Set Of Microcosms Research Articles

Aerobic Biodegradation of Hydrocarbons in High Temperature and Saline Groundwater

A series of laboratory microcosm experiments and a field pilot test were performed to evaluate the potential for aerobic biodegradation of aromatic hydrocarbons and methyl tert‐butyl ether (MtBE; a common oxygenate additive in gasoline) in saline, high temperature (>30° C) groundwater. Aquifer, sediment, and groundwater samples from two sites, one in Canada and another in Saudi Arabia, were incubated for 106 days to evaluate the changes in select hydrocarbon and MtBE concentrations and microbial community structure. Almost complete biodegradation of the aromatic hydrocarbons was found in the Saudi Arabian microcosm samples whereas the Canadian microcosm samples showed no significant biodegradation during the laboratory testing. MtBE degradation was not observed in either set of microcosms. Denaturing gradient gel electrophoresis analyses showed that, while the Canadian microorganisms were the most diverse, they showed little response during incubation. The microbial communities for the Saudi Arabian sample contained significant numbers of microorganisms capable of hydrocarbon degradation which increased during incubation.Based on the laboratory results, pilot‐scale testing at the Saudi Arabian field site was carried out to evaluate the effectiveness of enhanced aerobic biodegradation on a high temperature, saline petroleum hydrocarbon plume. Dissolved oxygen was delivered to the subsurface using a series of oxygen diffusion emitters installed perpendicular to groundwater flow, which created a reactive zone. Results obtained from the seven‐month field trial indicated that all the target compounds decreased with removal percentages varying between 33 percent for the trimethylbenzenes to greater than 80 percent for the BTEX compounds. MtBE decreased 40 percent on average whereas naphthalene was reduced 85 percent on average. Examination of the microbial population upgradient and downgradient of the emitter reactive zone suggested that the bacteria population went from an anaerobic, sulfate‐reducing dominated population to one dominated by a heterotrophic aerobic bacteria dominant population.These studies illustrate that field aerobic biodegradation may exceed expectations derived from simple laboratory microcosm experiments. Also, high salinity and elevated groundwater temperature do not appear to inhibit in situ aerobic biorestoration. © 2014 Wiley Periodicals, Inc.

Application of 13C-stable isotope probing to identify RDX-degrading microorganisms in groundwater

We employed stable isotope probing (SIP) with 13C-labeled hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) to identify active microorganisms responsible for RDX biodegradation in groundwater microcosms. Sixteen different 16S rRNA gene sequences were derived from microcosms receiving 13C-labeled RDX, suggesting the presence of microorganisms able to incorporate carbon from RDX or its breakdown products. The clones, residing in Bacteroidia, Clostridia, α-, β- and δ-Proteobacteria, and Spirochaetes, were different from previously described RDX degraders. A parallel set of microcosms was amended with cheese whey and RDX to evaluate the influence of this co-substrate on the RDX-degrading microbial community. Cheese whey stimulated RDX biotransformation, altered the types of RDX-degrading bacteria, and decreased microbial community diversity. Results of this study suggest that RDX-degrading microorganisms in groundwater are more phylogenetically diverse than what has been inferred from studies with RDX-degrading isolates.

Effect of isobutanol on toluene biodegradation in nitrate amended, sulfate amended and methanogenic enrichment microcosms

Isobutanol is an alternate fuel additive that is being considered because of economic and lower emission benefits. However, future gasoline spills could result in co-contamination of isobutanol with gasoline components such as benzene, toluene, ethyl-benzene and xylene. Hence, isobutanol could affect the degradability of gasoline components thereby having an effect on contaminant plume length and half-life. In this study, the effect of isobutanol on the biodegradation of a model gasoline component (toluene) was examined in laboratory microcosms. For this, toluene and isobutanol were added to six different toluene degrading laboratory microcosms under sulfate amended, nitrate amended or methanogenic conditions. While toluene biodegradation was not greatly affected in the presence of isobutanol in five out of the six different experimental sets, toluene degradation was completely inhibited in one set of microcosms. This inhibition occurred in sulfate amended microcosms constructed with inocula from wastewater treatment plant activated sludge. Our data suggest that toluene degrading consortia are affected differently by isobutanol addition. These results indicate that, if co-contamination occurs, in some cases the in situ half-life of toluene could be significantly extended.

Microcosm experiments to control anaerobic redox conditions when studying the fate of organic micropollutants in aquifer material

The natural processes occurring in subsurface environments have proven to effectively remove a number of organic pollutants from water. The predominant redox conditions revealed to be one of the controlling factors. However, in the case of organic micropollutants the knowledge on this potential redox-dependent behavior is still limited. Motivated by managed aquifer recharge practices microcosm experiments involving aquifer material, settings potentially feasible in field applications, and organic micropollutants at environmental concentrations were carried out. Different anaerobic redox conditions were promoted and sustained in each set of microcosms by adding adequate quantities of electron donors and acceptors. Whereas denitrification and sulfate-reducing conditions are easily achieved and maintained, Fe- and Mn-reduction are strongly constrained by the slower dissolution of the solid phases commonly present in aquifers. The thorough description and numerical modeling of the evolution of the experiments, including major and trace solutes and dissolution/precipitation of solid phases, have been proven necessary to the understanding of the processes and closing the mass balance. As an example of micropollutant results, the ubiquitous beta-blocker atenolol is completely removed in the experiments, the removal occurring faster under more advanced redox conditions. This suggests that aquifers constitute a potentially efficient alternative water treatment for atenolol, especially if adequate redox conditions are promoted during recharge and long enough residence times are ensured.

Influence of microorganisms and leaching on simazine attenuation in an agricultural soil

Simazine is an s-triazine herbicide world widely used for the control of broadleaf weeds. The influence of leaching and microorganisms on simazine attenuation in an agricultural soil long-term treated with this herbicide was studied. To elucidate the leaching potential of simazine in this soil, undisturbed soil columns amended with simazine were placed in a specially designed system and an artificial precipitation was simulated. To evaluate the simazine removal by soil microorganisms, three soil microcosm sets were established: i) control soil; ii) soil subjected to gamma irradiation (γ-soil) and iii) γ-soil inoculated with the simazine-degrading bacterium Pseudomonas sp. strain MHP41. The simazine-degrading microorganisms in soil were estimated using an indicator for respiration combined with MPN enumeration. The simazine removal in soil was monitored by GC-ECD and HPLC. In this agricultural soil the leaching of the applied simazine was negligible. The gamma irradiation decreased in more than one order of magnitude the cultivable heterotrophic bacteria and reduced the simazine-degrading microorganisms. Simazine was almost completely depleted (97%) in control soil by natural attenuation after 23 d, whereas in γ-soil only 70% of simazine was removed. The addition of the simazine-degrading strain MHP41 to γ-soil restored and upheld high stable simazine catabolic microorganisms as well as increased the simazine removal (87%). The results indicated that simazine is subjected to microbial degradation with negligible leaching in this agricultural soil and pointed out the crucial role of native microbiota in the herbicide removal.

«Prospero players»: recita e metamorfosi dell'io in Salman Rushdie

This paper explores in depth the microcosm set out by Salman Rushdie, in which the many perfomances of characters configure the bachtinian ‘pluridiscoursiveness’ as a simultaneous presence of multiples, metamorphic, voices.

Relative decay of Bacteroidales microbial source tracking markers and cultivated Escherichia coli in freshwater microcosms.

Fecal indicator bacteria (FIB), commonly used to regulate sanitary water quality, cannot discriminate among sources of contamination. The use of alternative quantitative PCR (qPCR) methods for monitoring fecal contamination or microbial source tracking requires an understanding of relationships with cultivated FIB, as contamination ages under various conditions in the environment. In this study, the decay rates of three Bacteroidales 16S rRNA gene markers (AllBac for general contamination and qHF183 and BacHum for human-associated contamination) were compared with the decay rate of cultivated Escherichia coli in river water microcosms spiked with human wastewater. The following five sets of microcosms were monitored over 11 days: control, artificial sunlight, sediment exposure, reduced temperature, and no autochthonous predation. Decay was characterized by estimation of the time needed to produce a 2-log reduction (t(99)). No treatment-associated differences in the decay of the 4 targets were evident except with reduced predation, where E. coli, qHF183, and BacHum markers had lower levels of decay by day 3. However, there were substantial target-associated differences. Decay curves for the AllBac marker indicated a larger persistent population than those of the other targets. Exposure to sunlight, sediment, and reduced predation resulted in more rapid decay of the human-associated markers relative to cultivable E. coli, but there were no differences in t(99) values among the 4 targets under control conditions or at reduced temperatures. Further evaluation of epidemiological relationships will be needed in order to relate the markers directly to health risk. These findings suggest that the tested human-associated markers can complement E. coli as indicators of the human impact on sanitary water quality under the constrained conditions described in this paper.

Factors Influencing the Persistence of Fecal Bacteroides in Stream Water

Laboratory microcosm experiments were used to assess the effects of environmental parameters on the persistence of the Bacteroides 16S rRNA genes derived from equine fecal samples in stream water to investigate the utility of Bacteroides spp. as fecal indicator organisms. Quantitative real-time polymerase chain reaction (qPCR) was used to measure gene concentrations over time with treatments designed to compare filtered vs. unfiltered stream water, fecal aggregate size, initial fecal concentrations, and water temperatures. Comparison of Bacteroides16S rRNA genes/mL in microcosms constructed with unfiltered stream water and filtered stream water indicated that stream water filtration to remove indigenous microorganisms followed by temperature had the largest effects on gene persistence. First-order exponential decay functions were fitted to the data from each microcosm constructed using unfiltered stream water, and the decay constants (k) ranged from 0.0071 h(-1) in the microcosms incubated at 5 degrees C to 0.0336 h(-1) in a set of microcosms incubated at 25 degrees C. Analysis of k calculated from the 10 experimental treatments indicated that k is more highly correlated to temperature than initial Bacteroides 16S rRNA gene starting concentrations. The equation resulting from graphing k (as the dependent variable) vs. temperature (as the independent variable) best fit a peak, Gaussian, 3 parameter function with a maximum decay at 30 degrees C, a r(2) of 0.83 and all parameters were significant (P < 0.0015). Thus this data suggest that factors that reduce biological activity, such as physical removal of stream microorganisms by filtration and low temperature, result in slower Bacteroides 16S rRNA gene decay.

Influence of Soil Minerals on the Rates and Products of Abiotic Transformation of Carbon Tetrachloride in Anaerobic Soils and Sediments

Rates and products of abiotic mineral-mediated carbon tetrachloride (CT) transformation were measured in microcosms prepared from natural soils and sediments that were incubated under iron-reducing and sulfate-reducing conditions, then sterilized to inhibit microbial activity. For one set of microcosms, the rate of CT disappearance was correlated with the concentration of weakly bound (MgCl2 extractable) Fe(II) in an experiment in which CT was repeatedly spiked into the microcosms. When pooling the results from all microcosms, however, there was no statistically significant positive correlation between CT transformation rate and the concentration of weakly bound Fe(II) or any other mineral species. There was, however, a statistically significant negative correlation between CT transformation rate and the concentration of Cr(II) extractable sulfur (CrES). Evidence from X-ray photoelectron spectroscopy in a related model system containing a mixture of FeS and pyrite ("aged FeS") showed that the decline in CT disappearance rate corresponded to a decrease in the abundance of FeS and an increase in the abundance of pyrite at the mineral surface. For aged FeS, the yield of chloroform (CF) also decreased as the abundance of pyrite at the surface increased, and there was an inverse relationship between the yields of CF and CS2.

Resolving uncertainty in the carbon economy of mycorrhizal fungi

Resolving uncertainty in the carbon economy of mycorrhizal fungi

English

Acid mine drainage (AMD) is a major environmental consequence of mining activity. This is a recurring problem around the world, and especially in some specific areas of United States, including Pennsylvania. Remediation of AMD has three requirements: pH neutralization, reduction of sulfate concentrations, and removal of dissolved metals. The aim of this study was to evaluate the sustainable waste material, crab-shell-chitin, as a multifunctional substrate for AMD remediation. The performance of chitin was evaluated under different raw water characteristics (comparative sites test), and compared with lactate and spent mushroom compost (comparative substrates test). Sacrificial, duplicate microcosms were prepared in serum bottles containing AMD water, sediment (microbial source), and the evaluated substrate. For the comparative sites test, three microcosm sets were prepared using AMD water from three different sites within central Pennsylvania, and all were treated with crab-shell-chitin. For the comparative substrates test, the AMD source was held constant and the substrate varied between crab-shell-chitin, sodium lactate, and spent mushroom compost. Microcosms were incubated in the dark, at room temperature, and under anoxic conditions for up to 50 days. Crab-shell-chitin (ChitoRem™ SC-20) increased the pH from pH 3.0 - 3.5 to near neutral in 2 - 3 days. Increases in pH were much faster in the microcosms containing chitin than with the other substrates. In microcosms containing chitin, steady alkalinity generation and acidity removal were observed at average rates of 35 and - 27 mg CaCO3/L-d, respectively. The activity of SO4 2- reducing bacteria was evident after 7 - 9 days of incubation, with reduction rates of 11.9 - 17.8 mg SO4 2- /L-d. Similar changes in alkalinity, acidity, and SO4 2- were also observed in lactate- containing microcosms, but they only started after 27 days. No alkalinity generation or sulfate reduction activity was observed in bottles containing spent mushroom compost. Aluminum and Fe removal was observed with all substrates, but it was much faster with chitin. Chitin was the only substrate able to partially remove manganese (>73%). The results of this study indicate that crab-shell-chitin is a promising material to be used as a substrate or amendment for AMD remediation. Its slowly fermentable nature makes it a suitable electron donor source to support the activity of sulfate reducing bacteria. In addition, the rapid release of its built-in carbonate minerals effectively neutralize acidic waters and facilitate the precipitation of dissolved metals.

Structure analysis and performance of a microbial community from a contaminated aquifer involved in the complete reductive dechlorination of 1,1,2,2‐tetrachloroethane to ethene

An anaerobic microcosm set up with aquifer material from a 1,1,2,2-tetrachloroethane (TeCA) contaminated site and amended with butyrate showed a complete TeCA dechlorination to ethene. A structure analysis of the microbial community was performed by fluorescence in situ hybridization (FISH) with already available and on purpose designed probes from sequences retrieved through 16S rDNA clone library construction. FISH was chosen as identification tool to evaluate in situ whether the retrieved sequences belong to primary bacteria responsible for the biodegradative reactions. FISH probes identified up to 80% of total bacteria and revealed the absence or the marginal presence of known TeCA degraders and the abundance of two well-known H(2)-utilizing halorespiring bacteria, Sulfurospirillum (32.4 +/- 8.6% of total bacteria) and Dehalococcoides spp. (14.8 +/- 2.8), thereby providing a strong indication of their involvement in the dechlorination processes. These results were supported by the kinetic and thermodynamic analysis which provided indications that hydrogen was the actual electron donor for TeCA dechlorination. The specific probes, developed in this study, for known dechlorinators (i.e., Geobacter, Dehalobacter, and Sulfurospirillum species) represent a valuable tool for any future in situ bioremediation study as well as a quick and specific investigation tool for tracking their distribution in the field.

Interactive Technology Assessment in the Real World

Participatory Technology Assessment (pTA) initiatives have usually been analyzed as if they existed in a social and political vacuum. This article analyzes the linkages that occur, in both directions, between the microcosm set up by a pTA exercise and the real world outside. This dual-dynamics perspective leads to a new way of understanding the function and significance of pTA initiatives. Rather than viewing them as a means to create the ideal conditions for real public debate, they are viewed here as an additional public arena in which sociotechnical controversies are played out. This perspective is developed from the analysis of an interactive technology assessment exercise conducted by the French National Institute for Agricultural Research, on the topic of genetically modified vines.

Monod Kinetics for Aerobic Biodegradation of Petroleum Hydrocarbons in Unsaturated Soil Microcosms

We use Monod kinetics to calibrate previously published data that documentthe aerobic biodegradation of hydrocarbon vapors in soil microcosms from a weathered petroleum spill site. Monod kinetics offer insight into biodegradation mechanics because they address biomass growth as well as substrate depletion. A blend of five aromatics and five alkanes dose the microcosm sets at four strengths, and a finite difference model describes the response superimposed across the constituent substrates. An observed initial biomass X0 of 125 g biomass/m(3) soil moisture and an endogendous decay rate b of 0.102 day(-1) calibrate all four dosages and agree with heterotrophic plate counts. Common maximum specific growth rates microMJ and half saturation constants KSJ calibrate each constituent across the four dosages. The biodegradable alkanes exhibit microMJ values ranging from 0.0190 to 0.0996 day(-1), while the aromatic rates vary from 0.0946 to 0.322 day(-1). One of the alkanes (2,2,4-trimethylpentane) is recalcitrant. The half saturation constants range from 0.000083 to 0.000355 g substrate/m(3) soil moisture for the biodegradable alkanes, which imply zero-order kinetics. The aromatic KSJ values vary from 5.02 to 14.3 g substrate/m(3) soil moisture, and suggest first-order kinetics. The yield YJ increases with dosage concentration for all the biodegradable constituents, varying from 0.0533 to 1.58 g biomass/g substrate.

Monod Kinetics for Aerobic Biodegradation of Calcium Magnesium Acetate

Monod kinetics were used to recalibrate published sets of soil microcosm data that document the aerobic biodegradation of calcium magnesium acetate in a highway shoulder. The natural attenuation is important because acetate can exert an appreciable oxygen demand on ground-water if it persists from the ground surface to the water table. Biomass dynamics were modeled, as well as acetate degradation, in the assumed abundance of oxygen and nutrients. The maximum specific growth rate (μM) and half saturation constant (KS) quantify the ability of an individual aerobe to degrade acetate and accordingly calibrate microcosm data from all locations in the shoulder. Thirty-two microcosm sets from SR-25 in southeastern Massachusetts yielded a calibrated μM of 0.00133 h[minus]1 and a KS of 0.087 kg acetate/m3 soil moisture. Calibrated (not measured) initial biomass concentrations varied from 10 to 1,000 μg biomass/g dry soil, with the largest values near the surface of the loamy sand cover layer and the smallest values above the capillary fringe consisting of uniform sand. The initial biomass concentrations and Monod kinetics yielded reaction rates consistent with field scale estimates of acetate degradation.

Impact of protists on the activity and structure of the bacterial community in a rice field soil.

Flooded rice fields have become a model system for the study of soil microbial ecology. In Italian rice fields, in particular, aspects from biogeochemistry to molecular ecology have been studied, but the impact of protistan grazing on the structure and function of the prokaryotic community has not been examined yet. We compared an untreated control soil with a gamma-radiation-sterilized soil that had been reinoculated with a natural bacterial assemblage. In order to verify that the observed effects were due to protistan grazing and did not result from sterilization, we set up a third set of microcosms containing sterilized soil that had been reinoculated with natural assemblage bacteria plus protists. The spatial and temporal changes in the protistan and prokaryotic communities were examined by denaturing gradient gel electrophoresis (DGGE) and terminal restriction fragment length polymorphism (T-RFLP) analysis, respectively, both based on the small-subunit gene. Sequences retrieved from DGGE bands were preferentially affiliated with Cercozoa and other bacteriovorous flagellates. Without protists, the level of total DNA increased with incubation time, indicating that the level of the microbial biomass was elevated. Betaproteobacteria were preferentially preyed upon, while low-G + C-content gram-positive bacteria became more dominant under grazing pressure. The bacterial diversity detectable by T-RFLP analysis was greater in the presence of protists. The level of extractable NH4+ was lower and the level of extractable SO4(2-) was higher without protists, indicating that nitrogen mineralization and SO4(2-) reduction were stimulated by protists. Most of these effects were more obvious in the partially oxic surface layer (0 to 3 mm), but they could also be detected in the anoxic subsurface layer (10 to 13 mm). Our observations fit well into the overall framework developed for protistan grazing, but with some modifications pertinent to the wetland situation: O2 was a major control, and O2 availability may have limited directly and indirectly the development of protists. Although detectable in the lower anoxic layer, grazing effects were much more obvious in the partially oxic surface layer.

Heterocypris (Crustacea: Ostracoda) from the Isole Pelagie (Sicily, Italy): Hatching phenology of resting eggs

The hatching phenology of Heterocypris resting eggs was investigated in laboratory controlled conditions. Microcosms were set up using dry sediments from three freshwater temporary ponds (Cavallo Bianco, Aria Rossa and Vallone della Forbice) of the island of Lampedusa (Sicily) and kept at different temperatures and photoperiods. Hatching time was modulated by different environmental factors. Initial anoxia, induced by the decomposition of the sediment's organic matter, delayed hatching in the microcosm set up with sediments from Vallone della Forbice which has a high organic matter content. Temperature and photoperiod in isolation did not seem to affect hatching significantly, while their interaction did. The coexistence of two female morphotypes with different reproductive modes could not be explained by a differential response to temperature and photoperiod. Coexistence was probably due to disturbance events, such as drying up of ephemeral pools. Some resting eggs (in different percentages in different microcosms) hatched only after a second hydration (after microcosms dried up). Hatching phenology is discussed in relation to genetic differences in egg responsiveness to hatching stimuli and to a bet‐hedging strategy in a year‐to‐year highly variable environment such as the ephemeral ponds of Lampedusa.

Aerobic Biodegradation of Methyl Tert-Butyl Ether in Gasoline-Contaminated Aquifer Sediments

Intrinsic biodegradation of methyl tert-butyl ether ~MTBE! in aquifer sediments under oxic conditions was investigated using laboratory microcosms. Aquifer samples were collected from three different areas ~source area, upgradient, and downgradient! of a shallow gasoline-contaminated aquifer within the Atlantic Coastal Plain Province located in Virginia. Biodegradation of MTBE was observed in the source-area microcosms in which MTBE declined from a starting concentration of 2.7 to 0.28 mg/L over a 58-day period, following an initial lag period of 20 days. The same set of microcosms was respiked with MTBE to an initial concentration of 4.8 mg/L and MTBE concentrations declined to 0.20 mg/L over a 52-day period with no lag in biodegradation. First-order MTBE biodegradation rates for the first and second periods were 0.03760.003 and 0.06360.003 day 21 , respectively. When another set of source-area micro- cosms was spiked with MTBE ~5 mg/L!, toluene and ethylbenzene ~1 mg/L each!, the initial lag period increased to 33 days but there was no significant change in the MTBE biodegradation rate~0.06560.026 day 21 ! and MTBE was not detected after 134 days. Biodegradation of MTBE was also observed in the microcosms constructed using aquifer sediment with only limited exposure to MTBE but the degradation rate was lower and statistically different ~0.02260.005 day 21 ! than the source area microcosms. Biodegradation of MTBE ceased when oxygen was depleted. Methyl tert-butyl ether did not biodegrade in the uncontaminated, upgradient microcosms; however, rapid biodegradation of toluene was observed. Methyl tert-butyl ether biodegradation appears to be limited in the absence of dissolved oxygen and in aquifer sediments where petroleum hydrocarbons including MTBE were not previously observed.

Bacteria and microbial-feeders modify the performance of a decomposer fungus

We studied whether the presence of a bacterium can affect the functioning or stability of simple fungal-based decomposer food chains. We constructed microcosms with 60 g washed mineral soil and four different food webs: (1) a fungus ( Cladosporium herbarum) alone; (2) a fungus and a fungal-feeding nematode ( Aphelenchoides sp.); (3) a fungus and a bacterium ( Escherichia coli); and (4) a fungus, a bacterium, a fungal- and a bacterial-feeding nematode ( Aphelenchoides sp. and Acrobeloides tricornus). Glucose was supplied as the sole carbon source. One replicate set of microcosms was kept at −2°C for the sixth and seventh week as an experimental disturbance. The microcosms were destructively sampled 10 times for food web effects (non-disturbed controls) and three times for freezing treatment. Fungal biomass growing alone was less efficient (i.e. it had higher respiration rate per unit biomass) than the other food webs. This did not, however, result in the greatest C loss in the long term, because the fungal biomass declined when growing alone. Presence of the bacterium increased the decomposition of dissolved organic carbon as much as the presence of the fungal-feeder, but their effects were not additive. Ammonium nitrogen concentration of the medium was higher in systems containing bacteria. Nematode populations and the bacterial biomass were not sensitive to the disturbance of freezing. Although the freezing disturbance decreased total fungal biomass in the absence of the bacterial energy channel, dissolved organic carbon decomposition was only incidentally retarded. In spite of their distinct role in the system functioning, the bacteria did not significantly alter the stability properties of the system. Thus, our results contradict some recent food-web based decomposition models, which predict that the effects of parallel energy channels on decomposition are additive. We discuss nutrient limitation and the dependence of fungal properties on the food-web configuration as explanations for the contradiction of theory and data. We did not find evidence supporting a hypothesis that an additional energy channel should stabilize flow through a food web, and hence decomposition. This is explained by high resilience of the reference system with a fungus alone, and by redundancy, i.e. the fact that the fungal-feeding nematode induced similar changes in the fungus than the bacterium.

Microbial degradation of simulated landfill leachate: solid iron/sulfur interactions

Microcosms were prepared to test if added mineral Fe 3+ and SO 4 2− could treat landfill leachate and to examine intrinsic microbial/mineral interactions related to natural attenuation. Two oxidized native sediments were used from central Oklahoma. Three types of anoxic microcosms were prepared which included the addition of: (1) mineral ferrihydrite (Fe(OH) 3); (2) mineral gypsum (CaSO 4 •2H 2O); and (3) no mineral amendments. Each received a synthetic leachate consisting of 2000 mg/l non-purgable organic carbon (NPOC). Measurements of substrate consumption, dissolved ions, mineral utilization/precipitation, and biological gases were made over 12 weeks. The added CaSO 4 2− and Fe(OH) 3 were used as electron acceptors: CaSO 4 2− by first order kinetics ( k≅0.12 week −1) and Fe 3+ by zero order kinetics ( k≅0.16 mM week −1). The addition of either CaSO 4 2− or Fe(OH) 3 did not increase organic carbon degradation rates over methanogenesis, which was predominate in the non-amended microcosm set. Adding solid electron acceptors promoted carbonate and sulfide mineral formation and controlled greenhouse gases including CH 4 and CO 2. It is suggested that reduced Fe and S minerals could be used to assess organic contaminant degradation occurring due to Fe 3+ and SO 4 2− microbial reduction processes for natural attenuation studies.