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| Titel |
Water-table height and microtopography control biogeochemical cycling in an Arctic coastal tundra ecosystem |
| VerfasserIn |
D. A. Lipson, D. Zona, T. K. Raab, F. Bozzolo, M. Mauritz, W. C. Oechel |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 9, no. 1 ; Nr. 9, no. 1 (2012-01-31), S.577-591 |
| Datensatznummer |
250006683
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| Publikation (Nr.) |
 copernicus.org/bg-9-577-2012.pdf |
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| Zusammenfassung |
| Drained thaw lake basins (DTLB's) are the dominant land form of the Arctic
Coastal Plain in northern Alaska. The presence of continuous permafrost
prevents drainage and so water tables generally remain close to the soil
surface, creating saturated, suboxic soil conditions. However, ice wedge
polygons produce microtopographic variation in these landscapes, with raised
areas such as polygon rims creating more oxic microenvironments. The peat
soils in this ecosystem store large amounts of organic carbon which is
vulnerable to loss as arctic regions continue to rapidly warm, and so there
is great motivation to understand the controls over microbial activity in
these complex landscapes. Here we report the effects of experimental
flooding, along with seasonal and spatial variation in soil chemistry and
microbial activity in a DTLB. The flooding treatment generally mirrored the
effects of natural landscape variation in water-table height due to
microtopography. The flooded portion of the basin had lower dissolved
oxygen, lower oxidation-reduction potential (ORP) and higher pH, as did
lower elevation areas throughout the entire basin. Similarly, soil pore
water concentrations of organic carbon and aromatic compounds were higher in
flooded and low elevation areas. Dissolved ferric iron (Fe(III))
concentrations were higher in low elevation areas and responded to the
flooding treatment in low areas, only. The high concentrations of soluble
Fe(III) in soil pore water were explained by the presence of siderophores,
which were much more concentrated in low elevation areas. All the
aforementioned variables were correlated, showing that Fe(III) is
solubilized in response to anoxic conditions. Dissolved carbon dioxide
(CO2) and methane (CH4) concentrations were higher in low
elevation areas, but showed only subtle and/or seasonally dependent effects
of flooding. In anaerobic laboratory incubations, more CH4 was produced
by soils from low and flooded areas, whereas anaerobic CO2 production
only responded to flooding in high elevation areas. Seasonal changes in the
oxidation state of solid phase Fe minerals showed that net Fe reduction
occurred, especially in topographically low areas. The effects of Fe
reduction were also seen in the topographic patterns of pH, as protons were
consumed where this process was prevalent. This suite of results can all be
attributed to the effect of water table on oxygen availability: flooded
conditions promote anoxia, stimulating dissolution and reduction of Fe(III),
and to some extent, methanogenesis. However, two lines of evidence indicated
the inhibition of methanogenesis by alternative e- acceptors such as Fe(III)
and humic substances: (1) ratios of CO2:CH4 evolved from anaerobic
soil incubations and dissolved in soil pore water were high; (2) CH4
concentrations were negatively correlated with the oxidation state of the
soluble Fe pool in both topographically high and low areas. A second set of
results could be explained by increased soil temperature in the flooding
treatment, which presumably arose from the increased thermal conductivity of
the soil surface: higher N mineralization rates and dissolved P
concentrations were observed in flooded areas. Overall, these results could
have implications for C and nutrient cycling in high Arctic areas where
warming and flooding are likely consequences of climate change. |
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