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Effect of organic loading on nitrification and denitrification in a marine sediment microcosm

J.M. Caffrey , N.P. Sloth , H.F. Kaspar , T.H. Blackburn
DOI: http://dx.doi.org/10.1111/j.1574-6941.1993.tb00028.x 159-167 First published online: 1 July 1993


The effects of organic additions on nitrification and dentrification were examined in sediment microcosms. The organic material, heat killed yeast, had a C/N ratio of 7.5 and was added to sieved, homogenized sediments. Four treatments were compared: no addition (control), 30 g dry weight (dw) m−2 mixed throughout the 10 cm sediment column (30M), 100 g dw m−2 mixed throughout sediments (100M), and 100 g dw m−2 mixed into top 1 cm (100S). After the microcosms had been established for 7–11 days, depth of O2 penetration, sediment-water fluxes and nitrification rates were measured. Nitrification rates were measured using three different techniques: N-serve and acetylene inhibition in intact cores, and nitrification potentials in slurris. Increased organic additions decreased O2 penetration from 2.7 to 0.2 mm while increasing both O2 consumption, from 30 to 70 mmol O2 m−2 d−1, and NO3 flux into sediments. Nitrification rates in intact cores were similar for the two methods. Highest rates occurred in the 30M treatment, while the lowest rate was measured in the 100S treatment. Total denitrification rates (estimated from nitrification and nitrate fluxes) increased with increased organic addition, because of the high concentrations of NO3 (40 μM) in the overlaying water. The ratio of nitrification: denitrification was used as an indication of the importance of nitrification as the NO3 supply for denitrificaion. This ratio decreased from 1.55 to 0.05 iwth increase organic addition.

Key words
  • Benthic fluxes
  • Nitrification
  • Organic loading
  • Microcosm
  • Denitrification

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