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Changing aquatic DOC export – implications for the terrestrial carbon sink

Heleen de Wit1, Martyn Futter2, Kari Austnes1, Sören Larsen3, Dag O. Hessen3
1 Norwegian Institute for Water Research, Oslo
2 Swedish University of Agricultural Sciences, Dtp. of Aquatic Sciences and Assesment, Uppsala
3 University of Oslo, CEES, Dept. of Biosciences, Oslo

O 7.1 in Controls of dissolved organic matter fluxes in ecosystems

14.07.2014, 11:15-11:35, H19

Climate change may alter the flux of aquatic dissolved organic carbon (DOC) from forests and wetlands, and may therefore affect the capacity of these ecosystems to sequester carbon. Aquatic DOC export can be significant compared with sequestration of carbon in catchment soils and biomass, especially in boreal and subarctic ecosystems. Top-down estimates of terrestrial carbon sequestration (using eddy covariance techniques) must correct for aquatic DOC export to avoid an overestimation of the terrestrial carbon sink. At larger spatial scales (landscapes, regions, countries), terrestrial carbon uptake is often estimated with bottom-up methods (forest inventories, models), supported by point-measurements of ecosystem carbon uptake. At these scales, the size of aquatic carbon export may be acknowledged as significant, but is usually not integrated in the estimation of the terrestrial carbon sink. In many examples of landscape carbon balances, it is unclear how vertical and lateral carbon fluxes are linked.

Here, we will present several studies that link climate, terrestrial features and aquatic carbon fluxes. In a carbon budget of Norway, we show how aquatic carbon fluxes compare to terrestrial carbon uptake in four contrasting drainage basins. In a space-for-time analysis of lake DOC export from Norwegian lake catchments, we show that catchment productivity could be an important control of DOC. In >20 year time series of Nordic headwater DOC export, we demonstrate climatic drivers of DOC export.

We will use these results to argue that DOC export is likely to change in the future, but that the implications of these changes for the terrestrial carbon storage are unknown. To a certain point, our present understanding of catchment processes allows us to make credible predictions of aquatic DOC export in a future climate. However, to predict what such changes in DOC export will imply for carbon storage in catchment soils and wetlands on the landscape scale is a different matter. The integration of vertical and lateral fluxes of carbon in relation to terrestrial carbon storage needs new research tools and experimental approaches.

References

De Wit et al., in revision. A carbon balance of Norway: terrestrial and aquatic carbon fluxes.

Larsen, S., Andersen, T., Hessen, D.O., 2011. Predicting organic carbon in lakes from climate drivers and catchment properties. Global Biogeochemical Cycles 25.

De Wit, H.A., Futter, M.N, Austnes, K. in prep. Climatic drivers of DOC export from Nordic catchments



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last modified 2014-04-09