Search for: All records

Abstract. Phytoremediation can be a cost-effective method of restoring contaminated soils using plants and associated microorganisms. Most studies follow the impacts of phytoremediation solely across the treatment period and have not explored long-term ecological effects. In 1995, a phytoremediation study was initiated near Fairbanks, Alaska, to determine how the introduction of annual grasses and/or fertilizer would influence degradation of petroleum hydrocarbons (PHCs). After 1 year, grass and/or fertilizer-treated soils showed greater decreases in PHC concentrations compared to untreated plots. The site was then left for 15 years with no active site management. In 2011, we re-examined the site to explore the legacy of phytoremediation on contaminant disappearance, as well as on plant and soil microbial ecology. We found that the recruited vegetation and the current bulk soil microbial community structure and functioning were all heavily influenced by initial phytoremediation treatment. The number of diesel-degrading microorganisms (DDMs) was positively correlated with the percentage cover of vegetation at the site, which was influenced by initial treatment. Even 15 years later, the initial use of fertilizer had significant effects on microbial biomass, community structure, and activity. We conclude that phytoremediation treatment has long-term, legacy effects on the plant community, which, in turn, impact microbial community structure and functioning. It is therefore important to consider phytoremediation strategies that not only influence site remediation rates in the short-term but also prime the site for the restoration of vegetation over the long-term. 

Subarctic ecosystems provide key services to local communities, yet they are threatened by pollution caused by spills and disposal of petroleum waste. Finding solutions for the remediation and restoration of subarctic soils is valuable for reasons related to human and ecosystem health, as well as environmental justice. 

An extensive plume of the emerging contaminant sulfolane has been found emanating from a refinery in Interior Alaska, raising questions about the microbial potential for natural attenuation and bioremediation in this subarctic aquifer. Previously, an aerobic sulfolane-assimilating Rhodoferax sp. was identified from the aquifer using stable isotope probing. Here, we assessed the distribution of known sulfolane-assimilating bacteria throughout the contaminated subarctic aquifer using 16S-rRNA-amplicon analyses of ~100 samples collected from groundwater monitoring wells and two groundwater treatment systems. One treatment system was an in situ air sparging system where air was injected directly into the aquifer. The other was an ex situ granular activated carbon (GAC) filtration system for the treatment of private well water. We found that the sulfolane-assimilating Rhodoferax sp. was present throughout the aquifer but was significantly more abundant in groundwater associated with the air sparge system. The reduction of sulfolane concentrations combined with the apparent enrichment of sulfolane degraders in the air sparging zone suggests that the addition of oxygen facilitated sulfolane biodegradation. To investigate other environmental controls on Rhodoferax populations, we also examined correlations between groundwater geochemical parameters and the relative abundance of the Rhodoferax sp. and found only manganese to be significantly positively correlated. The sulfolane-assimilating Rhodoferax sp. was not a major component of the GAC filtration system, suggesting that biodegradation is not an important contributor to sulfolane removal in these systems. We conclude that air sparging is a promising approach for enhancing the abundance and activity of aerobic sulfolane-degraders like Rhodoferax to locally stimulate sulfolane biodegradation in situ .