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TECHNICAL REPORTS

Ground Water Quality

Upflow Reactors for Riparian Zone Denitrification

Department of Earth Sciences, University of Waterloo, 200 University Ave. W., Waterloo, ON, Canada
Upper Thames River Conservation Authority, 1424 Clarke Road, London, ON, Canada

^* Corresponding author (wroberts{at}uwaterloo.ca)

Received for publication January 24, 2005. We used permeable reactive subsurface barriers consisting of a C source (wood particles), with very high hydraulic conductivities (0.1–1 cm s^–1), to provide high rates of riparian zone NO₃–N removal at two field sites in an agricultural area of southwestern Ontario. At one site, a 0.73-m³ reactor containing fine wood particles was monitored for a 20-mo period and achieved a 33% reduction in mean influent NO₃–N concentration of 11.5 mg L^–1 and a mean removal rate of 4.5 mg L^–1 d^–1 (0.7 g m^–2 d^–1). At the second site, four smaller reactors (0.21 m³ each), two containing fine wood particles and two containing coarse wood particles, were monitored for a 4-mo period and were successful in attenuating mean influent NO₃–N concentrations of 23.7 to 35.1 mg L^–1 by 41 to 63%. Mean reaction rates for the two coarse-particle reactors (3.2 and 7.8 mg L^–1 d^–1, or 1.5 and 3.4 g m^–2 d^–1) were not significantly different (p > 0.2) than the rates observed in the two fine-particle reactors (5.0 and 9.9 mg L^–1 d^–1, or 1.8–3.5 g m^–2 d^–1). A two-dimensional ground water flow model is used to illustrate how permeable reactive barriers such as these can be used to redirect ground water flow within riparian zones, potentially augmenting NO₃^– removal in this environment.

Abbreviations: HRT, hydraulic retention time • K, hydraulic conductivity • OC, organic carbon