Catchment-scale dissolved carbon concentrations and export estimates across six subarctic streams in northern Sweden

R Giesler,E M Karlsson,J Karlsson,S W Lyon,C Humborg,C.-M Mörth,E J Jantze,G Destouni

doi:10.5194/bg-11-525-2014

Abstract

Abstract. Climatic change is currently enhancing permafrost thawing and the flow of water through the landscape in subarctic and arctic catchments, with major consequences for the carbon export to aquatic ecosystems. We studied stream water carbon export in several tundra-dominated catchments in northern Sweden. There were clear seasonal differences in both dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) concentrations. The highest DOC concentrations occurred during the spring freshet while the highest DIC concentrations were always observed during winter baseflow conditions for the six catchments considered in this study. Long-term trends for the period 1982 to 2010 for one of the streams showed that DIC concentrations has increased by 9% during the 28 yr of measurement while no clear trend was found for DOC. Similar increasing trends were also found for conductivity, Ca and Mg. When trends were discretized into individual months, we found a significant linear increase in DIC concentrations with time for September, November and December. In these subarctic catchments, the annual mass of C exported as DIC was in the same order of magnitude as DOC; the average proportion of DIC to the total dissolved C exported was 61% for the six streams. Furthermore, there was a direct relationship between total runoff and annual dissolved carbon fluxes for these six catchments. These relationships were more prevalent for annual DIC exports than annual DOC exports in this region. Our results also highlight that both DOC and DIC can be important in high-latitude ecosystems. This is particularly relevant in environments where thawing permafrost and changes to subsurface ice due to global warming can influence stream water fluxes of C. The large proportion of stream water DIC flux also has implications on regional C budgets and needs to be considered in order to understand climate-induced feedback mechanisms across the landscape.

Highlights

Tundra soils at northern latitudes contain 30–50 % of the global soil stocks of C (Gorham, 1991; Tarnocai et al, 2009), representing a pool at least twice as large as that of the atmosphere
dissolved organic carbon (DOC) concentrations were generally highest at the first snowmelt peak of the spring freshet peaks in DOC concentration were noted during later high flow events
The observed seasonal variation in stream water dissolved inorganic carbon (DIC) and DOC concentrations coincides with a source shift from a subsurface dominated flow during baseflow conditions, i.e., autumn/winter, to surface dominated flow pathways during the spring freshet

Summary

Introduction

Tundra soils at northern latitudes contain 30–50 % of the global soil stocks of C (Gorham, 1991; Tarnocai et al, 2009), representing a pool at least twice as large as that of the atmosphere This pool may potentially be released either as CO2 or CH4 (Dutta et al, 2006; Shaver et al, 2006; Lee et al, 2010) or by increased leaching losses of dissolved C (Frey and Smith 2005; Dutta et al, 2006; Frey and McClelland, 2009) due to the polar amplification of climate change and changes in precipitation patterns seen in the past decades. Changes in temperature and hydrology could liberate large amounts of previously inactive carbon, for instance due to permafrost thawing (Schuur et al, 2009; Dorrepaal et al, 2009; Klaminder et al, 2008) or priming effects related to vegetation changes (Fontaine et al, 2007)

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Results

Conclusion