A large carbon pool and small sink in boreal Holocene lake sediments

Model-based estimates suggest that lake sediments may be a significant, long-term sink for organic carbon (C) at regional to global scales. These models have used various approaches to predict sediment storage at broad scales from very limited data sets. Here, we report a large-scale direct assessment of the standing stock and sedimentation rate of C for a representative set of lakes in Finland. The 122 lakes were selected from the statistically selected Nordic Lake Survey database, they cover the entire country and the water quality represents the average lake water quality in Finland. Unlike all prior estimates, these data use sediment cores that comprise the entire sediment record. The data show that within Finland, aquatic ecosystems contain the second largest areal C stocks (19 kg C m^-2) after peatlands (72 kg C m^-2), and exceed by significant amounts stocks in the forest soil (uppermost 75cm; 7.2 kg C m^-2) and woody biomass (3.4 kg C m^-2). Kauppi et al. (1997). The Finnish estimate extrapolated over the boreal region gives a total C pool in lakes 19-27 Pg C, significantly lower than the previous model-based estimates.