Stable Carbon and Nitrogen Isotopes in a Peat Profile Are Influenced by Early Stage Diagenesis and Changes in Atmospheric CO2 and N Deposition

In this study, we test whether the δ(13)C and δ(15)N in a peat profile are, respectively, linked to the recent dilution of atmospheric δ(13)CO(2) caused by increased fossil fuel combustion and changes in atmospheric δ(15)N deposition. We analysed bulk peat and Sphagnum fuscum branch C and N concentrations and bulk peat, S. fuscum branch and Andromeda polifolia leaf δ(13)C and δ(15)N from a 30-cm hummock-like peat profile from an Aapa mire in northern Finland. Statistically significant correlations were found between the dilution of atmospheric δ(13)CO(2) and bulk peat δ(13)C, as well as between historically increasing wet N deposition and bulk peat δ(15)N. However, these correlations may be affected by early stage kinetic fractionation during decomposition and possibly other processes. We conclude that bulk peat stable carbon and nitrogen isotope ratios may reflect the dilution of atmospheric δ(13)CO(2) and the changes in δ(15)N deposition, but probably also reflect the effects of early stage kinetic fractionation during diagenesis. This needs to be taken into account when interpreting palaeodata. There is a need for further studies of δ(15)N profiles in sufficiently old dated cores from sites with different rates of decomposition: These would facilitate more reliable separation of depositional δ(15)N from patterns caused by other processes. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s11270-011-1001-8) contains supplementary material, which is available to authorized users.