The organic carbon budget of a shallow arctic tundra lake on the Tuktoyaktuk Peninsula, N.W.T., Canada

Abstract

The organic carbon cycle of a shallow, tundra lake (mean depth 1.45 m) was followed for 5 weeks of the open water period by examining CO₂ fluxes through benthic respiration and anaerobic decomposition, photosynthesis of benthic and phytoplankton communities and gas exchange at the air-water interface. Total photosynthesis (as consumption of carbon dioxide) was 37.5 mmole C m⁻² d⁻¹, 83% of which was benthic and macrophytic. By direct measurement benthic respiration exceeded benthic photosynthesis by 6.6 mmole C m⁻² d⁻¹. The lake lost 1.4 × 10⁶ moles C in two weeks after ice melted by degassing C0₂, and 6.8 mmole C m⁻² d⁻¹ (1.5 × 10⁶ moles) during the remainder of the open water period; 2.2 mmole C m² d⁻¹ of this was release Of CO₂ stored in the sediments by cryoconcentration the previous winter. Anaerobic microbial decomposition was only 4% of the benthic aerobic respiration rate of 38 mmole C m⁻² d⁻¹. An annual budget estimate for the lake indicated that 50% of the carbon was produced by the benthic community, 20% by phytoplankton, and 30% was allochthonous material. The relative contribution of allochthonous input was in accordance with measurement of the δ¹⁵N of sedimented organic matter.