Upflow Reactors for Riparian Zone Denitrification
- Peter W. van Driel,
- William D. Robertson * and
- L. Craig Merkley
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.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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