Modeling Allochthonous Dissolved Organic Carbon Mineralization Under Variable Hydrologic Regimes in Boreal Lakes

• Published in: Ecosystems (New York) 2017-06, Vol.20 (4), p.781-795
• Main Authors: Vachon, Dominic, Prairie, Yves T., Guillemette, François, del Giorgio, Paul A.
• Format: Article
• Language: English
• Subjects: Age; Analysis; Aquatic resources; Biomedical and Life Sciences; Carbon dioxide; Carbon dioxide emissions; Dissolved organic carbon; Ecology; Environmental Management; Genetic transformation; Geoecology/Natural Processes; Hydrologic modeling; Hydrologic regime; Hydrology; Hydrology/Water Resources; Lakes; Life Sciences; Mathematical models; Mineralization; Modelling; Original Articles; Partial pressure; Plant Sciences; Reactivity; Surface water; Transit; Zoology
• ISSN: 1432-9840; 1435-0629
• DOI: 10.1007/s10021-016-0057-0

Here, we explore the interaction between hydrology and the reactivity of allochthonous dissolved organic carbon (DOCalloch) in determining the potential of DOCalloch to generate CO 2 through biological and photo-chemical mineralization in boreal lakes. We developed a mechanistic model that integrates the reactivity continuum (RC) concept to reconstruct in-lake mineralization of DOCalloch under variable hydrologic conditions using empirical measurements of DOCalloch concentrations and reactivity as model inputs. The model predicts lake DOCalloch concentration (L-DOCalloch) and its average overall reactivity ðKalloch Þ, which integrates the distribution of DOC alloch ages within the lake as a function of the DOC loading (DOCin), the initial reactivity of this DOCin (k₀), and the lake water residence time (WRT). The modeled DOCalloch mineralization rates and concentrations were in agreement with expectations based on observed and published values of ambient lake DOC concentrations and reactivity. Results from this modeling exercise reveal that the interaction between WRT and k₀ is a key determinant of the ambient concentration and reactivity of lake DOCalloch, which represents the bulk of DOC in most of these lakes. The steadystate (K̅alloch) also represents the proportion of CO₂ that can be extracted from DOCalloch during its transit through lakes, and partly explains the patterns in surface water pCO₂ oversaturation that have been observed across gradients of lake size and volume. We estimate that in-lake DOCalloch mineralization could potentially contribute on average 30–40% of the observed surface carbon dioxide partial pressure (pCO₂) across northern lakes. Applying the RC framework to in-lake DOCalloch dynamics improves our understanding of DOCalloch transformation and fate along the aquatic network, and results in a predictable mosaic of DOC reactivity and potential CO₂ emissions across lakes within a landscape.