Controlled laboratory microcosms with and without Arroyo Willows (Salix lasiolepis) were used to elucidate potential mechanisms of phytoremediation of hydrocarbon-contaminated groundwater at a contaminated oil field near Guadalupe, CA. Laboratory control allows us to examine the synergistic effects between the plants themselves and the rhizobial bacteria associated with them. Laboratory microcosms were set up in triplicate with (1) sodium azide-inhibited soil, (2) soil with active bacteria, and (3) soil with active bacteria and willows. Hydrocarbon-contaminated groundwater was recirculated through the root zone for 105 days. Biodegradation rates were estimated by measuring total petroleum hydrocarbon (TPH) concentration and monitoring chemical oxygen demand (COD). TPH results showed a decrease in all chambers, the smallest decrease was for the sodium azide control chambers and the largest was for the willow chambers. For an initial TPH concentration of 3.6 ± 0.61 mg/L, the soil only chambers dropped to 0.40 ± 0.036 mg/L, and the soil and willow chambers dropped to 0.26± 0.080 mg/L. These results show a statistically significant effect of the willow trees compared to soil alone, suggesting the trees did contribute to bioremediation under these conditions, either directly via phytodegradation or indirectly via phytostimulation of bacterial biodegradation.


Civil and Environmental Engineering

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Publisher's website: http://www.battelle.org.



URL: http://digitalcommons.calpoly.edu/cenv_fac/86