The effects of fluctuating climatic conditions and weather events on nutrient dynamics in a narrow mosaic riparian peatland

N tot , NO 3 -N, NO 2 -N, NH 4 -N, P tot , PO 4 -P, SO 4 , Fe, Ca, Al, K, Mg and dissolved O 2 concentrations, as well as water temperature, pH, Oxidation-Reduction Potential (ORP) and electric conductivity were measured in soil water and ground water sampled from different plant communities located along topo-edaphic gradients from moraine upland to stream valley in two small agricultural catchments in southeastern Estonia. The production rate and the N and P content in plant biomass were also analyzed. The mosaic soil and vegetation pattern had a significant influence on soil water quality. In the arable land, the mean annual concentration of total inorganic nitrogen (NH 4 -N + NO 2 -N + NO 3 -N) in piezometer water was 3-40 mg N 1 -1 but in the riparian grey alder forest (Alnus incana) total inorganic nitrogen never exceeded 1 mg N 1 -1 .The most significant reduction was in the average concentration of NO 3 -N content, which was reduced from 25 mg 1-1 under the arable land to 0.5 mg 1 -1 in both the alder forest and the sedge-dominated floodplain. The average P tot concentration also decreased under the alder stands, being 0.2-1.5 mg P 1 -1 in the arable land and less than 0.2 mg P 1 -1 in the alder forest. Wetland herb communities (Carex elata association, Filipendula ulmaria, Cirsium oleraceum and Aegopodium podagraria dominated communities) also had a significant influence on soil water quality, increasing the internal cycling of N and P within the peatland. The plant biomass (the sum of above- and below-ground biomass) of riparian and wetland communities accumulates up to 54.3 g N m -2 and up to 5.3 g P m -2 during the growth season. The following factors have the highest priority in weather-induced changes in the nutrient fluxes in riparian peatlands: (a) the duration of frozen surface, (b) snowpack peak water, (c) the precipitation pattern over the warm period, (d) the duration and continuity of certain weather, (e) the occurrence of night frost events and soil freeze-thaw cycles. When night frost events start, the importance of autumn rainfalls is enhanced, as the high water-table intensifies the denitrification process but also increases Ca, Mg, K, N and P losses released during the frost-thaw cycle.