Natural Attenuation of Trichloroethylene in Rhizosphere Soils at the Savannah River Site

Extensive trichloroethylene (TCE) groundwater contamination has resulted from discharges to a former seepage basin in the A/M Area at the Department of Energy's Savannah River Site. The direction of groundwater flow has been determined and a seep line where the contaminated groundwater is estimated to emerge as surface water has been identified in a region of the Southern Sector of the A/M Area. This study was undertaken to estimate the potential of four rhizosphere soils along the seep line to naturally attenuate TCE. Microcosms were setup to evaluate both biotic and abiotic attenuation of TCE. Results demonstrated that sorption to soil was the dominant mechanism during the first week of incubation, with as much as 90% of the TCE removed from the aqueous phase. Linear partitioning coefficients (K_d) ranged from 0.83 to 7.4?mL/g, while organic carbon partition coefficients (K_oc) ranged from 72 to 180?mL/gC. Diffu-sional losses from the microcosms appeared to be a dominant fate mechanism during the remainder of the experiment, as indicated by results from the water controls. A limited amount of TCE biodegradation was observed, and attempts to stimulate TCE biodegradation by either methanotrophic or methanogenic activity through amendments with methane, oxygen, and methanol were unsuccessful. The appearance of cis-1,2-dichloroethylene (c-DCE), and trans-1,2-dichloroethylene (t-DCE) confirmed the potential for anaerobic reductive dechlorination. However, these daughter products represented less than 5% of the initial TCE added. The sorption results indicate that natural attenuation may represent a viable remediation option for the TCE plume as it passes through the rhizosphere.     

Experimental restoration of a fen plant community after peat mining

Question: Which restoration measures (introduction of donor diaspore material, application of straw mulch, alteration of residual peat depths) contribute to the establishment of a fen plant community on minerotrophic surfaces after peat mining? Location: Rivière‐du‐Loup peatland, southern Québec, Canada at 100 m a.s.1. Methods: The effectiveness of introducing fen plants with the application of donor diaspore material was tested. The donor diaspore material, containing seeds, rhizomes, moss fragments, and other plant propagules, was collected from two different types of natural fens. We tested whether the application of straw mulch would increase fen species cover and biodiversity compared to control plots without straw mulch. Terrace levels of different peat depths (15 cm, 40 cm, and 56 cm) were created to test the effects of different environmental site conditions on the success of re‐vegetation. Results: Applying donor seed bank from natural fens was found to significantly increase fen plant cover and richness after the two growing seasons. Straw mulch proved to significantly increase fen plant richness. The intermediate terrace level (40 cm) had the highest fen plant establishment. Compared to reference sites, the low terrace level (15 cm) was richer in base cations, whereas the high terrace level (56 cm) was much drier. Conclusions: The application of donor diaspore material was demonstrated as an effective technique for establishing vascular fen plants. Further re wetting measures are considered necessary at the restoration site to create a fen ecosystem rather than simply restoring some fen species.     

Use of Shallow Basins to Restore Cutover Peatlands: Hydrology

Basins 20‐, 10‐, and 4‐m wide were excavated 15 to 20 cm into cutover peat fields near Lac Saint Jean, Québec, Canada to facilitate the establishment of Sphagnum mosses. Sphagnum diaspores (fragments) and straw mulch were spread over the excavated surfaces, a control peat field, and a mulch‐protected site without basins. Mean water tables in the 20‐, 10‐, and 4‐m wide basins and the mulch‐protected site were 27.2, 8.3, 11.4, and 9.7 cm higher, respectively, than in the control peat field in May to August 1996. Similar improvements were observed in 1997 (a drier summer). The higher water table was due to lowering of the peat surface with respect to the local water table, retention of meltwater and stormwater by the peripheral ridges formed during excavation, retention of water during drier periods by the groundwater mound beneath the ridges, and mulch. Soil moisture was always higher in the experimental basins than in the control peat field or in the mulch‐protected site, demonstrating the superior soil wetness characteristic of sites with basins and straw mulch. Water tension data signaled the absence of the capillary fringe (i.e., capillary drainage) near the surface for some finite period, thus possibly limiting water for best Sphagnum growth. At the experimental basins and mulch‐protected site, 100% of these periods lasted four or fewer days. In the control peat field, 20% of the periods when capillary drainage had occurred lasted more than four days, with one period of 17 days. The mulch protection alone provided considerable improvement in hydrological conditions compared with the control peat field, but the additional water retained in the experimental basins protected against Sphagnum desiccation and loss during more extreme dry periods.     

Energy and moisture considerations on cutover peatlands: surface microtopography, mulch cover and Sphagnum regeneration

This study examined (i) the effect of artificially created microtopography and straw mulch on the soil moisture and (ii) energy balance and the establishment of a Sphagnum cover on a cutover peatland. Straw mulch caused rainfall interception approaching 2 mm per event. Although interception represented 44% of the total rainfall over the measurement period, water that evaporated from the mulch used energy that would otherwise have been used to evaporate soil water. Thus, the net effect of interception by mulch was negligible. The soil heat flux below the mulch was only 13% of the bare soil value and was decoupled from the daily net radiation. Net radiation over the bare soil was 15% greater than over the mulch. However, because of the greater heat flux into the bare peat, the energy available for sensible and latent heat fluxes was similar between the mulch covered and bare peat. Average evaporation from mulch and bare soil was estimated to be 2.6 and 3.1 mm d⁻¹, respectively. Soil water tension 1 cm below the surface remained above −100 cm (mb) all season (100% of the time) when a mulch was used, compared to only 30% of the time in the bare soil. Correspondingly, the water table was sustained above the 40 cm depth, 60% of time in the mulch covered site, compared to only 40% of the time in the bare peat site. Negative relief elements of the microtopography were wetter and cooler than positive relief elements. However, when under a mulch, the negative relief elements provided no additional benefit, in terms of temperature or soil moisture amelioration. The control site with a mulch cover was equivalent or better than negative relief elements with a mulch cover. Taking into account the poorer performance of positive relief elements, even when mulch covered, the creation of surface microtopography reduced the overall moisture content of the site. Sphagnum established and spread only when the diaspores were protected with a straw mulch. All microtopography types tested had no effect on the establishment of Sphagnum mosses when the microtopography treatments, including positive and negative relief elements, were treated as a whole, although being in a depression helped Sphagnum establishment.     

Biodegradation of Trichloroethylene in Continuous-Recycle Expanded-Bed Bioreactors

Experimental bioreactors operated as recirculated closed systems were inoculated with bacterial cultures that utilized methane, propane, and tryptone-yeast extract as aerobic carbon and energy sources and degraded trichloroethylene (TCE). Up to 95% removal of TCE was observed after 5 days of incubation. Uninoculated bioreactors inhibited with 0.5% Formalin and 0.2% sodium azide retained greater than 95% of their TCE after 20 days. Each bioreactor consisted of an expanded-bed column through which the liquid phase was recirculated and a gas recharge column which allowed direct headspace sampling. Pulses of TCE (20 mg/liter) were added to bioreactors, and gas chromatography was used to monitor TCE, propane, methane, and carbon dioxide. Pulsed feeding of methane and propane with air resulted in 1 mol of TCE degraded per 55 mol of substrate utilized. Perturbation studies revealed that pH shifts from 7.2 to 7.5 decreased TCE degradation by 85%. The bioreactors recovered to baseline activities within 1 day after the pH returned to neutrality.     

Effects of Native Plant Species,Mycorrhizal Inoculum,and Mulch on Restoration of Reservoir Sediment Following Dam Removal,Elwha River,Olympic Peninsula,Washington

As dams across the country continue to age, successful restoration of dewatered reservoirs remains a critical factor in decisions regarding dam removal. Freshly exposed reservoir sediment may not support rapid reestablishment of native plant species due to poor fertility or absence of arbuscular mycorrhizal fungi propagules. This field study evaluated treatment effects involving combinations of native plants, mycorrhizal inoculum, and mulch on restoration of dewatered reservoir sediment over 20 months. Most plants, even those uninoculated, became mycorrhizal. In all treatments, sediment pH decreased, as did nitrogen and organic matter, compared to original reservoir sediment, while aggregate stability doubled from original anaerobic sediment. Revegetated plots with mulch had significantly greater vegetation cover and more native volunteer species compared to plots without mulch. The planted mulch treatment also decreased plot runoff tenfold, reducing erosion to the same degree. Indicators suggest that the primary benefit of mulch resulted in increased moisture retention making the planted mulch treatment most successful for restoration of reservoir sediment due to extensive native plant growth, improved soil characteristics, and reduced runoff and erosion compared to nonmulched plots. While results from this plot‐scale study suggest commercial mycorrhizal inoculum is unnecessary since natural inoculum sources sufficiently colonized plants, reservoir‐scale restoration may require creation of additional source areas to encourage rapid reestablishment of native plants and mycorrhizal fungi.     

Evolutionary and ecophysiological significance of sugar utilization by the peat moss Sphagnum compactum (Sphagnaceae) and the common charophycean associates Cylindrocystis brebissonii and Mougeotia sp. (Zygnemataceae)

? Premise of the study: The goal of this study was to illuminate the evolutionary history and ecological importance of plant mixotrophy-the uptake and utilization of exogenous organic compounds. ? Methods: We quantitatively assessed the effect of sugar amendments on laboratory growth of Sphagnum compactum as a representative emergent peat moss and two species of ecologically associated zygnematalean algae, Cylindrocystis brebissonii and Mougeotia sp. ? Key results: Together with observations published elsewhere, our results suggest that under carbon or light limitation, the uptake of exogenous sugars by cells of charophycean algae and peat mosses may help these organisms maintain positive carbon balance. Utilization of 1% glucose by aquatic-grown algae helped to relieve dissolved inorganic carbon limitation, enhancing photoautotrophic growth by factors of 9.0 and 1.7, respectively. After an 8-wk growth period, amendments of 1% and 2% glucose enhanced air-grown moss biomass by 28 and 39 times, respectively, that of controls lacking sugar amendments. After 9 wk, 1% fructose enhanced biomass by 21 times, and 2% sucrose enhanced biomass by 31 times. ? Conclusion: Our results indicate that plant mixotrophy is an early-evolved trait. The results also indicate that quantitative differences in sugar utilization by bryophytes and charophycean algae correlate with relative investments in protective cell-wall polyphenolics measured in previous studies, suggesting that sugar utilization may subsidize the cost of producing phenolic wall compounds in bryophytes.     

Increasing Soil Water Retention with Native‐Sourced Mulch Improves Seedling Establishment in Postmine Mediterranean Sandy Soils

Seasonal drought and heavily impeded soils reduce restoration success in Mediterranean‐type postmine soils, where up to 90% seedling mortality has been observed after 2 years. To alleviate these barriers, amendments were incorporated into the soil profile of a freshly mined sand quarry. Within the quarry, three 223 m² replicate sites contained two substrate amendments: 12% v/v native‐sourced mulch or gravel incorporated within the top 50 cm of the soil profile. Three remnant sites provided a “natural” reference system. Seeds of two autochthonous trees, Banksia attenuata (R.Br.) and B. menziesii (R.Br.) were sown across all treatments. Soil impedance, moisture, and seedling stomatal conductance were monitored for 2 years, at which point seedlings were excavated, and nutrient concentration, root morphology, and soil chemical properties were measured. Roots in all restoration treatments were restricted to the top 40 cm of the profile due to increases in soil impedance, regardless of amendment, compared to >70 cm in the natural system. Seedling mortality was greatest after the second summer in the control and inorganic amendment treatments, with stomatal conductance indicating severe drought stress. Survival in the organic treatment was 24–42% greater than the control, with higher soil moisture and stomatal conductance rates 2.5 times that of the control. The increased soil water retention by a native‐sourced mulch was shown to improve postmine restoration success for these native trees.     

Transformation capacities of chlorinated organics by mixed cultures enriched on methane, propane, toluene, or phenol

The degradation of trichloroethylene (TCE), chloroform (CF), and 1,2-dichloroethane (1,2-DCA) by four aerobic mixed cultures (methane, propane, toluene, and phenol oxidizers) grown under similar chemostat conditions was measured. Methane and propane oxidizers were capable of degrading both saturated and unsaturated chlorinated organics (TCE, CF, and 1,2-DCA). Toluene and phenol oxidizers degraded TCE but were not able to degrade CF, 1,2-DCA, or other saturated organics. None of the cultures tested were able to degrade perchloroethylene (PCE) or carbon tetrachloride (CC(4)). For the four cultures tested, degradation of each of the chlorinated organics resulted in cell inactivation due to product toxicity. In all cases, the toxic products were rapidly depleted, leaving no toxic residues in solution. Among the four tested cultures, the resting cells of methane oxidizers exhibited the highest transformation capacities (T(c)) for TCE, CF, and 1,2-DCA. The T(c) for each chlorinated organic was observed to be inversely proportional to the chlorine carbon ratio (Cl/C). The addition of low concentrations of growth substrate or some catabolic intermediates enhanced TCE transformation capacities and degradation rates, presumably due to the regeneration of reducing energy (NADH); however, addition of higher concentrations of most amendments reduced TCE transformation capacities and degradation rates. Reducing energy limitations and amendment toxicity may significantly affect T(c) measurements, causing a masking of the toxicity associated with chlorinated organic degradation. (c) 1995 John Wiley & Sons, Inc.     

Ammonia volatilization from tropical legume mulches and green manures on unlimed and limed soils

In the humid tropics, legumes are harvested and surface applied as mulch or incorporated as green manure. Studies on N dynamics and budgets from these systems report unaccounted losses of N. Ammonia volatilization may account for a significant percentage of these unexplained N deficits. The main objectives of this study were to: 1) determine the rate and amount of ammonia volatilization from organic amendments, both incorporated (green manure) and unincorporated (mulch), 2) compare ammonia volatilization of organic amendments on both acid (unlimed) and limed soils, and 3) correlate quality, i.e. polyphenolic and lignin concentration and carbon-to-nitrogen ratio, of the organic amendments with ammonia volatilization and net N mineralization. In an incubation experiment, ammonia volatilization losses and net N mineralization were measured from fresh leaflets of 10 legumes over a three-week period. Ammonia volatilization losses for the 10 species ranged from 3.4 to 11.8% of the total N applied in the organic amendment. Lignin content was negatively correlated to ammonia volatilization. Ammonia volatilized from mulches but not green manures, on both unlimed and limed soils, suggesting that ammonia volatilization is a surface phenomenon and not affected by soil pH. Net N mineralization was affected by species and soil pH, but was unaffected by placement (green manure or mulch). For the farmer in low-input agriculture where N tends to be limiting, volatilization losses of N from legume mulch systems could be on the same order of magnitude as crop removal.     

An exploratory study of peat and sawdust as enhancers in the (bio)degradation of n-dodecane

Current practice for dealing with oil spills involves the use of adsorbent materials to contain the pollution prior to bioremediation of the contaminated soil and adsorbent. This work presents a study of the effects of bioavailable carbon sources in the adsorbents peat and sawdust as organic nutrients for microorganisms specialized in degrading n-dodecane in soil and sawdust contaminated with hydrocarbon mixtures. An experimental bioremediation system was developed using n-dodecane, biomass adapted to n-dodecane, inorganic nutrients and the two adsorbents (sterilized). Bioreactors containing peat enhanced cell growth the most and also evolved more CO(2). An advantage of peat is that its soluble carbon sources can sustain higher cell densities compared to sawdust, and this may prove decisive when cultivating endogenous microorganisms for the aerobic bioremediation of soils contaminated with hydrocarbons. However, at the end of the 68-day experiment slightly higher n-dodecane removal was identified in the system containing sawdust-n-dodecane (99.6%) than in that with peat-n-dodecane (98.5%), evidencing the higher hydrocarbon retention capacity of peat. Based on this study, the use of sawdust instead of peat is recommended when an adapted inoculum is available for aerobic bioremediation of organic contaminants, whereas the use of peat is advisable to boost cell densities in order to improve the probability of sustaining a viable biomass in unfavorable conditions.     

Mineralization of Trichloroethylene by Heterotrophic Enrichment Cultures

Microbial consortia capable of aerobically degrading more than 99% of exogenous trichloroethylene (TCE) (50 mg/liter) were collected from TCE-contaminated subsurface sediments and grown in enrichment cultures. TCE at concentrations greater than 300 mg/liter was not degraded, nor was TCE used by the consortia as a sole energy source. Energy sources which permitted growth included tryptone-yeast extract, methanol, methane, and propane. The optimum temperature range for growth and subsequent TCE consumption was 22 to 37°C, and the pH optimum was 7.0 to 8.1. Utilization of TCE occurred only after apparent microbial growth had ceased. The major end products recovered were hydrochloric acid and carbon dioxide. Minor products included dichloroethylene, vinylidine chloride, and, possibly, chloroform.     

Diffusion of TCE Through Soil-Bentonite Slurry Walls

Diffusion experiments performed using both a dissolved solution of trichloroethylene (TCE) and a pool of free phase TCE adjacent to a simulated soil-bentonite (SB) wall are described. These tests examine a multi-layer system that includes both contaminated sand and a SB barrier. Results obtained from experiments with dissolved TCE as the primary source are shown to be consistent with those obtained with free-phase TCE as the source of contaminant. Diffusion and sorption coefficients of a soil-bentonite slurry wall are reported to be 3.5 × 10^?10 m ² /s and 0 cm ³ /g, respectively. These diffusion and sorption coefficients were used to evaluate the effectiveness of a hypothetical SB slurry wall located adjacent to a TCE spill.     

Microbial community structure and trichloroethylene degradation in groundwater

Trichloroethylene (TCE) is a prevalent contaminant of groundwater that can be cometabolically degraded by indigenous microbes. Groundwater contaminated with TCE from a US Department of Energy site in Ohio was used to characterize the site-specific impact of phenol on the indigenous bacterial community for use as a possible remedial strategy. Incubations of 14C-TCE-spiked groundwater amended with phenol showed increased TCE mineralization compared with unamended groundwater. Community structure was determined using DNA directly extracted from groundwater samples. This DNA was then analyzed by amplified ribosomal DNA restriction analysis. Unique restriction fragment length polymorphisms defined operational taxonomic units that were sequenced to determine phylogeny. DNA sequence data indicated that known TCE-degrading bacteria including relatives of Variovorax and Burkholderia were present in site water. Diversity of the amplified microbial rDNA clone library was lower in phenol-amended communities than in unamended groundwater (i.e., having Shannon-Weaver diversity indices of 2.0 and 2.2, respectively). Microbial activity was higher in phenol-amended ground water as determined by measuring the reduction of 2-(p-iodophenyl)-3(p-nitrophenyl)-5-phenyl tetrazolium chloride. Thus phenol amendments to groundwater correlated with increased TCE mineralization, a decrease in diversity of the amplified microbial rDNA clone library, and increased microbial activity.     

Sorption and Desorption of Napropamide in Sandy Soil Amended with Chicken Dung and Palm Oil Mill Effluent

Beach Ridges Interspersed with Swales (BRIS) is a sandy soil and in Malaysia it is found exclusively in the east coast of Peninsular Malaysia. It is a marginal soil because of its low nutrient and water-holding capacity. However, with proper management and organic matter amendments some areas with BRIS soil are cultivated. Napropamide is a selective herbicide widely used to control weeds in BRIS soil. No previous studies have been reported on the effects of organic matter amendments on napropamide sorption in BRIS soil. This study was conducted to determine sorption and desorption of napropamide in BRIS soil amended with chicken dung (CD) and palm oil mill effluent (POME) at 0, 20, 40, and 80 Mg ha^?1. Potential interaction of dissolved organic carbon (DOC) with napropamide and their competition for sorption sites were also determined. Sorption isotherm data were fitted to the log-transformed Freundlich's equation. Sorption of napropamide was higher in soils amended with CD and POME as compared to non-amended soil. At the same rates of application, sorption was higher in soil amended with CD than POME. The Freundlich's coefficient (K_f) values were 0.22, 3.96, and 41.6 for nonamended soil, soil amended with 80 Mg ha^?1 POME, and soil amended with 80 Mg ha^?1 CD, respectively. Desorption of napropamide showed positive hysteresis and the hysteresis were greater with higher rates of CD and POME. There was no association between napropamide and DOC extracted from BRIS soil amended with either CD or POME and also there were no competitions between napropamide and DOC extracted from either CD or POME for sorption sites of the soil samples.     

Similarity of bacterial communities in sawdust- and straw-amended cow manure composts

We analyzed bacterial communities in two cow manure composts derived from the same feed manure and composted in the same location, but composted with different carbon amendments, and in peat-based potting mixes amended with these composts. Bacterial communities were characterized by PCR-denaturing gradient gel electrophoresis (DGGE) analysis of extracted DNAs, and population fingerprints generated for each sample were compared. Sequence analyses of dominant DGGE bands revealed that members of the phylum Bacteroidetes were the most dominant bacteria detected in this study (19 of 31 clones). These analyses demonstrate that bacterial community profiles of individual composts were highly similar, as were profiles of compost-amended potting mixes. However, potting mix profiles differed substantially from the original compost profiles and from that of the peat base. These data indicate that highly similar bacterial populations were active in the two composts, and suggest that the effects of the initial carbon amendment on the mature compost bacterial communities were minor, while factors such as the feed manure and composting location may have been more influential.     

Comparative growth studies of the extreme thermophile Sulfolobus acidocaldarius in submerged and solidified substrate cultures

An attempt was made, for the first time, to exploit cultures on solidified substrates (SSC) as an alternative to submerged cultures (SmC) for growing extremophilic micro-organisms. The extreme thermophilic archaebacterium Sulfolobus acidocaldarius was grown on a number of carbon sources and, in all experiments, biomass yields and growth rates were always higher in SSC than in the corresponding SmC. Inoculum age significantly affected growth characteristics on both types of fermentation. Heavy growth of the micro-organism in SSC was observed on low-cost carbon sources such as starch. Wheat bran significantly enhanced growth characteristics when used to supplement starch media. The results of this work show that cultures on solid surfaces could be a promising alternative method for growing extreme thermophiles.     

Cadmium Sorption Characteristics of Soil Amendments and its Relationship with the Cadmium Uptake by Hyperaccumulator and Normal Plants in Amended Soils

In order to select appropriate amendments for cropping hyperaccumulator or normal plants on contaminated soils and establish the relationship between Cd sorption characteristics of soil amendments and their capacity to reduce Cd uptake by plants, batch sorption experiments with 11 different clay minerals and organic materials and a pot experiment with the same amendments were carried out. The pot experiment was conducted with Sedum alfredii and maize (Zea mays) in a co-cropping system. The results showed that the highest sorption amount was by montmorillonite at 40.82 mg/g, while mica was the lowest at only 1.83 mg/g. There was a significant negative correlation between the n value of Freundlich equation and Cd uptake by plants, and between the logarithm of the stability constant K of the Langmuir equation and plant uptake. Humic acids (HAs) and mushroom manure increased Cd uptake by S. alfredii, but not maize, thus they are suitable as soil amendments for the co-cropping S. alfredii and maize. The stability constant K in these cases was 0.14–0.16 L/mg and n values were 1.51–2.19. The alkaline zeolite and mica had the best fixation abilities and significantly decreased Cd uptake by the both plants, with K ≥ 1.49 L/mg and n ≥ 3.59.     

Evaluation of biodegradation potential of foam embedded Burkholderia cepacia G4

Foam embedded Burkholderia cepacia G4 removed up to 80 % and 60 % of a 3 mg/l solution of trichloroethylene (TCE) and a 2 mg/l solution of benzene, respectively. Removal of TCE and benzene decreased more than 50% when readily metabolizable carbon sources were present. TCE degradative activity was observed with G4 cells induced with phenol or benzene prior or after immobilization of cells. © Rapid Science Ltd. 1998