Small scale hydrological variation determines landscape CO₂ fluxes in the high Arctic.

We explored the influence of small-scale spatial variation in soil moisture on CO2 fluxes in the high Arctic. Of five sites forming a hydrological gradient, CO2 was emitted from the three driest sites and only the wettest site was a net sink of CO2. Soil moisture was a good predictor of net ecosystem exchange (NEE). Higher gross ecosystem photosynthesis (GEP) was linked to higher bryophyte biomass and activity in response to the moisture conditions. Ecosystem respiration (R-e) rates increased with soil moisture until the soil became anaerobic and then R (e) decreased. At well-drained sites R-e was driven by GEP, suggesting substrate and moisture limitation of soil respiration. We propose that spatial variability in soil moisture is a primary driver of NEE.