MICROBIAL ACTIVITY IN HEATING OIL CONTAMINATED SOIL UNDER FIELD AND CONTROLLED CONDITIONS

The impact of petroleum hydrocarbons represented by heating oil on soi l microbial activity was studied in a loamy sand under field and partl y controlled conditions (60% WHC). Overall microbial activity as repre sented by dehydrogenase and catalase activity increased severalfold un der both experimental conditions in the oil contaminated soils probabl y due to hydrocarbon degradation. This assumption is supported by a lo ss of n-alkanes in the field soils. Nitrification rates dropped to les s than 10% of control levels. This effect, together with the widening of the C/N-ratio through incorporation of hydrocarbons into soil organ ic matter, presumably led to N-imbalances in the contaminated soils. G rowth of vegetation was severely retarded in the oiled field soils. Th e storage of the rather fine-textured heavy soil at 60% WHC (controlle d conditions) prolonged the stimulatory effects of the added oil on de hydrogenase and catalase activity and intensified the depression of ni trification. However, no degradation of n-alkanes C-14-C-22 was observ ed under these conditions in contrast to the field experiments. Improv ed aeration due to seasonal variation in soil water content as occurre d under field conditions may have caused losses of n-alkanes by enhanc ed biodegradation from the field soils. Conclusions: Contamination of soil with petroleum hydrocarbons may have deleterious long-term effect s on soil ecosystems and their nutritional balances. The extent and du ration of these disturbances may vary sharply with environmental condi tions such as water content. Soil microbial activities combined with o ther parameters may serve as a useful means of assessing the effects o f hydrocarbon contamination.