Nutrient and temperature interactions in bioremediation of cryic soils

Low temperatures and lack of available nutrients often limit the rate of microbial petroleum hydrocarbon degradation in contaminated cryic soils. Proper management of both these parameters may increase microbial respiration in such soils. Interactions between nutrient level and temperature could impact management decisions for both factors, but these interactions have not previously been adequately described. Petroleum-contaminated soils from two Alaskan sites were studied in separate laboratory experiments. Nutrients and incubation temperatures were independently varied so interactions between the two could be studied. Soil from a gravel pad near Barrow, AK responded positively to temperatures increasing from 5°C to 20°C, and to addition of 50 or 100 mg/kg of supplemental nitrogen. Soil from Ft. Wainwright, AK responded positively as temperatures were increased from 1°C to 21°C, but microbial respiration decreased when temperatures were raised to 41°C. Microbial activity increased when 100 or 200 mg/kg of supplemental nitrogen was applied. In both soils, there were positive interactions between soil temperature response and addition of nitrogen fertilizer. Microbial response to soil warming was accentuated by proper nitrogen management, and response to fertilizer application was greatest when soil was warmed.