Long-term effects on microbial communities after a subarctic oil spill

A combination of microbial assays was used to examine soil population structure and community-level metabolism at the site of a 1976 experimental crude oil spill conducted in Alaska. Estimates of total bacterial numbers and soil C mineralization potentials were not significantly different between pristine and hydrocarbon-affected soils. In contrast, net N mineralization potential was lower, metabolically active (FDA stain) bacteria were less abundant and hydrocarbon degrading microbes were more abundant in the oiled soils. Additionally, the effects of dilution on the kinetics of community-level substrate use were examined in multiple substrate microplates. Microplate kinetic patterns varied less with dilution and by season in oiled soils. In oiled soils, absence of seasonal variation in soil C mineralization potentials, coupled with the microplate data, indicated that population diversity (evenness, richness or both) was diminished compared to the pristine soils. Further analysis of microplate data suggested that the communities surviving in the oiled soils may be considered metabolic generalists. By using several independent microbial assays, differences in soil microbial community structure attributable to oiling could be seen decades after the spill event.