A comprehensive study of nutrient losses, soil properties and groundwater concentrations in a degraded peatland used as an intensive meadow -: Implications for re-wetting

Most of the once ecologically valuable and widespread peatlands in Western Europe as well as in Mecklenburg-Vorpommern (North-Eastern Germany) have been drained in the course of the intensification of agricultural land use. Peat degradation and mineralisation frequently caused high nitrate-nitrogen (NO3- -N) tosses, white re-wetting may lead to elevated phosphorus concentrations in the Porewater. High concentrations of NO3--N and other solutes in a ditch draining a catchment (85 ha) dominated by degraded peatland under intensive grassland use gave reason to investigate the relationship between the spatial and temporal variability of the shallow groundwater quality on the one hand and soil properties, topography and hydrological dynamics on the other hand. Therefore, in addition to the ditch, three transects of dipwells were sampled and soil samples were taken along the transects at a high spatial resolution. Soil organic carbon C-org and total nitrogen N-t contents varied considerably from 0.8% to 40.9% and 0.08% to 2.87%, respectively. A trend surface analysis (TSA) of these soil properties showed a strong trend depending on the ground elevation and the distance to the adjacent drainage ditch, reflecting both a transition from mineral to organic soils and differences in peat formation and degradation connected to the topography and, consequently, to the depth to the groundwater table. Semivariogram analysis was performed using the normally distributed residuals of the TSA and showed for each transect a strong spatial dependence and short (5-26 m) ranges. If possible, soil sampling in peatlands should be conducted at short distance sampling intervals. The patterns of groundwater solute concentrations were complex. They were spatially and temporally very variable between as welt as within the transects, thus proving that a few groundwater samples are insufficient for a representative characterisation of the peatland status and for an evaluation of possible environmental impacts or potential consequences of re-wetting. Groundwater concentrations ranged from 0 to 65.4 mg l(-1) NO3--N and 0-1.95 mg l(-1) P-t, while during the same period, ditch water concentrations of 0-15.9 mg l(-1) NO3--N and 0.05 to 0.44 mg l(-1) P-t, respectively, were measured. Factor analysis of groundwater concentrations, topographical data, hydrological conditions and soil properties led to the identification of five factors explaining up to 80% of the observed variance of the data: (i) topography and soil chemical properties, (ii) biogeochemical processes, (iii) drainage effects, (iv) climatic effects and (v) dilution effects. (c) 2007 Elsevier B.V. All rights reserved.