimatic conditions and the historical trends of pollutants,
scientific literature is still rather controversial about the
role of ombrotrophic bogs as reliable record of past environmental
changes. Consequently, understanding whether all vegetational
and climatic “information” are effectively preserved in peat deposit
during humification becomes an essential aspect to be tested before
using bogs as natural archives.
The present work focuses on stable isotopic ratios, i.e., 13C/12C
(δ13C), 15N/14N (δ15N)
and 18O/16O (δ18O), and is based
on the assumption that , if bogs are consistent archives of environmental
changes, these types of “information” should be recorded also
into humic acids (HA), i.e. the fraction of peat more recalcitrant
and refractory to degradation.
Thus, an 81-cm long peat core, covering the last 2000 years,
was collected from the Etang de la Gruere（最初のeの頭に｀）
bog (Jura Mountains, Switzerland), cut into 3 cm slices, and HA
were isolated from each age dated layer. Stable isotopic ratios
(δ13C, δ15N and δ18O) were then
determined in bulk peat and corresponding HA samples.
As increase in the humification degree and a decrease of the
C/N ratio were observed along the profile. The δ13C
of both peat and HA showed a significantly similar trend with
depth (p = 0.0001), and the same significant correlation was observed
for the δ15N (p＜0.0001). Also the ratio between δ13C
and δ15N closely resembled the C/N ratio observed in
the peat and in HA (p＜0.0001）, thus underlining that the trend
of these isotopic ratios is preserved along the studied bog profile.
Consequently, our data seem to support both the role of HA as
recalcitrant, stable molecules with a long-term residence time,
and the potential of ombrotrophic bogs to be used as “archives”
of vegetational changes occurring (at least) in the last 2000
years. Although a certain relationship (p＜0.05) between peat and
corresponding HA was found also for δ18O, our data
did not allow the solving of the issue of its reliability as paleoenvironmental
proxy.
Keywords: C/N ratio; Humification; Isotopic signature; Natural
archives; Ombrogenic bogs; Paleovegetation and paleoclimate changes』
1. Introduction
2. Material and methods
2.1. Sampling site features
2.2. Sample collection
2.3. Humic acids isolation and humification degree indices
2.4. Elemental composition
2.5. Determination of stable isotopic ratios
2.6. Statistical analyses
3. Results and discussion
3.1. Peat humification degree with depth
3.2. δ13C and δ15N signature
3.3. δ18O signature
3.4. Implications for paleovegetational and paleoclimatic reconstructions
4. Conclusions
Acknowledgments
References