Combined assessment of methane oxidation and nitrification: an indicator of air-borne soil pollution?

Soil nitrification and CH, oxidation activity were measured in six forested soils in a region of southwestern Poland differently affected by heavy met als and hydrocarbon contamination from a coke production plant, road traffi c and general urban sources. A multivariate analysis of data from 80 sites within the six forested areas investigated identified Ni and an unidentifie d hydrocarbon (HI) as negatively affecting nitrification and CH4 oxidation in a model (P=0.02) that also included soil organic matter and pH. Univaria te statistical analysis of these two suspected toxicants demonstrated a neg ative influence of Ni on nitrification (P <0.05) within the two areas in wh ich soil Ni concentrations were highest. In addition, it revealed a negativ e influence of H I on CH4 oxidation (P <0.06) at the two sites with the hig hest soil concentrations of H1 among those sites where CH4 oxidation occurr ed. The distribution of nitrification and CH4 oxidation were inversely rela ted, as would be expected from their contrasting responses to soil disturba nces and inorganic N levels. Among sites where at least one of the two proc esses occurred. Ni or HI levels were high in only 18% of them, which is sig nificantly lower than the frequency of high pollutant concentrations (67%) among sites where neither nitrification nor CH4 oxidation occurred (P <0.05 ). The apparent ubiquity with which at least one of the two processes occur s in unpolluted soil samples suggests that combined measurement of nitrific ation and CH4 oxidation could serve as a useful pollution indicator compare d with processes which are selected more randomly for toxicological studies .