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TECHNICAL REPORTS

Bioremediation and Biodegradation

Bacterial Community Changes during Plant Establishment at the San Pedro River Mine Tailings Site

^a Dep. of Soil, Water, and Environmental Science, Univ. of Arizona, Tucson, AZ 85721-0038
^b Dep. of Animal Sciences, Univ. of Arizona, Tucson, AZ 85721-0038
^c Environmental Research Lab, 2601 E. Airport Drive, Tucson, AZ 85706

^* Corresponding author (rmaier{at}ag.arizona.edu).

Received for publication August 7, 2006. Mine tailings are moderately to severely impacted sites that lack normal plant cover, soil structure and development, and the associated microbial community. In arid and semiarid environments, tailings and their associated contaminants are prone to eolian dispersion and water erosion, thus becoming sources of metal contamination. One approach to minimize or eliminate these processes is to establish a permanent vegetation cover on tailings piles. Here we report a revegetation trial conducted at a moderately impacted mine tailings site in southern Arizona. A salt and drought-tolerant plant, four-wing saltbush [Atriplex canescens (Pursh) Nutt.], was chosen for the trial. A series of 3 by 3 m plots were established in quadruplicate on the test site to evaluate growth of four-wing saltbush transplants alone or with compost addition. Results show that >80% of the transplanted saltbush survived after 1.5 yr in both treatments. Enumeration of heterotrophs and community structure analysis were conducted to monitor bacterial community changes during plant establishment as an indicator of plant and soil health. The bacterial community was evaluated using denaturing gradient gel electrophoresis (DGGE) analysis of 16S rDNA PCR gene products from tailings samples taken beneath transplant canopies. Significant differences in heterotrophic counts and community composition were observed between the two treatments and unplanted controls throughout the trial, but treatment effects were not observed. The results suggest that compost is not necessary for plant establishment at this site and that plants, rather than added compost, is the primary factor enhancing bacterial heterotrophic counts and affecting community composition.

Abbreviations: ANOVA, analysis of variance • BLM, Bureau of Land Management • C, plots containing transplants with compost • CECL, University of Arizona Chorover Enviromental Chemistry Laboratory • CFU, colony-forming unit • DGGE, denaturing gradient gel electrophoresis • HIC, University of Arizona Superfund Basic Research Program Hazard Identification Core • ICP-MS, inductively coupled plasma–mass spectrometry • KNMDS, Kruskal's Non-Metric Multidimensional Scaling • NC, plots containing transplants with no compost, OSC, off-site control plots • SPRNCA, San Pedro River National Conservation Area • U, unplanted control plots • WQCL, University of Arizona Water Quality Center Lab