Do high iron concentrations in rewetted rich fens hamper restoration?

“In this study we address the question of the extent to which iron may be a limiting factor in restoring rich fens in the temperate climate zone of Europe. Rewetted fens that were heavily degraded in the past by draining over a long period, were compared with pristine fens or fens with slightly altered hydrological systems. The chemical composition of peat and of pore water was analysed and related to the composition of the vegetation of the fens. The species composition and chemistry of the topsoil of restored fens differed markedly from that of the other fens, while the chemistry of the pore water from deeper layers showed only minor differences. Multivariate analysis revealed that differences in species composition between both categories were strongly related to the concentration of Fe in the pore water in the topsoil. Restored sites with high iron concentrations in the pore water (> 100 mu mol.L-1) lacked many vascular plants and mosses typical of peat forming fens. Iron and inorganic phosphorus pools in the topsoil of most restored fens were much greater than in the reference fens. A higher soil phosphorus pool originated mainly from the iron-bound fraction. We conclude that these differences are strongly governed by local processes and not by regional differences in climate, which were associated with geographical distribution of the different fens studied. The strong accumulation of iron and phosphorus in restored fens is attributed to a long history of drainage, which enhanced the accumulation of oxidized iron in the topsoil and also lowered the concentrations of calcium, magnesium and sulphur through drainage-caused reoccurring oxidation-reduction and leaching processes. A high iron and associated high phosphorous content appears to be an important and possibly irreversible bottleneck to restoring biodiversity and accumulation of peat with a low degree of humification in degraded fens. If a degraded fen has a low iron content then it is more likely to be restorable.”

(Citaat: Aggenbach, C.J.S, Backx, H., et al., – Do high iron concentrations in rewetted rich fens hamper restoration? – Preslia 85(2013)3, p.405-420)