The effects of trace narasin on the biogeochemical N-cycle in a cultivated sandy loam.

Narasin is an antibiotic administered to broiler chickens to prevent coccidiosis. After storage, excreta containing parent narasin compounds is commonly spread as nitrogen fertilizer, yielding initial soil concentrations in the low μg·kg range. In soil, antibiotics have been found to modify one or more pathways in the biogeochemical nitrogen cycle.

The effect of ultralow-dose antibiotics exposure on soil nitrate and N2O flux.

Exposure to sub-inhibitory concentrations of antibiotics has been shown to alter the metabolic activity of micro-organisms, but the impact on soil denitrification and N2O production has rarely been reported. In this study, incubation and column transport experiments were conducted on soils exposed to as many as four antibiotics in the ng · kg(-1) range (several orders of magnitude below typical exposure rates) to evaluate the impact of ultralow dose exposure on net nitrate losses and soil N2O flux over time. Under anaerobic incubation conditions, three antibiotics produced statistically significant dose response curves in which denitrification was stimulated at some doses and inhibited at others.

Enhanced mixing and plume containment in porous media under time-dependent oscillatory flow.

Solute transport experiments were conducted in a decimeter scale flow cell packed with sand to study the potential for enhanced mixing of solutes in porous media and improved containment of injected plumes under multiple pumping-well driven, time-dependent oscillatory flow with respect to constant flow. Real-time imaging of the colorimetric reaction of Tiron (1,2-dihydroxybenzene-3,5-disulfonic acid) and molybdate was used to quantify mixing, whereas fluorescein was used to better examine plume size. Results from the small scale experiments clearly demonstrated the enhanced mixing of solutes under low Reynolds number oscillatory flow (a factor of 2 with respect to constant flow in homogeneous sand and a factor of 3 in layered sand), as the result of increased contact interface for solute diffusion.