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• W1495733764 abstract "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. INTRODUCTION The Guadalupe Oil Field is located on the coast of California near Santa Maria. The viscous crude from this site was thinned with a diluent from a nearby oil refinery to facilitate pumping. The diluent used at the site was transported through pipes to the oil field and stored in tanks. Many of these pipes, tanks and fittings leaked diluent into the sand dunes at 90 cataloged leakage sites with approximately 4 to 8 million gallons of leaked diluent. The diluent contamination is a mixture of hydrocarbons in the range of C10-C30. The site is comprised of more than 3000 acres of homogeneous sand adjacent to a river channel. The depth to groundwater fluctuates depending on the height of the sand dunes, ranging from 0 – 130 feet. Twenty feet below the water table there is a confining clay layer. Endangered species such as the red legged frog and snowy plover thrive at the site, and thus it is important that the dune ecosystems be kept intact as much as possible during remediation. For this reason phytoremediation would be particularly attractive. Due to the extensive cleanup efforts at the site, many traditional and novel remediation methods have been demonstrated. Biosparging, steam extraction, excavation, land treatment, and phytoremediation are some of the methods being evaluated at the site. Two phytoremediation field test sites have been established, one with a monoculture of arroyo willows, and another with a variety of native California species, including arroyo willows. It is hoped that by planting native species at the site bioremediation and ecological restoration can be achieved simultaneously-a technique we refer to as “ecoremediation.” However, it has been difficult to evaluate the efficacy of these plantings for phytoremediation due to the non-uniformity of the site. Variability of soil contamination levels, water flow, and sampling locations all contribute to the difficulty of evaluating phytoremediation in the field. Due to this difficulty, bench scale laboratory experiments were conducted to control these variables while investigating phytoremediation with arroyo willows. These experiments were designed primarily to determine if the willows stimulate biodegradation by soil microbes. Phytoremediation is a remediation technology that has been successful for the remediation of heavy metals and some volatile organic compounds. Phytoremediation research has been described as having five primary goals “(1) understand the mechanisms by which these technologies work, (2) develop appropriate testing protocols and methodologies that illustrate their utility, (3) improve predictive capabilities, (4) facilitate validation of the effectiveness and persistence of the technique, and (5) prepare guidelines for its implementation.” (Cunningham et. al 1997). Though each of these goals deserves attention, the first and fourth goals are the focus of this paper. This research is being conducted to evaluate the use of willow trees to degrade the aqueous hydrocarbon plumes under conditions mimicking those at the Guadalupe site. Growth chambers used in these experiments were based on a design previously used to evaluate degradation of trichloroethylene (TCE) by hybrid poplar trees (Orchard et. al 1999). The original design included both soil and foliar chambers so that volatile emissions from the soil and leaves could also be monitored. However, a companion study in our laboratory showed no volatilization of diluent hydrocarbons under these conditions (Elliot, 2002). Thus, due to the non-volatile nature of diluent, the top chamber from this model was removed and degradation was only measured from change in concentration of the water. Arroyo willows were grown in glass containers in sand collected from the field site. Diluent contaminated groundwater was recirculated through the root zone of the plants and the biodegradation rates of contaminant were measured. TPH was measured at the start and end of the experiment, chemical oxygen demand (COD) was also measured as an indicator of TPH to see degradation rates. Controls were run to check that there was no loss of contaminant to the chamber apparatus. The influence of the willows on biodegradation rate was examined by comparing biodegradation rates with and without willow trees in the soil. METHODS Biodegradation rates were measured with 3 sets of 3 chambers. The first set of chambers had autoclaved soil from the Guadalupe site inhibited with sodium azide with no willows. The second set of chambers has only soil from the Guadalupe site with no willows and the third set of chambers contained an Arroyo Willow grown in soil from the Guadalupe site (Figure 1.) Each chamber has an individual water reservoir, which contained groundwater from the Guadalupe site, collected up-gradient from the current field phytoremediation experimental site. This water was recirculated at a rate of 1 liter per day, to mimic site hydraulic conditions, using a peristaltic pump with silicone tubing (Figure 2.) Each chamber consists of a 4-liter glass jar, a drip tube, and a well tube. The drip tube is made of Viton tubing which has approximately 0.5 mm diameter holes cut in the sides of it. This drip tube is placed at the bottom of the jar so that the tube encircles the bottom of the jar. The well tube is made from six inches of Purflex® tubing with a 3⁄4 inch inside diameter and a piece of stainless steel woven wire cloth zip-tied to the end of it to be used as a screen. The mesh has a width opening of 0.0029 inches and Soil Inhibited with Sodium Azide Soil With Active Bacteria Soil and Willow FIGURE 1. Experimental design: Triplicate chambers for (1) Azide-inhibited soil, (2) Soil with active bacteria, and (3) Soil with active bacteria and willows. ROOT CHAMBER Covered with Foil (4-Liter) Effluent Pump Feed Pump" @default.
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• W1495733764 date "2003-01-01" @default.
• W1495733764 modified "2023-09-27" @default.
• W1495733764 title "Phytostimulation of Hydrocarbon Biodegradation By Arroyo Willows in Laboratory Microcosms" @default.
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