| Abstrakt: |
Drained thaw lake basins (DTLB) 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. Areas in the flooded areas had lower dissolved oxygen, lower oxidation-reduction potential (ORP) and higher pH, as did lower elevation areas of the landscape. Similarly, soil pore water concentrations of dissolved ferric iron (Fe III), organic carbon, and aromatic compounds were higher in flooded and low elevation areas. Dissolved carbon dioxide (CO2) and methane (CH4) concentrations were higher in low elevation areas. 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 significant dissimilatory Fe reduction occurred, especially in topographically low areas. This suite of results can all be attributed to the effect of water table on oxygen availability: flooded conditions promote anoxia, stimulating anaerobic processes, methanogenesis and Fe(III) reduction. Flooding also increased soil temperature, which might account for the higher N mineralization rates and dissolved P concentrations observed in flooded areas, though the latter could also have resulted from solubilization of Fe-P minerals under more reducing conditions. Overall, the results indicate that the microbial community is well-adapted for anaerobic respiration, in particular, dissimilatory Fe(III) reduction, and could have implications for some high Arctic areas where warming and flooding are likely consequences of climate change. [ABSTRACT FROM AUTHOR] |
