Modelling in situ activities of enzymes as a tool to explain seasonal variation of soil respiration from agro-ecosystems

Understanding in situ enzyme activities could help clarify the fate of soil organic carbon (SOC), one of the largest uncertainties in predicting future climate. Here, we explored the role of soil temperature and moisture on SOM decomposition by using, for the first time, modelled in situ enzyme activities as a proxy to explain seasonal variation in soil respiration. We measured temperature sensitivities (Q₁₀) of three enzymes (β-glucosidase, xylanase and phenoloxidase) and moisture sensitivity of β-glucosidase from agricultural soils in southwest Germany. Significant seasonal variation was found in potential activities of β-glucosidase, xylanase and phenoloxidase and in Q₁₀ for β-glucosidase and phenoloxidase activities but not for xylanase. We measured moisture sensitivity of β-glucosidase activity at four moisture levels (12%–32%), and fitted a saturation function reflecting increasing substrate limitation due to limited substrate diffusion at low water contents. The moisture response function of β-glucosidase activity remained stable throughout the year. Sensitivity of enzymes to temperature and moisture remains one of the greatest uncertainties in C models. We therefore used the response functions to model temperature-based and temperature and moisture-based in situ enzyme activities to characterize seasonal variation in SOC decomposition. We found temperature to be the main factor controlling in situ enzyme activities. To prove the relevance of our modelling approach, we compared the modelled in situ enzyme activities with soil respiration data measured weekly. Temperature-based in situ enzyme activities explained seasonal variability in soil respiration well, with model efficiencies between 0.35 and 0.78. Fitting an exponential response function to in situ soil temperature explained soil respiration to a lesser extent than our enzyme-based approach. Adding soil moisture as a co-factor improved model efficiencies only partly. Our results demonstrate the potential of this new approach to explain seasonal variation of enzyme related processes.     

Soil Lead Immobilization Using Phosphate Rock

Phosphate compounds of lead (Pb) are highly insoluble and their formation in contaminated soils would aid immobilization of Pb. The goal of the current research was to evaluate the immobilization of Pb by various treatments of phosphate rock on contaminated agricultural soils typical of Taiwan, and to determine the optimal amount of phosphate rock for use in field application. Samples of contaminated soil, each containing Pb concentrations ranging from 346 to 1873 mg kg^?1 were collected from arable land near a ceramic products manufacturing factory. Both batch immobilization experiments and in situ remediation were completed using phosphate rock additives. Results of the batch experiments demonstrate that the phosphate rock was effective in reducing Pb extractable by 0.1 M HCl, with a minimum reduction of 33–97% after 8 days of reaction, for initial Pb concentrations up to 1873 mg kg^?1. HCl-extractable Pb did not decrease after an additional 2-day reaction with a greater phosphate rock loading. It was also found that the reaction time had less effect on Pb immobilization than the amount of phosphate rock added. Results from in situ remediation experiments indicate that soil-extractable Pb was reduced by 93% (mean; range 85.2–97.2%), which is comparable with the results of the batch study. Additionally, the soil pH was increased from 6.25 (mean; range 5.96–6.76) to 7.2 (mean; range 6.92–7.53) after remediation. Based upon the HCl-extractable Pb content and the amount of phosphate rock added, various linear log-linear regression curves were obtained. These predictive equations have been used for field application. Our field results demonstrate that phosphate rocks have a potential to cost-effectively treat Pb-contaminated soils in Taiwan.     

Biodegradation of PAHs and PCBs in Soils and Sludges

Results from a multi-year, pilot-scale land treatment project for PAHs and PCBs biodegradation were evaluated. A mathematical model, capable of describing sorption, sequestration, and biodegradation in soil/water systems, is applied to interpret the efficacy of a sequential active–passive biotreatment process of organic chemicals on remediation sites. To account for the recalcitrance of PAHs and PCBs in soils and sludges during long-term biotreatment, this model comprises a kinetic equation for organic chemical intraparticle sequestration process. Model responses were verified by comparison to measurements of biodegradation of PAHs and PCBs in land treatment units; a favorable match was found between them. Model simulations were performed to predict on-going biodegradation behavior of PAHs and PCBs in land treatment units. Simulation results indicate that complete biostabilization will be achieved when the concentration of reversibly sorbed chemical (S _RA) reduces to undetectable levels, with a certain amount of irreversibly sequestrated residual chemical (S _IA) remaining within the soil particle solid phase. The residual fraction (S _IA) tends to lose its original chemical and biological activity, and hence, is much less available, toxic, and mobile than the “free” compounds. Therefore, little or no PAHs and PCBs will leach from the treatment site and constitutes no threat to human health or the environment. Biotreatment of PAHs and PCBs can be terminated accordingly. Results from the pilot-scale testing data and model calculations also suggest that a significant fraction (10–30%) of high-molecular-weight PAHs and PCBs could be sequestrated and become unavailable for biodegradation. Bioavailability (large K _d , i.e., slow desorption rate) is the key factor limiting the PAHs degradation. However, both bioavailability and bioactivity (K in Monod kinetics, i.e., number of microbes, nutrients, and electron acceptor, etc.) regulate PCBs biodegradation. The sequential active–passive biotreatment can be a cost-effective approach for remediation of highly hydrophobic organic contaminants. The mathematical model proposed here would be useful in the design and operation of such organic chemical biodegradation processes on remediation sites.     

Predicting the Phytoextraction Duration to Remediate Heavy Metal Contaminated Soils

The applicability of phytoextraction to remediate soils contaminated with heavy metals (HMs) depends on, amongst others, the duration before remediation is completed. The impact of changes in the HM content in soil occurring during remediation on plant uptake has to be considered in order to obtain a reliable estimate of the phytoextraction duration. To simulate the decrease in the HM content in soil and to assess the resulting decrease in the uptake of HMs by plants, contaminated soil was mixed with uncontaminated, but otherwise similar soil. Uptake of Cd, Pb, and Zn by the indicator plant Lupinus hartwegii and the Zn hyperaccumulator Thlaspi caerulescens (La Calamine ecotype) was a log-linear function of the in-situ measured HM soil solution concentrations. Over a wide range in dissolved Cd and Zn concentrations, uptake of these HMs by T. caerulescens was (much) greater than by L. hartwegii. Experimentally derived regression models describing the relationships between soil, soil solution, and plant were implemented in a HM mass balance model used to obtain estimates of the phytoextraction duration. For our target soils, estimates of the Cd phytoextraction duration using L. hartwegii or T. caerulescens increased significantly by more than 100 or 50 years when experimental soil—soil solution—plant relationships were used instead of the assumption of constant plant uptake of Cd. The two approaches gave similar results for phytoextraction of Zn by T. caerulescens.     

In situ Remediation of DDT-contaminated Soil Using a Two-Phase Cosolvent Flushing-Fungal Biosorption Process

The effectiveness of cosolvent soil flushing and fungal biosorption for the remediation of p,p′-DDT-contaminated soil was evaluated usingpacked soil columns in order to simulate an in situ soil flushing technique. Greater than 95% of p,p′-DDT (940 mg kg^-1) was desorbed from the soil by flushing with 40 or 80% 1-propanol. Increasing the cosolvent volume fraction increased the rate of p,p′-DDT removal from the soil, however, the extent of p,p′-DDT removal was not enhanced. A further enhancement in therate of p,p′-DDT removal was achieved by increasing the cosolventflow rate from 6 ml hr^-1 to 12 ml hr^-1 (pore water velocity from 18.9 to 37.8 cm hr^-1). The desorbed p,p′-DDT was removed from cosolvent wash solutions by partitioning onto fungal biomass. Biosorption of p,p′-DDT resulted in low concentrations of the organochlorine (3.3 μg ml^-1) remaining in thecosolvent effluent indicating that the cosolvent could be reused for further p,p′-DDT desorption. Using this technique, between 53 and 95 pore volumes were required to reduce p,p′-DDT concentrationsfrom 990 mg kg^-1 to below Australian and New Zealand Environmentaland Conservation Council (ANZECC) guidelines (50 mg kg^-1).     

利用生物活性污染物剥离技术修复Hg污染的工业土壤

The method to remove bioavailable amounts of heavy metals from a contaminated soil by using plants is defined as bioavailable contaminant stripping (BCS) and could safely be applied if the soil’s long-term ability to replenish the bioavailable pool is known. The aim of this study was to evaluate the ability of three common plant species selected, Brassica juncea, Poa annua, and Helianthus annus, to remove bioavailable amounts of mercury (Hg) from a contaminated industrial soil containing 15.1 mg kg-1 Hg. Trials were carried out under greenhouse conditions using pots (mesocosms). According to the precautionary principle, we modified the BCS remediation approach by adding a new step, in which mercury bioavailability was increased by the addition of a strong mobilizing agent, ammonium thiosulphate, (NH 4 ) 2 S 2 O 3 , to obtain an estimate of the likely long-term bioavailable Hg pool. The modified BCS remediation approach was called enhanced bioavailable contaminant stripping (EBCS). After one growth cycle, nearly all the bioavailable mercury (95.7%) was removed and the metal remaining in the soil was considered inert since it was neither extractable by (NH 4 ) 2 S 2 O 3 nor taken up by plants during a second growth cycle. The results demonstrated that EBCS appeared promising since it removed the most dangerous metal forms while substantially shortening the cleanup time.     

A minimum data set for evaluating the ecological soil functions in remediation projects

Purpose

Soil functioning becomes a matter of growing concern in soil remediation projects as, apart from preparing contaminated land for construction purposes, some parts of the sites are usually transformed into green spaces for recreation and inspiration. The objective of this paper is to develop and apply a minimum data set (MDS) for evaluating the ecological soil functions for green areas in remediation projects.

Materials and methods

The MDS was chosen from the previous applications in literature. Using a nonlinear scoring algorithm to transform observed data into sub-scores for evaluating ecological soil functions, the MDS was applied on the Kvillebäcken site in Sweden. The mean sub-scores of the individual soil quality indicators (SQIs) were integrated into a soil quality index to classify the soil into one of the five soil classes. Monte Carlo simulations were used to treat the uncertainties in the predicted soil class resulting from spatial heterogeneity of SQIs, a limited sampling size, and analytical errors.

Results and discussion

The suggested MDS consists of soil texture, content of coarse material, available water capacity, organic matter content, potentially mineralizable nitrogen, pH, and available phosphorus. The high mean sub-score for organic matter at Kvillebäcken indicated that the soil was rich on organic matter thus having a good water storage and nutrient cycling potential. However, the low mean sub-score for potentially mineralizable nitrogen indicated limited biological activity in the soil. The low mean sub-score for the content of coarse fragments indicated plant rooting limitations. Further, the soil quality index (that integrates the sub-scores for SQIs) corresponded to soil class 3 and a medium soil performance with a high certainty.

Conclusions

The suggested MDS can provide practitioners with relevant basic information on soil’s ability to carry out its ecological functions. The suggested scoring method helps to interpret and integrate information from different SQIs into a decision-making process in remediation projects.     

From Media to Molecules: New Approaches to the Detection of Micro-organisms in Water

Present methods for the detection of micro-organisms in the environment are slow, inefficient and often unreliable. Alternative approaches which are reliable and rapid, enabling results to be obtained within one working day, are required. The development of molecular techniques, in particular in situ hybridisation offers the potential for rapid and specific assays. This paper describes the use of oligonucleotide probes targeted against the 16S and 18S ribosomal RNA molecules of Escherichia coli and Cryptosporidium parvum for rapid and specific detection. In situ hybridisations with biotinylated peptide nucleic acid (PNA) probes in combination with the tyramide signal amplification (TSA) system enabled the specific detection of Escherichia coli and Cryptosporidium parvum within 3 hours. The C. parvum assay provided a species-specific alternative to the currently available fluorescent antibody approach.     

Effects of iron-based amendments on soil structure: a lab experiment using soil micromorphology and image analysis of pores

Purpose

Recent trends in soil green and sustainable remediation require an increased attention on environmental effects. The physical consequences of remediation practices on soil structure are very rarely investigated.

Material and methods

A laboratory experiment was carried out by adding iron grit to a sand (S), a silt loam (L), and a clay (C) soil subjected to several wetting-drying cycles. The physical effects of the treatment on soil pore system were identified and quantified combining physical measurements on repacked samples with image analysis of pores on resin-impregnated soil blocks and micromorphological analysis on thin sections.

Results and discussion

A negligible reduction of total porosity (P) resulted in S, and a slight increase was observed in the L and C soils. However, an important impact on soil structure was identified in pore size range >10 μm for the L and C soils, with the formation of new pores related to the differential shrink-swell behavior between soil matrix and added iron grains. Different plasticity of these soils also played a role in planar pore formation.

Conclusions

Effects of the addition of iron grit on soil pore system are strongly dependent on soil physical properties. The performed experiment showed that iron-based amendments can improve soil structure in low-plastic shrink-swell soil increasing porosity in the range of transmission pores (50–500 μm). This study showed the high potential of soil micromorphology and pore image analysis in order to evaluate the environmental impact of soil remediation practices.     

Photodegradation of Tri(Chloropropyl) Phosphate Solution by UV/O3

The prediction of the time and the efficiency of the remediation of contaminated soils using soil vapor extraction remain a difficult challenge to the scientific community and consultants. This work reports the development of multiple linear regression and artificial neural network models to predict the remediation time and efficiency of soil vapor extractions performed in soils contaminated separately with benzene, toluene, ethylbenzene, xylene, trichloroethylene, and perchloroethylene. The results demonstrated that the artificial neural network approach presents better performances when compared with multiple linear regression models. The artificial neural network model allowed an accurate prediction of remediation time and efficiency based on only soil and pollutants characteristics, and consequently allowing a simple and quick previous evaluation of the process viability.     

Evaluation of the atzB gene as a functional marker for the simazine-degrading potential of an agricultural soil

The occurrence of natural simazine-degrading bacteria could be an important limiting factor to the use of the herbicide in those agricultural soils with a wide history of herbicide applications. In this work the potential of an agricultural soil to degrade simazine and the effect of the addition of urea was assayed in both fertilised and unfertilised soil microcosms. A culture-independent approach based on the fluorescence in situ hybridisation (FISH) technique, using a specific oligonucleotide probe (AtzB1), was applied to detect simazine-degrading bacteria in the soil microcosms. The presence of the atzABC genes in the agricultural soil was confirmed by PCR from soil-extracted DNA. The percentage of AtzB1 probe-target cells in the urea-untreated soil was higher than in the urea-treated one. Moreover, the greatest percentage of AtzB1 probe-target cells in the urea-untreated soil was accompanied by a greater degradation rate, compared to the urea-fertilised one. Our results indicate that the proposed approach was sensitive enough to detect changes in the natural simazine degradation capacity of the soil after fertilisation practices, which typically involve a nitrogen increase.     

Physical extent,frequency, and intensity of phosphatase activity varies on soil profiles across a Douglas-fir chronosequence

In forest soils, the availability of phosphate is largely dependent on phosphatase activity. We used soil imprinting to compare in situ activity and fine-scale distribution of phosphatase on soil profiles located across forest chronosequences of four age classes young (5–6 yrs), canopy closure (24–30 yrs), stem exclusion (61–71 yrs), and older (90–103 yrs) of mixed Douglas-fir/paper birch stands regenerated after fire or clearcutting in southern interior British Columbia, Canada. Chromatography paper treated with a mixture of substrate and colorimetric reagent was applied directly to vertical soil surfaces, accessed through root windows. Stands older than 61 years had both the highest level of in situ phosphatase activity and larger, more intense regions of activity. Bray-extractable phosphorus was negatively related to imprintable phosphatase activity. We compared the changes in phosphatase activity with differences in the ectomycorrhizal fungal (EMF) community that had been documented previously in the same stands. Of 84 ectomycorrhizal fungi found on roots in at least two of the stand-age classes, eight taxa were positively correlated and one taxon (Rhizopogon vinicolor/vesiculosus) negatively correlated with high phosphatase activity. The frequency of three taxa appeared to be positively correlated with larger areas of activity on the soil profiles. By using an imprinting approach, this study was able to demonstrate, for the first time, that in situ phosphatase activity and physical attributes of that activity (i.e., number, size, and relative rates of each area of activity) were related to concentrations of soil nutrients and with the frequency of individual ectomycorrhizal fungi.     

Flumequine Uptake and the Aquatic Duckweed, Lemna minor L.

Phytotoxicity of Flumequine (F) on the aquatic duckweed, Lemna minor L., and plant drug uptake were evaluated by a simple ecotoxicological test. Flumequine, at all concentrations between 50 and 1000 μg L^-1 tested, affected the plant growth: leaves and roots were damaged, but duckweed continued to grow on a five weeks period. Furthermore, increasing drug concentrations decreased the chlorophyll b content in plants. These effects depend on F uptake by plants, which is quite high (from 0.72 to 13.93 μg g^-1 plant dry weight). Based on this activity, Lemna can be taken into consideration as a tool for in situ remediation of drug contaminated waters: the presence of Lemna significantly lower the F concentration in culture media on a five weeks period. Results strongly support its remediation capability.     

Assessment of the stability of chromium in remedied soils by Pannonibacter phragmitetus BB and its risk to groundwater

Purpose

Acid rain can accelerate the acidification of the chromium-contaminated soils, resulting in chromium releasing into soil solution and causing ecological risk. The current study aims to investigate the release of chromium in the remedied soils by Pannonibacter phragmitetus BB under the simulated acid rain leaching and to assess its risk to groundwater.

Materials and methods

P. phragmitetus BB was utilized to remedy the Cr(VI)-contaminated soils at two levels (80 and 1,276 mg kg^?1) by the column leaching experiment, and the chemical remediation with ferrous sulfate was used as a control. The remedied soils by P. phragmitetus BB and ferrous sulfate were leached under the simulated acid rain to evaluate the release of chromium. Furthermore, the risk of chromium release from the remedied soils to the groundwater was assessed by a fuzzy comprehensive evaluation method.

Results and discussion

The average concentrations of water-soluble Cr(VI) in the remedied soils by P. phragmitetus BB were reduced to less than 5.0 mg kg^?1. Under leaching situation with the simulated acid rain, the release of total chromium and Cr(VI) from the remedied soils by P. phragmitetus BB and ferrous sulfate declined rapidly with the extended leaching time. However, the release amounts of total chromium and Cr(VI) from the remedied soil by P. phragmitetus BB more efficiently deceased as compared with that by ferrous sulfate remediation. Carbonate-bounded, exchangeable, and organics-bonded chromium were the major chromium-releasing sources under the simulated rain leaching. After microbial remediation with P. phragmitetus BB and chemical remediation with ferrous sulfate, the risk grades of the remedied soils to groundwater declined from classes 11 to 5 and 6, respectively.

Conclusions

The risks of the remedied soils by both microbial remediation with P. phragmitetus BB and chemical remediation with ferrous sulfate to groundwater effectively decreased and microbial remediation more significantly declined the chromium risk to groundwater than chemical remediation.     

A method for linking in situ activities of hydrolytic enzymes to associated organisms in forest soils

A root window-based, enzyme-imprinted, membrane system has been modified to enable visualization of the activities of hydrolytic enzymes (acid phosphatase, aminopeptidase, chitinase, and β-glucosidase) in situ in forest soils. The approach can be used to correlate the distribution of enzyme activity with visible features such as roots, mycorrhizas, or mycelial mats. In addition, it enables accurate spatial soil sampling for analysis of microbial communities associated with enzyme activities. The substrates are colorimetric conjugates of napthol, where color develops instantly in the field, or fluorimetric conjugates of 4-methylumbelliferone, whose fluorescent products are detected by a gel-documenting system. The method will allow important questions about the relationship between taxonomic and functional diversity of soil microorganisms to be addressed and identification of enzyme activity hot-spots in soil.     

推进土壤污染防控与修复 厚植农业高质量发展根基

科学有效地开展土壤污染防控与治理修复,从农产品质量安全的源头上保证产地环境安全,已日益成为公众关注的热点。本文阐述了新时代土壤科学的新使命与功能定位,分析了我国农用地土壤污染防控与修复研究和实践的进展动态,从促进农业绿色发展和高质量发展出发,提出了我国土壤污染防控与治理修复及产业化发展的战略重点与技术路径。     

Stable isotope analysis reveals whether soil-living elaterid larvae move between agricultural crops

Tracking the movement of soil-living herbivores is difficult, albeit important for understanding their spatial ecology as well as for pest management. In this study the movement of Agriotes obscurus larvae between plots harbouring isotopically different plants was examined. Neither between maize and wheat nor between maize and grassland movement could be detected. These data suggest that Agriotes larvae rarely disperse between crops as long as local food supply is sufficient. Moreover, the current approach provides a new means to study the dispersal of soil invertebrates in situ.     

Responses of Saline Soil Properties and Cotton Growth to Different Organic Amendments

Application of organic waste to saline alkaline soils is considered to be a good practice for soil remediation. The effects of applying different organic amendments (e.g., cattle dung, vermicompost, biofertilizer) and earthworm inoculations (Eisenia fetida) on saline soils and cotton growth were investigated during 1 year of cotton cultivation. Compared to the control (applied with inorganic NPK fertilizer), applying organic amendments improved soil physicochemical properties. Biofertilizer application improved available nutrient content, reduced short-term soil electrical conductivity, and produced the highest cotton yield, whereas cattle dung and vermicompost applications resulted in higher soil organic matter content. Application of organic amendments significantly increased soil microbial biomass carbon during the flowering period, which sharply declined at harvest. This was especially true for the biofertilizer treatment, which also exhibited lower nematode abundance compared with the other organic materials. Earthworm inoculation following cattle dung application failed to significantly change soil physicochemical properties when compared to the treatments without earthworm inoculation. Results suggest that biofertilizer application to saline soil would improve soil nutrient status in the short-term, whereas cattle dung application would improve soil organic matter content and increase soil organism abundance to a greater extent. However, different strategies might be required for long-term saline soil remediation.     

Evaluation of fly ash,apatite and rice straw derived-biochar in varying combinations for in situ remediation of soils contaminated with multiple heavy metals

ABSTRACT

In

-situ sorbent amendment is a relatively low-cost, low-impact approach for remediation of soil contaminated with heavy metals (HMs), and thus is considered a way to be favored in developing countries. In this study, materials of non-hazardous, alkaline agronomic and industrial by-products were used as sorbents to explore their capacity of in situ immobilization of multiple HMs in mining-impacted arable soil. These sorbents included fly ash (FA), biochar (BC) and apatite (AP) and they were implemented with varying ratios of combinations. Results of soil microcosm tests showed that after incubation for 90 days, concentrations of Pb, Zn, and Cd in their exchangeable forms determined by a sequential extraction method significantly decreased in amended soils, as opposed to the unamended control. Of the five sets of amendments, the composite of FA, BC, and AP resulted in the maximum reduction (up to 80%) in the mobility of Pb, Zn, and Cd in soils. The mechanisms underlying the immobilization of HMs in amended soils might involve processes of surface precipitation, ion exchange and complexation, in which the physicochemical properties of sorbent materials played an important role. The immobilization efficacy of sorbent amendments on HMs in soil was further supported by pot experiments in which significant inhibition of HM accumulation in the belowground and aboveground tissues of maize was observed after 50-day cultivation in amended soils as compared with control soil. Together, these results suggest that the application of cost-saving and environmentally friendly materials derived from wastes as sorbents to remediate soils contaminated with multiple HMs is promising for developing countries like Vietnam.