Dynamics of redox processes in a minerotrophic fen exposed to a water table manipulation

Climate change studies foresee substantial changes in precipitation patterns in northern temperate regions, including an increased frequency of drought and intense rain events. To elucidate the impact of drying and rewetting on redox processes in peatlands we conducted a field scale manipulation experiment, tracing the below ground dynamics of dissolved inorganic carbon (DIC), methane (CH4), and electron acceptors in a minerotrophic fen. On three treatment plots, a drought phase of similar to 4 weeks was initiated by means of a drainage system and a mountable roof. Subsequently we simulated a heavy rainfall by irrigation, which raised the water table by 20-35 cm. Three plots served as control. Solute electron acceptor concentrations increased during drought and decreased after rewetting, consistent with treatment and weather. Changes in solid phase electron acceptor contents were not detected. Drought induced aeration regenerated electron acceptors and suppressed methanogenic activity. This suppressive effect persisted during and some 1-4weeks after rewetting, dependent on depth. Hydrogen- and acetate-dependent iron and sulfate reduction were thermodynamically viable processes in the peat as their energy gain exceeded the threshold for microbial metabolism of -23 kJ mol(-1). Hydrogenotrophic methanogenesis was apparently thermodynamically inhibited in most of the peat, but proceeded presumably in microenvironments. In the uppermost peat layers, partly above the water table level, iron and sulfate reduction and occasionally methanogenesis overlapped and aeration was limited. Thus, in these layers reductive processes could partly proceed even during drought As all processes, including methanogenesis, responded quickly to wetting events, the microbial community seemed to be well adapted to fluctuating redox conditions. This study demonstrated that the dense and highly decomposed material could still provide anaerobic habitats for microorganisms during drought and the depth distribution of redox processes was quite insensitive towards the water table manipulations, presumably due to formation of microenvironments. (C) 2009 Elsevier B.V. All rights reserved.