Geochemistry of three contrasting British peatlands: Complex patterns of cation availability and implications for microbial metabolism

Cation availability in peat may limit CH4 production and microbial activity and thereby impact on rates of organic matter accumulation and the chemical character of the peat. We quantify total, soluble, and exchangeable cation concentrations, Exchange Site Saturation Levels (ESSLs) and organic fractions in bog-peat profiles and compare these with fen peat. Total and soluble cation concentrations are not correlated and these and exchangeable cation concentrations are lower in bog than fen peat. In all sites these vary with depth and the distribution patterns of individual cations are unique. This is explained by variation in ESSL, which is negatively correlated with Cation Exchange Capacity (CEC). Total cation concentrations in bog peat are higher in the top and bottom fractions than in the middle. Soluble concentrations in surface bog peat are low, because cations are trapped due to low ESSL. This does not occur in fen peat, with lower CEC and higher ESSL. CEC is related to total organic matter content, not just to Sphagnum, which has been invoked as the explanatory variable of high CEC in peat bogs. There is a complexity in the mechanisms controlling cation availability in peat and we suggest that total, soluble and exchangeable cation fractions need to be taken into account in studies of cation limitation of microbial activity in organic soils. CEC may also chelate exo-enzymes, further inhibiting decay processes.