Drivers of northern peatland CO₂ fluxes revisited: interacting water level-temperature dependency

Peatlands are the largest terrestrial stores of organic carbon, but drainage has turned them into substantial sources of CO₂. While water level is widely recognized as the primary control of CO₂ emissions from peatlands, effective future management requires understanding its interaction with rising temperatures under a warming climate. Using 276 site-years of annual CO₂ flux observations across temperate and boreal peatlands, we apply explainable machine-learning to disentangle the combined effects of water table depths and temperature on ecosystem CO₂ exchange at annual scales. Across peatlands spanning diverse land-cover-including natural fens and bogs, croplands, grasslands, and extraction sites-CO₂ emissions exhibit a non-linear response to water table depth. Emissions decline when water tables are raised above 60-75 cm depth. Optimal mitigation requires water tables of 20 cm or higher. We find that deep water tables interact with temperatures to increase emissions at temperate sites. On a subset of 113 site-years of daily CO₂ flux data, we show that at warm temperatures, higher water tables suppress, whereas deeper water tables enhance temperature-driven CO₂ emissions from peatlands. We demonstrate that hydrology regulates the temperature sensitivity of peatland carbon release, revealing a key control on carbon-climate feedbacks under future warming.