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The isotopic composition of soil-derived N2O can help differentiate between N2O production pathways and estimate the fraction of N2O reduced to N2. Until now, δ18O of N2O has been rarely used in the interpretation of N2O isotopic signatures because of the rather complex oxygen isotope fractionations during N2O production by denitrification. The latter process involves nitrate reduction mediated through the following three enzymes: nitrate reductase (NAR), nitrite reductase (NIR) and nitric oxide reductase (NOR). Each step removes one oxygen atom as water (H2O), which gives rise to a branching isotope effect. Moreover, denitrification intermediates may partially or fully exchange oxygen isotopes with ambient water, which is associated with an exchange isotope effect. The main objective of this study was to decipher the mechanism of oxygen isotope fractionation during N2O production by denitrification and, in particular, to investigate the relationship between the extent of oxygen isotope exchange with soil water and the δ18O values of the produced N2O. We performed several soil incubation experiments. For the first time, Δ17O isotope tracing was applied to simultaneously determine the extent of oxygen isotope exchange and any associated oxygen isotope effect. We found bacterial denitrification to be typically associated with almost complete oxygen isotope exchange and a stable difference in δ18O between soil water and the produced N2O of δ18O(N2O/H2O) = (17.5 ± 1.2) ‰. However, some experimental setups yielded oxygen isotope exchange as low as 56% and a higher δ18O(N2O/H2O) of up to 37 ‰. The extent of isotope exchange and δ18O(N2O / H2O) showed a very significant correlation (R2 = 0.70, p < 0.00001). We hypothesise that this observation was due to the contribution of N2O from another production process, most probably fungal denitrification. An oxygen isotope fractionation model was used to test various scenarios with different magnitudes of branching isotope effects at different steps in the reduction process. The results suggest that during denitrification the isotope exchange occurs prior to the isotope branching and that the mechanism of this exchange is mostly associated with the enzymatic nitrite reduction mediated by NIR. For bacterial denitrification, the branching isotope effect can be surprisingly low, about (0.0 ± 0.9) ‰; in contrast to fungal denitrification where higher values of up to 30 ‰ have been reported previously. This suggests that δ18O might be used as a tracer for differentiation between bacterial and fungal denitrification, due to their different magnitudes of branching isotope effects. [ABSTRACT FROM AUTHOR]

Highlights: [•] Seasonal variations in CH4 concentration and δ13C value in urban air are pronounced. [•] Spatial distribution of CH4 indicate the areas of dominant methane fluxes. [•] The dominant flux was biogenic methane from man-made sewage irrigation fields. [•] Combustion and gas leakage sources showed minor impact. [•] CH4 and CO2 characteristics are governed by diverse processes. [Copyright &y& Elsevier]

Highlights: [•] Seasonal variation in CO2 concentration and δ13C value in air urban area was noted. [•] Spatial distribution of CO2 in Wrocław indicate the anthropogenically changed areas. [•] Coal or diesel/gasoline dominant CO2 origin was indicated for heating seasons. [•] Soil respiration dominant biogenic CO2 origin was indicated for vegetative season. [•] Significant influence of newly opened highway on the atmospheric CO2 was observed. [Copyright &y& Elsevier]

The article focuses on the study which determines the oxygen isotropic analyses of water samples at Budzislawskie Lake in Poland. The analyses of the water used Rayleigh distillation model to estimate the rate of evaporation from the lake's surface and its direct catchment. It was found out that the calculation of water from precipitation evaporated is 56 percent.

Information about the paper on isotopic study of the role of cyanobacterial bloom in a freshwater dam reservoir that was discussed at the European Society for Isotope Research (ESIR) meeting is presented. Sampling was made on a diurnal basis, that is, every 4 hours, at the time of the most intensive bloom. The study shows that the most intensive photosynthesis occurs at the surface at 10:00 but 14:00 at deeper sites and the delay was due to the vertical migration of cyanobacterial cells.

The article discusses the study which examines the diurnal variations of sulphate concentration and sulphur isotonic composition (δ34 S) of sulphate ion within the Sulejow reservoir in Central Poland. A number of water samples from the reservoir have been collected in July 26-27, 2006 and in February 2-3, 2007. Information about the results of the study is provided.

Nitrogen is an essential nutrient in the environment that exists in multiple oxidation states in nature. Numerous microbial processes are involved in its transformation. Knowledge about very complex N cycling has been growing rapidly in recent years, with new information about associated isotope effects and about the microbes involved in particular processes. Furthermore, molecular methods that are able to detect and quantify particular processes are being developed, applied and combined with other analytical approaches, which opens up new opportunities to enhance understanding of nitrogen transformation pathways. This review presents a summary of the microbial nitrogen transformation, including the respective isotope effects of nitrogen and oxygen on different nitrogen-bearing compounds (including nitrates, nitrites, ammonia and nitrous oxide), and the microbiological characteristics of these processes. It is supplemented by an overview of molecular methods applied for detecting and quantifying the activity of particular enzymes involved in N transformation pathways. This summary should help in the planning and interpretation of complex research studies applying isotope analyses of different N compounds and combining microbiological and isotopic methods in tracking complex N cycling, and in the integration of these results in modelling approaches., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Dominika Lewicka-Szczebak reports financial support was provided by Polish National Agency for Academic Exchange. Dominika Lewicka-Szczebak reports financial support was provided by National Science Centre Poland. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Bayesian stable isotope mixing models are widely used in geochemical and ecological studies for partitioning sources that contribute to various mixtures. However, none of the existing tools allows accounting for the influence of processes other than mixing, especially stable isotope fractionation. Bridging this gap, new software for the stable isotope Fractionation And Mixing Evaluation (FRAME) has been developed with a user-friendly graphical interface (malewick.github.io/frame). This calculation tool allows simultaneous sources partitioning and fractionation progress determination based on the stable isotope composition of sources/substrates and mixture/products. The mathematical algorithm applies the Markov-Chain Monte Carlo model to estimate the contribution of individual sources and processes, as well as the probability distributions of the calculated results. The performance of FRAME was comprehensively tested and practical applications of this modelling tool are presented with simple theoretical examples and stable isotope case studies for nitrates, nitrites, water and nitrous oxide. The open mathematical design, featuring custom distributions of source isotope signatures, allows for the implementation of additional processes that alternate the characteristics of the final mixture and its application for various range of studies., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2022 Lewicki et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Nitrite (NO 2 - ) is a crucial compound in the N soil cycle. As an intermediate of nearly all N transformations, its isotopic signature may provide precious information on the active pathways and processes. NO 2 - analyses have already been applied in 15 N tracing studies, increasing their interpretation perspectives. Natural abundance NO 2 - isotope studies in soils were so far not applied and this study aims at testing if such analyses are useful in tracing the soil N cycle. We conducted laboratory soil incubations with parallel natural abundance and 15 N treatments, accompanied by isotopic analyses of soil N compounds (NO 3 - , NO 2 - , NH 4 + ). The double 15 N tracing method was used as a reference method for estimations of N transformation processes based on natural abundance nitrite dynamics. We obtained a very good agreement between the results from nitrite isotope model proposed here and the 15 N tracing approach. Natural abundance nitrite isotope studies are a promising tool to our understanding of soil N cycling.

The isotopic composition of nitrous oxide (N 2 O) provides useful information for evaluating N 2 O sources and budgets. Due to the co-occurrence of multiple N 2 O transformation pathways, it is, however, challenging to use isotopic information to quantify the contribution of distinct processes across variable spatiotemporal scales. Here, we present an overview of recent progress in N 2 O isotopic studies and provide suggestions for future research, mainly focusing on: analytical techniques; production and consumption processes; and interpretation and modelling approaches. Comparing isotope-ratio mass spectrometry (IRMS) with laser absorption spectroscopy (LAS), we conclude that IRMS is a precise technique for laboratory analysis of N 2 O isotopes, while LAS is more suitable for in situ/inline studies and offers advantages for site-specific analyses. When reviewing the link between the N 2 O isotopic composition and underlying mechanisms/processes, we find that, at the molecular scale, the specific enzymes and mechanisms involved determine isotopic fractionation effects. In contrast, at plot-to-global scales, mixing of N 2 O derived from different processes and their isotopic variability must be considered. We also find that dual isotope plots are effective for semi-quantitative attribution of co-occurring N 2 O production and reduction processes. More recently, process-based N 2 O isotopic models have been developed for natural abundance and 15 N-tracing studies, and have been shown to be effective, particularly for data with adequate temporal resolution. Despite the significant progress made over the last decade, there is still great need and potential for future work, including development of analytical techniques, reference materials and inter-laboratory comparisons, further exploration of N 2 O formation and destruction mechanisms, more observations across scales, and design and validation of interpretation and modelling approaches. Synthesizing all these efforts, we are confident that the N 2 O isotope community will continue to advance our understanding of N 2 O transformation processes in all spheres of the Earth, and in turn to gain improved constraints on regional and global budgets., (© 2020 John Wiley & Sons, Ltd.)

The last step of denitrification, i.e. the reduction of N 2 O to N 2 , has been intensively studied in the laboratory to understand the denitrification process, predict nitrogen fertiliser losses, and to establish mitigation strategies for N 2 O. However, assessing N 2 production via denitrification at large spatial scales is still not possible due to lack of reliable quantitative approaches. Here, we present a novel numerical "mapping approach" model using the δ 15 N sp /δ 18 O slope that has been proposed to potentially be used to indirectly quantify N 2 O reduction to N 2 at field or larger spatial scales. We evaluate the model using data obtained from seven independent soil incubation studies conducted under a He-O 2 atmosphere. Furthermore, we analyse the contribution of different parameters to the uncertainty of the model. The model performance strongly differed between studies and incubation conditions. Re-evaluation of the previous data set demonstrated that using soils-specific instead of default endmember values could largely improve model performance. Since the uncertainty of modelled N 2 O reduction was relatively high, further improvements to estimate model parameters to obtain more precise estimations remain an on-going matter, e.g. by determination of soil-specific isotope fractionation factors and isotopocule endmember values of N 2 O production processes using controlled laboratory incubations. The applicability of the mapping approach model is promising with an increasing availability of real-time and field based analysis of N 2 O isotope signatures., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Rationale: Field measurement of denitrification in agricultural ecosystems using the 15 N gas flux method has been limited by poor sensitivity because current isotope ratio mass spectrometry is not precise enough to detect low 15 N 2 fluxes in the presence of a high atmospheric N 2 background. For laboratory studies, detection limits are improved by incubating soils in closed systems and under N 2 -depleted atmospheres., Methods: We developed a new procedure to conduct the 15 N gas flux method suitable for field application using an artificially N 2 -depleted atmosphere to improve the detection limit at the given precision of mass spectrometry. Laboratory experiments with and without 15 N-labelling and using different flushing strategies were conducted to develop a suitable field method. Subsequently, this method was tested in the field and results were compared with those obtained from the conventional 15 N gas flux method., Results: Results of the two methods were in close agreement showing that the denitrification rates determined were not biased by the flushing procedure. Best sensitivity for N 2  + N 2 O fluxes was 10 ppb, which was 80-fold better than that of the reference method. Further improvement can be achieved by lowering the N 2 background concentration below the values established in the present study., Conclusions: In view of this progress in sensitivity, the new method will be suitable to measure denitrification dynamics in the field beyond peak events., (© 2018 John Wiley & Sons, Ltd.)

Rationale: Isotopic signatures of N 2 O can help distinguish between two sources (fertiliser N or endogenous soil N) of N 2 O emissions. The contribution of each source to N 2 O emissions after N-application is difficult to determine. Here, isotopologue signatures of emitted N 2 O are used in an improved isotopic model based on Rayleigh-type equations., Methods: The effects of a partial (33% of surface area, treatment 1c) or total (100% of surface area, treatment 3c) dispersal of N and C on gaseous emissions from denitrification were measured in a laboratory incubation system (DENIS) allowing simultaneous measurements of NO, N 2 O, N 2 and CO 2 over a 12-day incubation period. To determine the source of N 2 O emissions those results were combined with both the isotope ratio mass spectrometry analysis of the isotopocules of emitted N 2 O and those from the 15 N-tracing technique., Results: The spatial dispersal of N and C significantly affected the quantity, but not the timing, of gas fluxes. Cumulative emissions are larger for treatment 3c than treatment 1c. The 15 N-enrichment analysis shows that initially ~70% of the emitted N 2 O derived from the applied amendment followed by a constant decrease. The decrease in contribution of the fertiliser N-pool after an initial increase is sooner and larger for treatment 1c. The Rayleigh-type model applied to N 2 O isotopocules data (δ 15 N bulk -N 2 O values) shows poor agreement with the measurements for the original one-pool model for treatment 1c; the two-pool models gives better results when using a third-order polynomial equation. In contrast, in treatment 3c little difference is observed between the two modelling approaches., Conclusions: The importance of N 2 O emissions from different N-pools in soil for the interpretation of N 2 O isotopocules data was demonstrated using a Rayleigh-type model. Earlier statements concerning exponential increase in native soil nitrate pool activity highlighted in previous studies should be replaced with a polynomial increase with dependency on both N-pool sizes., (© 2018 The Authors Rapid Communications in Mass Spectrometry Published by John Wiley & Sons, Ltd.)

Rationale: Enhanced nitrous oxide (N 2 O) emissions can occur following grassland break-up for renewal or conversion to maize cropping, but knowledge about N 2 O production pathways and N 2 O reduction to N 2 is very limited. A promising tool to address this is the combination of mass spectrometric analysis of N 2 O isotopocules and an enhanced approach for data interpretation., Methods: The isotopocule mapping approach was applied to field data using a δ 15 N sp N2O and δ 18 O N2O map to simultaneously determine N 2 O production pathways contribution and N 2 O reduction for the first time. Based on the isotopic composition of N 2 O produced and literature values for specific N 2 O pathways, it was possible to distinguish: (i) heterotrophic bacterial denitrification and/or nitrifier denitrification and (ii) nitrification and/or fungal denitrification and the contribution of N 2 O reduction., Results: The isotopic composition of soil-emitted N 2 O largely resembled the known end-member values for bacterial denitrification. The isotopocule mapping approach indicated different effects of N 2 O reduction on the isotopic composition of soil-emitted N 2 O for the two soils under study. Differing N 2 O production pathways in different seasons were not observed, but management events and soil conditions had a significant impact on pathway contribution and N 2 O reduction. N 2 O reduction data were compared with a parallel 15 N-labelling experiment., Conclusions: The field application of the isotopocule mapping approach opens up new prospects for studying N 2 O production and consumption of N 2 O in soil simultaneously based on mass spectrometric analysis of natural abundance N 2 O. However, further studies are needed in order to properly validate the isotopocule mapping approach., (Copyright © 2018 John Wiley & Sons, Ltd.)

Rationale: Fungal denitrifiers can contribute substantially to N 2 O emissions from arable soil and show a distinct site preference for N 2 O (SP(N 2 O)). This study sought to identify another process-specific isotopic tool to improve precise identification of N 2 O of fungal origin by mass spectrometric analysis of the N 2 O produced., Methods: Three pure bacterial and three fungal species were incubated under denitrifying conditions in treatments with natural abundance and stable isotope labelling to analyse the N 2 O produced. Combining different applications of isotope ratio mass spectrometry enabled us to estimate the oxygen (O) exchange accelerated by denitrifying enzymes and the ongoing microbial pathway in parallel. This experimental set-up allowed the determination of δ 18 O(N 2 O) values and isotopic fractionation of O, as well as SP(N 2 O) values, as a perspective to differentiate between microbial denitrifiers., Results: Oxygen exchange during N 2 O production was lower for bacteria than for fungi, differed between species, and depended also on incubation time. Apparent O isotopic fractionation during denitrification was in a similar range for bacteria and fungi, but application of the fractionation model indicated that different enzymes in bacteria and fungi were responsible for O exchange. This difference was associated with different isotopic fractionation for bacteria and fungi., Conclusions: δ 18 O(N 2 O) values depend on isotopic fractionation and isotopic fractionation may differ between processes and organism groups. By comparing SP(N 2 O) values, O exchange and the isotopic signature of precursors, we propose here a novel tool for differentiating between different sources of N 2 O., (Copyright © 2017 John Wiley & Sons, Ltd.)

An automated sample preparation unit for inorganic nitrogen (SPIN) coupled to a membrane inlet quadrupole mass spectrometer (MIMS) was developed for automated and sensitive determination of the 15 N abundances and concentrations of nitrate, nitrite, and ammonium in aqueous solutions without any sample preparation. The minimum N concentration for an accurate determination of the 15 N abundance is 7 μmol/L for nitrite and nitrate, with a relative standard deviation (RSD) of repeated measurements of <1%, and 70 μmol/L with an RSD < 0.4% in the case of ammonium. The SPIN-MIMS system provides a wide dynamic range (up to 3500 μmol/L) for all three N species for both isotope abundance and concentration measurements. The comparison of parallel measurements of 15 N-labeled NH 4 + and NO 3 - from soil extracts with the denitrifier method and the SPIN-MIMS system shows a good agreement between both methods.

Rationale: The gaseous N losses mediated by soil denitrifiers are generally inferred by measuring N 2 O fluxes, but should include associated N 2 emissions, which may be affected by abiotic soil characteristics and biotic interactions. Soil fauna, particularly anecic earthworms and euedaphic collembola, alter the activity of denitrifiers, creating hotspots for denitrification. These soil fauna are abundant in perennial agroecosystems intended to contribute to more sustainable production of bioenergy., Methods: Two microcosm experiments were designed to evaluate gaseous N emissions from a silty loam and a sandy soil, both provided with litter from the bioenergy crop Silphium perfoliatum (cup-plant) and inoculated with an anecic earthworm (Lumbricus terrestris), which was added alone or together with an euedaphic collembola (Folsomia candida). In experiment 1, litter-derived N flux was determined by adding 15 N-labelled litter, followed by mass spectrometric analysis of N 2 and N 2 O isotopologues. In experiment 2, the δ 18 O values and 15 N site preference of N 2 O were determined by isotope ratio mass spectrometry to reveal underlying N 2 O formation pathways., Results: Lumbricus terrestris significantly increased litter-derived N 2 emissions in the loamy soil, from 174.5 to 1019.3 μg N 2 -N kg -1 soil, but not in the sandy soil (non-significant change from 944.7 to 1054.7 μg N 2 -N kg -1 soil). Earthworm feeding on plant litter resulted in elevated N 2 O emissions in both soils, derived mainly from turnover of the soil mineral N pool during denitrification. Folsomia candida did not affect N losses but showed a tendency to redirect N 2 O formation pathways from fungal to bacterial denitrification. The N 2 O/(N 2  + N 2 O) product ratio was predominantly affected by abiotic soil characteristics (loamy soil: 0.14, sandy soil: 0.26)., Conclusions: When feeding on S. perfoliatum litter, the anecic L. terrestris, but not the euedaphic F. candida, has the potential to cause substantial N losses. Biotic interactions between the species are not influential, but abiotic soil characteristics have an effect. The coarse-textured sandy soil had lower gaseous N losses attributable to anecic earthworms. Copyright © 2016 John Wiley & Sons, Ltd., (Copyright © 2016 John Wiley & Sons, Ltd.)

Rationale: The aim of this study was to determine the impact of isotope fractionation associated with N2O reduction during soil denitrification on N2O site preference (SP) values and hence quantify the potential bias on SP-based N2O source partitioning., Methods: The N2O SP values (n = 431) were derived from six soil incubation studies in N2-free atmosphere, and determined by isotope ratio mass spectrometry (IRMS). The N2 and N2O concentrations were measured directly by gas chromatography. Net isotope effects (NIE) during N2O reduction to N2 were compensated for using three different approaches: a closed-system model, an open-system model and a dynamic apparent NIE function. The resulting SP values were used for N2O source partitioning based on a two end-member isotopic mass balance., Results: The average SP0 value, i.e. the average SP values of N2O prior to N2O reduction, was recalculated with the closed-system model, resulting in -2.6 ‰ (±9.5), while the open-system model and the dynamic apparent NIE model gave average SP0 values of 2.9 ‰ (±6.3) and 1.7 ‰ (±6.3), respectively. The average source contribution of N2O from nitrification/fungal denitrification was 18.7% (±21.0) according to the closed-system model, while the open-system model and the dynamic apparent NIE function resulted in values of 31.0% (±14.0) and 28.3% (±14.0), respectively., Conclusions: Using a closed-system model with a fixed SP isotope effect may significantly overestimate the N2O reduction effect on SP values, especially when N2O reduction rates are high. This is probably due to soil inhomogeneity and can be compensated for by the application of a dynamic apparent NIE function, which takes the variable reduction rates in soil micropores into account., (Copyright © 2016 John Wiley & Sons, Ltd.)

Rationale: The oxygen isotope anomaly, Δ(17) O, of N2 O and nitrate is useful to elucidate nitrogen oxide dynamics. A comparison of different methods for Δ(17) O measurement was performed., Methods: For Δ(17) O measurements, N2 O was converted into O2 and N2 using microwave-induced plasma in a quartz or corundum tube reactor, respectively, or conversion was carried out in a gold wire oven. In each case, isotope ratios were measured by isotope ratio mass spectrometry., Results: All the tested methods showed acceptable precision (coefficient of variation <2.4 % at 160 nmol N2 O) with high sample size but the sample size dependence was lowest when using microwave-induced plasma in a corundum tube reactor., Conclusions: The use of microwave-induced plasma in a corundum tube yields best results for Δ(17) O measurement on N2 O gas samples., (Copyright © 2015 John Wiley & Sons, Ltd.)

Rationale: This study aimed (i) to determine the isotopic fractionation factors associated with N2O production and reduction during soil denitrification and (ii) to help specify the factors controlling the magnitude of the isotope effects. For the first time the isotope effects of denitrification were determined in an experiment under oxic atmosphere and using a novel approach where N2O production and reduction occurred simultaneously., Methods: Soil incubations were performed under a He/O2 atmosphere and the denitrification product ratio [N2O/(N2 + N2O)] was determined by direct measurement of N2 and N2O fluxes. N2O isotopocules were analyzed by mass spectrometry to determine δ(18)O, δ(15)N and (15)N site preference within the linear N2O molecule (SP). An isotopic model was applied for the simultaneous determination of net isotope effects (η) of both N2O production and reduction, taking into account emissions from two distinct soil pools., Results: A clear relationship was observed between (15)N and (18)O isotope effects during N2O production and denitrification rates. For N2O reduction, diverse isotope effects were observed for the two distinct soil pools characterized by different product ratios. For moderate product ratios (from 0.1 to 1.0) the range of isotope effects given by previous studies was confirmed and refined, whereas for very low product ratios (below 0.1) the net isotope effects were much smaller., Conclusions: The fractionation factors associated with denitrification, determined under oxic incubation, are similar to the factors previously determined under anoxic conditions, hence potentially applicable for field studies. However, it was shown that the η(18)O/η(15)N ratios, previously accepted as typical for N2O reduction processes (i.e., higher than 2), are not valid for all conditions., (Copyright © 2014 John Wiley & Sons, Ltd.)

Rationale: The contribution of fungal denitrification to the emission of the greenhouse gas nitrous oxide (N2O) from soil has not yet been sufficiently investigated. The intramolecular (15)N site preference (SP) of N2O could provide a tool to distinguish between N2O produced by bacteria or fungi, since in previous studies fungi exhibited much higher SP values than bacteria., Methods: To further constrain isotopic evidence of fungal denitrification, we incubated six soil fungal strains under denitrifying conditions, with either NO3(-) or NO2(-) as the electron acceptor, and measured the isotopic signature (δ(18)O, δ(15)Nbulk and SP values) of the N2O produced. The nitrogen isotopic fractionation was calculated and the oxygen isotope exchange associated with particular fungal enzymes was estimated., Results: Five fungi of the order Hypocreales produced N2O with a SP of 35.1 ± 1.7 ‰ after 7 days of anaerobic incubation independent of the electron acceptor, whereas one Sordariales species produced N2O from NO2(-) only, with a SP value of 21.9 ± 1.4 ‰. Smaller isotope effects of (15)Nbulk were associated with larger N2O production. The δ(18)O values were influenced by oxygen exchange between water and denitrification intermediates, which occurred primarily at the nitrite reduction step., Conclusions: Our results confirm that SP of N2O is a promising tool to differentiate between fungal and bacterial N2O from denitrification. Modelling of oxygen isotope fractionation processes indicated that the contribution of the NO2(-) and NO reduction steps to the total oxygen exchange differed among the various fungal species studied. However, more information is needed about different biological orders of fungi as they may differ in denitrification enzymes and consequently in the SP and δ(18)O values of the N2O produced., (Copyright © 2014 John Wiley & Sons, Ltd.)

Rationale: N2O isotopomer ratios may provide a useful tool for studying N2O source processes in soils and may also help estimating N2O reduction to N2. However, remaining uncertainties about different processes and their characteristic isotope effects still hamper its application. We conducted two laboratory incubation experiments (i) to compare the denitrification potential and N2O/(N2O+N2) product ratio of denitrification of various soil types from Northern Germany, and (ii) to investigate the effect of N2O reduction on the intramolecular (15)N distribution of emitted N2O., Methods: Three contrasting soils (clay, loamy, and sandy soil) were amended with nitrate solution and incubated under N2 -free He atmosphere in a fully automated incubation system over 9 or 28 days in two experiments. N2O, N2, and CO2 release was quantified by online gas chromatography. In addition, the N2O isotopomer ratios were determined by isotope-ratio mass spectrometry (IRMS) and the net enrichment factors of the (15)N site preference (SP) of the N2O-to-N2 reduction step (η(SP)) were estimated using a Rayleigh model., Results: The total denitrification rate was highest in clay soil and lowest in sandy soil. Surprisingly, the N2O/(N2O+N2) product ratio in clay and loam soil was identical; however, it was significantly lower in sandy soil. The IRMS measurements revealed highest N2O SP values in clay soil and lowest SP values in sandy soil. The η(SP) values of N2O reduction were between -8.2 and -6.1‰, and a significant relationship between δ(18)O and SP values was found., Conclusions: Both experiments showed that the N2O/(N2O+N2) product ratio of denitrification is not solely controlled by the available carbon content of the soil or by the denitrification rate. Differences in N2O SP values could not be explained by variations in N2O reduction between soils, but rather originate from other processes involved in denitrification. The linear δ(18)O vs SP relationship may be indicative for N2O reduction; however, it deviates significantly from the findings of previous studies., (Copyright © 2013 John Wiley & Sons, Ltd.)

Rationale: An enhanced analytical approach for analyzing gaseous products from (15)N-enriched pools has been developed. This technique can be used to quantify nitrous oxide (N2O) and dinitrogen (N2) fluxes from denitrification. It can also help in distinguishing different N2- and N2O-forming processes, such as denitrification, nitrification, anaerobic ammonium oxidation or co-denitrification., Methods: The measurement instrumentation was based on a commercially available automatic preparation system allowing collection and separation of gaseous samples. The sample transfer paths, valves, liquid nitrogen traps, gas chromatography column and open split of the original system were modified. A reduction oven (Cu) was added in order to eliminate oxygen and measure N2O-N as N2. Gases leaving the separation system entered an isotope ratio mass spectrometer where masses (28)N2, (29)N2 and (30)N2 were measured., Results: The enhanced technique enabled rapid simultaneous measurement of stable isotope ratios (29)N2/(28)N2 and (30)N2/(28)N2 originating from dinitrogen alone (N2) and from the sum of the denitrification products (N2 +N2O) as well as the determination of (15)N enrichment in N2O. The (15)N fraction in the N pool undergoing N2 and N2O production ((15)X(N)) and the contribution of N2 and N2O originating from this pool (d) were determined with satisfactory accuracy of better than 3.3% and 2.9%, respectively., Conclusions: The precision and accuracy of this method were comparable with or better than previously reported for similar measurements. The proposed method allows for the analysis of all quantities within one run, thus reducing the measurement and sample preparation time as well as increasing the reliability of the results., (Copyright © 2013 John Wiley & Sons, Ltd.)

Oxygen and hydrogen stable isotopic compositions of precipitation, lake water and groundwater were used to quantitatively asses the water budget related to water inflow and water loss in natural lakes, and mixing between lake water and aquifer groundwater in a mining area of the Lignite Mine Konin, central Poland. While the isotopic composition of precipitation showed large seasonal variations (δ(2)H from-140 to+13 ‰ and δ(18)O from-19.3 to+7.6 ‰), the lake waters were variously affected by evaporation (δ(2)H from-44 to-21 ‰ and δ(18)O from-5.2 to-1.7 ‰) and the groundwater showed varying contribution from mixing with surface water (δ(2)H from-75 to-39 ‰ and δ(18)O from-10.4 to-4.8 ‰). The lake water budget was estimated using a Craig-Gordon model and isotopic mass balance constraint, which enabled us to identify various water sources and to quantify inflow and outflow for each lake. Moreover, we documented that a variable recharge of lake water into the Tertiary aquifer was dependent on mining drainage intensity. A comparison of coupled δ(2)H-δ(18)O data with hydrogeological results indicated better precision of the δ(2)H-based calculations.

We have applied both palynological and carbon and nitrogen isotopic analyses of PM10 (particulate matter with a diameter of 10 μm or less) to trace its origin and to assess the anthropogenic impact for the area under study. The PM10 samples were collected in Wrocław (SW Poland) by the Regional Inspectorate for Environment Protection during the year 2007. The usefulness of the palynological observations in the case of PM10 is much lower than that for total suspended particles due to the resolution of absorbed particles, but is still helpful for distinguishing C(3)/C(4) plants that indicate long-distance transport of pollutants. The δ(13)C(PM10) values varied seasonally from-26.9 to-25.1‰. The δ(15)N(PM10) values showed chaotic fluctuations and varied from 5.0 to 13.7‰. Our results indicated that during the heating period, the PM10 particles in Wrocław are derived mainly from local home heaters, whereas in the growing period, PM10 particles are derived from local transport and are partially generated by the industrial application of coal combustion outside the city of Wrocław.

This paper describes results of chemical and isotopic analysis of inorganic carbon species in the atmosphere and precipitation for the calendar year 2008 in Wrocław (SW Poland). Atmospheric air samples (collected weekly) and rainwater samples (collected after rain episodes) were analysed for CO2 and dissolved inorganic carbon (DIC) concentrations and for δ13C composition. The values obtained varied in the ranges: atmospheric CO2: 337-448 ppm; δ13CCO2 from -14.4 to -8.4‰; DIC in precipitation: 0.6-5.5 mg dm(-3); δ13CDIC from -22.2 to +0.2‰. No statistical correlation was observed between the concentration and δ13C value of atmospheric CO2 and DIC in precipitation. These observations contradict the commonly held assumption that atmospheric CO2 controls the DIC in precipitation. We infer that DIC is generated in ambient air temperatures, but from other sources than the measured atmospheric CO2. The calculated isotopic composition of a hypothetical CO2 source for DIC forming ranges from -31.4 to -11.0‰, showing significant seasonal variations accordingly to changing anthropogenic impact and atmospheric mixing processes., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

The stable isotopic analyses of molecular oxygen dissolved in water (delta18O(DO)) and dissolved inorganic carbon (delta13C(DIC)), supplemented with basic chemical measurements, have been carried out on a diurnal basis to better understand the dynamics of photosynthesis and respiration in freshwater systems. Our observations have been carried out in a lowland dam reservoir, the Sulejow Lake (central Poland), during the summer cyanobacterial bloom. All data obtained, isotopic, hydrochemical, and biological, show a high mutual consistency. Namely, the lowest delta18O(DO) values, obtained at 10:00 and 14:00 (16.0 and 15.5 per thousand, respectively), correspond to the highest amount of cyanobacterial cells observed (66 and 63 mg dm(-3), respectively), whereas the minimum delta13C(DIC) (-10.6 per thousand) obtained at 22:00 corresponds to the maximum content of organic matter (110 mg dm(-3)). This evidence suggests that isotopic assays of delta18O(DO) and delta13C(DIC) are a reliable tool for the quantitative study of biochemical processes in freshwater systems.