| Summary: | This thesis presents the first direct flux measurements of land/atmosphere carbon dioxide (CO[subscript 2]) exchange at managed lowland peatlands in the East Anglian Fens, UK. The dynamics and magnitude of land/atmosphere CO[subscript 2] exchange were quantified at semi-natural and regenerating ex-arable fens located at the Wicken Fen Nature Reserve in Cambridgeshire. Eddy covariance measurements were made at the semi-natural fen throughout two thermally and hydrologically dissimilar periods during 2009 and 2010, and at the regenerating former-arable fen over the complete annual cycle of 2010. The study sites were characterised by strong seasonal variation in CO[subscript 2] exchange. The semi-natural fen was a net source of 85.47±25.78 g CO[subscript 2]-C m[superscript -2] between 20th March and 31st December 2009, and a small net sink of -22.66±18.85 g CO[subscript 2]-C m[superscript -2] for the same period of 2010. Photosynthesis and ecosystem respiration were both higher during warm conditions of 2009 compared to 2010, but enhanced rates of ecosystem production were outweighed by large CO[subscript 2] losses during warm and dry conditions in autumn. The large interannual variability in CO[subscript 2] exchange illustrates the sensitivity of semi-natural fens to climatic variability and change, and highlights the need to maintain high water levels to prevent large losses of soil carbon to the atmosphere as CO[subscript 2]. The regenerating fen functioned as a small net source of 21.24±17.11 g CO[subscript 2]-C m[superscript -2] yr[superscript -1]. On the basis of values currently used to represent CO[subscript 2] losses from arable fens, the annual CO[subscript 2] balance for the ex-arable fen in 2010 indicates the net CO[subscript 2] benefit of fenland rehabilitation was an avoided loss of -87.7±17.11g CO[subscript 2]-C m[superscript -2] yr[superscript -1]. The results from the regenerating site imply that a more adaptive water management strategy will be needed if the environmental conditions required for peat formation and net carbon capture are to be restored.
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