Climate, Nitrogen Depostion and Terrestrial Vegetation As Major Drivers of Lake DOC and Stoichiometry

Wednesday, 17 December 2014
Dag Olav Hessen, Søren Larsen and Tom Andersen, University of Oslo, Oslo, Norway
By using data for nitrogen deposition, temperature, runoff and GIS-data for a range of catchment-specific properties, the effect of these variables on elemental export and ratios between carbon (C), nitrogen (N), phosphorus (P) and silicate (Si) in downstream lakes was assessed in Norwegian boreal catchments based on data from nearly 1000 lakes. The study covered a wide range of anthrophogenic N-deposition from south to north (max: 2 g m-2 yr-1, min: 0.1 g m-2 yr-1) as well as highly variable climate and catchment and lake properties. Inorganic N in lakes was positively correlated with N-deposition, while organic N was closely associated with allochthonous DOC. The ratio of NO3: total N as well as NO3: total P and NO3:SiO2 showed a strong variability, and most of this variability could be explained by N-deposition, terrestrial vegetation as inferred from NDVI, temperature, runoff and the fraction of bogs in the catchment. The “global change” induced changes in element concentrations and elemental ratios could profoundly affect the lake metabolism and community composition. By linking these data with downscaled climate change predictions we may also predict future shifts in element export and element ratios in various lakes with reasonable accuracy.