Uni-Bayreuth grafik-uni-bayreuth


Blodau, C*; Lischeid, G; Knorr, KH; Reiche, M; Küsel, K; Goldberg, S; Muhr, J; Hentschel, K; Borken, W; Gebauer, G; Weyer, C; Hamberger, A; Horn, M; Drake, HL; Peiffer, S; Matzner, E: Impact of experimental drainage and rewetting on biogeochemical processes in a northern fen
Vortrag, International Symposium Soil processes under extreme meteorological conditions, Bayreuth: 25.02.2007 - 28.02.2007

An increase of global temperatures and intensity and frequency of precipitation has been predicted, particularly for northern latitudes. Enhanced summer dryness and intensified rainfall will likely cause changes in the carbon, sulfur, iron, and nutrient dynamics in affected wetlands but to date little is known about the intensity and the time scales on which the involved biogeochemical processes will respond to climatic change. Moreover, studies are lacking that identify and causally explain observed effects on the ecosystem scale. The first year of ecosystem experiments at a fen in the mountains near Bayreuth, Germany, showed that the water table could be successfully manipulated by the use of drainage systems and precipitation exclusion. Due to preceding and concurrent drought, the net decrease compared to controls was limited to about 10 cm, however. Even this small decrease lead to a mobilization of sulfate, increases in electric conductivity, decreases in pH, and the degassing of dissolved gases. In contrast, soil respiration fluxes were not affected. Due to the high water content remaining, reductive processes apparently continued concurrently to oxidative processes and were concentrated on the uppermost 20 cm of the soils. Drying and rewetting lead to increased exo-enzymatic activity and prolonged time lags of methanogenesis in the incubations with the uppermost soils. In controlled long-term mesocosm experiments, in which the water table was lowered by 30 to 40 cm, the dynamics of carbon turnover, oxidation and reduction dynamics could be identified clearly. The overall carbon balance of the mesocosms remained unaffected, apparently by predominance of the carbon turnover in the near surface peat and compensation between photosynthesis and soil respiration. Dessication lead to reoxidation and replenishment of electron acceptor pools in the soils and inhibition of methanogenesis on the time scale of months. Even in these experiments, however, reductive processes, such as sulfate reduction and methanogenesis, occurred in the unsaturated soil. The dynamics of biogeochemical processes in poorly permeable wetland soils subjected to drying wand rewetting is thus more complex than previously assumed. It is likely characterized by a spatiotemporal continuum of oxidative and reductive processes, whose net balance shifts with changes in water content and permeability for oxygen.

Letzte Änderung 19.03.2007