Groundwater is one of the largest continental carbon (C) pools, but it is unclear where this C comes from and how long it resides in the subsurface before being released to the atmosphere through inland waters. The aim of this project is to unravel the magnitude, sources and age of C in groundwater aquifers within the Krycklan Catchment study. Twelve groundwater wells of different depth are sampled for carbon age, bulk groundwater age and concentrations of various carbon species, including dissolved organic and inorganic carbon and methane. The project will enable the quantification of legacy effects of groundwater in the C cycle and potential delays in the response of C emissions from groundwater-fed inland waters to changes in land C uptake. The project results will have implications for the development of more accurate landscape C models.