Effects of nutrient content, moisture content and salinity on mineralization of hexadecane in an Arctic soil

Bioremediation is often considered to be a feasible clean-up method for hydrocarbon contaminated sites. Several factors such as low temperatures and limited nutrient and moisture availability, are supposed to reduce hydrocarbon biodegradation in contaminated Arctic soils. In previous studies, fertilizing Arctic soils has led to both increased and decreased hydrocarbon mineralization. Identifying limiting factors is therefore considered to be of importance for increased bioremediation efficiency. In this laboratory study, the effects of increased salinity (ionic strength) and varying concentrations of nutrient and soil moisture on hexadecane mineralization in a hydrocarbon contaminated and nutrient deficient high Arctic soil were assessed.Ammonium chloride (NH4Cl) was added to give nitrogen concentrations ranging from 0 to 1000 mg NH4–N/kg soil, corresponding to molar cation concentrations of NH4+ from 0 to 71 mmol/kg soil. Parallel experiments with equivalent cation concentrations of Na+ were obtained by adding sodium chloride (NaCl). Soil samples with combinations of NH4+ and Na+ were also included. Soil moisture content varied from 10 to 20%.Fertilizing with NH4–N increased the total hexadecane mineralization compared to unfertilized soil at all concentrations investigated. Increased salinity in soil caused by addition of NH4+ and Na+ extended the acclimation time but did not have an inhibitory effect on the total hexadecane mineralization at the end of the experiment. After 36 days incubation the total hexadecane mineralization was about 12% of initial concentration in all soil samples added NH4+. In soil samples added Na+ the mineralization was similar to unfertilized control, about 3.5%. In soils with highest moisture content (20%) the total hexadecane mineralization was reduced compared to soils with 10, 12 and 15% moisture, presumably as a consequence of oxygen shortage. Highest mineralization rates were found in soil samples added 50–200 mg NH4–N/kg at 10% moisture, where 50–58 mg hexadecane/kg/day was mineralized.