Nitrogen Cycling and Nitric Oxide Emissions in Oil-Impacted Prairie Soils

Abstract

A remote site in the Tallgrass Prairie Preserve of Oklahoma (The Nature Conservancy) was contaminated with crude oil from a pipeline break and is being bioremediated using landfanning techniques. Landfarming is designed to stimulate microbial-based catabolism of petroleum through combined dilutiodmixing and fertilization-based effects. To evaluate nitrogen-based effects during remediation, the site was sectioned and treated with urea, ammonium sulfate, or ammonium nitrate. Samples were obtained from prairie soil without chemical nitrogen addition and with or without hydrocarbon contamination. Nitrogen cycling dynamics were followed by measuring ammonium, nitrite, nitrate, and volatile nitric oxide (NO,) levels. Nitrifying and denitrifying bacterial numbers were estimated and compared to soil oxygen, carbon dioxide, and methane levels as well as to overall total petroleum hydrocarbon (TPH) reduction. For a prairie ecosystem of this type, a high level of fertilization, particularly with nitrogen, can have ecological effects almost as profound as the petroleum contamination itself. Fertilization of the oil-contaminated soil with the reduced and/or oxidized forms of nitrogen quickly resulted in elevated steady-state levels of both ammonium and nitrate, and exceptionally high levels of NO, released from soil. Although nitrogen fertilization increased microbial nitrogen metabolism and nitrogen cycling, it had minimal effects on the overall remediation efficiency.

Effect of Environmental Factors on the Abundance of Culturable Nitrate Reducing/Denitrifying Bacteria from Contaminated and Uncontaminated Tallgrass Prairie Soil

“…Leaks from oil pipelines had contaminated the sites with crude oil (J6-F, J6-NF, LF) or with a mixture of brine and oil (G5, G7). The sites had been partially remediated as described previously (Sublette et al, 2005;Sublette et al, 2007a;Duncan et al, 1998;Duncan et al, 1999). Briefly, the contaminated sites were contaminated during 1996-2000 but still contained low levels of TPH and Na + and Cl -(Tables 1.a and 1.b) when sampled for the current study.…”

“…Sodium and chloride levels varied widely, with sodium ranging from 350-600 mg/ kg soil (Sublette et al, 2004). On the other hand, LF, containing soil contaminated by a spill of crude oil, was remediated in 1996 and 1997 by mixing the contaminated soil with the uncontaminated soil plus nitrogen-containing fertilizer (Duncan 1998(Duncan , 1999. During that time, TPH levels decreased to about a third of the original level and plants grew over most of the site, but they were primarily weedy, non-native, undesirable species.…”

Multi-Species Ecotoxicity Assessment of Petroleum-Contaminated Soil

“…It has been shown repeatedly that after an initial lag period, the rate of bioremediation first increases then slows, with most activity taking place within a 2-to 5-month span or in 10 to 12 months for a soil low in organic matter, and little mineralization after that (Bossert et al, 1984; Salanitro et al, 1997;Fisher and King, 1994;Duncan et al, 1998). Bossert et al (1984) noted an increase in humification after the active mineralization phase.…”