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Nitrate Removal from Floodwater Overlying Flooded Soils and Sediments¹

ABSTRACT

The floodwater NO₃^– removal rate of intermittently-flooded fresh water swamp soils and continuously-flooded saline marsh soils of southern Louisiana was quantitatively characterized in a laboratory study. Of the two areas studied, the marsh area was the more effective sink for NO₃^– contaminated waters with an average initial removal rate of 9.15 ppm N/day. After correcting for the rate of NO₃^– diffusion, the microbial NO₃^– removal rate was calculated to be 7.64 ppm N/day. The swamp soil had a removal rate of 4.38 ppm N/day. The microbial NO₃^– removal rate for this area, after correcting for diffusion, was 2.50 ppm N/day. Studies on samples of floodwater separated from the soil showed the active site of microbial NO₃^– reduction to be the soil-water interface or within the soil, but not in the floodwater. Additions of organic matter to a mineral soil flooded for rice (Oryza sativa L.) culture decreased the thickness of the aerobic-anaerobic zone at the soil-water interface and increased the rate of NO₃^– reduction.

Key Words: NO₃^– diffusion • NO₃^– reduction • anaerobic • denitrification • redox potential

¹ Contribution from the Agronomy Dep., Louisiana State University, Baton Rouge 70803. This study was supported in part by US Environmental Protection Agency Project R-800428.

² Associate and Professor, respectively. The senior author is currently Research Soil Scientist, Department of Army, Corps of Engineers, Waterways Experiment Station, Environmental Effects Laboratory, Vicksburg, Miss. 39180.

Received for publication January 29, 1974.