Seasonal variability of carbon dioxide fluxes over a heterogeneous low tundra ecosystem

The seasonal carbon dioxide (CO2) budget and its associated environmental controlling parameters, soil moisture, soil temperature and depth to frost were investigated throughout the growing period during the summer of 2004. The study site is located within the low arctic tundra environment at Daring Lake, NWT (62⁰52’N, 111⁰35’W). The CO2 fluxes from an area of heterogeneous tundra composition were intensely monitored. The net seasonal CO2 budget was approximated to be 10.2 g C-CO2 m-2 for 100 days (DOY 159-259) of the 2004 snow-free study period. The CO2 flux dynamic was found to differ between 4 identified seasonal periods—melt, pre-green, green and senescence. The controlling environment parameters (soil moisture, and temperature) as well as, the controlling meteorological variables, (photosynthetic photon flux density (PPFD)) were collected to derive relationships with the CO2 fluxes. Additionally, the energy and radiation budgets, air temperature and relative humidity were collected throughout the duration of the study period. An investigation of the spatial variability of soil moisture, depth to frost and soil temperature was examined to determine the spatial distribution and organisation of these parameters. Moran’s (I) test of spatial autocorrelation revealed that the study area displayed a limited degree of global spatial autocorrelation during long periods between, and directly following, precipitation events. Local tests of spatial autocorrelation demonstrated that prominent spatial patterns consisted of localised clusters and “hot-spots.” The determination of relative source contributions to the CO2 flux using a detailed footprint analysis scheme indicated that the degree of heterogeneity was large within the study area that no single vegetative community could be identified throughout the study period. However, groups of key species were adequately formulated in order to identify the flux contributions from these groupings. In general, seasonality played a strong role in dictating CO2 flux contributions from the vegetation groupings