Stream dissolved organic carbon in a changing tundra landscape

Reiner Giesler1, Jan Karlsson1
1 Climate Impacts Research Centre, Dep. of Ecology and Environmental Science, Umeå University

O 7.2 in Controls of dissolved organic matter fluxes in ecosystems

14.07.2014, 11:35-11:55, H19

Streams are sensitive sentinels for environmental change by their integration of processes in terrestrial and aquatic systems. Tundra landscapes in arctic regions are today undergoing drastic changes due to thawing permafrost that potentially can have large impacts on stream dissolved organic carbon concentrations and fluxes. Upland tundra-dominated streams in northern Sweden have their peak in DOC during the spring flood and the lowest concentrations are found during baseflow conditions. These patterns may, however, change with increasing thaw depths in permafrost affected tundra landscapes. We have observed seasonally exceptional high concentrations (up to 90 mg L-1) of uncolored dissolved organic carbon (DOC) found upland headwater streams in the north Swedish tundra. Peaks in uncolored DOC have been observed during baseflow conditions in early autumn (mid August–September). The DOC is clearly separated from the DOC earlier in the season by qualitative characteristics such as SUVA and C:N ratio. Peaks in DOC during the spring snow melt are around 10 mg L-1 in the upland streams studied and more colored than the observed autumn peak DOC concentrations. The autumn peaks were not detectable at the lower reaches of the catchment and may indicate that the uncolored DOC is highly degradable but this remains to be tested. We suggest that the uncolored DOC reflects on-going changes in the terrestrial environment responding in their delivery of carbon (C) to the recipient aquatic systems. Such changes have been noted as changes in the extent of cryoturbated soils and increased thaw depths of the active layer. The uncolored carbon is a hitherto unknown effect of a changing tundra landscape that may have large implications for the positive feedback on the global climate warming because of the large quantities of C that is stored in tundra soils. We suggest that current climate change mobilizes the stored C in upland tundra soils and cause a substantial increase in headwater stream C emissions and water-borne C losses.

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Letzte Änderung 04.04.2014