Abstract
Agricultural activities that involve animal wastes can result in the contamination of subsurface soils by nitrates (NO3). In saturated or nearly saturated soils, microbial biobarriers are a common method used to remove contaminants from water. This study evaluated the presence of NO3 in the soil profile beneath a cattle corral and the use of biobarriers to prevent the movement of NO3 through these semiarid vadose zone soils. Soils from beneath the pen contained as much as 330 mg kg−1 (330 ppm) nitrate-nitrogen (NO3-N), and a well located ~50 m (~55 yd) from the pens contained 18 mg L−1 (18 ppm) NO3-N, indicating that denitrification activity in the surface soils of the corral had not prevented NO3 from migrating into deeper soils where denitrification activity was limited by electron donor (i.e., carbon [C] substrate) availability. Biobarriers used to intercept the percolating soil water contaminated with NO3 included a control that contained only sand and treatment biobarriers that contained sand blended with sawdust, soybean (Glycine max L.) oil, or sawdust and soybean oil. A distinctive attribute of the study was that the biobarriers were installed near the surface of a semiarid soil well above the water table. Results show that all of the treatment biobarriers removed NO3 from percolating soil water. Water collected from beneath the control barriers contained 99 mg L−1 (99 ppm) NO3-N while NO3-N levels in water that moved through the sawdust, soybean oil, and sawdust plus soybean oil barriers averaged 4, 17, and 28 mg L−1 (4, 17, and 28 ppm) NO3-N for removal efficiencies of 96%, 83%, and 72%, respectively. In waters from the sawdust plus soybean oil barriers, 6.8 mg L−1 (6.8 ppm) nitrite-N was detected. With all three substrate combinations, biobarrier life was such that barriers of this type should last for many years before substrates need to be replaced.
- © 2013 by the Soil and Water Conservation Society
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