Title: Nitrification and denitrification gene abundances in swine wastewater anaerobic lagoons Authors
Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 3, 2011
Publication Date: March 1, 2011
Citation: Ducey, T.F., Shriner, A.D., Hunt, P.G. 2011. Nitrification and denitrification gene abundances in swine wastewater anaerobic lagoons. Journal of Environmental Quality. 40:610-619. Interpretive Summary: Anaerobic lagoons are a common management practice in the North and South Carolinas. They are used to store and passively treat feces and urine collected from confined swine production operations. These systems have the potential for significant environmental impacts. One of the major unresolved questions is their cycling of nitrogen. In this study we examined eight commercial anaerobic swine wastewater lagoons. We searched for the presence of four genes involved in nitrogen cycling processes. The genes of interested were amoA, which encodes the ammonia monooxygenase gene, nirS and nirK, which encode nitrite reductases, and nosZ which encodes the gene nitrous oxide reductase. The gene nosZ is responsible for converting the greenhouse gas nitrous oxide to dinitrogen gas, which has no environmental impact. Our analyses identified the presence of all four genes in all of the lagoons, at levels typically found in natural ecosystems. The genes amoA and nirK were affected by several lagoon chemical characteristics. Additionally, levels of nosZ were predictive for the disparity between actual and potential denitrification enzyme activity. This finding may help in the creation of practices that optimally manage nitrogen in natural ecosystems.
Technical Abstract: Although anaerobic lagoons are used globally for livestock waste treatment, their detailed microbial cycling of nitrogen is only beginning to become understood. Within this cycling, nitrification can be performed by organisms which produce the enzyme ammonia monooxygenase (AMO). For denitrification, the reduction of nitrite to nitric oxide can be catalyzed by two forms of nitrite reductases (Nir), and N2O-N can be reduced by nitrous oxide reductase by the gene nosZ. The objectives of this investigation were as follows: 1) quantify the abundance of the amoA, nirK, nirS, and nosZ genes; 2) evaluate the influence of environmental conditions on their abundances; and 3) evaluate their abundance relative to denitrification enzyme activity (DEA). The analyses were via Real-Time quantitative PCR (qPCR), with samples collected from eight typical, commercial anaerobic, swine wastewater lagoons located in the Carolinas. The four genes assayed in this study were present in all eight lagoons. Their abundances relative to total bacterial populations were 0.04% (amoA), 1.33% (nirS), 5.29% (nirK), and 0.27% (nosZ). When compared to lagoon chemical characteristics, both amoA and nirK correlated with several measured variables. Neither nirS nor nosZ correlated with any measured environmental variables. While no gene measured in this study correlated with actual or potential DEA, nosZ did correlate with the disparity between potential and actual DEA. As with other investigations, analyses of these genes provide useful insight while revealing the underlying greater complexity of nitrogen cycling within swine waste lagoons.