Organic carbon concentration and source in sub-arctic lake sediment : Spatial and temporal differences in five headwater lakes, Abisko, Sweden

Sequestration and burial of organic carbon (OC) in lake sediment represents a significant sink in the global carbon cycle. Changes in burial rates are therefore of interest from a climate change perspective, particularly in Arctic regions currently experiencing accelerated warming. Carbon fluxes in lakes are affected by both lake- and catchment characteristics, such as catchment size and lake morphometry. The aim with this report is to evaluate temporal and spatial variability in OC content, with a specific focus on identifying the source of OC to lakes. The upper sediment in five headwater lakes in northern Sweden were sampled using a gravity corer and analyzed with Isotope Ratio Mass Spectrometer (EA-IRMS). A literature review of studies from the same region was performed to estimate the sedimentation rate of the study lakes and contextualize the results. The results showed 50 % increases of C and N concentrations and generally decreasing δ15N values in the top 5 cm of sediment. δ13C values became enriched in two of the lakes towards the sediment surface (up to -21 ‰), while becoming more depleted in the other three lakes (down to -28 ‰). Multivariate analysis further showed two distinct clusters among the study lakes, likely reflecting differences in the primary OC source. The conclusion from this report is that the OC content has increased during the last ~50 years, possibly because of warmer temperatures. The results also suggests that lake morphometry and catchment size are the most important factors influencing the source of OC.