Experimental measurement of sediment nitrification and denitrification in Hamilton Harbour,Canada |
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Authors: | Klapwijk A Snodgrass W J |
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Institution: | (1) Departments of Chemical and Civil Engineering, McMaster University, L8S4L7 Hamilton, Ontario, Canada;(2) Department of Sanitary Engineering, Wageningen University, Wageningen, The Netherlands |
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Abstract: | This research examines the role of sediment nitrification and denitrification in the nitrogen cycle of Hamilton Harbour. The
Harbour is subject to large ammonia and carbon loadings from a waste-water treatment plant and from steel industries. Spring
ammonia concentrations rapidly decrease from 4.5 to 0.5 mg 1−1, while spring nitrate concentrations increase from 1 to 2 mg l−1, by mid-summer. A three-layer sediment model was developed. The first layer is aerobic; in it, oxidation of organics and
nitrification occurs. The second layer is for denitrification, and the third layer is for anaerobic processes. Ammonia sources
for nitrification include diffusion from the water column, sources associated with the oxidation of organics, sources from
denitrification and from anaerobic processes. Diffusion of oxygen, ammonia and nitrate across the sediment-water interface
occurs. Temperature effects are modelled using the Arrhenius concept. A combination of zero-order kinetics for nitrate or
ammonia consumption with diffusion results in a half-order reaction, with respect to the water column loss rate to sediments.
From experimental measurement, the rate of nitrification is 200 mg N 1−1 sediment per day, while that of denitrification is 85 mg N 1–1 sediment per day at 20 °C. The Arrhenius activation energy
is estimated as 15 000 cal/ mole-K and 17 000 cal/ mole-K for nitrification and denitrification, respectively, between 10
°C and 20 °C. Calculations of the flux of ammonia with the sediments, using the biofilm model, compare favourably with experimental
observations. The ammonia flux from the water column is estimated to account for 20% of the observed decrease in water column
stocks of ammonia, while the nitrate flux from the water column is estimated to account for 25% of the total nitrogen produced
by the sediments. |
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Keywords: | sediments water column nitrification denitrification experiments modelling |
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