Factors affecting the summer carbon dioxide budget of subarctic wetland tundra

This study reports on 27 days of CO2 flux measurements from wetland tundra in the vicinity of Churchill, Manitoba, Canada. Fluxes were measured continuously using a portable, gradient measurement system which is described in detail. The measurements apply to a climatically normal summer in terms of solar radiation, temperature and precipitation. The environment consists of a hummocky fen underlain by permafrost with a thick layer of organic soils. Sedges dominated the hummocks and mosses the hollows. The measurement period was composed of a dry period when the water table receded below the lowest terrain elements and a wet period when there was standing water in the hollows. On average for the measurement period, and on most days, the carbon balance was positive, meaning that carbon loss through respiration exceeded the gain through photosynthesis. Respiration was greater and photosynthesis less during the dry period than the wet period. The magnitude of the daily average CO2 flux in this study was comparable to summer fluxes measured in similar ecosystems. The implications of a net carbon loss during the most photosynthetically active period are discussed.