B51F-0487
SOURCES AND FATE OF DIC IN SWEDISH STREAMS

Friday, 18 December 2015
Poster Hall (Moscone South)
Audrey Campeau1, Marcus Wallin1, Kevin H Bishop2, Reiner Giesler3, Carl-Magnus Mörth4 and Jason J Venkiteswaran5, (1)Uppsala University, Uppsala, Sweden, (2)Swedish University of Agricultural Science, Uppsala, Sweden, (3)Umeå University, Umeå, Sweden, (4)SLU Swedish University of Agricultural Sciences Umeå, Umeå, Sweden, (5)Wilfrid Laurier University, Department of Geography and Environmental Studies, Waterloo, ON, Canada
Abstract:
DIC export by streams and rivers is a major component of the global C cycle. However, many questions remain about the source and fate of aquatic DIC and CO2. Stable carbon isotope δ13C can provide information about the source and evolution of DIC and CO2 along hydrological networks. But the interpretation of δ13C values must be made with caution, since several biogeochemical processes affect the isotopic signal. In this study, we developed a systematic approach resolving these influences when interpreting large-scale patterns in δ13C-DIC and δ13C-CO2 values with regard to the source and fate of C in low order streams. We analyzed δ13C-DIC values in streams from four different regions of Sweden. Taken together they span large gradients in climate, geomorphology and lithology. The source of the DIC pool was predominantly biogenic in three of the regions (δ13C-DICsource = -17.4), but not the northernmost, where a clear geogenic input could be identified (δ13C-DICsource =-8.2 ). Our results suggest that soil respired CO2 is the main source of stream CO213C-CO2source=-22.9) in all four regions, yet aquatic processes can also be a contributing component of the DIC pool in streams, with corresponding influence on the δ13C values. Once CO2 was in the stream, degassing was the primary control on its fate. However, there were indications that aquatic biological processes added CO2, (by DOC degradation) in the southernmost region, and that CO2 was removed (by photosynthesis) in the most central region. Correctly interpreted, the carbon stable isotope data can serve as a powerful tool for identifying the source and fate of stream DIC.