The effect of precipitation chemistry upon anion and cation fluxes from the surface layer of ombrotrophic mires in the UK.
Replicate cores and monoliths bearing intact vegetation were sampled from the acrotelm and surface litter layer of ombrotrophic mires across a gradient in precipitation chemistry in the UK. Leaves from Calluna vulgaris shrubs growing on the surface of these mires were also sampled. During a 1 year study the monoliths were subjected to 1200 mm of simulated rainfall of the same chemical composition as they received in the field and drainage water was analysed periodically for component anions and cations. The results showed that changes in the chemical quality of precipitation in the UK has induced changes in the N cycling and base status within the acrotelm and surface litter layer of ombrotrophic mires. Ammonium concn were dependent upon ion exchange reactions whereas NO3 concn were more dependent upon biologically mediated processes. The results of total element chemistry in C. vulgaris stands showed that leaves contained higher N and lower P and Mg concn in areas receiving high concn of chemical components delivered in precipitation associated with industrial and domestic atmospheric emissions. Fluxes of all of the ions from monoliths were highly seasonal, and generally reflected fluctuations in nutrient uptake by the vegetation and activity of soil microbes and fauna. Unlike NH4+, NO3 and P were rapidly immobilized in the acrotelm and surface litter layer of mires in areas receiving high H, N and S atmospheric inputs. Total P concn in this layer were highest in areas receiving high concn of H, N and S in precipitation. This probably reflected the rate of litter decomposition and hence the mineralization of organic P; and may be linked to the chemical composition of C. vulgaris leaves.