Anaerobic Incubation Research Articles

Anaerobic degradation of perfluorooctanoic acid (PFOA) in biosolids by Acidimicrobium sp. strain A6

Anaerobic incubations were performed with biosolids obtained from an industrial wastewater treatment plant (WWTP) that contained perfluorooctanoic acid (PFOA), and with per- and polyfluoroalkyl substances- (PFAS) free, laboratory-generated, biosolids that were spiked with PFOA. Biosolid slurries were incubated for 150 days as is, after augmenting with either Acidimicrobium sp. Strain A6 or ferrihydrite, or with both, Acidimicrobium sp. Strain A6 and ferrihydrite. Autoclaved controls were run in parallel. Only the biosolids augmented with both, Acidimicrobium sp. Strain A6 and ferrihydrite showed a decrease in the PFOA concentration, in excess of 50% (total, dissolved, and solid associated). Higher concentrations of PFOA in the biosolids spiked with PFOA and no previous PFAS exposure allowed to track the production of fluoride to verify PFOA defluorination. The buildup of fluoride over the incubation time was observed in these biosolid incubations spiked with PFOA. A significant increase in the concentration of perfluoroheptanoic acid (PFHpA) over the incubations of the filter cake samples from the industrial WWTP was observed, indicating the presence of a non-identified precursor in these biosolids. Results show that anaerobic incubation of PFAS contaminated biosolids, after augmentation with Fe(III) and Acidimicrobium sp. Strain A6 can result in PFAS defluorination.

Electrochemical and Structural Modifications of Humic Acids in Aerobically and Anaerobically Incubated Peat

Exposure to oxygen and aerobic biological activity during drought periods alters the availability of terminal electron acceptors (TEA) in the peat catotelm layer. We investigated the changes in the electrochemical and chemical characteristics of humic acids (HA) induced by subjecting air-dried sphagnum peat to biological oxidation or reduction during a 90-day incubation experiment. Structural modifications of HAs from anaerobically (HAred) and aerobically (HAox) incubated peat were investigated by ATR-FTIR, UV–vis, and EEM fluorescence spectroscopy. Number and strength of acid groups were characterized by titration, while changes in redox properties were characterized by cyclic voltammetry and quantified by coulometry with mediated electrochemical oxidation (MEO). Exposure to oxygen had small effects, but compared to anaerobic incubation, decreased by 20% the capacity of HA to reduce the radical ion of 2,2′-Azinobis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS●−), passing from 2.77 ± 0.13 mmole- gHA−1 in HAred to 2.21 ± 0.10 mmole- gHA−1 in HAox. Pseudo-first-order electron transfer kinetic constants were 13.3 ± 1.2 s−1 for HAox and 16.7 ± 1.4 s−1 for HAred. Alterations in the hydrological status of the catotelm have minor effects on the actual in situ availability of organic TEA, but if coupled to intensified biological activity they may result in significant variations of greenhouse gases emissions.

Soil mineralization as effects of plant growth promoting bacteria isolated from microalgae in wastewater and rice straw application in a long-term paddy rice in Central Viet Nam

This study investigates the effects of rice straw and potential nitrogen fixing Bacillus subtilis (Bacillus sp.) isolated from seafood wastewater on carbohydrate- and nitrogen mineralization from a long-term rice paddy soil by four weeks anaerobic incubation. Soil collected at the depth of 0–15 cm from a long-term rice paddy cultivation, and set up as following: (1) Control (10 g air dry soil), (2) Rice straw (control ＋ 0.2% rice straw w/v), (3) Bacillus sp., and (4) Combine (rice straw 0.2% w/v and Bacillus sp.) was subjected to an incubator in dark at room temperature/ submerge condition for 4 weeks anaerobic incubation. As showed in results, content of decomposed carbohydrate ranged from 83–447 mg kg −1 soil. Content of extracted carbohydrate was not affected by rice straw application, but significant decreased with bacillus or rice straw-bacillus combine inoculation (2.0–2.2 times decreased) compared to Control treatment, which is closely to the initial soil extraction carbohydrate. In contrary, mineralization nitrogen increased 120% in Bacillus sp. inoculation compared to Control treatment, but Rice straw and Combine treatments resulted in immobilization more than nitrogen mineralization. Inoculation of Bacillus subtilis is recommended as a good environment friendly method to enhance the soil fertility and reduce nitrogen immobilization. Further research within rice plant is therefore needed to consolidate the preliminary results.

Wood-Ljungdahl pathway utilisation during in situ H2 biomethanation

Biogas production from organic waste is a waste-to-energy technology with the potential to contribute significantly to sustainable energy production. Upgrading of biogas using in situ biomethanation with hydrogen has the potential for surplus electricity storage, and delivery of biogas with a methane content of >90%, allowing for easier integration into the natural gas grid, as well as conversion to other products. Microbial communities in biomethanation reactors undergo changes, however, these changes are largely unexplored. In the present study, metagenome-resolved protein stable isotope probing (Protein-SIP) was applied to laboratory scale batch incubations operating under anaerobic digestion, and (pre-adapted) biomethanation conditions, fed with 13C-labelled bicarbonate, in order to gain insight into the microbial activities during CO2-reduction. The strongest and most microbially diverse isotopic incorporation was observed in the pre-adapted biomethanation incubation. Furthermore, divergent incorporation of 13C-labelled bicarbonate was also observed in the Wood-Ljungdahl pathway, with the anaerobic digester incubations primarily showing labelled proteins in the peripheral pathways leading toward production of energy and biomass. The pre-adapted biomethanation incubations consumed H2 and CO2, but did not convert it to CH4, suggesting the production of acetate in these incubations, which was supported by heavy labelling of key enzymes in the Wood-Ljungdahl pathway. Twelve (ten high quality) metagenome-assembled genomes (MAGs) coding for 13C-incorporated proteins were extracted from the metagenome, eight of which contained one or more of the key genes in the Wood-Ljungdahl pathway, one of which was affiliated to Methanosarcina. Together, the findings in the present study deepen our knowledge surrounding microbial communities in biomethanation systems, and contribute to the development of better strategies for implementation of biogas upgrading and microbial management.

Comparison of laboratory methodologies to determine soil nitrogen mineralization from organic residues

Recycling organic waste for use as fertilizer requires prior knowledge of mineral nitrogen (N) availability for crops. Estimation of soil N release or potentially mineralizable N is an important tool for the design of fertilization strategies that aim to minimize the use of N fertilizer. The aerobic incubation method is considered a standard technique to measure soil potential to mineralize N. In this study, alternative methods of aerobic incubation were evaluated to help overcome its limitations (long time and equipment). In this regard, biological methods (anaerobic incubation at 7 and 14 days) and chemical extraction (hot KCl) procedures were examined. To determine potentially mineralizable N, a silty clay loam soil was fertilized with spent mushroom substrates and anaerobic digestates from different origins (C/N ratio of 4 to 38). Based on the results, chemical extraction emerges as a reliable alternative to the aerobic incubation method, particularly when the C/N ratio of the organic residues ranges from 12 to 15. Moreover, its implementation in routine soil laboratories is straightforward and faster, and it does not require any special equipment.

Microbiology of barrier component analogues of a deep geological repository.

Canada is currently implementing a site selection process to identify a location for a deep geological repository (DGR) for the long-term storage of Canada's used nuclear fuel, wherein used nuclear fuel bundles will be sealed inside copper-coated carbon steel containers, encased in highly compacted bentonite clay buffer boxes, and sealed deep underground in a stable geosphere. Because a DGR must remain functional for a million years, it is important to examine ancient natural systems that serve as analogues for planned DGR components. Specifically, studying the microbiology of natural analogue components of a DGR is important for developing an understanding of the types of microorganisms that may be able to grow and influence the long-term stability of a DGR. This study explored the abundance, viability, and composition of microorganisms in several ancient natural analogues using a combination of cultivation and cultivation-independent approaches. Samples were obtained from the Tsukinuno bentonite deposit (Japan) that formed ∼10 mya, the Opalinus Clay formation (Switzerland) that formed ∼174 mya, and Canadian shield crystalline rock from Northern Ontario that formed ∼2.7 bya. Analysis of 16S rRNA gene amplicons revealed that three of the ten Tsukinuno bentonite samples analyzed were dominated by putative aerobic heterotrophs and fermenting bacteria from the phylum Actinobacteria, whereas five of the Tsukinuno bentonite samples were dominated by sequences associated with putative acidophilic chemolithoautotrophs capable of sulfur reduction. The remaining Tsukinuno bentonite samples, the Northern Ontario rock samples, and the Opalinus Clay samples generated inconsistent replicate 16S rRNA gene profiles and were associated primarily with contaminant sequences, suggesting that the microbial profiles detected were not sample-specific but spurious. Culturable aerobic heterotroph abundances were relatively low for all Tsukinuno bentonite samples, culturable anaerobic heterotrophs were only detected in half of the Tsukinuno samples, and sulfate-reducing bacteria (SRB) were only detected in one Tsukinuno sample by cultivation. Culture-specific 16S rRNA gene profiles from Tsukinuno clay samples demonstrated the presence of phyla Bacteroidetes, Proteobacteria, Actinobacteria, and Firmicutes among aerobic heterotroph cultures and additional bacteria from the phyla Actinobacteria and Firmicutes from anaerobic heterotroph plate incubations. Only one nucleic acid sequence detected from a culture was also associated with its corresponding clay sample profile, suggesting that nucleic acids from culturable bacteria were relatively rare within the clay samples. Sequencing of DNA extracted from the SRB culture revealed that the taxon present in the culture was affiliated with the genus Desulfosporosinus, which has been found in related bentonite clay analyses. Although the crystalline rock and Opalinus Clay samples were associated with inconsistent, likely spurious 16S rRNA gene profiles, we show evidence for viable and detectable microorganisms within several Tsukinuno natural analogue bentonite samples.

Fate of a biobased polymer via high-solid anaerobic co-digestion with food waste and following aerobic treatment: Insights on changes of polymer physicochemical properties and the role of microbial and fungal communities

Degradation of bioplastics in food-waste-treating anaerobic digestion (AD) plants is becoming an increasingly concerning issue as they are inevitably mixed with food waste during the waste collection process. The aim of this study was to assess the degradation of PBAT/PLA based biopolymer bags during mesophilic and thermophilic AD, co-digested with food waste, and subsequent aerobic post-treatment. After the AD process, no discernable biological degradation was observed for all of the PBAT/PLA polymers. The comparison of FTIR, XRD, TG analysis and contact angle analysis between raw and degraded PBAT/PLA polymer revealed structural changes after anaerobic incubation. Subsequent aerobic treatment facilitated the degradation of the PBAT/PLA polymers from thermophilic AD, which was attributed to the polymer-degrading microorganisms Brevundimonas and Sphingobacterium. Physical disintegration of the PBAT/PLA polymer was observed under thermophilic conditions. Those undegraded polymer fragments could affect digestate quality and increase the risk of releasing microplastics into the environment.

Spent Craft Brewer's Yeast Reduces Production of Methane and Ammonia by Bovine Rumen Microbes

Methane and ammonia are byproducts of rumen fermentation that do not promote animal growth, and methane is a key contributor to anthropogenic climate disruption. Cows eructate every few breaths and typically emit 250–500 L of methane gas daily. Significant research is focused on finding diets and additives that lower the production of methane and ammonia. Emerging research has shown that humulones and lupulones, molecules that are found in the cones of hops (Humulus lupulus), have potential in this regard. These molecules, which are also key flavor components in beer, are biologically active: they are known inhibitors of Gram-positive bacteria. Ruminants' sophisticated digestive systems host billions of microorganisms, and these systems' outputs will likely be affected in the presence of brewer's yeast (Saccharomyces cerevisiae). So-called spent yeast is produced during the beer-brewing process and contains humulones and lupulones in concentrations that vary by beer style, but it is generally discarded as waste. Our research suggests that adding spent craft brewer's yeast to rumen microbes by single time-point 24-h in vitro incubations suppresses production of methane and ammonia. This project examines the correlation between the quantities of hop acids in spent yeast and the production of methane and ammonia by bovine rumen microbes in vitro. We determined, by HPLC, the hop acid concentrations in spent yeast obtained from six beer styles produced at a local brewery. We performed anaerobic incubation studies on bovine rumen microbes, comparing the effects of these materials to a baker's yeast control and to the industry-standard antibiotic monensin. Results include promising decreases in both methane (measured by GC–FID) and ammonia (measured by colorimetric assay) in the presence of craft brewer's yeast, and a strong correlation between the quantities of hop acids in the spent yeast and the reduction of methane and ammonia. Notably, two of the yeast samples inhibited methane production to a greater degree than the industry-standard antibiotic monensin. Our results suggest that spent brewer's yeast has potential to improve ruminant growth while reducing anthropogenic methane emission.

Antagonistic Effects of Lipids Against the Anti-Escherichia coli and Anti-Salmonella Activity of Thymol and Thymol-β-d-Glucopyranoside in Porcine Gut and Fecal Cultures In Vitro.

Strategies are sought to reduce the carriage and dissemination of zoonotic pathogens and antimicrobial-resistant microbes within food-producing animals and their production environment. Thymol (an essential oil) is a potent bactericide in vitro but in vivo efficacy has been inconsistent, largely due to its lipophilicity and absorption, which limits its passage and subsequent availability in the distal gastrointestinal tract. Conjugation of thymol to glucose to form thymol-β-d-glucopyranoside can decrease its absorption, but in vivo passage of effective concentrations to the lower gut remains suboptimal. Considering that contemporary swine diets often contain 5% or more added fat (to increase caloric density and reduce dustiness), we hypothesized that there may be sufficient residual fat in the distal intestinal tract to sequester free or conjugated thymol, thereby limiting the availability and subsequent effectiveness of this biocide. In support of this hypothesis, the anti-Salmonella Typhimurium effects of 6 mM free or conjugated thymol, expressed as log10-fold reductions of colony-forming units (CFU) ml−1, were diminished 90 and 58%, respectively, following 24-h in vitro anaerobic fecal incubation (at 39°C) with 3% added vegetable oil compared to reductions achieved during culture without added oil (6.1 log10 CFU ml−1). The antagonistic effect of vegetable oil and the bactericidal effect of free and conjugated thymol against Escherichia coli K88 tested similarly were diminished 86 and 84%, respectively, compared to reductions achieved in cultures incubated without added vegetable oil (5.7 log10 CFU ml−1). Inclusion of taurine (8 mg/ml), bile acids (0.6 mg/ml), or emulsifiers such as polyoxyethylene-40 stearate (0.2%), Tween 20, or Tween 80 (each at 1%) in the in vitro incubations had little effect on vegetable oil-caused inhibition of free or conjugated thymol. Based on these results, it seems reasonable to suspect that undigested lipid in the distal gut may limit the effectiveness of free or conjugated thymol. Accordingly, additional research is warranted to learn how to overcome obstacles diminishing bactericidal activity of free and conjugated thymol in the lower gastrointestinal tract of food-producing animals.

Factors limiting microbial N2O and CO2 production in a cultivated peatland overlying an acid sulphate subsoil derived from black schist

Factors limiting the production of the greenhouse gases nitrous oxide (N2O) and carbon dioxide (CO2) were investigated in three incubation experiments conducted with soil from top- and subsoil horizons of a peatland which had an acid sulphate mineral subsoil derived from black schists. The effect of moisture was investigated by equilibrating undisturbed soil samples from three horizons (H2, Cg and Cr) at −10, −60 or −100 cm matric potential and measuring the gas production. In the second experiment, the effects of temperature and various substrates were studied by incubating disturbed soil samples in aerobic conditions at 5 or 20 °C, and measuring basal respiration and N2O production before and after adding water, glucose or ammonium into the soil. In the third experiment, the effects of added glucose and/or nitrate on the denitrification in soil samples from four horizons (H1, H2, Cg and Cr were investigated by acetylene inhibition and monitoring of N2O production during a 48-h anaerobic incubation. The production of CO2 in the topmost peat horizon was largest at −10 cm matric potential, and it was larger than those in the mineral subsoil also at −60 and −100 cm potentials. In contrast, drainage seemed to increase N2O production, whereas in the wettest condition the production of N2O in the mineral subsoil was small and the peat horizon was a sink of N2O. Lowering of temperature (from 20 °C to 5 °C) decreased CO2 production, as expected, but it had almost no role in the production of N2O in aerobic conditions. Glucose addition increased the aerobic production of CO2 in peat, but it had a minor effect in the mineral horizons. Lack of C source (glucose) was limiting anaerobic N2O production in the uppermost peat horizon, while in all other horizons, nitrate proved to be the most limiting factor. It is concluded that peatlands with black schist derived acid sulphate subsoil horizons, such as in this study, have high microbial activity in the peaty topsoil horizons but little microbial activity in the mineral subsoil. These findings are contrary to previous results obtained in sediment-derived acid sulphate soils.

Sulfur-Based Denitrification in Streambank Subsoils in a Headwater Catchment Underlain by Marine Sedimentary Rocks in Akita, Japan

Sulfur-based denitrification may be a key biogeochemical nitrate (NO3−) removal process in sulfide-rich regions, but it is still poorly understood in natural terrestrial ecosystems. We examined sulfur-driven NO3− reduction using streambank soils in a headwater catchment underlain by marine sedimentary rock in Akita, Japan. In a catchment exhibiting higher sulfide content in streambed sediment, we sampled two adjacent streambank soils of streambank I (two layers) and of streambank II (eight layers). Anaerobic long-term incubation experiments (40 days, using soils of streambank I) and short-term incubation experiments (5 days, using soils of streambank II) were conducted to evaluate variations of N solutes (NO3−, NO2−, and NH4+), N gases (NO, N2O), and the bacterial flora. In both experiments, two treatment solutions containing NO3− (N treatment), and NO3− and S2O32− (N + S treatment) were prepared. In the N + S treatment of the long-term experiment, NO3− concentrations gradually decreased by 98%, with increases in the SO42−, NO2−, NO, and N2O concentrations and with not increase in the NH4+, indicating denitrification had occurred with a high probability. Temporal accumulation of NO2− was observed in the N + S treatment. The stoichiometric ratio of SO42− production and NO3− depletion rates indicated that denitrification using reduced sulfur occurred even without additional S, indicating inherent S also served as an electron donor for denitrification. In the short-term incubation experiment, S addition was significantly decreased NO3− concentrations and increased NO2−, NO, and N2O concentrations, especially in some subsoils with higher sulfide contents. Many denitrifying sulfur-oxidizing bacteria (Thiobacillus denitrificans and Sulfuricella denitrificans) were detected in both streambank I and II, which dominated up to 5% of the entire microbial population, suggesting that these bacteria are widespread in sulfide-rich soil layers in the catchment. We concluded that the catchment with abundant sulfides in the subsoil possessed the potential for sulfur-driven NO3− reduction, which could widely influence N cycling in and NO3− export from the headwater catchment.

Strengthen “the sustainable farm” concept via efficacious conversion of farm wastes into methane

With escalating global demand for renewable energy, exploitation of farm wastes (i.e., agriculture straw wastes (ASWs), livestock wastewater (LW) and sewage sludge (SS)) has been considered to attain maximum methane yield (MY) via anaerobic digestion (AD). Results pointed that mixture of SS and LW as anaerobes’ source with 20 g of ASWs/300 mL of working volume achieved maximum MY and volatile solid (VS) removal efficiency of 0.44 (±0.05) L/gVS and 51.4 (±4.1)%, respectively. This was mainly because of emerging heavy duty bacterial species (i.e., Syntrophorhabdaceae and Synergistaceae) and archaeal community (i.e, Methanosarcina and Methanoculleus) after 70 days of anaerobic incubation. This was acquired along with boosting enzymatic activity, especially xylanase, cellulase and protease up to 71.5(±7.9), 179.3(±14.3) and 207.2(±16.2) U/100 mL, respectively. Furthermore, the digestate contained high concentrations of NH4+ (960.1±(76.8) mg/L), phosphorus (126.3±(10.1) mg/L) and trace metals, making it a good candidate as organic fertilizer.

Qualitatively and quantitatively investigating the metabolism of 20(S)-protopanaxadiol-type ginsenosides by gut microbiota of different species.

Ginsenosides Rb1, Rb2, Rb3 and Rc, four major protopanaxadiol (PPD)-type ginsenosides, can be metabolized by gut microbiota. The composition of gut microbiota varies in different species. Existing publications have reported the metabolite fates of ginsenosides by gut microbiota from single species. However, their microbiota-related metabolic species differences have not been evaluated yet. In current study, in vitro anaerobic incubations of PPD-type ginsenosides with gut microbiota from humans, rabbits and rats were conducted. The metabolites of each ginsenoside were then identified by LC-MS. A total of 15 metabolites from the four ginsenosides were identified. The major metabolic pathways were stepwise removals of the C-20 and C-3 sugar moieties to obtain aglycone PPD. The results showed that the hydrolysis rate of C-20 terminal β-D-glucopyranosyl was significantly higher than those of α-L-arabinopyranosyl, β-D-xylopyranosyl and α-L-arabinofuranosyl in different species. The activity of β-glucosidase, the metabolic rates of parent compounds and the formation rates of their metabolites were significantly higher in gut microbiota from rabbits than from humans and rats. Our research draws researchers' attention to the species differences of microbiota-related drug metabolism.

In vitro study of the effect of quinoa and quinoa polysaccharides on human gut microbiota.

It has been shown that whole grains and dietary fiber are important for their fermentation characteristics in the large intestine, drawing more and more attention to quinoa and quinoa polysaccharides. In this study, we evaluated the prebiotic effect of quinoa seeds and quinoa polysaccharides after human simulated digestion. The modulatory effect of the quinoa and quinoa polysaccharides (QPs) on the gut microbiota was evaluated by the in vitro fermentation using human fecal microbiota. The yield of polysaccharides extraction was 15.45%. The digestibility of the cooked and uncooked quinoa after simulation of human digestion was 69.04% and 64.09%, respectively. The effect on the microbiota composition and their metabolic products was determined by the assessment of pH, short‐chain fatty acids (SCFAs), and changes in the bacterial population. After 24 hr anaerobic incubation, the total SCFAs of cooked, uncooked quinoa, and quinoa polysaccharides were 82.99, 77.11, and 82.73 mM, respectively with a pH decrease. At the phylum, genus, and class level, it has been found that the quinoa substrates enhance the growth of certain beneficial bacteria such as Prevotella and Bacteroides. Quinoa polysaccharides can be considered prebiotic due to their ability to increase Bifidobacterium and Collinsella. Principal component analysis (PCA) showed that there was a distinct modulating effect on the fecal microbiota which represents different distribution. Our research suggests that quinoa and quinoa polysaccharides have a prebiotic potential due to their association with the positive shifts in microbiota composition and short‐chain fatty acids production, which highlights the importance of further studies around this topic.

Degradation of bioplastics in organic waste by mesophilic anaerobic digestion, composting and soil incubation

The aim of the study was to assess the effects of high concentrations (10 % w/w, data projected for 2030) of commercial bioplastics, i.e. starch based shopping bags (SBSB) and polylactic acid (PLA) tableware, in the organic fraction of municipal solid wastes (MSW) on compost quality obtained by pilot-scale dry mesophilic anaerobic digestion and subsequent composting of the digestate.After the biological processes, 48.1 % total solids (TS) of SBSB and 15 % TS of PLA degraded, resulting in a high bioplastics content (about 18 % TS) in compost. Subsequent compost incubation in soils indicated that bioplastics degraded by pseudo-zero order kinetics (0.014 and 0.010 mg C cm−2 d-1 for SBSB and PLA, respectively), i.e. complete degradation was expected in 1.6 years (SBSB) and 7.2 years (PLA), confirming the intrinsic biodegradability of bioplastics. Nevertheless, enhancing the rate and amount of bioplastics degradation during waste management represents a goal to decrease the amount of bioplastics reaching the environment.

Biodegradation potential of polycyclic aromatic hydrocarbons in Taihu Lake sediments

ABSTRACT To assess the biodegradation potential of polycyclic aromatic hydrocarbons (PAHs) in sediments, sediment microcosms were constructed with sediments collected from six lake zones with different trophic statuses in Taihu Lake. The presence and concentration of PAH-degrading bacteria (PDB) were estimated by the most probable number (MPN) method. After 85 d of aerobic and anaerobic incubation, spiked PAHs (phenanthrene, pyrene, and benzo[a]pyrene) were partially degraded by indigenous sediment microorganisms. Large differences in PAH degradation were observed depending on the molecular size of the PAHs. The PAH removal efficiency in sediments under aerobic conditions was higher than that under anaerobic conditions. MPN analyses showed a higher abundance of degrading microflora in the high PAH-contaminated sites than in the low PAH-contaminated sites. Moreover, the anaerobic PDB populations in the sediments from the six different sites were much higher than those of aerobic PDB. The PAH biodegradation capability in sediments was associated with the geochemical conditions and bacterial populations. PDB showed a broad spatial distribution, thereby implying that they played an important role in the natural attenuation and cycling of PAHs in Taihu Lake. This work indicates that PAHs remain a concern in Taihu Lake sediments and can provide useful information for further bioremediation of PAH-contaminated sediments.

Effects of nitrogen addition on anaerobic oxidation of methane in Zoige Plateau peatlands

Anaerobic oxidation of methane (AOM), an important biological process to reduce global methane emissions to the atmosphere, can utilize methane as an electron donor to reduce sulfate, nitrate, nitrite, iron, manganese, AQDS (9,10-anthraquinone-2,6-disulfonate), etc.; thus, AOM has been a hot topic in global climate change research in recent years. In addition, nitrogen deposition of terrestrial ecosystems can input more nitrogen to nitrogen-limited peatlands, which could impact the AOM process. However, the effect of nitrogen addition on AOM is not well studied. Here, we investigated the effects of two forms of nitrogen on the vertical distribution (0–100 cm) of AOM in the Zoige peatlands (China) using an anaerobic incubation experiment. The results show that the concentrations of inorganic nitrogen species changed with nitrogen addition, but it did not significantly promote the potential of AOM. The cumulative AOM of treatments without nitrogen (CK) and ammonium chloride (Nred) was 2343.43 ± 18.96 µg·g−1 and 2340.76 ± 16.11 µg·g−1, respectively, which were significantly higher than that of sodium nitrate (Nox) addition treatment (2098.13 ± 13.59 µg·g−1). In addition, the potential of AOM increased with depth, but different soil layers had different responses to the two forms of nitrogen, which could reflect the variable need for different forms of nitrogen in the different soil layers. The soilwatercontent(SWC), dissolved organic carbon (DOC), iron content (Fe3+), and pH played important roles in the potential of AOM in the Zoige peatlands. Overall, our results found that nitrogen addition did not increase the potential of AOM, but instead had an inhibitory effect on it. This study provides a basis for understanding the response of AOM to nitrogen addition in peatlands, which has important implications for global climate change.

Effects of harvesting intensity, vegetation control and fertilization on 5–20 year post-harvest N availability in boreal jack pine and black spruce forest soils in northern Ontario, Canada

The impact of harvesting intensity, vegetation control and fertilization on soil N availability 5–20 years post-harvest was determined at 18 jack pine and black spruce forests in northern Ontario, Canada. The study sites are affiliated with the North American long-term soil productivity (LTSP) study. Boreal forest growth is commonly N limited and young stands approaching crown closure acquire most of their N from the soil. The study sites represented a range of soil types and were harvested with three levels of organic matter removal (stem-only harvest, full-tree harvest and full-tree harvest with organic horizon removal by blading). Three study sites had multiple applications of glyphosate to control competing vegetation and one site included a trial with two applications of N, P, K fertilizer to the full-tree harvest treatment. We used short-term anaerobic laboratory incubations and in-situ closed top tube growing season incubations to determine mineralizable N and net N mineralization, respectively. Profile (organic plus mineral horizons) mineralizable N pools were higher in operational clearcut (stem-only and full-tree harvesting) treatments compared to the uncut reference forest 10–14 years post harvest. Full-tree harvesting with blading significantly reduced profile mineralizable N pools at this time compared to operational harvesting, while the same treatment at one upland site also reduced net N mineralization pools. Profile mineralizable N pools and microbial biomass C and N were lower in full-tree compared to stem-only harvesting treatments, suggesting that increased slash retention with stem-only harvesting was playing a role in enhanced soil N availability at a time when plantations were approaching a period of greater N demand. Fertilization and vegetation control treatments had few effects on N indices, although net N mineralization pools for the stem-only and full-tree harvest that also had the repeated herbicide treatment were consistently, but not significantly, lower than non-herbicided treatments. Soil N indices were useful predictors of dominant height growth for jack pine to a greater degree than for black spruce, and soil N concentrations were as effective at predicting height growth as more resource intensive measurements. Our results point to the importance of continued monitoring of soil and stand conditions at these LTSP sites as treatment effects on soil N cycling and site productivity will likely continue to evolve. At this stage of stand development, full-tree harvesting plus organic horizon removal, followed by operational harvesting has led to lower soil N availability than operational tree-length harvesting, and stands with understory vegetation control are now showing indications of reduced N availability.

Kinetics of antimony biogeochemical processes under pre-definite anaerobic and aerobic conditions in a paddy soil

While the transformation of antimony (Sb) in paddy soil has been previously investigated, the biogeochemical processes of highly chemical active Sb in the soil remain poorly understood. In addition, there is a lack of quantitative understanding of Sb transformation in soil. Therefore, in this study, the kinetics of exogenous Sb in paddy soils were investigated under anaerobic and aerobic incubation conditions. The dissolved Sb(V) and the Sb(V) extracted by diffusive gradient technique decreased under anaerobic conditions and then increased under aerobic conditions. The redox reaction of Sb occurred, and Sb bioavailability significantly decreased after 55 days of incubation. The kinetics of Fe and the scanning transmission electron microscopy analysis revealed that the Fe oxides were reduced and became dispersed under anaerobic conditions, whereas they were oxidized and re-aggregated during the aerobic stage. In addition, the redox processes of sulfur and nitrogen were detected under both anaerobic and aerobic conditions. Based on these observations, a simplified kinetic model was established to distinguish the relative contributions of the transformation processes. The bioavailability of Sb was controlled by immobilization as a result of S reduction and by mobilization as a result of Fe reductive dissolution and S oxidation, rather than the pH. These processes coupled with the redox reaction of Sb jointly resulted in the complex behavior of Sb transformation under anaerobic and aerobic conditions. The model-based method and findings of this study provide a comprehensive understanding of the Sb transformation in a complex soil biogeochemical system under changing redox conditions.

Modelling evaluation of key cadmium transformation processes in acid paddy soil under alternating redox conditions

The intermittent flooding conditions in acid paddy field can substantially affect the phytoavailability of cadmium (Cd), but the underlying mechanisms controlling Cd transformation are still poorly understood, and furthermore the corresponding models for predict the Cd phytoavailability during pre-harvest drainage phase are still lacked. In this study, Cd-spiked paddy soil was incubated under anaerobic condition for 40 days and then aerobic condition for 15 days. The transformation of Cd speciation and the redox cycling of Fe/N/S was investigated. During anaerobic incubation, the dissolved and exchangeable Cd rapidly decreased, which were mainly attributed to enhanced adsorption on the surface of organic matter with the increasing soil pH. Moreover, the reductive dissolution of Fe oxides induced the release of soil colloids, which result in increasing the surface sites to immobilize Cd. In addition, the formation of Cd sulfide contributed to slight decrease the availability of Cd. However, when oxygen was re-introduced into the system, the rapid decrease of soil pH and surface sites resulted in the release of adsorption on soil surfaces, and oxidative dissolution of Cd sulfide also contributed to the increase of Cd availability. The kinetic models were established based on the key elementary reactions for soil biogeochemical processes on the transformation of Cd fractions. The kinetic models were applied to calculate the potential available Cd in acid paddy soils samples (pH ≤ 6.0) from the field, and moreover, the dissolved Cd was estimated from the surface complexation model (SCM) by incorporating the changes of soil pH. The concentration of model-predicted dissolved Cd during drainage phase had a stronger correlation with the Cd content in rice grain than that of chemical extraction methods. Our results demonstrated that it was feasible to use the kinetic models and SCM to predict Cd phytoavailability during drainage phase of acid paddy field.