Watershed mires are infrequent on the Middle-Russian Upland and their role in carbon sequestration is poorly known, preventing a comprehensive assessment of the contribution of these ecosystems to carbon exchange with the atmosphere. The article discusses the results of determining the carbon reserves in peat deposits of watershed mires formed in depressions of karst origin and having different genesis in the north-east of the Middle-Russian Upland. To calculate the carbon reserves, peat samples were collected and their botanical composition and physico-chemical parameters were studied. The bulk density, ash content, carbonate content and mass fraction of carbon in the peat samples were determined, from which the organic carbon content was calculated. This value was the highest in woody-Sphagnum mesotrophic (54.3 %), woody (45 %), and herb-Sphagnum (43.3 %) eutrophic peat. The calculation of carbon reserves in peat shows that the highest values are characteristic of herb-Sphagnum mesotrophic peat (456.4 kgC/m2). Layer-by-layer accumulation of peat deposits ensures the formation of a total carbon pool per unit area of mires. The estimation of total carbon reserves indicates that the duration of mire development
and the wetness conditions, which influence the structure of the forming peat deposit and the rate of vertical peat increment, have facilitated the highest carbon accumulation in the mixed peat deposit of an oligotrophic mire that emerged in the Boreal period of the Holocene (2909 kgC/m2). In mires with a discontinuous or floating deposit, which started developing in the sub-Atlantic period, carbon reserves are significantly lower, despite the build-up of the peat deposit thickness (1224–1385 kgC/m2). Our results reflect the contributions of different types of watershed mires to carbon deposition in peat deposits.