Respiration modelling and CO2 budget assessment in the southern Baltic raised bog: Evaluating the impact of water table thresholds for ecosystem functioning

Peatlands significantly influence global carbon cycling through their capacity for long-term carbon sequestration. Understanding how these ecosystems respond to changing hydrological and thermal conditions is crucial, particularly in the context of ongoing climate change scenarios. This study provides an analysis of carbon dioxide fluxes and their relationship to water table depth (WTD) and soil temperature (TS) at the Baltic raised bog in Kusowo, northern Poland, measured over three contrasting hydrological years (2020−2022). Eddy covariance techniques revealed that the annual carbon dioxide budget strongly depended on WTD, with lower water levels associated with increased ecosystem respiration and net CO 2 emissions. Model simulations highlighted a nonlinear, synergistic interaction between TS and WTD, with WTD emerging as the primary driver of ecosystem respiration. The findings indicate that optimal carbon dioxide sequestration can only be maintained under sufficiently high water levels. Under drier, more aerobic conditions, even moderate increases in TS amplify respiration rates, highlighting the enhanced sensitivity of carbon losses when hydrological thresholds are exceeded. Our findings underscore the importance of adaptive water management strategies to sustain peatlands as effective carbon sinks through the accumulation of carbon in peat. • Baltic raised bog was near CO 2 -neutral over three study years. • Threshold at ±20 cm WTD shifts Baltic raised bog from sink to source of CO 2 . • Optimal net CO 2 uptake for Baltic raised bog at ±12 cm water table depth. • Warming and drought may jointly amplify CO 2 emissions by >30 %.