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| Titel |
Characterization of the degree of decomposition and CO2 and CH4 production rates in three pristine ombrotrophic bogs in Southern Patagonia |
| VerfasserIn |
Tanja Broder, Klaus-Holger Knorr, Harald Biester, Christian Blodau |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250053420
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| Zusammenfassung |
| Peatlands of Southern Patagonia receive increasing attention in research, although they
represent only a small fraction of the global peatland area. A very low population density and
negligible nutrient deposition have conserved large and pristine bogs and mires, representing
archives for paleoclimate and past environmental conditions.
Controls of carbon storage and decomposition processes have been intensively studied in
northern bogs and thus most factors constraining decomposition have been previously
described. For Southern Patagonian peatlands yet only few studies exist and a verification of
these controls and patterns in these southern ecosystems has so far not been achieved. To
obtain a general characterization, we investigated the degree of decomposition and CO2 and
CH4 production rates at three ombrotrophic bogs in vicinity of Punta Arenas, Chile, and
compared the results to a well studied Canadian bog. The three sites differed in
terms of precipitation, seaspray input, and vegetation. Furthermore, at all three sites
distinct ash layer occurred that can be expected to affect peat decomposition. Peat
solid phase was characterized by C and N contents, FT-IR absorption spectra, and
trace element contents; pore water was analyzed for dissolved gases and major ion
concentrations.
The highest degree of decomposition was found at the driest site with a humification
index of up to 1.4 as calculated from FT-IR measurements; the other sites were mostly below
1.0. This is very low compared to Mer Bleue, Canada (up to 1.73). C/N ratios were mostly in
a range from 40 to 100, with a more or less decreasing trend with depth. There was no
consistent pattern of the degree of decomposition at all three sites and the degree was rather
varying with depth. The identified ash layers seemed to have an enhancing effect
on decomposition, as we observed a higher degree of decomposition above each
distinct ash layer. Furthermore, a strong negative correlation between C/N ratio and
humification index could be calculated for all three sites (0.01 level of significance;
n=77).
Pore water concentrations of CO2 increased with depth and highest concentrations of the
different sites ranged from 4000 to 6000 μmol L-1. A similar pattern could be seen for CH4
concentrations with highest values of 250 to 3000 μmol L-1. Steepest concentration
gradients occurred in the upper 75 cm. Highest CO2 and CH4 concentrations occurred at the
site with lowest degree of decomposition and intermediate precipitation, while the driest
and most decomposed site showed lowest methane concentrations. An obvious
different pattern of methane and carbon dioxide production could clearly be seen at
CO2:CH4 ratio, which is much higher at the highly decomposed site (~ 5-10) compared
to the other two investigated bogs (~2.5). This may also be an effect of higher
seaspray-input, which might have caused the higher sulfate concentrations observed at the
driest site. Compared to similar measurements on the Canadian Mer Bleue bog,
methane concentrations exhibit a much higher concentration range, while carbon
dioxide concentrations were comparably low (5000-7000 μmol L-1 in Mer Bleue,
CDN).
Overall, there was no gradual increase in the degree of decomposition in the catotelm
region, but the profiles seemed to reflect a record of the paleo-environmental conditions. As
the ash layers obviously enhanced decomposition, interpretation needs to be done with care,
though. All investigated Patagonian bogs were less decomposed compared to a northern bog
and highest decomposition was found at the driest site, which is consistent with
previous studies. Differences in CO2 and CH4 production may be explained by
inhibition of methanogenesis by enhanced sulfate concentrations due to seaspray input. |
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