Redox potentials in relation to water levels in different mire types in the Netherlands and Poland

Abstract

In mires in the Netherlands and Poland redox potentials were measured in situ in 8-fold at 15 cm below the peat surface in 10 m2 plots. Measurements were repeated 2–4 times in time at ca. 240 locations. Simultaneously, water levels were recorded in piezometers and water samples were analysed for pHwater. pHKCl was determined in peat samples. The relationship between water levels and measured redox potential was different in different mire types (Poor fen and bogs, Moderately-rich fens and Fen meadows). Moderately-rich fens did not differ from each other in redox potential at high water levels. Poor fens and bogs and Fen meadows showed a considerable variation in redox potentials at water levels between 0–25 cm. Moderately-rich fens (undrained) on solid peat showed distinctly lower redox potentials than bogs and poor fen at water levels of 20–30 cm, which points to the poorly decomposable character (low electron activity) of the organic matter in bogs and poor fen. Moderately-rich fens on solid peat showed distinctly lower redox potentials than in fen meadows at water levels deeper than 30 cm, which points to the strongly humified character (hardly any labile components left, low microbial activity, high redox potentials) of drained fen meadows compared to moderately-rich fen. In Fen meadows when water levels were below 40 cm to the peat surface, redox potentials were high and constant irrespective of the water levels. We concluded that a combination of water level and redox potential provides a much more ecologically relevant description of the site conditions in mires than water levels only. Redox measurements integrate both physical conditions and (seasonal) microbial activity.