Dual Isotope Research Articles

Tracing freshwater sources and particle discharge in Kongsfjorden: insights from a water isotope approach

Arctic fjords are inherently vulnerable to global warming, particularly because of the substantial freshwater influx resulting from the melting of glaciers. In this study, precipitation, river water, surface ice, and seawater samples from Kongsfjorden were collected to identify the main sources of freshwater. The dual water isotope (δ18O and δD) results and temperature–salinity profiles revealed that between 0% and 7% freshwater contributed to the fjord’s water. Furthermore, different freshwater sources for surface and deep water were identified by the dual water isotope analysis. Turbidity profiles confirmed the alter in particle discharge associated with surface runoff and subglacial discharge. Our study highlighted the sensitivity of water isotope analysis in elucidating the hydrological processes within the fjord system and demonstrated its potential for investigating the impact of meltwater on biological processes in the Arctic.

Source identification of nitrate in groundwater of an agro-pastoral ecotone in a semi-arid zone, northern China: Coupled evidences from MixSIAR model and DOM fluorescence

In the extensive agro-pastoral ecotone of northern China, groundwater is a valuable resource, but it suffers from severe nitrate pollution. However, the extent of the contributions of agricultural and pastoral activities to nitrate accumulation in the groundwater of the region remains unclear. This study aimed to identify the main sources of groundwater nitrate in Chahannur Basin, a typical agro-pastoral ecotone in the semi-arid zone of northern China, using the MixSIAR model based on dual stable isotopes and dissolved organic matter (DOM) fluorescence. The hydrochemical and isotopic results showed that the groundwater has high concentrations of nitrate (up to 208.19 mg/L) with weak denitrification, and nitrate accumulation is mainly driven by mixed input from different sources. The MixSIAR model results indicated that the largest contributors to groundwater nitrate accumulation are manure & sewage, followed by soil nitrogen, chemical fertilizers, and atmospheric deposition. According to the DOM fluorescence characteristics, the groundwater is strongly affected by livestock and poultry waste, followed by soil humic substances. Moreover, the DOM fluorescence results further supported the MixSIAR model results based on the significant correlation between the contributions of nitrate sources and the percentages of fluorescent components, jointly confirming that the main source of nitrate in groundwater is manure and sewage, followed by soil nitrogen. These findings indicate that coupled evidences from the MixSIAR model and DOM fluorescence could be applied to identify the sources of nitrate in groundwater, and this coupling can provide valuable information for local authorities to achieve sustainable groundwater management.

Elucidating the Fate of the Organochlorine Pesticide Chlordecone under Abiotic Reductive and Oxidative Processes: Kinetics, Transformation Products, and C vs Cl Isotope Fractionation.

Pollution of French West Indies (FWI) soils by the organochlorine pesticide chlordecone poses environmental and societal concerns due to its long-term persistence. Assessing chlordecone degradation remains challenging due to analytical constraints to identify transformation products. Here, multielement compound-specific isotope analysis (ME-CSIA) was used to identify changes in stable isotope signatures of chlordecone produced during abiotic transformation reactions under reducing and oxidative conditions. Effective chlordecone transformation was shown in reactions with zerovalent iron (ZVI), vitamin B12 and sodium sulfide (VSS), alkaline ascorbic acid (AA), and sodium persulfate activated by microwave irradiation (MWPS). Significant enrichment of 13C and 37Cl was observed in all abiotic reactions, with εC,bulk and εCl,bulk values ranging from -4.3 ± 0.4‰ to -2.3 ± 0.2‰ and from -2.6 ± 0.4‰ to -1.3 ± 0.3‰, respectively. Distinct mechanisms were evidenced in dual isotope plots, resulting in Λ values of 1.17 ± 0.28 for ZVI, 1.26 ± 0.50 for VSS, 2.06 ± 0.30 for AA, and 2.90 ± 0.50 for MWPS. Two major products were formed, 10-monohydrochlordecone and 8-monohydrochlordecone. Cl-CSIA data suggested that the first Cl substitution at the C10-position likely produced secondary Cl isotope effects (via nucleophilic substitution). Overall, results suggest that ME-CSIA can help quantify in situ chlordecone degradation, distinguishing between different ongoing degradation mechanisms and fingerprinting pollutant sources from chlordecone formulations (Curlone).

Quercus acutissima exhibits more adaptable water uptake patterns in response to seasonal changes compared to Pinus massoniana

BackgroundSeasonal precipitation variability significantly affects water use in forests; however, whether water uptake is adapted to changes in precipitation, particularly whether it could affect the coexistence of tree species, has rarely been quantified in forest systems. MethodIn this study, dual stable isotopes and the Li-6400 portable photosynthesis system were used to determine the water sources of a mixed conifer (Pinus massoniana) and broadleaf (Quercus acutissima) forest and changes in hydraulic characteristics during the dry and wet seasons in a southern hilly region of China. ResultsAlthough the hydraulic characteristics of P. massoniana were lower than those of Q. acutissima, it maintained a stable water source from the deep soil layer and a higher stomatal conductance (Gs), leading to a higher transpiration rate (Tr) during the growing seasons. Q. acutissima mainly absorbed water from deeper soil layers in the dry season and took up from shallow soil layers in the wet season. Its Gs values exhibited sensitivity to precipitation, while it maintained a lower Tr value during the growing seasons. The excessive water-use strategy observed in P. massoniana may confer weak drought-tolerance during higher frequency and more intense extreme precipitation events, whereas Q. acutissima may exhibit better ecological adaption to precipitation changes. ConclusionsThe overlap of water niches in mixed forests did not appear to affect the coexistence of tree species. The present study provides insights into reforestation and water management in the southern hilly regions of China.

Dissolved N pollution and its biogeochemical constraints along a river-sea continuum of a typical dense oyster mariculture coastal water, northwest South China Sea

Dissolved nutrients, including nitrate (NO3–-N) and its dual isotopes (δ15N-NO3– and δ18O-NO3–) were systematically studied along a river-sea continuum area, wherein dense oyster mariculture is implemented, to constrain the pollution sources and biogeochemical cycling mechanisms of nitrogen (N). Total dissolved N, mainly composed of inorganic N, showed strong anthropogenic influence. Based on MixSIAR model results, N pollution was predominantly sourced from sewage/wastewater (55.9~64.3%). Nutrient stoichiometry revealed DIP and DSi stress, and surface water in the riverine region was severely eutrophic. The occurrences of eutrophication and changes in nutrient stoichiometry were significantly related varying N pollution sources in different in summer and winter. N dynamics were controlled by anthropogenic influence and physical mixing. However, due to insignificance biological processes involving denitrification, phytoplankton assimilation, N2 fixation, and nitrification, including insignificant isotopic fractionations associated with these processes, and poor fitting of both the Rayleigh Model and Open system Model on the measured data, it is speculated that several folds of reductions in N load and eutrophication along the river-sea continuum, could be attributed to the combinations of significant N drawdown by dense oyster mariculture as well as nutrient dilution due to physical mixing of river and seawater during winter and summer.

Contrasting nitrogen dynamics across the Mid‐Atlantic Bight shelfbreak front: Insights from nitrate dual isotopes and nitrifier gene abundance

AbstractObservations and model studies suggest that front dynamics can enhance phytoplankton productivity. This study tested whether frontal systems also increase the abundance of nitrifying microbes and nitrogen recycling during repeat sampling transects across the Mid‐Atlantic Bight shelfbreak in July 2019. We measured ammonium concentrations, nitrate dual isotopes (δ15N, δ18O), and ammonia monooxygenase subunit A (amoA) genes of ammonia‐oxidizing archaea (AOA) and bacteria (AOB). In subsurface shelf waters, ammonium concentrations exceeded 2 μmol L−1, due to a temporary imbalance in regeneration from sinking particles and subsequent nitrification. The inverse correlation between nitrate δ15N values and ammonium concentrations confirmed nitrate was partially or entirely from local nitrification on the shelf. In contrast, the shelfbreak frontal zone and slope sea subsurface waters had much lower ammonium concentrations (0.1–0.2 μmol L−1) due to tight coupling between ammonium regeneration and nitrification. The deviation of nitrate δ15N and δ18O from algal uptake‐driven 1 : 1 ratio suggests concurrent nitrification in the euphotic zone. The shelfbreak front acted as an ecological boundary where AOA and AOB amoA gene numbers were partitioned, with AOAs abounding in slope waters and AOBs in shelf waters, likely due to ammonium availability. At certain slope stations, deep‐water nutrient inputs via isopycnal lifting induced by Gulf Stream intrusions caused unexpectedly high phytoplankton biomass, which doubled nitrifier abundance and potentially stimulated both ammonium regeneration and nitrification. These findings demonstrate distinct distributions of nitrifying microbes along the salinity gradient from shelf to slope and highlight the significant influence of coastal ocean‐western boundary current interactions on nitrogen biogeochemistry.

Dual carbon isotopes (δ13C and Δ14C) were used to reveal the main sources and input fluxes of dissolved inorganic carbon in a karst reservoir in winter

In karst areas, the dissolved inorganic carbon (DIC) concentrations in aquatic systems are typically higher than that in non-karst areas due to intensive carbonate rock weathering. Understanding the sources and input fluxes of DIC in karst reservoirs is crucial for regional carbon cycle studies. This study utilized dual carbon isotopes (δ13CDIC and Δ14CDIC) to estimate the contribution rates and input fluxes of DIC from various sources in Aha Reservoir (AHR), located in southwestern China. Our results indicated that the DIC concentrations (22.33–32.79 mg L−1) and δ13CDIC values (−10.02‰ to −8.55‰) were nearly homogeneous both vertically and laterally in the reservoir (p > 0.05). The Δ14CDIC values (−246.31‰ to −137.86‰) were homogeneous along the vertical profile (p > 0.05), but showed significant horizontal variation (p < 0.05), with values decreasing from −149.57 ± 10.27‰ to −232.85 ± 2.37‰ at the mouths of the inflowing rivers. We found that the inflowing rivers were the primary DIC sources to AHR, contributing 70% of the total input, while groundwater and atmospheric CO2 contributions were relatively minor, at 18% and 12%, respectively. The Jinzhong River (JZR), influenced by industrial and domestic wastewater discharge, contributed the largest DIC input flux at 2.01 t/(km2·mon). In contrast, the Youyu River (YYR), influenced by acidic mine drainage, and the Baiyan River (BYR), influenced by agricultural activities, contributed relatively smaller DIC input fluxes of 1.29 t/(km2·mon) and 1.03 t/(km2·mon), respectively. This study highlights the significant impact of anthropogenic activities on DIC input in AHR, with industrial and domestic wastewater discharges having a greater influence than agricultural activities and acidic mine wastewater inputs. These findings underscore the critical need to manage and mitigate the impacts of human activities on karst reservoir ecosystems.

True Digestibility of Tryptophan in Plant and Animal Protein

BackgroundProtein quality, evaluated using Digestible Indispensable Amino Acid Score (DIAAS), requires ileal digestibility values of individual indispensable amino acids (IAAs) in each protein. However, true tryptophan (Trp) digestibility has rarely been quantified in humans. ObjectiveTo measure the true Trp digestibility and DIAAS of 2H-intrinsically labeled plant and animal protein sources in humans, using the dual isotope tracer technique. MethodsThe true Trp digestibility of 2H intrinsically labeled plant proteins such as whole mung bean (n = 6) and dehulled mung bean (n = 6), chickpea (n = 5), and yellow pea (n = 5), and protein from animal source foods such as egg white (n = 6), whole egg (n = 6), chicken meat (n = 6), and goat milk (n = 7) was determined against the known digestibility of U-13C spirulina whole cell protein as reference, except for goat milk protein that was measured against free crystalline 13C-Trp as reference. Banked samples from earlier studies conducted to determine true IAA digestibility of different protein sources were used for the analysis. DIAAS was calculated for each test protein using digestibility corrected IAA scores (mg IAA/g of protein) in comparison with the IAA requirement score for adults. ResultsThe true Trp digestibility of whole mung bean, dehulled mung bean, chickpea, yellow pea, egg white, whole egg, chicken meat, and goat milk were 67.6 ± 3.7%, 74.5 ± 4.4%, 72.6 ± 2.3%, 72.5 ± 2.2%, 89.7 ± 2.5%, 91.4 ± 2.6%, 95.9 ± 2.2%, and 92.8 ± 2.9%, respectively. The true Trp digestibility of plant protein sources was significantly lower than that of animal protein sources (P < 0.05). Trp was not a limiting IAA in all the tested proteins. ConclusionThe true Trp digestibility determined in this study ranged from 67.6 ± 3.7% to 95.9 ± 2.2% for whole mung bean and chicken meat, respectively, and adds to the database of individual true IAA digestibility of different protein sources. Trial registration numberThis study was registered in Clinical Trials Registry of India (CTRI) with registration numbers CTRI/2017/11/010468, CTRI/2020/04/024512, and CTRI/2018/03/012265.

Dual isotope analysis reveals the COVID-19 lockdown impact on nitrate aerosol sources and formation pathways in Shanghai

Nitrate (NO3−) is an important contributor to PM2.5 which can adversely affect the environment and human health. A noticeable decrease in NOx concentrations has been reported due to the lockdown measures implemented to curb the spread of Corona Virus Disease 2019 (COVID-19). However, questions remain, regarding the nonlinear relationship between NOx and NO3−. Here, we collected PM2.5 samples in two periods, before and during the lockdown of COVID-19 in Shanghai. Dual isotopes (δ18O-NO3− and δ15N-NO3−) of NO3− were measured to investigate the formation pathways and potential sources of NO3−. The results showed that the concentration of NO3− decreased significantly during the lockdown period compared to the period before the lockdown. Additionally, the hydroxyl pathway was the dominant contributor to NO3− production during the lockdown period, while N2O5 hydrolyses dominated the formation of NO3− before the lockdown. This change is largely attributable to alterations in the oxidative potential of the environment. In comparison to the period preceding the lockdown, the relative contributions of each NOx source remained largely unchanged throughout the lockdown periods. Nevertheless, the concentration of NO3− contributed by each NOx source exhibited a notable decline, particularly the mobile sources and coal combustion. Furthermore, the reduction extent of NO3− due to the lockdown period was also greater than the reduction during the Clean Air Actions (2013–2017). Our findings provide evidence that the COVID-19 lockdown led to a decrease in NO3− concentration due to changes in the formation pathway and reductions in NOx emissions from various sources.

Tracing nitrogen sources and transformation characteristics in a large basin with spatially heterogeneous pollution distribution

This study used dual stable isotopes to examine nitrate sources and geographical distribution in the Liao River Basin (LRB), one of China's seven major river basins. During a normal hydrological season in April 2021, water samples were taken from the main streams of the Liao River (MLR), Shuangtaizi River (STR), Hun River (HR), Taizi River (TZR), and Daliao River (DLR). Monitoring results indicated that 93% of the water samples had a total nitrogen level exceeding the Class IV limit (1.5 mg/L) of the ‘Environmental Quality Standards (EQS) for surface water’, indicating a serious nitrogen pollution status. 71.3% of the total nitrogen on average was in the form of nitrate. The scatterplots of δD-H2O and δ18O-H2O showed that water in TZR and DLR were mainly affected by precipitation, while MLR, STR and HR were additionally impacted by evaporation and groundwater. The overall δ15N and δ18O of NO3− varied from 7.7‰ to 17.9‰ and 0.6‰–11.2‰, respectively. The correlations between δ15N-NO3- and δ18O-NO3-, along with attribution results from the Bayesian isotopic mixing model, indicated a predominant role of manure/sewage (MS) pollution in affecting river nitrate, accounting for 78% of total nitrate in MLR and 72% in DLR. A positive correlation between δ15N-NO3- and δ18O-NO3- in MLR indicated the occurrence of denitrification process. Overall, attribution results showed that the primary nitrate sources varied in different river systems within such a large basin, mainly due to spatially varied land use and human activities. Tailored nitrogen management strategies should be implemented to address the main anthropogenic pressures.

Potential impact of climate change on dietary grain protein content and its bioavailability-a mini review.

The changing global climate brings a gradual yet constant and adverse shift in crop production. Grain crop plants, particularly cereals and legumes, respond varyingly to adverse climate, including reduction in grain yield and changes to their nutrient densities. An understanding of specific changes to crop systems under differing climatic conditions can help in planning diets to meet human nutrient sufficiency. Grain protein content is also affected by adverse environmental factors. Deficits in protein yield, linked to changes in grain or seed protein and antinutrient concentrations, have been reported in major food crops when exposed to elevated carbon dioxide, high temperature, drought, and humidity. These changes, in addition to affecting the quantity of indispensable or essential amino acids (IAA), also impact their bioavailability. Therefore, it is important to assess consequences of climate change on grain protein quality. An important tool to measure grain protein quality, is measuring its digestibility at the level of the ileum and its IAA concentration, linked to a metric called the Digestible IAA Score (DIAAS). A minimally invasive technique called the dual isotope tracer technique, which measures IAA digestibility after simultaneous administration of two different intrinsically labelled protein sources, one a test protein (2H/15N) and one a reference protein (13C) of predetermined digestibility, has been used in evaluation of grain protein IAA digestibility, and promises more in the evaluation of changes based on climate. This review discusses climate induced changes to grain protein quality through the prism of IAA digestibility, using the dual isotope tracer technique.

Disentangling external loadings, hydrodynamics and biogeochemical controls on the fate of nitrate in a coastal embayment

Nitrogen, as an essential nutrient, largely contributes to the coastal eutrophication. However, the accurate depiction and evaluation of how external loadings, hydrodynamics, and biogeochemical reactions mediate the occurrence, transport, and transformation of nitrate (NO3-) within coastal embayment still pose ongoing challenges to date. In this study, we took advantage of dual isotopes of NO3- to track external NO3- loadings, radium and dual isotopes of H2O to characterize the influences of hydrodynamic on NO3- transport, δ18O-NO3- and δ18O-H2O along with microbial analysis to explore major NO3- biogeochemical reactions in Tolo Harbour, Hong Kong. The multiple isotopic evidence showed that NO3- in surface harbour water was predominantly contributed by precipitation in wet season and its impact was strengthened by stratification. In dry season, NO3- in the surface harbour water became largely influenced by benthic input and biogeochemical reactions due to intensified vertical mixing. Based on NO3- mass balance model, biogeochemical reaction, especially nitrification, was found to be the major process to secure the closure of NO3- budget and increase NO3- inventory from wet to dry season. Hydrodynamics redistributed the external NO3- loadings and mediated nitrogen biogeochemical reactions, both of which further synergistically regulated the fate of NO3- in the embayment.

Leaf isotopes reveal tree diversity effects on the functional responses to the pan-European 2018 summer drought.

Recent droughts have strongly impacted forest ecosystems and are projected to increase in frequency, intensity, and duration in the future together with continued warming. While evidence suggests that tree diversity can regulate drought impacts in natural forests, few studies examine whether mixed tree plantations are more resistant to the impacts of severe droughts. Using natural variations in leaf carbon (C) and nitrogen (N) isotopic ratios, that is δ13C and δ15N,as proxies for drought response, we analyzed the effects of tree species richness on the functional responses of tree plantations to the pan-European 2018 summer drought in seven European tree diversity experiments. We found that leaf δ13C decreased with increasing tree species richness, indicating less drought stress. This effect was not related to drought intensity, nor desiccation tolerance of the tree species. Leaf δ15N increased with drought intensity, indicating a shift toward more open N cycling as water availability diminishes. Additionally, drought intensity was observed to alter the influence of tree species richness on leaf δ15N from weakly negative under low drought intensity to weakly positive under high drought intensity. Overall, our findings suggest that dual leaf isotope analysis helps understand the interaction between drought, nutrients, and species richness.

Dietary protein splanchnic uptake and digestibility via stable isotope tracers.

Dietary proteins are broken down into peptides across the gastrointestinal tract, with skeletal muscle being a primary deposition site for amino acids in the form of incorporation into, for example, metabolic and structural proteins. It follows that key research questions remain as to the role of amino acid bioavailability, of which protein digestibility and splanchnic sequestration (absorption and utilization) of amino acids are determining factors, impact upon muscle protein synthesis (MPS) in clinical states. Elevated splanchnic amino acid uptake has been implicated in anabolic resistance (i.e. attenuated anabolic responses to protein intake) observed in ageing, though it is unclear whether this limits MPS. The novel 'dual stable isotope tracer technique' offers a promising, minimally invasive approach to quantify the digestion of any protein source(s). Current work is focused on the validation of this technique against established methods, with scope to apply this to clinical and elderly populations to help inform mechanistic and interventional insights. Considerations should be made for all facets of protein quality; digestibility of the protein, absorption/utilization and subsequent peripheral bioavailability of amino acids, and resultant stimulation of MPS. Stable isotope tracer techniques offer a minimally invasive approach to achieve this, with wide-ranging clinical application.

The addition of mycoprotein to a mixed-meal impacts postprandial glucose kinetics without altering blood glucose concentrations: a randomised controlled trial

BackgroundMycoprotein is a high-fibre food previously shown to reduce postprandial glucose concentrations when ingested within a mixed-meal. We applied a dual stable isotope tracer approach to determine whether this is due to a reduced rate of appearance of glucose, in participants of ranging BMI.MethodsTwenty-four adults (F = 8, BMI 30 ± 6 kg·m−2) attended 2 trials in a double-blind, randomised, cross-over design. Participants ingested two energy and macronutrient matched milk-based drinks (enriched with 1000 mg [U-13C6] glucose in a subset of 12 participants), containing 50 g glucose and either 0 (CON) or 20 g (MYC) mycoprotein. A primed continuous intravenous infusion of D-[6,6-2H2] glucose determined plasma glucose kinetics over 6 h. Postprandial time-course, and AUC, of glucose and insulin concentration, rate of disappearance (RdT) and appearance of exogenous (RaEx), endogenous (EGP), and total (RaT) plasma glucose were assessed using two- and one-way ANOVA.ResultsDrink ingestion increased blood glucose and serum insulin concentrations (P < 0.05) and were comparable between conditions (P > 0.05). Both RaT and RdT were higher with MYC compared with CON over 6 h (mean 6 h glucose appearance and disappearance increased by 5 and 9%, respectively, P < 0.05). RaEx was not affected by MYC ingestion over 6 h (P > 0.05). The mean contribution of EGP to total glucose appearance was 15% greater with MYC, with a trend towards significance (P = 0.05). There was no relationship between BMI and the response to MYC ingestion for any of the variables (P < 0.05).ConclusionThe ingestion of mycoprotein within a mixed-meal impacted postprandial glucose kinetics, but not blood glucose or serum insulin concentrations, in individuals of ranging BMI.Clinical trial registry number and websiteThis trial was registered at clinicaltrials.gov as NCT04084639 and can be accessed at https://clinicaltrials.gov/ct2/show/NCT04084639.

Deciphering and quantifying nitrate sources and processes in the central Yellow Sea using dual isotopes of nitrate

Anthropogenic activities pose significant challenges to the accumulation of coastal nitrogen (N). Accurate identification of nitrate (NO3−) sources is thus essential for mitigating excessive N in many marginal seas. We investigated the dual isotopes of NO3− in the central Yellow Sea to elucidate the sources and cycling processes of NO3−. The results revealed significant spatial variability in NO3− concentrations among the Yellow Sea Surface Water (YSSW), Changjiang Diluted Water (CDW), Yellow Sea Cold Water Mass (YSCWM), and Taiwan Warm Current Water (TWCW). Stratification played a crucial role in restricting vertical nutrient transport, leading to distinct nutrient sources and concentrations in different water masses. The dual NO3− isotopic signature indicated that atmospheric deposition was the primary source of surface NO3−, contributing approximately 30 % to the NO3− in the YSSW. In the NO3−-rich CDW, the heavier δ15N-NO3− and δ18O-NO3− suggested incomplete NO3− assimilation. Organic matter mineralization and water stratification played crucial roles in the accumulation of nutrients within the YSCWM and TWCW. Notably, regenerated NO3− accounted for approximately half of the NO3− stored in the YSCWM. A synthesis of NO3− dual isotope data across the coastal China seas revealed significant spatial and seasonal variations in the N source. The study emphasized the dynamics of coastal NO3− supply, which are shaped by the complex interconnections among marine, terrestrial, and atmospheric processes. Our approach is a feasible method for exploring the origins of N amidst the escalating pressures of anthropogenic nutrient pollution in coastal waters.

Effect of Partial Substitution of Chemical Fertilizers with Organic Fertilizers on N2O and NO Emissions from a Peach Orchard

Organic fertilizer substitution has been promoted as a weight loss, efficient, and diversified fertilizer substitution technology in agricultural production. However, there is a lack of comprehensive assessment of the impact of organic fertilizers on N2O and NO emissions from orchards. In this study, N2O and NO emissions from peach orchards were observed annually using static dark box-gas chromatography to compare the effects of chemical fertilizer application alone and partial replacement of chemical fertilizer treatment on NO emissions from peach orchards. The results showed that the partial replacement of chemical fertilizers with organic fertilizers reduced the total N2O and NO emissions from peach orchards by 15.0 % and 9.4 %, respectively. The N2O and NO emission factors were reduced by 21.3 % and 21.1 %. The mineral N content of the soil in the organic fertilizer treatment was lower than that in the chemical fertilizer treatment alone. The organic fertilizer treatment increased the contribution of AOA to nitrification and decreased the contribution of AOB, thus reducing N2O and NO from nitrification. In addition, the results of the dual isotope mixing model[δ18O(N2O/H2O) vs. δ15NSP] indicated that the bacterial denitrification/nitrifying bacterial denitrification (bD/nD) process served as the primary pathway for N2O emissions in peach orchards. Partial substitution with organic fertilizers enhanced soil denitrification, resulting in larger reductions in the amounts of N2O and NO. Therefore, partial substitution of organic fertilizer is a viable measure to mitigate nitrogen oxide emissions from orchards and to achieve green and low-carbon development in agriculture.

Dual-carbon isotope analysis of benzene polycarboxylic acids for tracking black carbon across different environments

Black carbon (BC) is ubiquitous in the environment and is a significant component of the refractory carbon pool. However, its sources, biogeochemical processes, and environmental residence times are poorly understood. One important reason is that the technical protocols for isolating/analyzing BC vary across different matrices, thereby bringing inconsistency among studies on BC in different environment media. Benzene polycarboxylic acids (BPCA), produced by nitric acid oxidation of the condensed aromatic structure that is common in BC and BC-like substances, has been proven to be a useful molecular proxy for tracking BC in the Earth's surface. Here, we introduce a new technical approach for the compound-specific dual-carbon isotope (δ13C and Δ14C) analysis of BPCA. The BPCA compounds are isolated using preparative liquid chromatography, in which trifluoroacetic acid is used in the mobile phase instead of phosphoric acid. This allows complete removal of solvent from the isolated BPCA fraction, so that conversion of BPCA isolates into CO2 can be done by conventional oxidation methods for off-line Δ14C analysis with accelerator mass spectrometry. Liquid chromatography (void column)-stable carbon isotope ratio mass spectrometry is employed to measure δ13C of the isolated BPCA, leaving as much BPCA carbon amount as possible for 14C analysis. Blockage of oxidation chamber due to incomplete oxidation of other organic acids in the samples is avoided thanks to preliminary isolation of BPCA. We tested the approach by applying it to solid and dissolved BC species in a suite of environmental reference materials, including maize char, coal, riverine natural organic matter (NOM 2R101N), marine sediment (SRM 1941b), urban dust (SRM 1649b), and coke-polluted soils. We assessed the offsets of BPCA-δ13C and BPCA-Δ14C values caused by procedural carbon contaminations to correct measured carbon isotopic values. Paired δ13C-Δ14C data of individual BPCA were plotted to validate and demonstrate the ability of this dual carbon isotope technique in tracking BC across different environmental matrices. We observed slightly different δ13C-Δ14C signatures among individual BPCA, indicating that the less condensed BC may have younger apparent radiocarbon ages.

Legacy and emerging per- and polyfluoroalkyl substances (PFASs) in agricultural soils affected by fluorochemical manufacturing facilities, North China: Occurrence, region-specific distribution, substitution trend and source appointment

Accompanied with restriction of legacy per- and polyfluoroalkyl substances (PFASs), numbers of emerging PFASs are widely detected in the environment. However, information on environmental occurrences and behaviors of emerging PFASs were scarce in agricultural soils. In this study, the spatial distributions, sources, substitution trends and ecological risk assessment of 31 legacy and emerging PFASs were investigated in 69 agricultural soils from Fuxin, North China. The 26 out of 31 PFASs were detected with concentrations of 57.36 - 1271.06 pg/g dry weight. Perfluorooctanoic acid (PFOA) and hexafluoropropylene oxide dimer acid (HFPO-DA) were predominant in legacy and emerging PFASs, respectively. Based on principal component and dual carbon-nitrogen stable isotope analysis, atmosphere, fluorochemical activities and river irrigation were main sources of PFASs. Substitution trends indicated HFPO-DA and short chain perfluoroalkyl carboxylic acids (C4 - C7) as main alternatives of PFOA, and 6:2 fluorotelomer sulfonic acid (6:2 FTSA) and sodium p-perfluorous nonenoxybenzene sulfonate (OBS) as major substitutes to perfluorooctanesulfonic acid (PFOS). The calculated risk quotient values (< 0.006) only indicated potential low ecological risk of 7 target PFASs in agricultural soils. The results of this study broadened out the information of PFAS contamination in agricultural soils, which were significant for PFAS supervision in China.

Effect of hydrogen isotopic offset and input data on the isotope-based estimation of plant water sources

The stable isotope of water has been widely used to investigate plant water resources with the assumption that root water uptake and plant water transport is a non-isotopic fractionation process. However, recent research revealed that significant isotopic offsets between xylem water and potential water sources, which may result in errors when estimating plant water sources. We test five different input data modes in Bayesian isotope mixing model [only δ18O (M−O), only δD (M−D), δD after subtracting the deviation with respect to the soil water line (SW-excess) from the δD of xylem samples (M−SD), δD and δ18O (M−OD), and δD and δ18O after subtracting the SW-excess from the δD of xylem samples (M−OSD)] to identify sources of water absorbed by Chinese wolfberries (Lycium chinense Miller). The results showed that there was significant difference (p < 0.05) between the M−O and M−D modes. The evaluation indexes (RESE, N, MaxE, MinE, MAPE) performed well in the M−SD, M−O, and M−OSD modes. Furthermore, the M−SD, M−OSD, and M−O had consistent contribution proportions for the three soil layers. In addition, the corrected δD values in the dual and single isotope modes performed better than the original δD in quantifying water source contribution. This study provides critical insights into choosing a suitable method for isotope-based identification of plant water sources.