Soil Microbiome Dynamics During Pyritic Mine Tailing Phytostabilization: Understanding Microbial Bioindicators of Soil Acidification

Challenges to the reclamation of pyritic mine tailings arise from in situ acid generation that severely constrains the growth of natural revegetation. While acid mine drainage (AMD) microbial communities are well-studied under highly acidic conditions, fewer studies document the dynamics of microbial communities that generate acid from pyritic material under less acidic conditions that can allow establishment and support of plant growth. This research characterizes the taxonomic composition dynamics of microbial communities present during a 6-year compost-assisted phytostabilization field study in extremely acidic pyritic mine tailings. A complementary microcosm experiment was performed to identify successional community populations that enable the acidification process across a pH gradient. Taxonomic profiles of the microbial populations in both the field study and microcosms reveal shifts in microbial communities that play pivotal roles in facilitating acidification during the transition between moderately and highly acidic conditions. The potential co-occurrence of organoheterotrophic and lithoautotrophic energy metabolisms during acid generation suggests the importance of both groups in facilitating acidification. Taken together, this research suggests that key microbial populations associated with pH transitions could be used as bioindicators for either sustained future plant growth or for acid generation conditions that inhibit further plant growth.National Institute of Environmental and Health Sciences (NIEHS) Superfund Research Program (SRP) [P42 ES004940]Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Bacterial Rhizoplane Colonization Patterns of Buchloe dactyloides Growing in Metalliferous Mine Tailings Reflect Plant Status and Biogeochemical Conditions

Plant establishment during phytostabilization of legacy mine tailings in semiarid regions is challenging due to low pH, low organic carbon, low nutrients, and high toxic metal(loid) concentrations. Plant-associated bacterial communities are particularly important under these harsh conditions because of their beneficial services to plants. We hypothesize that bacterial colonization profiles on rhizoplane surfaces reflect deterministic processes that are governed by plant health and the root environment. The aim of this study was to identify associations between bacterial colonization patterns on buffalo grass (Buchloe dactyloides) rhizoplanes and both plant status (leaf chlorophyll and plant cover) and substrate biogeochemistry (pH, electrical conductivity, total organic carbon, total nitrogen, and rhizosphere microbial community). Buffalo grass plants from mesocosm- and field-scale phytostabilization trials conducted with tailings from the Iron King Mine and Humboldt Smelter Superfund Site in Dewey-Humboldt, Arizona, were analyzed. These tailings are extremely acidic and have arsenic and lead concentrations of 2-4 g kg-1 substrate. Bacterial communities on rhizoplanes and in rhizosphere-associated substrate were characterized using fluorescence in situ hybridization and 16S rRNA gene amplicon sequencing, respectively. The results indicated that the metabolic status of rhizoplane bacterial colonizers is significantly related to plant health. Principal component analysis revealed that root-surface Alphaproteobacteria relative abundance was associated most strongly with substrate pH and Gammaproteobacteria relative abundance associated strongly with substrate pH and plant cover. These factors also affected the phylogenetic profiles of the associated rhizosphere communities. In summary, rhizoplane bacterial colonization patterns are plant specific and influenced by plant status and rhizosphere biogeochemical conditions.National Institute of Environmental and Health Sciences (NIEHS) Superfund Research Program (SRP) [P42 ES004940, R01 ES01709]; National Science Foundation Graduate Research Fellowhip Program (NSF GRFP) [DGE-1143953]12 month embargo; published online: 2 June 2017This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Phytostabilization of mine tailings using compost-assisted direct planting: Translating greenhouse results to the field

Standard practice in reclamation of mine tailings is the emplacement of a 15 to 90 cm soil/gravel/rock cap which is then hydro-seeded. In this study we investigate compost-assisted direct planting phytostabilization technology as an alternative to standard cap and plant practices. In phytostabilization the goal is to establish a vegetative cap using native plants that stabilize metals in the root zone with little to no shoot accumulation. The study site is a barren 62-hectare tailings pile characterized by extremely acidic pH as well as lead, arsenic, and zinc each exceeding 2000 mg kg(-1). The study objective is to evaluate whether successful greenhouse phytostabilization results are scalable to the field. In May 2010, a 0.27 ha study area was established on the Iron King Mine and Humboldt Smelter Superfund (IKMHSS) site with six irrigated treatments; tailings amended with 10, 15, or 20% (w/w) compost seeded with amix of native plants (buffalo grass, arizona fescue, quailbush, mountain mahogany, mesquite, and catclaw acacia) and controls including composted (15 and 20%) unseeded treatments and an uncomposted unseeded treatment. Canopy cover ranging from 21 to 61% developed after 41 months in the compost-amended planted treatments, a canopy cover similar to that found in the surrounding region. No plants grew on unamended tailings. Neutrophilic heterotrophic bacterial counts were 1.5 to 4 orders of magnitude higher after 41 months in planted versus unamended control plots. Shoot tissue accumulation of various metal(loids) was at or below Domestic Animal Toxicity Limits, with some plant specific exceptions in treatments receiving less compost. Parameters including % canopy cover, neutrophilic heterotrophic bacteria counts, and shoot uptake of metal(loids) are promising criteria to use in evaluating reclamation success. In summary, compost amendment and seeding, guided by preliminary greenhouse studies, allowed plant establishment and sustained growth over 4 years demonstrating feasibility for this phytostabilization technology. (C) 2016 Elsevier B.V. All rights reserved.NIEHS Superfund Research Program [2 P42 ES04940]24 month embargo; published online: 13 May 2016This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Establishment of a Vegetation Cover at the Iron King Mine and Humboldt Smelter Superfund Site: Evaluation of Compost-Assisted Phytostabilization

Mine tailings pose a health risk for populations and ecosystems in the Southwest; this is why effective, and low-cost solutions for the long term are needed. This work is groundbreaking since little information is available with regards to applying greenhouse studies of phytostabilization to the field for mine tailing remediation. Mine tailings from Iron King Mine and Humboldt Smelter Superfund (IKMHSS) site can be considered one of the worst scenarios due to the extreme conditions which prevent the growth of a vegetation cap. The high concentration of metals, such as arsenic and lead, highly acidic, lack of the nutrients carbon and nitrogen in the soil structure, and low microbial communities are factors that negatively affect plant growth. This project provides practical field-scale applications for the use of phytostabilization, which uses plants to create a vegetation cap that stabilizes metals in the root zone while preventing wind and water erosion in mine tailings. The project is divided into three main studies: (1) the assessment of the translation of successful greenhouse results to the field of phytostabilization using compost-assisted direct planting. This includes the use of different rates of compost as an amendment and different desert native plant species in addition to some potential parameters that could be used as indicators of a successful modification of biochemical and physical environment from a disturbed soil towards a more healthy soil when compost assisted direct planting phytostabilization is used; (2) the second study aims to evaluate the effect of the phytostabilization strategy on reducing windborne transport of particle and metal(loids) following the establishment of the vegetation cap. The results indicate that the vegetation resulted from direct planting decreases dust emissions from IKMHSS mine tailings; and (3) the third study focuses on one of the most important requirements for phytostabilization application in the field, the performance of the different plant species selected from the greenhouse studies. This performance was evaluated as the metal accumulation in aerial plant tissue based on metal concentration guidelines from the National Research Council as well as changes in the composition of plant species and canopy cover with time. The results derived from the translation of compost–assisted direct plating based on successful greenhouse results are showing the capacity of this technology on a field scale by maintaining a canopy cover over time that decreases mobilization by not hyper-accumulating metals in the aerial tissue and by preventing windborne particle dispersion with the potential of disrupting contamination pathways.Release after 30-Oct-2018Originally set to release after 30-Sep-2017; contacted by author on 09-Nov-2017 to extend embargo through 30-Apr-2018, contacted by author 19-Feb-2018 to extend through 30-Oct-2018; kimberl

Integrating soil genomics into the study of biosphere-atmosphere trace gas fluxes

International audienceMicroorganisms play a significant role in shaping the composition of Earth’s atmosphere. Soils host rich microbial communities whose biogeochemical processes have both leading-order impacts on climate variability and susceptibility to global change feedbacks. Yet, the microbial actors and genetic diversity driving trace gas cycling in soils remain poorly understood, challenging attempts to model microbial contributions to biosphere-atmosphere interactions. New methods for integrating soil genomics into the study of biosphere-atmosphere trace gas fluxes are needed. Here, we present our approach for uncovering the genetic underpinnings of the microbe-mediated biogeochemical transformations in soils that drive significant trace gas fluxes. In past work, we constrained soil microbial contributions to biosphere-atmosphere exchange of carbonyl sulfide (COS or OCS)—a promising photosynthetic tracer—through controlled laboratory studies. This approach revealed microbial groups and types of carbonic anhydrase enzymes driving COS consumption by soil microbes,1 and identified coupled biological-abiotic processes driving soil COS emissions2, helping to build genome-informed constraints to biosphere-atmosphere interactions. We will present current efforts to extend this approach to constrain microbial contributions to trace gas fluxes in the Biosphere 2 tropical rainforest. We use the experimental ecosystem to control environmental drivers and amplify biosphere-atmosphere interaction within the enclosed structure. Using a suite of trace gas analyzers (concentrations and isotopomers) and measurement tools (probes, chambers) in key ecosystem locations (soil, stem, leaf, atmosphere) we constrain ecosystem fluxes across drought and rewet conditions. By integrating trace gas measurements and soil genomics data, we will test current understanding of the microbial genomics behind soil N2O emissions and develop new hypotheses regarding microbes and pathways driving soil VOC cycling

Phytoremediation Reduces Dust Emissions from Metal(loid)-Contaminated Mine Tailings

Environmental and health risk concerns relating to airborne particles from mining operations have focused primarily on smelting activities. However, there are only three active copper smelters and less than a dozen smelters for other metals compared to an estimated 500000 abandoned and unreclaimed hard rock mine tailings in the US that have the potential to generate dust. The problem can also extend to modern tailings impoundments, which may take decades to build and remain barren for the duration before subsequent reclamation. We examined the impact of vegetation cover and irrigation on dust emissions and metal­(loid) transport from mine tailings during a phytoremediation field trial at the Iron King Mine and Humboldt Smelter Superfund (IKMHSS) site. Measurements of horizontal dust flux following phytoremediation reveals that vegetated plots with 16% and 32% canopy cover enabled an average dust deposition of 371.7 and 606.1 g m^–2 y^–1, respectively, in comparison to the control treatment which emitted dust at an average rate of 2323 g m^–2 y^–1. Horizontal dust flux and dust emissions from the vegetated field plots are comparable to emission rates in undisturbed grasslands. Further, phytoremediation was effective at reducing the concentration of fine particulates, including PM₁, PM_2.5, and PM₄, which represent the airborne particulates with the greatest health risks and the greatest potential for long-distance transport. This study demonstrates that phytoremediation can substantially decrease dust emissions as well as the transport of windblown contaminants from mine tailings