Drivers of long-term variability in CO₂ net ecosystem exchange in a temperate peatland

Land–atmosphere exchange of carbon dioxide (CO₂) in peatlands exhibits marked seasonal and inter-annual variability, which subsequently affects the carbon (C) sink strength of catchments across multiple temporal scales. Long-term studies are needed to fully capture the natural variability and therefore identify the key hydrometeorological drivers in the net ecosystem exchange (NEE) of CO₂. Since 2002, NEE has been measured continuously by eddy-covariance at Auchencorth Moss, a temperate lowland peatland in central Scotland. Hence this is one of the longest peatland NEE studies to date. For 11 years, the site was a consistent, yet variable, atmospheric CO₂ sink ranging from −5.2 to −135.9 g CO₂-C m⁻² yr⁻¹ (mean of −64.1 ± 33.6 g CO₂-C m⁻² yr⁻¹). Inter-annual variability in NEE was positively correlated to the length of the growing season. Mean winter air temperature explained 87% of the inter-annual variability in the sink strength of the following summer, indicating an effect of winter climate on local phenology. Ecosystem respiration (R_eco) was enhanced by drought, which also depressed gross primary productivity (GPP). The CO₂ uptake rate during the growing season was comparable to three other sites with long-term NEE records; however, the emission rate during the dormant season was significantly higher. To summarise, the NEE of the peatland studied is modulated by two dominant factors: <br><br> - phenology of the plant community, which is driven by winter air temperature and impacts photosynthetic potential and net CO₂ uptake during the growing season (colder winters are linked to lower summer NEE), <br><br> - water table level, which enhanced soil respiration and decreased GPP during dry spells. <br><br> Although summer dry spells were sporadic during the study period, the positive effects of the current climatic trend towards milder winters on the site's CO₂ sink strength could be offset by changes in precipitation patterns especially during the growing season