Environmental factors influencing the rate of hydrocarbon oxidation in temperate lakes

Abstract

Rates of hydrocarbon biodegradation were estimated by following O2 uptake during mineral oil oxidation or oxidation of [1-14C]hexadecane to 14CO2, when these substrates were added to natural water samples from Wisconsin [USA] lakes. A lag phase preceded hydrocarbon oxidation, the length of which depended on population density or on factors influencing growth rate and on the presence of nonhydrocarbon organic compounds. Hydrocarbon oxidation was coincident with growth and presumably represented the development of indigenous hydrocarbon-degrading microorganisms in response to hydrocarbon additions. In detailed studies in Lake Mendota, despite the continued presence of hydrocarbon-degrading microorganisms in water samples, seasonal variations in the rates of mineral oil and hexadecane oxidation occurred which correlated with seasonal changes in temperature and dissolved inorganic N and P. The temperature optimum for oil biodegradation remained at 20-25.degree. C throughout the year, so that temperature was the main limiting factor during winter, spring and fall. During summer, when temperatures were optimal, nutrient deficiencies limited oil biodegradation, and higher rates could be obtained by addition of N and P. The rates of hydrocarbon biodegradation were thus high only for about 1 mo. of the ice-free period, when temperature and nutrient supply were optimal. Nutrient limitation of oil biodegradation was also demonstrated in 25 nutrient-poor lakes of northern Wisconsin, although in almost every case oil-degrading bacteria were detected. Knowledge of temperature and nutrient limitations thus will help in predicting the fate of hydrocarbon pollutants in freshwater.