Impact of long-term hydrologic disturbance on a permafrost floodplain in Northeast Siberia

Min Jung Kwon1, Mathias Goeckede2, Martin Heimann2, Nikita Zimov3, Sergey Zimov3
1 Max Planck Institute for Biogeochemistry, University of Jena, Jena, Germany
2 Max Planck Institute for Biogeochemistry, Jena, Germany
3 Northeast Science Station, Cherskii, Russia

O 2.1 in Environmental controls on fluxes and processes in ecosystems

15.07.2014, 15:30-15:50, H18

Organic carbon stored in Arctic soils is currently estimated to be 1672 Pg C (Tarnocai et al., 2009), which is about half of the global belowground carbon storage. Given the anticipated regional warming trend under global climate change, this large carbon reservoir is at risk to be partially decomposed and released to the atmosphere in the forms of CO2 and CH4.

The presented study aims at evaluating the stability of the permafrost carbon pools under modified environmental conditions, i.e. enhanced drought stress in the warm season which is likely to increase for parts of the Arctic under future climate change. We focused on investigating the effects of manipulated hydrology on carbon flux patterns as well as vegetation community structures in a wet tussock tundra ecosystem near the town of Cherskii in Northeastern Siberia (68° 36’N, 161° 20’E). Part of this site has been drained since 2004 by a drainage ditch, significantly lowering the soil water table except for spring flooding season. In both drained and a nearby undisturbed (reference) site, we measured the fluxes of CO2 (NEE, ER) and CH4  with closed chamber systems over a period of 3 weeks in summer and 4 weeks in fall 2013. In addition, at both sites we monitored vegetation community structures, extractable nitrogen availability, and active layer, water table, and temperature conditions. Most of these observations could be compared to data from a reference period 2002-05 to evaluate long-term trends for both disturbance regimes.

All CO2 flux components did not show significant differences between the two sites when compared on a daily basis. However, shifts were found when correlating fluxes to environmental factors, with the dominant controls (soil and air temperature, and water table depth – WTD) being differently weighed for drained and reference conditions, resp. This implies that the two sites would show different net CO2 flux when measured continuously. For the CH4 flux, at the undrained site (with higher WTD) we observed net emissions that were about one order of magnitude higher compared to the drained site. Concerning the vegetation structure, Eriophorum is dominant in a reference site whereas Carex in drained site. Overall, we found systematic effects of the decade-long hydrologic disturbance on most biogeochemical and biogeophysical parameters that we measured. At the same time, changes in CO2 flux patterns were found to be comparatively small, indicating that both production and consumption rate of CO2 have been affected. Consequentially, shifts in the CH4 fluxes appear to be the dominating factor for the net effect of the drainage disturbance on the net carbon budget of this site.

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Letzte Änderung 19.06.2014