Characteristics of Dissolved Organic Carbon in Boreal Lakes: High Spatial and Inter‐Annual Variability Controlled by Landscape Attributes and Wet‐Dry Periods

• Published in: Water resources research 2021-11, Vol.57 (11), p.n/a
• Main Authors: Pugh, E. A., Olefeldt, D., Leader, S. N., Hokanson, K. J., Devito, K. J.
• Format: Article
• Language: English
• Subjects: Allochthonous deposits; Annual precipitation; Annual variations; Aromaticity; boreal plains; Carbon; Chemical composition; Chemical precipitation; Climate; Climate sensitivity; Coefficient of variation; Coefficients; Dissolved organic carbon; Dry periods; Flow paths; Food chains; Food webs; Gas exchange; Geology; Greenhouse gases; Humid climates; Hydrogeomorphology; hydrologic flow path; Lake water; Lakes; Nutrient cycles; Organic carbon; Precipitation; Spatial variability; Spatial variations; surficial geology; SUVA254; Variability; water residence time; Watersheds
• ISSN: 0043-1397; 1944-7973
• DOI: 10.1029/2021WR030021

Concentration and chemical composition of dissolved organic carbon (DOC) influence several lake functions; greenhouse gas exchange, nutrient cycling, food webs, and water treatability. To assess spatial and inter‐annual controls on DOC characteristics, 34 lakes were sampled annually for 8 years on the Boreal Plains, Western Canada—a region with heterogeneous surficial geology, and a sub‐humid climate with pronounced inter‐annual wet‐dry periods. Large spatial variability in long‐term average DOC concentration (10–49 mg C L−1) and aromaticity (SUVA254: 1.2–3.9 L mg−1 C m−1) among lakes was found. Higher DOC concentrations and aromaticity were associated with lakes in watersheds with fine‐textured surficial geology and with relatively large contributions through shallow, organic‐rich flow paths. Lake DOC aromaticity was also higher in lakes with lower evaporative enrichment, regardless of surficial geology, indicating shorter lake water residence times and less within‐lake degradation of allochthonous DOC. High inter‐annual variability for both DOC and aromaticity was observed, with coefficients of variation at 10.9 ± 4.6% and 11.1 ± 2.5% among lakes, respectively. Inter‐annual variability in DOC concentrations had low synchronicity among lakes, with patterns of variability linked to surficial geology and primarily responsive to short‐term cumulative precipitation. Conversely, inter‐annual variability in aromaticity had high synchronicity among lakes, driven by longer‐term cumulative precipitation and shifts in lake water residence times. Our study shows it is necessary to consider lake hydrogeomorphic setting and climate to understand spatial and inter‐annual variability in lake DOC characteristics and associated lake functions, and that Boreal Plains lakes have high climate sensitivity. Key Points Spatial variability of lake dissolved organic carbon characteristics were driven by dominant flow paths dictated by surficial geology Inter‐annual variability of lake dissolved organic carbon concentrations were driven by changing terrestrial sources Aromaticity of lake dissolved organic carbon was highly sensitive to inter‐annual wet‐dry periods on the Boreal Plains