Nitrate and sulphate dynamics in peat subjected to different hydrological conditions: Batch experiments and field comparison

摘要

Conservation of ecosystems that depend on water management and water quality has to be considered. We combined a field monitoring and batch experiments to better understand the impact of hydrological perturbations on peatland functioning. Factors influencing the dynamics of nitrate and sulphate concentration observed in two sites with different hydrological conditions in a south Normandy peatland were determined through the comparison of field and lab experiment. The effects of nitrate input, and oxic or anoxic conditions on nitrate and sulphate concentrations were investigated in bioreactors, using peat samples from field sites influenced by different hydrologic regimes. In this experiment, peat samples were subjected to similar conditions to address the effects of NO3- and O_2 concentrations (chemical effects), and the effect of hydrologic regimes and peat soil moisture (physical effects) on nitrate and sulphate dynamics.Cl-, SO42- and NO3- were monitored for 215h. Nitrate was significantly reduced in most experiments. A complete nitrate reduction after 215h in soil under anoxic conditions was observed. A denitrification process was also found under aerobic conditions depending on the peat site sampling, i.e. depending on the hydrological conditions. This process was interpreted as a heterotrophic denitrification. Sulphate monitoring revealed that 400mgL~(-1) were produced in peat from the peat site with high hydrologic fluxes under aerobic conditions. Clear differences in chloride concentration (deviance analysis, P<0.05), sulphate concentration and nitrate consumption dynamics (deviance analysis, P<0.0001) were observed, for similar experimental chemical conditions, between the samples from the two peat sites. These differences were related to the field chemical variations observed and they indicate that part of the field nitrate and sulphate dynamics is linked to different bacterial activity and not only to nutrient fluxes variations.