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Landfill cover soils oxidize a considerable fraction of the methane produced by landfilled waste. Despite many efforts this oxidation is still poorly quantified. In order to reduce the uncertainties associated with methane oxidation in landfill cover soils, a simulation model was developed that incorporates Stefan–Maxwell diffusion, methane oxidation, and methanotrophic growth. The growth model was calibrated to laboratory data from an earlier study. There was an excellent agreement between the model and the experimental data. Therefore, the model is highly applicable to laboratory column studies, but it has not been validated with field data. A sensitivity analysis showed that the model is most sensitive to the parameter expressing the maximum attainable methanotrophic activity of the soil. Temperature and soil moisture are predicted to be the environmental factors affecting the methane oxidizing capacity of a landfill cover soil the most. Once validated with field data, the model will enable a year-round estimate of the methane oxidizing capacity of a landfill cover soil. [Copyright &y& Elsevier]

Presents a study conducted on factors influencing methane emmission from a freshwater wetland in Belgium. Monitoring of drainage capacity and depth of methane production influence on methane emmision; Statistical analysis of emmision data from March to December, 1997; What sites with bad natural drainage and fairly bad natural drainage showed; Description of field experiment; Results of the study.

Abstract: Inhibitors are applied to improve the efficiency of N fertilizer use and to reduce N losses from the soil. However, little information is available on the effects of a urease inhibitor, hydroquinone (HQ), and a nitrification inhibitor, dicyandiamide (DCD), on urea-derived mineral N in the rhizosphere of rice plants and in the standing water. Furthermore, this is important to understand the contribution of rice plants to gaseous N losses in the presence of inhibitor(s). A rhizobox was used to simultaneously study urea-derived mineral N in the soil at increasing distances from rice roots, and the effect of growing plants on the behavior of fertilizer-N in soil. The combined application of urea (U) with DCD showed a significantly positive effect on rice growth. The redox potentials in the rhizosphere soil were higher in the presence than in the absence of DCD, especially when rice plants entered their vigorous growth stage. During the entire experimental period, NH4 +–N concentrations in the rhizosphere of rice plants were smaller in the U+DCD and U+HQ+DCD treatments than in the U and U+HQ treatments. On days 20 and 60 after fertilization, the U+DCD and U+HQ+DCD treatments showed a smaller concentration of (NO3 − +NO2 −)–N in soil less than 0.5cm from the rhizobox, compared to the U treatment. During the early period of rice growth, the NH4 +–N concentration of the standing water was higher in the presence than in the absence of DCD. However, there were no significant differences in NH4 +–N among all treatments after 20 days. In the absence of rice plants, also, the application of DCD and especially DCD and HQ, always increased the level of NH4 +–N and pH in the standing water. Thus, rice plants might reduce potential gaseous N losses from a urea-fertilized, flooded soil, due to the stimulating effect on rice growth in the presence of DCD or DCD+HQ. The N2O emissions from the urea-fertilized, rice-planted soil significantly decreased when DCD or DCD+HQ was used. From the results obtained, we conclude that DCD and DCD+HQ together with U can be an effective tool to improving crop growth and reducing N loss as N2O in rice cultivation, and that the use of a rhizobox is useful to study the interaction between plant uptake and the behavior of fertilizer-N in soil. [Copyright &y& Elsevier]

Abstract: Liming or vermicomposting eliminates pathogens from wastewater sludge, but might affect CO2 and N2O emissions when added to soil. Soil incubated at 40%, 60%, 80% and 100% of its water holding capacity (WHC) was amended with limed or unlimed wastewater sludge, vermicompost or inorganic fertilizer, while emissions of N2O and CO2 and mineral N concentrations were monitored in aerobic incubation experiment for 7 days. Application of unlimed wastewater sludge significantly increased the emission of CO2 compared to the unamended soil, but not the other treatments except when unlimed wastewater sludge was added to soil incubated at 60% WHC. The emission of CO2, was generally largest in soil incubated at 60% WHC and lowest in soil incubated at 100% WHC. The emission of N2O after 1 day was significantly larger in soil amended with unlimed wastewater sludge compared to the other treatments, but not when soil was incubated at 100% WHC. The emission of N2O increased with increased soil water content. The concentration of NH4 + was largest in soil amended with limed or unlimed wastewater sludge and lowest in the unamended soil and soil water content had no clear effect on it. In soil incubated at 40%, 60% and 80% WHC, the largest amount of NO3 − was found in soil amended with inorganic fertilizer and vermicompost and the lowest in the soil amended with unlimed wastewater sludge. The concentration of NO3 − in soil decreased when the soil water content increased in all treatments, except in the soil amended with unlimed wastewater sludge. It was found that water content affected the emission of CO2 of N2O and the concentration of NO3 −, but not the amount of NH4 + and NO2 − in soil. Application of unlimed wastewater sludge increased the emissions of CO2 and N2O and the concentrations of NH4 +, but decreased the amount of NO3 − in soil. [Copyright &y& Elsevier]

Abstract: A field plots experiment was carried out to assess the effects of repeated application of municipal solid waste compost in comparison to farmyard manure on the accumulation and distribution of trace metals, as well as organic carbon and nitrogen in Tunisian calcareous soil. Compared with untreated soil, the application of the two organic amendments significantly increased the organic carbon and nitrogen contents of the soil. Particle-size fractionations showed that carbon and nitrogen were mainly found to occur in the macro-organic matter fraction (80%). The two organic amendments significantly increased organic carbon in the macro-organic and mineral >150μm fraction and the 150–50μm fraction, as well as the organic nitrogen in 150–50μm and macro-organic fraction. Compared with farmyard manure, municipal solid waste compost significantly increased total Cd, Cu, Pb and Zn contents in the topsoil. These trace metals were mainly present in the macro-organic matter fraction. Significant increases of Cu, Zn and Pb were detected in the 150–50μm, <50μm and macro-organic fractions after application of municipal solid waste compost. A significant increase of Cd content was only observed in the 150–50μm fraction. The trace metals also showed different fractionation patterns when the BCR sequential extraction scheme was applied on untreated and compost-treated soil. The residual fraction was found to be the major fraction, especially for Cu, Cr, Ni and Zn. In contrast, Cd was mainly present in the acid-extractable and reducible fraction, whereas Pb was mainly associated with the reducible fraction. [Copyright &y& Elsevier]

Nitrate (NO3 −) contamination of surface- and groundwater is an environmental problem in many regions of the world with intensive agriculture and high population densities. Knowledge of the sources of NO3 − contamination in water is important for better management of water quality. Stable nitrogen (δ 15N) and oxygen (δ 18O) isotope data of NO3 − have been frequently used to identify NO3 − sources in water. This review summarizes typical δ 15N- and δ 18O-NO3 − ranges of known NO3 − sources, interprets constraints and future outlooks to quantify NO3 − sources, and describes three analytical techniques (“ion-exchange method”, “bacterial denitrification method”, and “cadmium reduction method”) for δ 15N- and δ 18O-NO3 − determination. Isotopic data can provide evidence for the presence of dominant NO3 − sources. However, quantification, including uncertainty assessment, is lacking when multiple NO3 − sources are present. Moreover, fractionation processes are often ignored, but may largely constrain the accuracy of NO3 − source identification. These problems can be overcome if (1) NO3 − isotopic data are combined with co-migrating discriminators of NO3 − sources (e.g. 11B), which are not affected by transformation processes, (2) contributions of different NO3 − sources can be quantified via linear mixing models (e.g. SIAR), and (3) precise, accurate and high throughput isotope analytical techniques become available. [Copyright &y& Elsevier]

Abstract: Soils in Mexico are often contaminated with hydrocarbons and addition of waste water sludge and earthworms accelerates their removal. However, little is known how contamination and subsequent bioremediation affects emissions of N2O and CO2. A laboratory study was done to investigate the effect of waste water sludge and the earthworm Eisenia fetida on emission of N2O and CO2 in a sandy loam soil contaminated with the polycyclic aromatic hydrocarbons (PAHs): phenanthrene, anthracene and benzo(a)pyrene. Emissions of N2O and CO2, and concentrations of inorganic N (ammonium (NH4 +), nitrite (NO2 −) nitrate (NO3 −)) were monitored after 0, 5, 24, 72 and 168h. Adding E. fetida to the PAHs contaminated soil increased CO2 production rate significantly 2.0 times independent of the addition of sludge. The N2O emission rate from unamended soil expressed on a daily base was 5μgNkg−1 d−1 for the first 2h and increased to a maximum of 325μgNkg−1 d−1 after 48h and then decreased to 10μgNkg−1 d−1 after 168h. Addition of PAHs, E. fetida or PAHs+ E. fetida had no significant effect on the N2O emission rate. Adding sludge to the soil sharply increased the N2O emission rate to >400μgNkg−1 d−1 for the entire incubation with a maximum of 1134μgNkg−1 d−1 after 48h. Addition of E. fetida, PAHs or PAHs+ E. fetida to the sludge-amended soil reduced the N2O emission rate significantly compared to soil amended with sludge after 24h. It was found that contaminating soil with PAHs and adding earthworms had no effect on emissions of N2O. Emission of N2O, however, increased in sludge-amended soil, but addition of earthworms to this soil and contamination reduced it. [Copyright &y& Elsevier]

Abstract: A technique to measure biological methane oxidation in landfill cover soils that is gaining increased interest is the measurement of stable isotope fractionation in the methane. Usually to quantify methane oxidation, only fractionation by oxidation is taken into account. Recently it was shown that neglecting the isotope fractionation by diffusion results in underestimation of the methane oxidation. In this study a simulation model was developed that describes gas transport and methane oxidation in landfill cover soils. The model distinguishes between 12CH4, 13CH4, and 12CH3D explicitly, and includes isotope fractionation by diffusion and oxidation. To evaluate the model, the simulations were compared with column experiments from previous studies. The predicted concentration profiles and isotopic profiles match the measured ones very well, with a root mean square deviation (RMSD) of 1.7vol% in the concentration and a RMSD of 0.8‰ in the δ 13C value, with δ 13C the relative 13C abundance as compared to an international standard. Overall, the comparison shows that a model-based isotope approach for the determination of methane oxidation efficiencies is feasible and superior to existing isotope methods. [Copyright &y& Elsevier]

Approximately 60% of Mexico (1.973 × 106 km2) is arid or semi-arid with vegetation dominated by N2 fixing shrubs, such as mesquite (Prosopis juliflora). Little is known, however, how these ecosystems contribute to production of nitrous oxide (N2O), a known greenhouse gas. We investigated this by adding inorganic fertilizer (20 mg ammonium (NH4+) N kg-1 soil) to soil at different water contents (40%, 60%, 80%, and 100% of water-holding capacity (WHC)) sampled under the canopy of mesquite and outside its canopy, while production of carbon dioxide (CO2) and nitrous oxide (N2O), and dynamics NH4+, nitrite (NO2-), and nitrate (NO3-)) were monitored. The CO2 production rate was 1.5 times larger for soil sampled under the canopy of mesquite compared to soil sampled outside the canopy of shrubs and lower in soil incubated at 100% WHC compared to the other treatments. Production of N2O increased with increased water content within the first day, but decreased in soil at 80% and 100% WHC thereafter. The production of N2O was 1.9 times larger for soil sampled under the canopy of mesquite compared to soil sampled outside its canopy. The addition of 20 mg NH4+-N increased production of N2O 1.8-fold. It was found that the cumulative production of N2O was larger from soil sampled under the canopy of mesquite than outside it when amended with inorganic fertilizer and increased with increased water content of the soil within a day. The relationship between the emission of CO2 and N2O, water-holding capacity are discussed. [ABSTRACT FROM AUTHOR]

The effect of straw and vinasses on the N mineralization–immobilization turnover of celery residues was investigated in a field experiment in Flanders (Belgium). The field was laid out in raised beds on a loamy sand soil. At the start of the experiment, 15N-labelled celery residues (4t dry matter (DM)ha−1) were mixed with straw (12tDMha−1) in order to immobilize the released celery-N followed by an incorporation of vinasses (4tDMha−1) after 200 days aiming to remineralize the immobilized N. Total N, mineral N and their 15N enrichments as well as microbial biomass N were determined at regular time intervals. During the first 62 days after the incorporation, straw immobilized the celery derived 15N in the microbial biomass and reduced the total celery-15N losses from the top 25cm by 38%. However, after 62 days, the N immobilization ceased due to low temperatures (<10°C) in the raised beds, and was followed by natural remineralization of immobilized celery-15N (without addition of vinasses) at a moment when the risk of nitrate leaching was still high. Hence, straw was not able to reduce the celery-N losses during the complete winter period. The addition of vinasses in spring caused no real positive priming effect, although it did increase the amount of remineralized celery-15N (7.6% of celery derived 15N) compared to the straw treatment without vinasses (1.7% of celery derived 15N) probably due to an apparent added nitrogen interaction caused by displacement reactions with the soil microbial biomass. In conclusion, in raised beds, it is not possible to reduce nitrate leaching and to achieve a synchronization between the N release from crop residues and N demand by the following crop by using straw and vinasses to manipulate the N release from crop residues. [Copyright &y& Elsevier]

A new on-line analytical setup for 15N measurements of total dissolved nitrogen (TDN) has been developed through the coupling of a high-temperature catalytic (Ce(IV)O2) oxidation furnace, a Cu reduction furnace, and an isotope ratio mass spectrometer. The detection limit for accurate δ15N measurements is 20 mg of N L-1. For N-containing compounds dissolved in water, a standard deviation on N concentration measurements of 0.2 mg of N L-1, independent of N concentration, has been found. Reproducibility on δ15N increased with increasing N concentration, with standard deviations varying from 0.8 to 0.1‰ in the range of 20-100 mg of N L-1. Salt matrixes, in which the N species might be dissolved, could influence the analysis capacity and continuity, mainly at concentrations above 0.1 M. To our knowledge, this system is the first successful on-line setup capable of performing routine δ15N and N concentration measurements of the TDN pool. Potential applications are large and are believed to result in an increased insight in N cycling and dissolved organic nitrogen behavior in terrestrial and aquatic ecosystems. [ABSTRACT FROM AUTHOR]

Abstract: Twenty-two long-term measurements of direct N2O emissions from soils in an intensive agricultural area were used for the validation of the process-based DNDC model (version 8.3P). Model simulations were evaluated for temporal patterns of N2O, NH4 +, NO3 − and water-filled pore space (WFPS) and total N2O emissions. Several soil and crop input parameter adjustments to the model were evaluated but only the recalculation of the WFPS at wilting point and at field capacity, using pedotransfer functions, resulted in a clear improvement of the simulated variables (WFPS in all cases, N2O in some cases). Therefore, only this adjustment was made to DNDC 8.3P. This change, however, resulted for some cases (both cropland and grassland) in retardation of nitrate leaching and to a lesser extent of NH4 + to the deeper soil layers. The goodness of fit of the simulated temporal pattern of N2O varied considerably between sites. The total simulated N2O emissions from cropland showed a good agreement with the measurements, although there was a systematic overestimation of 7.4kgN2O-Nha−1. Grassland soils, in contrast, gave a low agreement between total simulated and measured N2O losses. On the basis of all measured data a regional emission factor of 3.16 with a 95% confidence interval of −0.89 to 7.21 could be calculated. DNDC simulations resulted in an emission factor of 6.49 with a 95% confidence interval of 4.04–8.93. The overall outcome of the N2O emission measurements and DNDC simulations were compared with several empirical regression models, which may be applicable for a temperate climate system. All of the tested regression models showed reliable results up to a N2O emission of 10kgN2O-Nha−1. Higher emissions, however, were systematically underestimated. Though DNDC both under- and overestimated specific sites, the general agreement, over the whole range between measurements and simulations of total N2O losses (simulations=0.82×meas.+6.2), was better than for the different regression models. [Copyright &y& Elsevier]

Following mineralization of N-rich crop residues, large amounts of mineral N can be released into the soil. Manipulating N mineralization of crop residues may be an option to reduce NO3- in soil. The potential to manipulate the N release from vegetable crop residues by using organic wastes was tested under field conditions. At the start of the experiment, cauliflower (Brassica oleracea L. var. botrytis L.) residues (~73 Mg fresh matter ha 1) together with an immobilizer waste (~5 Mg C ha-1 of straw, green waste compost, sawdust, or paper sludge) were incorporated into a silt loam soil. After 154 d, a remineralizing waste (~1 Mg C ha-1 of vinasse or dairy sludge) was incorporated. During the field experiment, the mineral N content in the soil was measured at regular time intervals, and net N release, NO3- leaching, and denitrification were simulated using a N mineralization-immobilization model coupled to a N3- leaching model. Straw, green waste compost, and sawdust were able to immobilize between 54 and 68% of the N released by the cauliflower residues and reduced N3- leaching by 56 to 68%. Paper sludge released an extra amount of N due to its low C/N ratio. No consistent remineralization of N could be found in any of the treatments, probably due to an unsuitable composition of the remineralizer wastes. Manipulating N release of N-rich crop residues by using organic wastes may be a suitable method to reduce N3- leaching; however, stimulating remineralization of immobilized N by the start of the following spring may not be easy to achieve. [ABSTRACT FROM AUTHOR]

Abstract: Landfilling is one of the most common ways of municipal solid waste disposal. Degradation of organic waste produces CH4 and other landfill gases that significantly contribute to global warming. However, before entering the atmosphere, part of the produced CH4 can be oxidised while passing through the landfill cover. In the present study, the oxidation rate of CH4 was studied with various types of compost as possible landfill cover. The influence of incubation time, moisture content and temperature on the CH4 oxidation capacity of different types of compost was examined. It was observed that the influence of moisture content and temperature on methane oxidation is time-dependent. Maximum oxidation rates were observed at moisture contents ranging from 45% to 110% (dry weight basis), while the optimum temperature ranged from 15 to 30°C. [Copyright &y& Elsevier]

Abstract: In a laboratory study, organic biological wastes (OBW) were screened for their potential to manipulate the N release from vegetable crop residues in two phases: an immobilization and remineralization phase. During the first phase, celery leaves (Apium graveolens L.) were mixed with an immobilizer waste (straw, two green waste composts (GWC1 and GWC2), saw dust, paper sludge and tannic acid) in order to immobilize N released from crop residues. During the second phase, the treatments received a remineralizer waste (malting sludge, vinasses, molasses and dairy sludge) in order to stimulate remineralization of immobilized N. Straw showed the most pronounced N immobilization (on average 30.2mgNkg−1). N immobilization with tannic acid, saw dust and GWC2 was slower and less pronounced (on average 16.4, 15.9 and 8.0mgNkg−1, respectively). GWC1 and paper sludge immobilized almost no N. Only when GWC1 was mixed with vinasses, remineralization was observed (up to 55.4mgNkg−1) during a 30 days period. For all other remineralizers, positive priming effects were scarce and short-lived. Manipulating the N release of N-rich crop residues may be a suitable method to reduce the nitrate concentration in soil after incorporation of crop residues. Especially, easily decomposable waste materials (i.e. low lignin content) with a large C:N ratio seem to have a potential to immobilize N. However, stimulating remineralization of immobilized N seems not easy to accomplish. [Copyright &y& Elsevier]

Old-growth forests of southern Chile represent an important reserve of temperate (rain) forests in the world. Wetter and colder forest ecosystems appear to be more efficient in conserving and recycling N such that mostly non-plant available N species are lost, which could be indicated by more depleted δ 15 N values of the soil and plants. Hydrological N loss from the old-growth forests in southern Chile occurs mainly via dissolved organic nitrogen and not via dissolved inorganic N. Forest disturbances ( e.g . fire, clear-cutting or enhanced N deposition) cause (abrupt) changes in ecosystem N-cycling processes. In this study, we hypothesized that δ 15 N signatures of soil profiles under old-growth forests could be used as an integrator for ecosystem N-cycling, and changes of these δ 15 N profiles could be valuable to assess ecosystem resilience towards disturbances. Six old-growth forests were selected in the phytogeographical region of the Valdivian rain forest in southern Chile. One of the sites has been partly burned in February 2002. First, we observed that ecosystems with higher mean annual precipitation and lower mean annual temperature were relatively more depleted in 15 N. Secondly, we found that a forest fire caused a 100-fold increase of the nitrate export and induced an enrichment of the soil δ 15 N signal in the upper 20 cm. [ABSTRACT FROM AUTHOR]

Little is known concerning the N mineralization or N immobilization of (vegetable) root residues in soil. The (bio)chemical composition of a range of vegetable root residues (large and fine roots of red cabbage, white cabbage, Brussels sprouts, savoy cabbage, and leek), and plant parts of two green manures (ryegrass and white mustard) was determined by standard chemical analysis (total C, total N, and C:N ratio) and by a modified Stevenson fractionation method (water-soluble, hemicellulose, cellulose, and lignin fraction). Fresh chopped crop residues, homogenously mixed with a sandy loam soil, were incubated during 4 months at constant temperature (21 °C) and constant moisture content (14% w/w). The net N mineralization of each residue was determined by destructive sampling. All fine roots, except these of Brussels sprouts, showed a net N release throughout the incubation. All large roots showed a slight N immobilization at the start of the incubation, but at the end of the incubation a small net N release was observed, except for Brussels sprouts. The roots of Brussels sprouts immobilized N throughout the entire incubation. The leaves of the green manures released more N than both stems (only for white mustard) and roots. It was possible to fit a first-order kinetics model to 8 of the 14 N mineralization patterns: AN(t)=AN(1-exp(-kt)). For the six other residues where the first-order model could not be fitted, the amount of N mineralized at the end of the incubation was taken as an estimate of the AN parameter. Both the mineralization parameters AN and k were correlated to a large number of (bio)chemical parameters. The amount of mineralized N, AN, was best correlated with the C:N ratio (R=-0.86), and the rate constant k was best correlated with the lignin:N ratio (R=-0.94). The predictive relationship between the N mineralization of vegetable root residues and green manures and their (bio)chemical composition has the advantage that is independent of the length of the incubation time. The critical C:N ratio, i.e. the break point between net N mineralization and net N immobilization (AN=0) was found to be 36.6. [Copyright &y& Elsevier]

Abstract Evaluations of soil organic carbon (SOC) stocks are often based on assigning a carbon density to each one of a number of ecosystems or soil classes considered, using data from soil profiles within these categories. A better approach, in which the use of classification methods by which extrapolation of SOC data to larger areas is avoided, can only be used if enough data are available at a sufficiently small scale. Over 190 000 SOC measurements (0–24 cm) have been made in the Flemish cropland (the Northern part of Belgium) in the 1989–2000 period. These SOC data were grouped into 3-year periods and as means plus standard deviation per (part of) community (polygons). This large dataset was used to calculate SOC stocks and their evolution with time, without data extrapolation. Using a detailed soil map, larger spatial groups of polygons were created based on soil texture and spatial location. Linear regression analysis showed that in the entire study area, SOC stocks had decreased or at best had remained stable. In total, a yearly decrease of 354 kton OC yr-1 was calculated, which corresponds with a net CO2 emission of 1238 kton CO2 yr-1 . Specific regions with a high carbon sequestration potential were identified, based on SOC losses during the 1989–2000 period and the mean 1999 SOC content, compared to the average SOC content of soils in Flanders with a similar soil texture. When restoring the SOC stocks to their 1990 level, we estimated the carbon sequestration potential of the Flemish cropland soils to be some 300 kton CO2 yr-1 at best, which corresponds to a 40-year restoration period. In conclusion, we can say that in regions where agricultural production is very intense, carbon sequestration in the cropland may make only a very modest contribution to a country's effort to reduce greenhouse gas emissions. [ABSTRACT FROM AUTHOR]

High autotrophic nitrogen removal rates of 858 mg N L−1 day−1 or 1.55g N m−2 day−1 were obtained in a lab-scale rotating biological contactor treating an ammonium rich influent. It was postulated that ammonium was removed as dinitrogen gas by a sequence of aerobic ammonium oxidation to nitrite taking place in the outer biofilm layer and anaerobic ammonium oxidation with nitrite as electron acceptor occuring in the deeper biofilm layer. Chemical evidence for anaerobic ammonium oxidation within intact biofilm sludge from a lab-scale rotating biological contactor could be provided, without direct identification of responsible organisms catalysing this reaction. 15N tracer techniques were used for identification and quantification of nitrogen transformations. In batch tests with biofilm sludge at dissolved oxygen concentrations lower than 0.1 mg L−1, ammonium and nitrite did react in a stoichiometric ratio of 1:1.43 thereby forming dinitrogen. 15N isotope dilution calculations revealed that anaerobic ammonium oxidation was the major nitrogen transformation leading to concomitant ammonium and nitrite removal. Isotopic analysis of the produced biogas showed that both ammonium-N and nitrite-N were incorporated in N2. [Copyright &y& Elsevier]