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The Role of Denitrification in the Nitrogen Cycle of New England Salt Marshes

出版	Massachusetts Institute of Technology, 2002
URL	http://books.google.com.hk/books?id=VSceAQAAIAAJ&hl=&source=gbs_api

註釋I used direct measurements of nitrogen gas (N2) fluxes and a 15N stable isotope tracer to determine the contribution of denitrification to salt marsh sediment N cycling. Denitrification in salt marsh tidal creekbottoms is a major sink for groundwater nitrate of terrestrial origin. I studied creekbottom denitrification by direct measurements of N2 fluxes in closed chambers against a low-N2 background. I undertook experiments and simulation modeling of sediment N2 fluxes in closed chambers to optimize the key experimental parameters of this approach. Denitrification in these sediments was driven by the degradation of labile organic matter pools which are depleted during long incubations. Sediment thickness was the most important parameter controlling the required incubation time. Errors of up to 13% with gas headspaces and 80% with water headspaces resulted from headspace N2 accumulation and the resulting collapse of the sediment-water diffusion gradient. These errors could be eliminated by using headspaces of sufficient thickness. Headspace flushing to reduce ammonium accumulation did not affect denitrification rates, but caused transient disturbance of N2 flux rates. Direct measurements of 02, C02, N2, and inorganic N fluxes from the sediments of a salt marsh tidal creek were made in order to examine the interaction of denitrification with the carbon, oxygen, and N cycles. Organic carbon concentration and lability were the primary controls on metabolic rates. C02/N flux ratios averaged 6.1, indicating respiration driven by algal biomass.