Drainage Ratio as a Strong Predictor of Allochthonous Carbon Budget in Hemiboreal Lakes

We assessed the allochthonous organic carbon (OC) budgets for thirteen hemiboreal lakes using a simple equilibrium model coupled with a Bayesian framework for estimating parameter distribution and uncertainty. Model inputs consisted of hydro- logical, bathymetric and chemical data that are easily measurable at the lake and basin scale. Among the model outputs were mean OC loads (5– 123 g m-2 y-1 ), exports (1.10-3 –108 g m-2 y-1 ), mineralization (3–12 g m-2 y-1 ), and sedimenta- tion (2–6 g m-2 y-1 ). ‘‘Active’’ lake-catchment systems received and emitted the largest amounts of allochthonous OC, whereas lakes depending mostly on atmospheric inputs exhibited much more modest OC fluxes. Simulated organic carbon retention varied accordingly from 12% in some drainage lakes to 99% in seepage lakes. Lake al- lochthonous OC loads and exports were strongly correlated to drainage ratio (catchment area/lake area, R2 : 0.89 and 0.92, respectively) and to forest ratio (catchment forested area/lake area, R2 : 0.86 and 0.89), but not to wetland ratio. The simplicity of the model makes it easily transposable to a large variety of lakes. For a better insight into carbon processing, we suggest to follow a more integrative approach accounting for interactions between lake hydrology and catchment land cover.

The authors are grateful to Hilary Dugan (Univer- sity of Wisconsin-Madison) for assistance during the coding process and Sirje Vilbaste (Estonian University of Life Sciences). This research was funded by Estonian Research Council grants (PUT 777, PSG 32) by IUT 21-2 of the Estonian Ministry of Education and Research, and by MARS project (Managing Aquatic ecosystems and water Re- sources under multiple Stress) funded under the 7th EU Framework Programme, Theme 6 (Envi- ronment including Climate Change), Contract No.: 603378 (http://www.mars-project.eu), as well as the USA NTL LTER program.