THE ORGANIC-CARBON BUDGET OF A SHALLOW ARCTIC TUNDRA LAKE ON THE TUKTOYAKTUK PENINSULA, NWT, CANADA - ARCTIC LAKE CARBON BUDGET

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 fl uxes through benthic respiration and anaerobic decomposition, photosyn thesis of benthic and phytoplankton communities and gas exchange at th e 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 macrop hytic. By direct measurement benthic respiration exceeded benthic phot osynthesis by 6.6 mmole C m-2 d-1. The lake lost 1.4 x 10(6) moles C i n two weeks after ice melted by degassing CO2, and 6.8 mmole C m-2 d-1 (1.5 x 10(6) moles) during the remainder of the open water period; 2. 2 mmole C m-2 d-1 of this was release of CO2 stored in the sediments b y cryoconcentration the previous winter. Anaerobic microbial decomposi tion 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 phytoplankto n, and 30% was allochthonous material. The relative contribution of al lochthonous input was in accordance with measurement of the deltaN-15 of sedimented organic matter.