Lake-size dependent physical forcing drives carbon dioxide and methane effluxes from lakes in a boreal landscape

• Published in: Limnology and oceanography Vol. 58; no. 6; pp. 1915 - 1930
• Main Authors: Kankaala, Paula, Huotari, Jussi, Tulonen, Tiina, Ojala, Anne
• Format: Journal Article
• Language: English
• Published: Waco, TX John Wiley and Sons, Inc 01.11.2013; American Society of Limnology and Oceanography
• Subjects: Earth sciences; Earth, ocean, space; Exact sciences and technology; Hydrology; Hydrology. Hydrogeology; Marine and continental quaternary; Surficial geology; Scandinavia; Europe; Finland; drainage basins; carbon dioxide; atmospheric emission; boreal environment; lacustrine environment; mixing; methane; concentration; lakes; turbulence; organic carbon; stability
• ISSN: 0024-3590; 1939-5590
• DOI: 10.4319/lo.2013.58.6.1915

We studied the concentrations and diffusive fluxes of carbon dioxide (CO₂) and methane (CH₄) in 12 lakes in a size range of 0.004–35 km² and mean total organic carbon (TOC) range of 6–25 mg L−1, located in the southern boreal area of Finland. TOC, mainly originating from the catchment, was the best predictor of concentrations and areal CO₂ effluxes in the whole lake-area range, but among the lakes with an area < 1 km² having an anoxic hypolimnion during summer, the areal effluxes were also related to lake size and an index of turbulence. The concentration and areal effluxes of CH₄ from the lakes’ pelagic zones were related more closely to lake-size–related water column stability and turbulent mixing than directly to TOC. The total regional flux estimate from 619 lakes in the region of 1600 km² showed that seven lakes with an area of 10–50 km² were responsible for 57–69% of the pelagic CO₂ effluxes and about half of the sum of pelagic and littoral CH₄ effluxes from the lakes. The proportion accounted for by the small lakes (area < 1 km²) in the gas effluxes was 1.4–2.1 times higher, 18–26% for CO₂ and 21–26% for CH₄, than their areal proportion (12.5%) in the landscape, although numerically these small lakes predominate in the whole lake population (96%).