Abstract. Riverine wetlands are created and transformed by geomorphological processes that determine their vegetation composition, primary production and soil accretion, all of which are likely to influence C stocks. Here, we compared ecosystem C stocks (trees, soil and downed wood) and soil N stocks of different types of riverine wetlands (marsh, peat swamp forest and mangroves) whose distribution spans from an environment dominated by river forces to an estuarine environment dominated by coastal processes. We also estimated soil C sequestration rates of mangroves on the basis of soil C accumulation. We predicted that C stocks in mangroves and peat swamps would be larger than marshes, and that C, N stocks and C sequestration rates would be larger in the upper compared to the lower estuary. Mean C stocks in mangroves and peat swamps (784.5 ± 73.5 and 722.2 ± 63.6 MgC ha−1, respectively) were higher than those of marshes (336.5 ± 38.3 MgC ha−1). Soil C and N stocks of mangroves were highest in the upper estuary and decreased towards the lower estuary. C stock variability within mangroves was much lower in the upper estuary (range 744–912 MgC ha−1) compared to the intermediate and lower estuary (range 537–1115 MgC ha−1) probably as a result of a highly dynamic coastline. Soil C sequestration values were 1.3 ± 0.2 MgC ha−1 yr−1 and were similar across sites. Estimations of C stocks within large areas need to include spatial variability related to vegetation composition and geomorphological setting to accurately reflect variability within riverine wetlands.

Deforestation and degradation of wetlands are important causes of carbon dioxide emissions to the atmosphere. Accurate measurements of carbon (C) stocks and sequestration rates are needed for incorporating wetlands into conservation and restoration programs with the aim for preventing carbon emissions. Here, we assessed 5 whole ecosystem C stocks (trees, soil and downed wood) and soil N stocks of riverine wetlands (mangroves, marshes and peat swamps) within La Encrucijada Biosphere Reserve in the Pacific coast of Mexico. We also estimated soil C sequestration rates of mangroves on the basis of soil accumulation. We hypothesized that riverine wetlands have large C stocks, and that upland mangroves have larger C and soil N stocks 10 compared to lowland mangroves. Riverine wetlands had large C stocks with a mean of 784.5 ± 73.5 Mg C ha −1 for mangroves, 722.2 ± 83.4 Mg C ha −1 for peat swamps, and 336.5 ± 38.3 Mg C ha −1 for marshes. C stocks and soil N stocks were in general larger for upland (833.0 ± 7.2 Mg C ha −1 ; 26.4 ± 0.5 Mg N ha −1 ) compared to lowland mangroves (659.5 ± 18.6 Mg C ha −1 ; 13.8 ± 2.0 Mg N ha −1 ). Soil C sequestration values 15 were 1.3 ± 0.2 Mg C ha −1 yr −1 . The Reserve stores 32.5 Mtons of C or 119.3 Mtons of CO 2 , with mangroves sequestering (via soil accumulation) 27 762±0.5 Mg C ha −1 every year.