Impact of Environmental Variability on Net Ecosystem CO2 Exchange from 2008-2018 at a High Arctic Mesic Tundra Site

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Braybrook, Christina
Carbon Dioxide Exchange , Net Ecosystem Exchange (NEE) , High Arctic , Inter-Annual Variability , Mesic Tundra , Normalized Difference Vegetation Index (NDVI)
Arctic terrestrial carbon (C) budgets are shifting with respect to net ecosystem CO2 exchange (NEE), and its component fluxes; i.e., gross primary production (GPP) and ecosystem respiration (Reco) under amplified high latitude climate change. Determining whether Arctic ecosystems are behaving as net sinks or net sources is important as these scenarios are associated with various feedback mechanisms, either mitigating or enhancing atmospheric CO2 concentrations. Given the vast C stores in Arctic soils and permafrost, these processes can have significant impacts on atmospheric CO2 concentrations. This research investigates how growing season NEE has varied from 2008 to 2018 at the Cape Bounty Arctic Watershed Observatory (CBAWO) (74.92˚N, 109.58˚W) on Melville Island, Nunavut, Canada. The eddy covariance technique and standardized processing tools were used to observe inter-annual variability of NEE, GPP, and Reco and the relative importance of environmental variables in explaining variability of growing season CO2 fluxes. Overall, this site showed strong inter-annual variability in growing season NEE (range of -46.01 g C m-2 to 11.25 g C m-2) with GPP the most likely source of this variability, i.e., GPP rates were more variable compared to Reco. Inter-annual variability of growing season NEE appeared to be strongly driven by growing degree days (GDD) in warmer years, suggesting that temperature must reach a threshold in order to drive photosynthesis sufficiently to offset respiration. This deviated slightly in 2014, the second strongest CO2 sink across observed years (-21.24 g C m-2), but with reduced cumulative GDD. This is believed to be a result of delayed ecosystem response to previous environmental conditions favorable for strong CO2 uptake. CO2 fluxes also showed varying importance in the context of environmental variables at different temporal aggregations, with the remote sensing vegetation index showing strong importance for Reco, compared to GPP and NEE, suggesting a significant contribution of autotrophic respiration to Reco at this mesic site. This research reveals unique characteristics between inter-annual growing season CO2 flux patterns for a mesic tundra landscape and environmental drivers that overall, contribute to our understanding of High Arctic tundra CO2 dynamics.
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