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The aim of this study was to establish the main drivers of the spatial variability in growing season CH flux within an arctic wetland ecosystem. During 3 years (2011-2013) we measured CH flux and potential drivers, e.g., CO fluxes (net ecosystem exchange (NEE), gross primary productivity (GPP) and ecosystem respiration), temperature, water table depth, pore-water concentration of organic acids (e.g., acetate) and the vascular plant composition and density. The study included 16-20 main plots (C) and in 2013 also experimental plots (10 excluded muskoxen grazing, 9 snow fence and 10 automated chamber plots) distributed over 0.3 km. The results show a 1.8-times difference in CH flux magnitude inter-annually and 9- to 35-times spatially (depending on year and treatment). During all 3 years GPP was a strong driver of the variability in C plots. Accordingly, the plant productivity related variables NEE, GPP and acetate were singled out as the strongest drivers of the variability in 2013, when all variables were measured on a majority of the plots. These variables were equally strong drivers of the spatial variability in CH flux regardless of whether experimental plots were included in the analysis or not. The density of Eriophorum scheuchzeri was the strongest driver of the spatial variability in NEE, GPP and acetate. In conclusion, changes in vegetation composition or productivity of wet arctic ecosystems will have large impacts on their carbon balance and CH flux, irrespective of whether these changes are driven directly by climate change or by biotic interactions, such as grazing. [ABSTRACT FROM AUTHOR]

It is demanded currently in public discussions to rewet peatlands and re-establish their function as nutrient sinks. But due to high phosphorus (P) concentrations in the pore water of rewetted peatlands (40–420 μM) it is hypothesized that they can act as a surplus P source for adjacent surface waters and consequently support the eutrophication of such waters. Our detailed investigations of processes at the redox interface in four fens with different geochemical character show the dependence of P retention from the chemistry of the pore water. The precipitation of Fe(III) oxyhydroxide led to high retention of phosphorus and other substances such as DOC and sulphate in the eutrophic fens. When molar Fe/P ratios were larger than about 3 the initially high P concentrations in the anaerobic pore water (20–210 μM) decreased to concentrations below 1 μM under aerobic conditions. Thus, after rewetting high pore water concentrations of P do not automatically result in an increased P load to adjacent surface waters compared to pre-rewetting conditions. An enhanced P export to adjacent surface waters from eutrophic fens can be expected when the Fe/P ratio is smaller than 3 in the anaerobic pore water. In our investigations of natural, oligotrophic to mesotrophic fens the precipitation of Fe(III) oxyhydroxide was inhibited by the formation of stable dissolved Fe ∼ humic complexes. P retention in these fens was only related to the DOC concentrations at the redox interface, so that lower DOC concentrations concurred with higher P retention. The P equilibrium concentrations in an aerobic environment can be higher than that of eutrophic fens with Fe/P ratios larger than about 3 in the anaerobic pore water. [ABSTRACT FROM AUTHOR]