HR: 1330h
AN: NB33C-05    [Abstracts]
TI: The Effect of Flow on Periphyton Structure and Nitrate Removal
AU: * Arnon, S
EM: s-arnon@northwestern.edu
AF: Department of Civil and Environmental Engineering Northwestern University, 2145 Sheridan Rd., Evanston, IL 60208 United States
AU: Packman, A
EM: a-packman@northwestern.edu
AF: Department of Civil and Environmental Engineering Northwestern University, 2145 Sheridan Rd., Evanston, IL 60208 United States
AU: Gray, K
EM: k-gray@northwestern.edu
AF: Department of Civil and Environmental Engineering Northwestern University, 2145 Sheridan Rd., Evanston, IL 60208 United States
AB: High nutrient levels in surface waters are a persistent worldwide problem. Natural and constructed wetlands are frequently employed to reduce nutrients levels from non-point sources, such as agriculture activity. However, there is little understanding of the variation in nitrate removal with flow conditions, and it is difficult to control peaks of nitrogen, especially in the spring when flows tend to be high and there is substantial agricultural nutrient input. 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, which, in turn, promotes a superior habitat and carbon source for denitrifying bacteria. We are evaluating this hypothesis in a series of studies designed to improve understanding of the interplay between periphyton assemblage characteristics, overlying flow conditions, and the rate of denitrification. We are conducting laboratory experiments in a model wetland system (250 cm long and 20 cm wide). Nitrate removal is evaluated by monitoring changes in the concentrations of nitrate, nitrite, ammonium and total nitrogen in the system under different fluid velocities (0.05, 0.5 and 5 cm/s). Temporal changes in the periphyton assemblage characteristics are quantified using a combination of confocal microscopy, algal identification, and microbial enumeration. We also utilize micro-profiling with oxygen and nitrate micro-sensors to evaluate chemical heterogeneity in the periphyton and sediments. Combined knowledge of the response of the microbial system 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.
DE: 1871 Surface water quality
DE: 1890 Wetlands
SC: North American Benthological Society [NB]
MN: 2005 Joint Assembly