ABSTRACT
Microbial transformations of nitrification and denitrification are the main sources of nitrous oxide (N2O) from soils. Relative contributions of both processes to N2O emissions were estimated on an agricultural soil using 15N isotope tracers (15NH4+ or 15NO3-), for a 10-day batch experiment. Under unsaturated and saturated conditions, both processes were significantly involved in N2O production. Under unsaturated conditions, 60% of N-N2O came from nitrification, while denitrification contributed around 85-90% under saturated conditions. Estimated nitrification rates were not significantly different whatever the soil moisture content, whereas the proportion of nitrified N emitted as N2O changed from 0.13 to 2.32%. In coherence with previous studies, we interpreted this high value as resulting from the decrease in O2 availability through the increase in soil moisture content. It thus appears that, under limiting aeration conditions, some values for N2O emissions through nitrification could be underestimated.
Subject(s)
Air Pollutants/metabolism , Bacteria/metabolism , Environmental Monitoring/methods , Greenhouse Effect , Nitrous Oxide/metabolism , Biotransformation , Fertilizers , Isotope Labeling , Nitrogen Isotopes , Soil PollutantsABSTRACT
The transfer of organic pollutants was studied through soil columns using 13[C]-labelled pentachlorophenol (PCP) as a model compound. The organic carbon content and the 13[C]/12[C] ratio were measured in two soil sections, 0-3 cm and 3-6 cm, and in percolated water using an Elemental Analyser coupled with a Magnetic Mass Sector. The mass balance of carbon was evaluated and the amount of PCP was calculated in each compartment of the soil-water systems. The results show that more than 80% of the PCP-derived 13[C] remained in the upper layer of the soil column. Approximately 20% was transferred to the lower soil layer, and less than 1% was found in the water leachates. The 13[C]-labelled tracers may thus be used as an alternative to radioactive compounds to follow the fate of organic pollutants in soil and water under field conditions.
