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Presented at the NABS Annual meeting, Anchorage, Alaska, 2006
in Biogeochemistry 1
Flow conditions and substrate geometry strongly influence benthic denitrification
S. Arnon, A.I. Packman, and K.A. Gray.Department of Civil and Environmental Engineering, Northwestern University, IL, USA
Observations of nitrogen transformations in the Des Plaines River Wetland Demonstration Project (Wadsworth, IL) indicate that the emplacement of benthic mesh netting increases the rate of denitrification by providing a favorable and uniform substrate for thick periphyton growth. Here we use a combination of macro- and micro-scale observations, in laboratory wetland-models, to show that interplay between hydrodynamic transport, local chemical conditions, and microbial metabolism controls denitrification in benthic microbial communities. While it is usually assumed that interfacial transport and nutrient removal both increase monotonically with the overlying flow velocity, we observed substantially greater bulk nitrate removal under slower velocities (0.05 and 0.5 cm s-1) than under a faster velocity (5 cm s-1), with the greatest rate of nitrate removal occurring under the intermediate flow condition. Combined knowledge of the response of the microbial community and bulk denitrification rates to the system geometry and flow conditions will support the development of improved strategies that rely on periphytic growth to enhance denitrification rates in natural and constructed wetlands.
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