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Highlights: [•] Litter quality is a major determinant of decomposition. [•] Mixed-species litter can give a negative and positive additive effect. [•] Stand type effect was observed for the forest litter mixture only. [•] Nutrient depletion can occur in long-term in Eucalyptus plantation. [•] Final decay rate is also essential to explain the remaining mass. [Copyright &y& Elsevier]

To identify different NO3 − sources in surface water and to estimate their proportional contribution to the nitrate mixture in surface water, a dual isotope and a Bayesian isotope mixing model have been applied for six different surface waters affected by agriculture, greenhouses in an agricultural area, and households. Annual mean δ15N–NO3 − were between 8.0 and 19.4‰, while annual mean δ18O–NO3 − were given by 4.5–30.7‰. SIAR was used to estimate the proportional contribution of five potential NO3 − sources (NO3 − in precipitation, NO3 − fertilizer, NH4 + in fertilizer and rain, soil N, and manure and sewage). SIAR showed that “manure and sewage” contributed highest, “soil N”, “NO3 − fertilizer” and “NH4 + in fertilizer and rain” contributed middle, and “NO3 − in precipitation” contributed least. The SIAR output can be considered as a “fingerprint” for the NO3 − source contributions. However, the wide range of isotope values observed in surface water and of the NO3 − sources limit its applicability. [Copyright &y& Elsevier]

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]

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]

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]

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]

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]

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]

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]

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]