Nitrate Deposition Research Articles

Evidence of the Uyunbulak Salt Lake Water Recharge in the Kumish Basin, Xinjiang, China, from Boron Isotopes

The reserves of nitrate (NO3-) mineral resources in the Turpan-Hami Basin in Xinjiang rank second after those in the Atacama Desert in Chile, South America. Considerable attention has been devoted to nitrogen (N) sources of NO3- deposits in recent years due to the increase in demand for NO3- fertilizers in agriculture and chemical industries. However, although the potassium nitrate (KNO3) deposits in the Uyunbulak salt lake in the Kumish basin, Xinjiang, China, have received increasing attention from numerous researchers in recent years, they all focused on the study of nitrate sources and agreed that the nitrate source in the Kumish basin is mainly atmospheric sedimentation. Studies on their water sources are scarce; for salt lake nitrate deposits, water supply also plays a crucial role in the genesis of the deposit. As a sensitive indicator, a boron isotope is often used to indicate water bodies from different sources. However, the presence of NO3- ions in water will interfere with the determination of boron isotopes, so the research on boron isotopes in nitrate salt lakes has been hindered. In this study, the three-step ion exchange method published by Ma et al. (2020) was used to eliminate the influence of NO3- ions in water on boron isotope determination, so as to reveal the water supply of Uyunbulak Salt Lake in Kumish basin by using boron isotopes which are more sensitive to water types. In this study, ice and snow meltwater, fissure water, groundwater, and surface water samples were collected from the Kumish basin and analyzed for the determination of boron (B) isotopic and hydrochemical compositions during the migration process of water bodies to reveal the recharge relationship between the water bodies from the northwestern margin of the basin and the study area. The obtained hydrochemical composition results showed a gradual increase in the salinity of the water body from 556 to 7372 mg/L from the northwestern to the southeastern parts of the basin, resulting in a gradual change in the hydrochemical facies type of Uyunbulak salt lake to NaCl. This finding suggested that the water body migrates from the northwestern to southeastern parts of the basin. The results of B isotope composition indicated two types of water bodies from different sources, namely, the ice and snow meltwater of the Southern part of the Tianshan Mountains and groundwater of the basin, exhibiting B isotope composition ranges of 26.66–27.26‰ and 12.75–15.19‰, respectively. These two types of water bodies are mixed at the Uzong spring (Q1). The ice and snow meltwater in the mixed water accounted for 46%, while the groundwater accounted for 54%. The mixed water continues to recharge the Uyunbulak Salt Lake in the southeastern part of the basin.

Petrography, mineralogy, and geochemistry of nitrogenous shale in the Western Desert of Egypt: implications for paleoenvironment

Besides nitrate deposits located in the Atacama Desert of Chile and the Mojave Desert of California, the present work documents, for the first time, the occurrence of potassium nitrate as oval-suboval-shaped aggregations associated with the Late Maastrichtian-Early Paleocene Dakhla Shale and the Paleocene-Early Eocene Esna Shale encountered in the northeastern part of the Kharga Oasis, particularly at G. Um El-Ghanayem and G. Ghaneima. Consequently, integrated petrographic, mineralogical, and geochemical investigations were carried out for shale deposits and nitrate salts to reconstruct the paleoenvironmental conditions of shale, reveal the extent to which nitrate salts are genetically related to the paleoenvironment of shale deposits, and build up a complete scenario about the source and the formation mechanism of nitrate salts. The overall results showed that the studied shale deposits were sourced from mafic igneous and quartzose sedimentary provenances where humid climatic conditions were dominant; the transported detrital particles were then settled down under oxidizing bottom water and shallow depositional conditions. Moreover, the nitrate salts are of an epigenetic origin and sourced from the microbial nitrification of organic matter and the wet atmospheric deposition that is believed to be triggered by the active volcanic eruptions during the Late Eocene/Early Oligocene transition where warm climatic conditions prevailed.

Atmospheric deposition of reactive nitrogen to a deciduous forest in the southern Appalachian Mountains.

Assessing nutrient critical load exceedances requires complete and accurate atmospheric deposition budgets for reactive nitrogen (Nr). The exceedance is the total amount of Nr deposited to the ecosystem in excess of the critical load, which is the amount of Nr input below which harmful effects do not occur. Total deposition includes all forms of Nr (i.e., organic and inorganic) deposited to the ecosystem by wet and dry pathways. Here we present results from the Southern Appalachian Nitrogen Deposition Study (SANDS), in which a combination of measurements and field-scale modeling was used to develop a complete annual Nr deposition budget for a deciduous forest at the Coweeta Hydrologic Laboratory. Wet deposition of ammonium, nitrate, nitrite, and bulk organic N were measured directly. The dry deposited Nr fraction was estimated using a bidirectional resistance-based model driven with speciated measurements of Nr air concentrations (e.g., ammonia, ammonium aerosol, nitric acid, nitrate aerosol, bulk organic N in aerosol, total alkyl nitrates, and total peroxy nitrates), micrometeorology, canopy structure, and biogeochemistry. Total annual deposition was ~6.7 kg N ha-1 yr-1, which is on the upper end of Nr critical load estimates recently developed for similar ecosystems in the nearby Great Smoky Mountains National Park. Of the total (wet + dry) budget, 51.1% was contributed by reduced forms of Nr , with oxidized and organic forms contributing ~41.3% and 7.6%, respectively. Our results indicate that reductions in deposition would be needed to achieve the lowest estimates (~3.0 kg N ha-1 yr-1) of Nr critical loads in southern Appalachian forests.

Comparison of vertical and horizontal atmospheric deposition of nitrate at Central European mountain-top sites during three consecutive winters

Nitrogen (N) deposition, a key process of atmospheric self-cleaning, represents an important pathway for nutrients and pollutants to ecosystems. Enhanced N deposition flux contributes to acidification, eutrophication and loss of biodiversity. N-NO3− concentrations in rime and snow were measured at 10 Czech plots situated in borderline mountains in 2009–2011 winters. The results were put in context with data-driven geostatistical modelling results of annual wet vertical and horizontal deposition. Our hypotheses were that: (i) rime and snow would be more polluted in the highly industrialized north than in the south, (ii) the N-NO3− concentrations would differ in the three winters studied, and (iii), that N-NO3− rime deposition is not negligible in Central European mountain ranges. Our results indicated that winter N-NO3− concentrations were significantly higher in rime than in snow and that there were much larger between-site differences in N-NO3− concentrations for rime than for snow. Relatively large differences were found between individual years. Atmospheric input of N-NO3− in winter was dominated by vertical deposition, i.e., snow. Modelled results showed that mean winter rime deposition corresponded to about 6–25 %, and mean winter snow deposition made up 25–72.5 % of mean annual N-NO3− wet-only deposition. Model N-NO3−occult deposition estimated from throughfall and total (wet and dry) deposition is highly uncertain, however: N throughfall is not a relevant proxy for estimation of realistic total N deposition due to N exchange between the tree canopy and atmosphere.

Au Single Atom Supported on TiO2 Drives Hole Mitigation for the Enhanced Photooxidation of Hg0

Noble metal-supported TiO2 has excellent photocatalytic activity for the oxidation of Hg0 due to the Mott–Schottky barrier that prevents the recombination of photogenerated hole–electron pairs. However, surface noble-metal atoms usually cause low atomic utilization, of which the inner layer cannot participate in the oxidation and is hence not beneficial for improving the photocatalytic activity. Single-atom-based catalysts (SAC) have an extreme atomic efficiency, reducing the amount of noble metals and significantly improving photocatalytic activity. Herein, 0.1% Au single atom (SA)-doped Ti4+ defect TiO2 (0.1% Au–Ti1-xO2) with Au–(O)4 coordination was used for the photooxidation of Hg0. Second, the influence of the coordination on the separation of photogenerated electron–hole pairs, the transfer direction of charges, and the oxidation of Hg0 was thoroughly explored using transient photovoltage (TPV), in situ X-ray photoelectron spectroscopy (XPS), density functional theory (DFT), etc. Finally, the influence of SO2 and NO on the photooxidation of Hg0 was discussed using in situ diffuse reflection infrared Fourier transform spectroscopy (DRIFTS). 0.1% Au–Ti1-xO2 had a much higher photooxidation efficiency of Hg0 than 0.1% Au/TiO2. Moreover, the Au–(O)4 coordination significantly promoted the separation of photogenerated electron–hole pairs by driving the mitigation of photogenerated holes. Additionally, 0.1% Au–Ti1-xO2 exhibited a remarkable resistance to SO2 and NO because Au SA effectively avoided the deposition of nitrates and sulfates. This study provides a valuable surface engineering strategy for the atomic-level dispersion of noble metal-modified TiO2.

Nitrate dynamics and source identification of rainwater in Beijing during rainy season: Insight from dual isotopes and Bayesian model

Anthropogenic reactive nitrogen emissions have a significant impact on atmospheric chemical composition and earth surface ecosystem. As one of the most important sinks of atmospheric nitrogen, the wet deposition of nitrate (rainwater NO3−) has been widely concerned. Yet, the sources and transformation processes of wet deposited NO3− were not well revealed in megacity during rainy season in the context of global climate change. Here, we investigated the concentrations of nitrogen components and dual isotopes of rainwater nitrate collected in Beijing during July to August 2021 (rainy season). The main findings showed that the concentrations of NH4+-N, NO3−-N, and NO2−-N ranged 0.5– 6.7 mg L−1, 0.3– 4.5 mg L−1, and 0.05– 0.18 mg L−1, respectively, with the average relative percentages of 69 %, 29 %, and 2 %. The stoichiometry analysis of characteristic ion ratios indicated that the contribution of municipal wastes and agricultural sources to rainwater NH4+-N is relatively significant, while traffics were the major contributor of NO3−-N instead of the fixed emission. Rainwater δ15N-NO3− and δ18O-NO3− presented slightly 15N-depleted characteristic compared to previous studies with the average values of −3.9 ± 3.1 ‰ and 58.7 ± 12.6 ‰. These isotope compositions suggesting an origin of rainwater NO3− from the mixing of multi-sources and was mainly generated via the pathway of OH radical oxidization. Further source apportionment of rainwater NO3− by Bayesian mixing model evaluated that traffic (30.3 %) and soil (30.3 %) emissions contributed mostly to NO3−, while the contribution of biomass burning (18.8 %) and coal combustion (20.6 %) were relatively lower. This study highlighted the important role of dual isotopes in rainwater nitrate source identification and formation processes in megacity.

On the seasonality of long-range transport of acidic pollutants in East Asia

East Asia currently has the largest SO2 and NO x emissions in the world. The long-range transport (LRT) of acidic pollutants in this region is of great concern but the extent is not well understood. Here results from combined long-term (⩾20 years) atmospheric deposition monitoring and air trajectory analysis in East Asia were reported. The results showed that despite the large decrease of SO2 and NO x emissions in Taiwan, annual deposition of non-sea-salt sulfate (nss-) in northern Taiwan showed no decreasing trend during 1994–2020. However, when divided seasonally, both nss- and nitrate () deposition had a significant decreasing trend in the summer but not in the winter. Similar patterns were found for Japan and Korea. Air trajectory models in combination with a regional emission map indicate that LRT from eastern China contributed up to 70% of the winter deposition of nss- and in Taiwan and up to 50% in Japan and Korea. The results indicate that LRT obscured the efficacy of local pollution control measures in East Asia and suggest that transboundary air pollution regulations are required to combat acid deposition.

Modeling particulate nitrate in China: Current findings and future directions.

Particulate nitrate (pNO3) is now becoming the principal component of PM2.5 during severe winter haze episodes in many cities of China. To gain a comprehensive understanding of the key factors controlling pNO3 formation and driving its trends, we reviewed the recent pNO3 modeling studies which mainly focused on the formation mechanism and recent trends of pNO3 as well as its responses to emission controls in China. The results indicate that although recent chemical transport models (CTMs) can reasonably capture the spatial-temporal variations of pNO3, model-observation biases still exist due to large uncertainties in the parameterization of dinitrogen pentoxide (N2O5) uptake and ammonia (NH3) emissions, insufficient heterogeneous reaction mechanism, and the predicted low sulfate concentrations in current CTMs. The heterogeneous hydrolysis of N2O5 dominates nocturnal pNO3 formation, however, the contribution to total pNO3 varies among studies, ranging from 21.0% to 51.6%. Moreover, the continuously increasing PM2.5 pNO3 fraction in recent years is mainly due to the decreased sulfur dioxide emissions, the enhanced atmospheric oxidation capacity (AOC), and the weakened nitrate deposition. Reducing NH3 emissions is found to be the most effective control strategy for mitigating pNO3 pollution in China. This review suggests that more field measurements are needed to constrain the parameterization of heterogeneous N2O5 and nitrogen dioxide (NO2) uptake. Future studies are also needed to quantify the relationships of pNO3 to AOC, O3, NOx, and volatile organic compounds (VOCs) in different regions of China under different meteorological conditions. Research on multiple-pollutant control strategies involving NH3, NOX, and VOCs is required to mitigate pNO3 pollution, especially during severe winter haze events.

Rapid improvement of lake acid–base status in Atlantic Canada following steep decline in precipitation acidity

Policy measures resulted in reductions in acidic emission of sulfur and nitrogen in North America. Here, we conducted trend analyses on a 37-year database for atmospheric depositions and lake ( n = 78) chemistry in the provinces of Nova Scotia, New Brunswick, and Newfoundland and Labrador, in Canada. Sulfate, and particularly nitrate deposition, began to decrease strongly around the year 2000, resulting in strong pH increases in precipitation. Recovery was observed in most lakes with significant increases in pH and Gran alkalinity (AlcG). A piecewise regression approach detected coherent breaks and overlapping confidence intervals in the break years for precipitation pH and lake AlcG (to a lesser extent for lake pH), suggesting a rapid lake response to the sudden changes in acidic inputs. However, an increase in organic acid after 2000 decreases the rate of acid neutralizing capacity recovery nearly by half in about a third of the studied lakes. Despite the positive pH and AlcG trends, a significant proportion of lakes still have pH and calcium values below the recommended thresholds for aquatic life.

Impacts of post-depositional processing on nitrate isotopes in the snow and the overlying atmosphere at Summit, Greenland

Abstract. The effect of post-depositional processing on the preservation of snow nitrate isotopes at Summit, Greenland, remains a subject of debate and is relevant to the quantitative interpretation of ice-core nitrate (isotopic) records at high snow accumulation sites. Here we present the first year-round observations of atmospheric nitrate and its isotopic compositions at Summit and compare them with published surface snow and snowpack observations. The atmospheric δ15N(NO3-) remained negative throughout the year, ranging from −3.1 ‰ to −47.9 ‰ with a mean of (−14.8 ± 7.3) ‰ (n=54), and displayed minima in spring which are distinct from the observed spring δ15N(NO3-) maxima in snowpack. The spring average atmospheric δ15N(NO3-) was (−17.9 ± 8.3) ‰ (n=21), significantly depleted compared to the snowpack spring average of (4.6 ± 2.1) ‰, while the surface snow δ15N(NO3-) of (−6.8 ± 0.5) ‰ was in between the atmosphere and the snowpack. The differences in atmospheric, surface snow and snowpack δ15N(NO3-) are best explained by the photo-driven post-depositional processing of snow nitrate, with potential contributions from fractionation during nitrate deposition. In contrast to δ15N(NO3-), the atmospheric Δ17O(NO3-) was of a similar seasonal pattern and magnitude of change to that in the snowpack, suggesting little to no changes in Δ17O(NO3-) from photolysis, consistent with previous modeling results. The atmospheric δ18O(NO3-) varied similarly to atmospheric Δ17O(NO3-), with summer low and winter high values. However, the difference between atmospheric and snow δ18O(NO3-) was larger than that of Δ17O(NO3-). We found a strong correlation between atmospheric δ18O(NO3-) and Δ17O(NO3-) that is very similar to previous measurements for surface snow at Summit, suggesting that atmospheric δ18O(NO3-) versus Δ17O(NO3-) relationships were conserved during deposition. However, we found the linear relationships between δ18O and Δ17O(NO3-) were significantly different for snowpack compared to atmospheric samples. This likely suggests the oxygen isotopes are also affected before preservation in the snow at Summit, but the degree of change for δ18O(NO3-) should be larger than that of Δ17O(NO3-). This is because photolysis is a mass-dependent process that would directly affect δ18O(NO3-) in snow but not Δ17O(NO3-) as the latter is a mass-independent signal. Although there were uncertainties associated with the complied dataset, the results suggested that post-depositional processing at Summit can induce changes in nitrate isotopes, especially δ15N(NO3-), consistent with a previous modeling study. This reinforces the importance of understanding the effects of post-depositional processing before ice-core nitrate isotope interpretation, even for sites with relatively high snow accumulation rates.

Impact of tree species diversity on throughfall deposition in a young temperate forest plantation

Throughfall deposition is an important pathway via which particles, aerosols and gases can move from the atmosphere to the forest floor, which can greatly impact forest biodiversity and functioning. Although throughfall deposition biochemistry has been well studied in forest ecosystems, less is known about how throughfall deposition is modified by tree species diversity. To disentangle the effects of tree species identity and diversity on throughfall deposition, we installed rain gauges in a 10-year-old tree diversity experiment. With these rain gauges, we monitored throughfall biweekly, and performed chemical analyses monthly for all the major ions (Na+, Cl−, SO42−-S, K+, Ca2+, Mg2+, PO43−-P, NO3−-N and NH4+-N), for a period of one year. Based on these data, we analysed species identity (i.e. whether throughfall deposition depended on the tree species present in the overstorey), and diversity effects (i.e. whether throughfall deposition depended on tree species richness). We confirmed species identity effects on throughfall deposition. Presence of pine led to higher throughfall deposition of inorganic nitrogen, and lower amounts of phosphorus, calcium and magnesium reaching the forest floor. Additionally, species characteristics and stand structural characteristics, i.e. basal area and canopy cover, emerged as key factors driving throughfall deposition of sodium, chloride, nitrate, sulphate and potassium. Tree species diversity effects on throughfall deposition were also present, mostly via increased basal area and canopy cover, leading to increased throughfall deposition of inorganic nitrogen, sulphate, chloride, sodium and potassium. Our findings thus suggest that tree species diversity enhances throughfall deposition of most ions that we analysed, potentially increasing nutrient availability for below-canopy plant communities. Given that inorganic nitrogen and sulphur are major atmospheric pollutants, increased deposition in mixed plots might affect ecosystem functioning. Further research will be needed to determine the extent of this impact.

Agricultural ammonia dry deposition and total nitrogen deposition to a Swiss mire

Mires are among the ecosystems most affected by eutrophication caused by excessive nitrogen (N) inputs via N deposition of ammonium (NH4+), nitrate (NO3–), nitric acid (HNO3), nitrogen dioxide (NO2), and ammonia (NH3). As NH3 emissions are mostly generated by agriculture, a particular conflict of interest exists in areas where agricultural production systems are located nearby sensitive ecosystems, as often is the case in Switzerland. Therefore, this study aimed at quantifying and evaluating total N inputs to a mire in the Swiss Alpine foothills during 2007–2019, focusing on NH3 dry deposition. Three surface–vegetation–atmosphere transfer models were used to estimate dry deposition of NH3 based on micrometeorological data in combination with monthly passive sampler NH3 concentration measurements. NH3-N dry deposition summed up to 1.5–5.2 kg N ha–1 a–1, while total N loads were 11.5–14.2 kg N ha–1 a–1, well beyond the critical N loads for raised bogs (5–10 kg N ha–1 a–1), and also higher than the lower limits for oligotrophic fens and mountain hay meadows (10 kg N ha–1 a–1). Hence, the mire studied is most likely negatively affected by eutrophication, which could ultimately lead to biodiversity loss and ecosystem instability. This is particularly remarkable as the monthly NH3 concentrations at the study site (0.4–4.7 µg m–3) are comparatively low for Switzerland.

Tracing nitrate sources and transformations using △17O, δ15N, and δ18O-NO3− in a coastal plain river network of eastern China

Identifying the sources and transformations of riverine nitrate plays a critical role in mitigating nitrogen enrichment of river networks. Several previous studies have used δ18O-NO3− to quantitatively assess riverine nitrate contributed by atmospheric nitrate and terrestrial sources, but their results have great uncertainty due to the wide range of δ18O-NO3− values and isotopic fractionation during nitrogen-cycling processes in terrestrial environment. The nitrate 17O anomaly (△17O-NO3−), as an unambiguous tracer of atmospheric nitrate, is a promising tool to effectively separate atmospheric nitrate from microbially produced nitrate. However, to our knowledge, △17O-NO3− approach has not been previously applied to identify nitrate pollution sources in plain river networks of eastern China. In this study, we used a multiple isotope approach (δD/δ18O-H2O and δ15N/δ18O/△17O-NO3−) for the first time to quantitatively identify sources and transformations of riverine nitrate in a hypereutrophic coastal plain river network namely Wen-Rui Tang River located in eastern China, which is a region receiving high inputs of atmospheric nitrogen deposition. The △17O-NO3− values in precipitation and river water during the study period (April–June of 2021) varied from 14.83‰ to 31.39‰ and from − 2.82‰ to 9.66‰, respectively. The δD/δ18O-H2O values revealed that river water mainly originated from recent precipitation with little evaporation. Moreover, the δ15N/δ18O-NO3− values indicated that microbial nitrification, not denitrification, was the predominant nitrogen-cycling process in the watershed. Based on a Bayesian mixing model (Stable Isotope Analysis in R, SIAR) using δ15N/△17O-NO3−, municipal sewage was identified as the dominant nitrate source (50.5 ± 11.7%), followed by soil nitrogen (23.8 ± 13.7%), atmospheric nitrate deposition (14.3 ± 2.9%), and nitrogen fertilizer (11.4 ± 8.7%). Finally, an uncertainty analysis for nitrate source apportionment demonstrated that the greatest uncertainty was associated with soil nitrogen, followed by municipal sewage, nitrogen fertilizer, and atmospheric nitrate deposition. This study provides important scientific information on riverine nitrate source apportionment to guide pollution control/remediation strategies and highlights the benefits of utilizing △17O-NO3− to enhance nitrate source apportionment.

Elucidating sources of atmospheric NOX pollution in a heavily urbanized environment using multiple stable isotopes

Atmospheric deposition of nitrogen (N) from rain and aerosols can be a significant non-point source – particularly in urbanized coastal areas and contribute to coastal eutrophication and hypoxia. Here, we present geochemical and isotopic data from surface waters coupled with an 18-month time series of geochemical and isotopic data measured on wet and dry deposition over Hong Kong from June 2018. Dual stable isotopes of nitrate (δ15N-NO3− and δ18O-NO3−) of rain and total suspended particulates (TSP) were analyzed to trace the sources and understand seasonal pattern of atmospheric nitrate. The δ15N of TSP, δ15N-NO3 in rain and TSP ranged from +0.94 to +17.6‰, −4.1 to +3.0‰ and −1.3 to +9.0‰ respectively. δ15N varied seasonally with higher values in winter and lower values in summer. This variation can be explained by a change in the sources of atmospheric NOx driven by the East Asian Monsoon. It was found that most NOx comes from coal burning in winter and a mix of vehicle emissions, fossil fuel combustion and lightning in summer. Moreover, the estimated dry and wet deposition of nitrate and ammonium in Hong Kong is around 18 kg N ha−1 annually, which is of the same order of magnitude as N released by sewage effluents and groundwater. This implies that atmospheric N deposition over the N-limited waters of the eastern side of Hong Kong could contribute significantly to the N budget. Therefore, atmospheric N deposition may alter the local N marine cycling, thus monitoring its impact is crucial for water quality in Southern China.

Effect of cross-linker's incorporation into two adhesive systems with self-etch mode applied on sound and caries-affected dentin

This study investigated the effect of incorporation of two cross-linkers agents, proanthocyanidin (PA) or epigallocatechin-3-gallate (EGCG), into two adhesive systems with a self-etch approach, on microtensile bond strength (μTBS), nanoleakage (NL), and in inhibition potential of MMP's activity, in immediate (24 h) time and after 12 months of water storage (12 M), on sound dentin (SD) or caries affected dentin (CAD). Dentin middle surfaces of 96 human molars were exposed, and half of them were submitted to a microbiological cariogenic challenge. Specimens were randomly allocated into twelve groups (n = 8) according to the following factors under study: 1. adhesive incorporation at three levels (1 wt% EGCG x 1 wt% PA x Control); 2. dentin status (CAD x SD); 3. adhesive approach: AUSE (Ambar Universal, FGM) or CSE (Clearfil SE Bond, Kuraray). Data of μTBS were evaluated according to 3-way-repetead measures ANOVA and Bonferroni post-hoc (p ˂ 0.05). No group showed statistical difference at different times (24 h × 12 M) regardless of the substrate (SD or CAD), p = 0.65. In general, CSE showed higher BS when compared with AUSE (p < 0.001), and SD presented higher values than CAD (p < 0.001), when these factors were evaluated individually. There was statistical interaction between dentin status versus time (SD-12 M > SD-24 h = CAD-12 M = CAD-24 h). The enzymatic activity was more intense for CAD groups, except for AUSE + PA. All groups exhibit silver nitrate deposits along the bonding interface. The cross-linkers tested appear to have no advantage when applied to caries affected dentin.

Mechanism and Properties of UO2–Graphene Composite Fuel Prepared by In Situ Synthesis

A nucleation method based on a composite of uranium dioxide (UO2) and graphene is presented by in situ synthesis, and the relevant mechanism and fuel properties are investigated. UO2–graphene composite fuel powders containing graphene volume (2%, 4%, 6%, and 8%) were prepared using a nucleation method through the reactive deposition of uranyl nitrate and aqueous ammonia on graphene by controlling the reaction parameters. The composite fuel pellets were prepared using spark plasma sintering (SPS). The results showed that the uniformity of UO2–graphene powder prepared by in situ synthesis reached up to 96.39%. An analysis on the relevant phase structure showed that only UO2 and graphene existed in the sintered pellets at 1723 K, graphene and UO2 were not destroyed during the reaction, and the pellet densities for the in-situ synthesis were 95.56%TD, 95.32%TD, 95.08%TD, and 94.76%TD for graphene contents of 2%, 4%, 6%, and 8%, respectively. The thermal conductivities of pellets at 293 K increased by 12.27%, 20.13%, 27.47%, and 34.13%, and by 18.36%, 35.00%, 47.07%, and 58.93% at 1273 K for 2%, 4%, 6%, and 8% graphene contents, respectively. The performance of graphene in the fuel was superior at high temperatures, which overcame shortcomings due to the low thermal conductivity of UO2 at high temperatures. SEM results showed that the grain sizes of the pellets prepared by synthesis in situ were 10–30 μm, and there was no obvious pore at the grain boundary because the grains were closely bound. The graphene was uniformly coated by UO2, and the thermal conductivity of the pellets improved upon the formation of a bridging heat conduction network.

Formulation and evaluation of proniosome loaded sertaconazole nitrate for topical application

Proniosomal technology is a novel solution for poorly soluble drugs. Proniosomes are water-soluble carrier particles which are coated with non-ionic surfactants. Proniosomal gels were prepared by coacervation phase separation method using non-ionic surfactants, lipid carriers and cholesterol as a membrane stabilizer. FTIR compatibility studies revealed that the drug and excipients were compatible. All formulations were evaluated for pH, drug content, extrudability, spreadability, viscosity, in-vitro, ex-vivo, skin irritation and stability studies. Among formulations prepared, F80H1 has shown higher % EE (83.02) and least diffusion through dialysis membrane i.e., 17.68%. With ex-vivo studies, F80H1 formulation has shown highest skin deposition and lower flux of sertaconazole nitrate through the rat skin. F80H1 was selected as final optimized formulation. F80H1 exhibited good stability and SEM studies revealed that the vesicles were spherical in shape. The optimized formulation was found to follow zero order release kinetics and korsmeyer-peppas release mechanism. F80H1 found to be non-irritant and stable from skin irritation and stability studies.

Genesis of the Dawadi potassium nitrate deposit in Lop Nor, China

Nitrate deposits are rare worldwide, especially potassium nitrate deposits; furthermore, their genesis remains disputed. There is a rare salt-lake type potassium nitrate deposit in the Dawadi area of Lop Nor at the eastern margin of the Tarim Basin, and the ore bodies show coexisting solid and liquid phases. Additionally, there are large sulphate-type potash deposits in the adjoining Luobei Depression, south of the Dawadi area. To determine why there are two different types of potash deposits in adjacent depressions with similar climates, field geological surveys were conducted and samples collected. It was found that the Tertiary clastic layer at the periphery of the Dawadi deposit was rich in high-salinity brine, with nitrate contents of up to 495–16,719 mg/L, much higher than those in the Luobei Depression, 1–35 mg/L. Additionally, a type of deep hydrothermal (Ca–Cl) brine was found in the fault zones, with nitrate contents of up to 8044 mg/L, dozens of times greater than that of ordinary groundwater. Using comprehensive analysis and research, we concluded that the Dawadi and Luobei depressions belong to different hydrological systems with no connection between them; thus, the two deposits belong to different metallogenic systems. Furthermore, groundwater played an important role in the mineralization of the potassium nitrate deposit, and a deep source may have been an important source of the ore-forming materials. The fault system widely developed in Lop Nor provides favorable channels for deep hydrothermal recharge, and the groundwater and deep hydrothermal brine could provide the source for the nitrate mineralization in the Dawadi Depression through water–rock reactions.

Nitrogen Cycling and Biosignatures in a Hyperarid Mars Analog Environment.

The hyperarid Atacama Desert is a unique Mars-analog environment with a large near-surface soil nitrate reservoir due to the lack of rainfall leaching for millennia. We investigated nitrogen (N) cycling and organic matter dynamics in this nitrate-rich terrestrial environment by analyzing the concentrations and isotopic compositions of nitrate, organic C, and organic N, coupled with microbial pathway-enzyme inferences, across a naturally occurring rainfall gradient. Nitrate deposits in sites with an annual precipitation of <10 mm carry atmospheric δ15N, δ18O, and Δ17O signatures, while these values are overprinted by biological cycling in sites with >15 mm annual precipitation. Metagenomic analyses suggest that the Atacama Desert harbors a unique biological nitrogen cycle driven by nitrifier denitrification, nitric oxide dioxygenase-driven alternative nitrification, and organic N loss pathways. Nitrate assimilation is the only nitrate consumption pathway available in the driest sites, although some hyperarid sites also support organisms with ammonia lyase- and nitric oxide synthase-driven organic N loss. Nitrifier denitrification is enhanced in the “transition zone” desert environments, which are generally hyperarid but see occasional large rainfall events, and shifts to nitric oxide dioxygenase-driven alternative nitrifications in wetter arid sites. Since extremophilic microorganisms tend to exploit all reachable nutrients, both N and O isotope fractionations during N transformations are reduced. These results suggest that N cycling on the more recent dry Mars might be dominated by nitrate assimilation that cycles atmospheric nitrate and exchanges water O during intermittent wetting, resulting stable isotope biosignatures could shift away from martian atmospheric nitrate endmember. Early wetter Mars could nurture putative life that metabolized nitrate with traceable paleoenvironmental isotopic markers similar to microbial denitrification and nitrification stored in deep subsurface.

Influence of atmospheric deposition on biogeochemical cycles in an oligotrophic ocean system

Abstract. The surface mixed layer (ML) in the Mediterranean Sea is a well-stratified domain characterized by low macronutrients and low chlorophyll content for almost 6 months of the year. In this study we characterize the biogeochemical cycling of nitrogen (N) in the ML by analyzing simultaneous in situ measurements of atmospheric deposition, nutrients in seawater, hydrological conditions, primary production, heterotrophic prokaryotic production, N2 fixation and leucine aminopeptidase activity. Dry deposition was continuously measured across the central and western open Mediterranean Sea, and two wet deposition events were sampled, one in the Ionian Sea and one in the Algerian Basin. Along the transect, N budgets were computed to compare the sources and sinks of N in the mixed layer. In situ leucine aminopeptidase activity made up 14 % to 66 % of the heterotrophic prokaryotic N demand, and the N2 fixation rate represented 1 % to 4.5 % of the phytoplankton N demand. Dry atmospheric deposition of inorganic nitrogen, estimated from dry deposition of nitrate and ammonium in aerosols, was higher than the N2 fixation rates in the ML (on average 4.8-fold). The dry atmospheric input of inorganic N represented a highly variable proportion of biological N demand in the ML among the stations, 10 %–82 % for heterotrophic prokaryotes and 1 %–30 % for phytoplankton. As some sites were visited on several days, the evolution of biogeochemical properties in the ML and within the nutrient-depleted layers could be followed. At the Algerian Basin site, the biogeochemical consequences of a wet dust deposition event were monitored through high-frequency sampling. Notably, just after the rain, nitrate was higher in the ML than in the nutrient-depleted layer below. Estimates of nutrient transfer from the ML into the nutrient-depleted layer could explain up to a third of the nitrate loss from the ML. Phytoplankton did not benefit directly from the atmospheric inputs into the ML, probably due to high competition with heterotrophic prokaryotes, also limited by N and phosphorus (P) availability at the time of this study. Primary producers decreased their production after the rain but recovered their initial state of activity after a 2 d lag in the vicinity of the deep chlorophyll maximum layer.