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

The impact of petroleum hydrocarbons represented by heating oil on soil microbial activity was studied in a loamy sand under field and partly controlled conditions (60% WHC). Overall microbial activity as represented by dehydrogenase and catalase activity increased severalfold under both experimental conditions in the oil contaminated soils probably due to hydrocarbon degradation. This assumption is supported by a loss of n-alkanes in the field soils. Nitrification rates dropped to less than 10% of control levels. This effect, together with the widening of the C/N-ratio through incorporation of hydrocarbons into soil organic matter, presumably led to N-imbalances in the contaminated soils. Growth of vegetation was severely retarded in the oiled field soils. The storage of the rather fine-textured heavy soil at 60% WHC (controlled conditions) prolonged the stimulatory effects of the added oil on dehydrogenase and catalase activity and intensified the depression of nitrification. However, no degradation of n-alkanes C-14-C-22 was observed under these conditions in contrast to the field experiments. Improved aeration due to seasonal variation in soil water content as occurred under field conditions may have caused losses of n-alkanes by enhanced biodegradation from the field soils. Conclusions: Contamination of soil with petroleum hydrocarbons may have deleterious long-term effects on soil ecosystems and their nutritional balances. The extent and duration of these disturbances may vary sharply with environmental conditions such as water content. Soil microbial activities combined with other parameters may serve as a useful means of assessing the effects of hydrocarbon contamination.