Microbial inoculants and fertilization for bioremediation of oil in wetlands

Bioremediation is an attractive alternative to physical methods of oil spill cleanup in wetlands where the ecosystem can be easily damaged. Because populations of oil-degrading microorganisms are usually low in wetlands, there is potential for increasing bioremediation through bioaugmentation in conjunction with N and P supplementation. Eight microbial inoculant products were added to microcosms containing soil from a salt marsh. Four of these products were also used in mesocosms containing Spartina alterniflora grown in a glasshouse. In unfertilized microcosms, the extent of oil degraded as measured by carbon dioxide evolution during 90 days, was 30% higher in the product with the highest activity than was recorded in the control with oil by 36%. None of the products when added to the fertilized soil increased activity above that of the fertilized control with oil. Addition of oil to microcosms increased populations of hydrocarbon-degrading microorganisms, but bioaugmentation products did not increase populations. Neither addition of products nor fertilization enhanced the disappearance of oil in mesocosms in the glasshouse. Approximately 50% of the weathered oil disappeared in 41 d for all treatments. Because bioaugmentation did not enhance oil degradation, it seems that natural populations of hydrocarbon-degrading microorganisms were adequate in the salt marsh soil for bioremediation