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Given the wide dependency on surface water used to supply drinking water, agricultural irrigation, and industrial activities, nitrate pollution has posed a serious concern in the Tigris River in recent years. The main objective of this study was to develop an understanding of the spatiotemporal patterns of nitrate distribution in the Tigris River through an integrated approach using hydrological data, physicochemical parameters, and model-based analysis. Eighty-four monthly sampling campaigns from forty monitoring locations along the Tigris River were carried out from January 2011 to December 2018. Obtained results demonstrated that the dynamics were strongly correlated with the length of transport the accumulation processes of and promoted a concentration effect. High distance and flow rates along the river system (p < 0.05). High flow rates in the upper courses of the river system favored physical transport of and promoted a dilution effect. However, low flow rates in the lower sections favored JWMM concentration of 7.0±1.96 g m-3 was observed in February 2018 downstream in the river. No significant seasonal effect in concentrations were observed. These results were supported by the changes in dissolved oxygen concentration and pH in the river system and indicated high nitrification rates and elevated accumulation, particularly downstream in the river. This modeling approach has also confirmed field observations of dynamics with 65% of the variances in the river system being explained by the model. [ABSTRACT FROM AUTHOR]

While the formation and evolution of nitrate in airborne particles are extensively investigated, little is known about the processing of nitrate in clouds. Here we present a detailed investigation on the in-cloud formation of nitrate, based on the size-resolved mixing state of nitrate in the individual cloud residual and cloud-free particles obtained by single particle mass spectrometry, and also the mass concentrations of nitrate in the cloud water and PM2.5 at a mountain site (1690 m a.s.l.) in southern China. The results show a significant enhancement of nitrate mass fraction and relative intensity of nitrate in cloud water and the cloud residual particles, respectively, reflecting a critical role of in-cloud processing in the formation of nitrate. We first exclude the gas phase scavenging of HNO3 and the facilitated activation of nitrate-containing particles as the major contribution for the enhanced nitrate, according to the size distribution of nitrate in individual particles. Based on regression analysis and theoretical calculations, we then reveal a critical role of in-cloud formation of nitrate via N2O5 hydrolysis, even during the daytime, attributed to the diminished light in clouds. Nitrate is highly related (R2 = ~0.6) to the variation of [NOx][O3], temperature and droplet surface area in clouds. Accounting for droplet surface area greatly enhances the predictability of the observed nitrate compared with using [NOx][O3] and temperature. The substantial contribution of N2O5 hydrolysis to nitrate in clouds during the daytime was reproduced by a multiphase chemical box model. Assuming that the photolysis rate is 30% of the default setting, the overall contribution of N2O5 hydrolysis pathway to nitrate formation increases by ~20% in clouds. Given that N2O5 hydrolysis acts as a major sink of NOx in the atmosphere, further model updates would improve our understanding about the processes contributing to nitrate production in cloud and the cycling of odd nitrogen. [ABSTRACT FROM AUTHOR]

This paper contributes to the integration of the study of multiple (i) spatial scales, (ii) resource systems, and (iii) points in time in natural resource governance by introducing a strategy of layering action situations. In the Institutional Analysis and Development Framework, action situations can be studied singularly, in comparison, or as networks of action situations. Building on this work, we propose to complement an established action situation with new ones derived from the evolution of the case. This preserves the initial action situation and thereby enables scholars to keep track of institutional change within and beyond it. We illustrate the approach by studying a case of groundwater pollution by nitrate in a German region of intensive livestock farming. [ABSTRACT FROM AUTHOR]

To fully decipher the role of nitrate photolysis on the atmospheric oxidative capacity in snow‐covered regions, NOx flux must be determined with more precision than existing estimates. Here, we introduce a method based on dynamic flux chamber measurements for evaluating the NOx production by photolysis of snowpack nitrate in Antarctica. Flux chamber experiments were conducted for the first time in Antarctica, at the French‐Italian station Concordia, Dome C (75°06'S, 123°20'E, 3233 m a.s.l) during the 2019–2020 summer campaign. Measurements were gathered with several snow samples of different ages ranging from newly formed drifted snow to 6‐year‐old firn. Contrary to existing literature expectations, the daily average photolysis rate coefficient, JNO3¯, did not significantly vary between differently aged snow samples, suggesting that the photolabile nitrate in snow behaves as a single‐family source with common photochemical properties, where a JNO3¯ = (2.37 ± 0.35) × 10−8 s−1 (1σ) has been calculated from December 10th 2019 to January 7th 2020. At Dome C summer daily average NOx flux, FNOx, based on measured NOx production rates was estimated to be (4.3 ± 1.2) × 108 molecules cm−2 s−1, which is 1.5–7 times less than the net NOx flux observed previously above snow at Dome C using the gradient flux method. Using these results, we extrapolated an annual continental snow sourced NOx budget of 0.017 ± 0.003 Tg·N y−1, ∼2 times the nitrogen budget, (N‐budget), of the stratospheric denitrification previously estimated for Antarctica. These quantifications of nitrate photolysis using flux chamber experiments provide a road‐map toward a new parameterization of the σNO3−(λ,T)ϕ(T,pH) product that can improve future global and regional models of atmospheric chemistry. Key Points: Photolabile nitrate in snow behaves as a single‐family source with common photochemical propertiesNew quantification of snow‐nitrate photolysis using flux chamber experimentsNOx snow‐source could be better defined and differences in photolytic mechanics of Antarctica's different regions could be addressed [ABSTRACT FROM AUTHOR]

Elevated nitrate concentrations in groundwater are a common challenge for water management. One important factor in this context is higher frequencies and intensities of wet‐dry cycles that may cause increased nitrate concentrations in groundwater due to nitrate flushes after drought termination. Yet systematic studies on regional‐scale impacts of droughts on groundwater nitrate concentrations are missing so far. Here we analyzed time series of 44 shallow groundwater wells and 41 springs all across the German Federal State Baden‐Wuerttemberg from 2000 to 2018 to characterize patterns of post‐drought nitrate increase in groundwater. In general, half of the exceptional nitrate concentrations, which exceeded the 80th percentile of long‐term nitrate measurements, could be related to droughts in the research timeframe. The 2003 drought event stood out in terms of drought severity and post‐drought nitrate concentration increases in our data. The great majority (91%) of all monitoring sites showed at least one exceptionally high nitrate concentration in the 4 years following the 2003 drought event. Springs were mainly located in forests of steep low mountain ranges and wells in cropland of flat river valleys. Therefore, delay times between drought intensity and nitrate concentration increases as well as magnitudes of nitrate concentration increase were diverse among wells and springs. We derived two distinct nitrate response patterns: (i) nitrate increases immediately following drought events (more common for springs and fractured rock aquifers) and (ii) delayed nitrate increases (more common for wells and porous aquifers). Springs generally showed quicker (median of 101 days) but weaker (median of +1.3 mg/L) post‐drought nitrate increases than wells (185 days, +3.4 mg/L). Only few sites exhibited no post‐drought nitrate increase and post‐drought mean‐nitrate concentrations of groundwater reservoirs were extraordinarily high in 2006. Overall, we demonstrate that post‐drought nitrate increase in groundwater is omnipresent, while different landscapes and hydrogeological characteristics create a diverse regional pattern. As severe droughts become more frequent in a changing climate, post‐drought nitrate increase may intensify problems regarding water quality and supply. [ABSTRACT FROM AUTHOR]

We report the seasonal variability of temperature, nutrients, and total and size‐fractionated chlorophyll‐a (Chl‐a) in nearshore waters off northern Baja California (nBC), under conditions of the marine heatwave and El Niño that occurred in the northeastern Pacific during 2014–2015. Compared with the mean annual cycle (2008–2015), our study period was characterized by warmer waters, nitrate‐impoverished, and with very low Chl‐a concentration, which was closely associated with strong stratification and reduced upwelling conditions off nBC. Temperature anomalies were >2.0°C by the end of 2014 when the marine heatwave prevailed, decreased during the spring‐early summer upwelling season of 2015, and returned to >2.5°C by the end of 2015 when El Niño appeared along the coast of nBC. As in 2008–2012 and closely coupled with upwelling, a seasonal cycle of total Chl‐a was recorded under these abnormally warm conditions. However, relative to the mean annual cycle, total Chl‐a and nitrate concentrations were significantly reduced (19%–55% and 40%–81%, respectively), with negative anomalies throughout the study period. Moreover, the seasonal evolution of the size‐fractionated Chl‐a concentration showed that smaller cells (<5 μm) systematically contributed with the largest fraction (>60%) of the total Chl‐a. Our findings indicate that the sequential occurrence of the marine heatwave in 2014 and El Niño in 2015 had a significant and sustained impact limiting the nitrate supply and reducing the total Chl‐a in nearshore waters off nBC. In conclusion, our data reveal that a shift toward an oligotrophic state occurred in coastal waters off nBC during the warm period of 2014–2015. Key Points: A significant reduction of nitrate concentrations and total chlorophyll‐a (Chl‐a) was attributed to the marine heatwave in 2014 and El Niño in 2015Size‐fractionated Chl‐a showed that small cells (<5 μm) contributed with the largest fraction (>60%) of the total Chl‐a during 2014–2015A shift toward an oligotrophic state occurred in nearshore surface waters off northern Baja California during the warm period of 2014–2015 [ABSTRACT FROM AUTHOR]

This study aims to a the health safety of water wells in some areas of the left side of Mosul city from nitrate compounds that have negative effects on consumer health such as blue baby syndrome and cancerous diseases: 168 water samples were collected from twelve wells spread in the region during the autumn and winter seasons to measure the concentration Nitrate ions and Nitrate pollution index (NPI) calculation. The results of the study indicated that the concentration of nitrate ions in the studied water samples ranged between (0.39 to 10.88), at means ranging from (1.23 to 9.66) ppm the relative rise in concentration in the water of some wells is attributed to pollution with wastewater, while the values of NPI was less than 0.0 and thus It is classified as non-polluted water category. [ABSTRACT FROM AUTHOR]

Electrochemical reduction is currently one of promising methods for nitrate removal from water, yet most treatment approaches have problems of high cost and energy consumption. In this work, a low current density was applied in electrochemical reduction of nitrate. Copper-modified titanium (Cu/Ti) electrodes with optimal electrochemical activity and fastest kinetics were firstly screened. Thirty minutes of electrodeposition time and neutral pH were found to have the greatest nitrate reduction rate of 83.14%. To further improve the removal of nitrate, activated carbon (AC) and copper-modified activated carbon (Cu/AC) particles were applied to construct three-dimensional reaction systems, with removal rates of nitrate of 88.72% and 96.05%, respectively. The average conversion rates of nitrate to ammonia nitrogen increased from 15.28% to 42.68% and 62.64% in AC- and Cu/AC-based reaction systems, respectively. Oxidation of Cu(0) on surfaces of Cu/Ti cathode and Cu/AC particles to Cu(I) was revealed by X-ray photoelectron spectroscopy (XPS) and Cu LMM spectra analysis. Besides, results of water chemistry characteristics indicated the conversion of AC to carbonate ion. It could be concluded that enhanced nitrate reduction of Cu/Ti-based reaction system was attributed by Cu particle- and AC-mediated electron transfer. This study provided a reference for low-cost electrochemical reduction of nitrate. [ABSTRACT FROM AUTHOR]

Effects of controlled nutrient additions on a prairie stream were studied using a before‐after‐control‐impact paired design. The site is in a reference condition with low soluble nitrate (NO3) and phosphate (soluble reactive phosphorus [SRP]) in summer (3 μg NO3‐N/L, 4 μg SRP/L). Nutrients were added to two reaches over the growing season at two levels (Low Dose — 39 μg NO3‐N/L and 4.4 SRP/L; High Dose — 119 μg NO3‐N/L and 15.6 μg SRP/L). Continuously measured dissolved oxygen (DO) and changes in aquatic flora were compared to an upstream Control. Enrichment led microalgae and filamentous algae to increase in density, areal coverage, and thickness, and the magnitude of the changes were largely concordant with dosing (more in the High Dose); algal growth also suppressed macrophytes in the High Dose. Enrichment caused significant increases in diel DO swings whose magnitudes were consistent with dosing level. In the High Dose, benthic algae flourished in the growing season and then senesced en masse in fall. The decomposing algae led DO to crash (ca. 0 mg/L on the bottom), but DO impacts were out‐of‐sync with peak algal growth and photosynthesis, which occurred weeks earlier. This finding provides a plausible explanation as to why high DO delta in streams impacts aquatic life even when concurrently measured DO is not low. When DO crashed, DO was longitudinally patchy, some areas having low DO near the bottom, others near saturation. Geomorphology and exposure to wind may have caused this pattern. Research Impact Statement: Dissolved oxygen problems in streams can occur after peak algal primary productivity. They can occur later as algae die, out‐of‐sync with peak growth and photosynthesis. [ABSTRACT FROM AUTHOR]

Summary: Nitrate pollution is a growing environmental threat that affects both ground‐ and surface‐water. The typically used technique for nitrate elimination in wastewater treatment plants cannot be applied for all water streams as it necessitates a highly developed technical infrastructure. Field denitrification beds comprise one strategy to treat surface water containing high nitrate loads, which typically is due to the increasing agricultural land use. Here, the water passes through a basin containing a cheap carbon material as electron donor that provides the environmental niche for a complex microbial biocenosis. The microorganisms catalyse the hydrolysis of the polymeric organic carbon substrate and a variety of fermentative and respiratory pathways that are in the end supposed to lead to an efficient denitrification process. This review article integrates our current knowledge on environmental and operating parameters of and within denitrification beds including biotic and abiotic factors influencing the nitrate removal efficiency. Steering of these two factors can allow to minimise pollution swapping and the formation of greenhouse gases. [ABSTRACT FROM AUTHOR]

The process of ice crystal formation by ejecting salt into a pore solution increases the solution's concentration. However, the redistribution law of solutes in ice-containing soils is not well understood. We designed new equipment to obtain the unfrozen solution and study the nitrate redistribution. Our work investigates the mechanism of nitrate redistribution during the freezing of a saturated medium system. The results showed that the polysized grain samples had a higher freezing rate and lower salt discharge efficiency than the monosized grain samples. The influence of the freezing temperature and the initial concentration on the nitrate redistribution was dependent on the medium's particle size. For the samples with particle sizes between 150 and 250 um, the ejection efficiency decreased with the increase of the freezing temperature and decreased with the increase of the initial concentration at the same frozen ratio. However, for the samples with particle sizes between 250 and 500 um, the two factors had no significant effect on the nitrate expulsion. These results will provide a theoretical basis for the treatment of nitrate in groundwater. [ABSTRACT FROM AUTHOR]

Nitrate (NO3−), which is mainly oxidized from NO2 by the OH radical (OH·) and O3 in the atmosphere, is a major component of inorganic aerosols. However, the contributions of the OH· and O3 pathways to NO3− in urban aerosols and the influence of air pollution to both pathways remain unclear. Oxygen isotopes of NO3− were measured for PM2.5 in Beijing in 2014. The Δ17O‐NO3− values (17.0–32.8‰) were significantly higher in winter (27.2 ± 3.6‰) than in summer (24.2 ± 1.3‰). By estimating contributions of O3 to the NOx cycle, the Δ17O values of NO3− endmembers produced via the NO2 + OH· (P1), NO3· + DMS/HC (P2), and N2O5 hydrolysis (P3) pathways were calculated for each observation. The contributions of the three pathways (P1: 32 ± 10%, P2: 34 ± 10%, and P3: 34 ± 20% annually) were calculated using the Stable Isotope Analysis in R model. We found that NO3− formation was dominated by the O3 oxidation pathways (P2 + P3; 68 ± 23% annually, 73 ± 21% in spring, 59 ± 23% in summer, 75 ± 20% in autumn, and 69 ± 22% in winter). Moreover, PM2.5, NO2, and NO3− pollution decreased the importance of the OH· pathway relative to the O3 pathways for NO3− production. However, O3 pollution increased the importance of the OH· pathway relative to the O3 pathways for NO3− production. These results provided a comprehensive analysis on the oxygen isotope records in particulate NO3− for understanding the relative importance of major oxidation pathways of NO2. Atmospheric pollution substantially influenced the pathways of NO2 oxidation to NO3− in city environments. Plain Language Summary: Air pollution is a major environmental and public health issue; to strengthen studies on haze formation mechanisms is a national environment demand. Although monitoring works have been widely conducted on atmospheric particulates, it has long been difficult to quantify production mechanisms of key chemical components. Combined oxygen isotopes (18O, 17O) of nitrate with the Stable Isotope Analysis in R model, we evaluated the fractional contributions of three major oxidation pathways (NO2 + OH· [P1], NO3· + DMS/HC [P2], and N2O5 hydrolysis [P3]) to the NO3− of PM2.5. We found that annually 68 ± 23% of NO3− in PM2.5 at Beijing was produced by the O3 oxidation pathways (P2 + P3). Moreover, PM2.5, NO2, and NO3− pollution decreased the importance of the OH· pathway relative to the O3 pathways for NO3− production. Our results provided a comprehensive analysis on the oxygen isotope records in particulate NO3− for understanding the relative importance of major oxidation pathways of NO2. Atmospheric pollution substantially influenced the pathways of NO2 oxidation to NO3− in city environments. Key Points: Δ17O signatures of NO3− in PM2.5 at Beijing were reportedContributions of major oxidation pathways to NO3− of PM2.5 were evaluatedAir pollution changed the importance of OH· pathway relative to O3 pathways for NO3− production [ABSTRACT FROM AUTHOR]

Abstract The effects of biochar on soil properties including nutrients have been reported in previous studies, but few studies targeted on soil nitrogen. Moreover, there remains a lack of studies considering the liberation of ammonia during the ammonium (N-NH 4 +) adsorption process. Our study aimed to fill this research gap. A pot incubation experiment was conducted for 84 days, with ten different soils and four rates of wood chip-based biochar (0.5, 2, 4, and 8%). Biochar's effect on soil ammonium was inconsistent and insignificant in most of the incubated soils at all biochar rates. This finding contradicted our Langmuir model, which estimated maximum ammonium adsorption capacity of biochar as 6.66 mg of N-NH 4 + per g of biochar. Soil response in nitrate (N-NO 3 −) and dissolved organic carbon (DOC) followed a similar declining trend in all soils in both incubation periods, with the effect boosted according to the biochar application rate. The Langmuir isotherm estimated the maximum N-NO 3 − adsorption capacity of our biochar as 11.3 mg g−1. Soil original properties determined amount of nitrate and DOC reduction after biochar addition. Our result also indicated poor estimation of ammonium adsorption by biochar due to the liberation of ammonia. As a result, we strongly recommend that ammonia liberation should be considered during adsorption experiments and more studies in this field. Highlights • Wide range of soils included in the experiment. • Biochar amendment reduces soil N ‐ NO 3 − and soil dissolved organic carbon content. • Soil original properties determine amount of biochar induced N ‐ NO 3 − reduction. • Ammonia loose has effect on estimation of N ‐ NH 4 + adsorption by biochar. [ABSTRACT FROM AUTHOR]

A rural subdivision in south central Wisconsin was instrumented with monitoring wells and lysimeters before, during, and after its construction to examine the impacts of the unsewered subdivision on groundwater quality and quantity. Prior to construction, the 78‐acre (32 ha) site was farmland. Sixteen homes were constructed beginning in 2003. Initial monitoring from 2002 to 2005 showed that groundwater beneath the site had been impacted by previous agricultural use, with nitrate‐N values as high as 30 mg/L and some detections of the herbicide atrazine. Our 12‐year study shows that the transition from agricultural to residential land use has changed groundwater quality in both negative and positive ways. Although groundwater elevations showed typical seasonal fluctuations each year, there were no measurable changes in groundwater levels or general flow directions during the 12‐year study period. Chloride values increased in many wells, possibly as a result of road salting or water softener discharge. Nitrate concentrations varied spatially and temporally over the study period, with some initial concentrations substantially above the drinking water standard. In some wells, nitrate and atrazine levels have declined substantially since agriculture ceased. However, atrazine was still present at trace concentrations throughout the site in 2014. Wastewater tracers show there are small but detectable impacts from septic effluent on groundwater quality. Particle traces based on a groundwater flow model are consistent with the hypothesis that septic leachate has impacted groundwater quality. Article impact statement: This long‐term study shows that septic effluent has affected groundwater quality and that shorter‐term studies may not reveal this. [ABSTRACT FROM AUTHOR]

Nitrate is necessary for agricultural productivity, but it is also one of the most common water contaminants in developed countries. The riverbank filtration (RBF) systems in Káraný (Czechia), with nearly 500 wells regularly distributed along 22 km of the alluvium aquifer/river interface, presents a unique field laboratory where the adverse effects of intensive agriculture on groundwater can be traced from >50 years of nitrate concentration records. The largest control over nitrate concentrations in the RBF systems has been the mixing of the river-water component (low in nitrate) with the local recharge, which has a nitrate content of 100-250 mg/L. The mixing is mainly controlled by the intensity of the effective precipitation. Increases in nitrate concentration are caused by rapid hydraulic pulse propagation during the high-recharge periods to the discharge areas. In contrast, during dry periods, the river-water fraction dilutes nitrate in wells. The lowest nitrate content occurs above the weirs on the river, as well as in those areas where the alluvial aquifer is partly fed by older and/or denitrified groundwater from deeper zones of the underlying sandstone aquifer. High nitrate concentrations occur in wells where the low saturated thickness of the alluvial aquifer limits the inflow of river water. This study shows that factors affecting nitrate concentrations in the alluvium are numerous, and that long-term sampling is necessary to distinguish the oscillations caused by variability in the recharge intensity from decade-long trends controlled by the fertilizer load and nitrate lag time in the aquifer. [ABSTRACT FROM AUTHOR]

In this study, we assess the validity of an African-scale groundwater pollution model for nitrates. In a previous study, we identified a statistical continental-scale groundwater pollution model for nitrate. The model was identified using a pan-African meta-analysis of available nitrate groundwater pollution studies. The model was implemented in both Random Forest (RF) and multiple regression formats. For both approaches, we collected as predictors a comprehensive GIS database of 13 spatial attributes, related to land use, soil type, hydrogeology, topography, climatology, region typology, nitrogen fertiliser application rate, and population density. In this paper, we validate the continental-scale model of groundwater contamination by using a nitrate measurement dataset from three African countries. We discuss the issue of data availability, and quality and scale issues, as challenges in validation. Notwithstanding that the modelling procedure exhibited very good success using a continental-scale dataset (e.g. R2 = 0.97 in the RF format using a cross-validation approach), the continental-scale model could not be used without recalibration to predict nitrate pollution at the country scale using regional data. In addition, when recalibrating the model using country-scale datasets, the order of model exploratory factors changes. This suggests that the structure and the parameters of a statistical spatially distributed groundwater degradation model for the African continent are strongly scale dependent. [ABSTRACT FROM AUTHOR]

The Environmental Protection Agency of the Campania region in Italy (ARPAC) manages a groundwater quality monitoring network. For almost all the polluted waters, the key parameter driving the classification is the concentration of nitrate; hence, the Campania region, in coherence with the EU regulations, outlined the vulnerable areas and undertook remediation policies. The best groundwater quality is recorded for carbonate aquifers of the Apennine chain; on the contrary, the Tyrrhenian coastal plains are affected by severe contamination, with a locally very contaminated groundwater of the shallow and also the deeper aquifers. The study is especially focused on a large coastal plain of Campania region, where nitrate concentration sometimes exceeds 200 mg/L. The study, based on almost 200 sampling points for the whole region during the period 2003-2015 (approx two samples per year), verified the effectiveness of the groundwater monitoring network, the present distribution of nitrate in groundwater, and the evolution of nitrate trends at different scales: regional, groundwater body, and single well, using spatial and time series statistical approaches. Significant variations in contamination evolution within the study area have been observed and the correlation with land use has been highlighted. [ABSTRACT FROM AUTHOR]

Abstract We performed continuous observations (2012–2015) of total peroxy nitrates (PNs) and total organic nitrates (ONs) at Suzu on the Noto peninsula, Japan. It was found that PNs and ONs showed similar seasonal variations with maximum concentrations in spring and minimum concentrations in summer. Concentrations of PNs and ONs were high for air masses originating from the Asian continent from winter to spring, whereas they were independent of air mass origin from spring to summer. In summer, PNs and ONs indicated similar diurnal variations with maximum concentrations during daytime and minimum concentrations during nighttime. Such diurnal variations of PNs and ONs were small in winter. Diurnal variations of PNs in spring were similar to those in summer, whereas such diurnal variations were not observed for ONs in spring. In the cold season, PNs and ONs have long atmospheric lifetimes and local photochemical production rates of PNs and ONs are slow, whereas the converse is true in the warm season. Therefore, concentration variations of PNs and ONs are governed primarily by long-range transport in the cold season and by local photochemical production in the warm season. Highlights • Continuous observations of PNs and ONs were performed at Noto Peninsula, Japan. • PNs and ONs showed characteristic seasonal and diurnal variations. • The main variable factor of PNs and ONs is long-range transport in the cold season. • PNs and ONs are influenced mainly by photochemical production in the warm season. [ABSTRACT FROM AUTHOR]

Abstract Monthly analytical results for more than two years long of δ15N and δ18O of nitrate in wet deposition are reported for a tropical city of Zhanjiang in the southernmost mainland China, in an effort to elucidate NO x sources and its oxidation pathways to nitrate. The results showed that monthly variations of δ18O NO 3 - responded well to changes in sunshine hours, with lower δ18O NO 3 - values corresponding to longer sunshine hours. This pattern suggests that NO x oxidation via the OH radical was the predominant pathway, which, by estimate, accounted for 87% in winter and 94% in summer, for nitrate formation. Remarkably, we found that the δ18O NO 3 - here are prominently low relative to previous studies, likely due to that annual sunshine hours in this tropical city is relatively long. Moreover, available data of reported δ18O NO 3 - in wet deposition showed an increasing trend with latitude, reflecting a shift of the predominant NO x oxidation pathways from those via the OH radical in low latitudes to those via O 3 in high latitudes, corresponding to the decrease of sunshine hours. A temporarily co-variation of δ15N NO 3 - and δ18O NO 3 - was observed, exhibiting higher values in dry winter and lower values in wet summer, which was attributed to the washout effect on the dual isotopes. During wet seasons, complete nitrate washout suggests that δ15N NO 3 - in precipitation should be similar to the nitrate formed in the atmosphere, and thereby can be used for source apportionment. A Bayesian model showed that the source of atmospheric nitrate deposition is mainly natural (61%) in Zhanjiang, with less anthropogenic contribution. Highlights • OH radical is the predominant pathway for nitrate formation in this tropical city. • Rainfall washout exerts an effect on δ15N NO 3 - and δ18O NO 3 - values. • The source of atmospheric nitrate deposition is mainly natural in this tropical city. [ABSTRACT FROM AUTHOR]

Abstract Nitrate is an important pollutant found in environmental samples. Nitrate and nitrite pose various environmental as well as health hazards. Different methods of determining nitrate in various environmental samples developed during previous years include spectrophotometric, chemiluminescence, electrochemical detection, chromatographic, capillary electrophoretic, spectrofluorimetric methods. Out of these, methods based on spectroscopic detection of nitrate have been discussed in this review article due to their easy availability, high sensitivity, low detection limit, economical and facile nature. Methods based on spectrophotometry, Raman Spectroscopy, IR and FTIR Spectroscopy, atomic absorption spectroscopy (AAS), fluorescence spectroscopy, chemiluminescence, mass spectroscopy, molecular emission cavity analysis (MECA), electron paramagnetic resonance spectrometry (EPR) and nuclear magnetic resonance spectroscopy (NMR) have been reviewed. The basic principle, detection limits, detection range, RSD%, sample throughput/h, advantages and disadvantages have been discussed. Graphical abstract fx1 Highlights • Spectroscopic methods for detection of nitrate and nitrite have been reviewed. • Their basic principle, advantages and disadvantages have been mentioned. • Detection limits, detection range, RSD%, sample throughput/h have been tabulated. • Literature survey of more than 200 research papers has been presented. [ABSTRACT FROM AUTHOR]

This paper examines the interaction of different policies used to control two types of agricultural pollution. Pollution control policy is efficient when both pollution types are controlled by taxes, although a tax increase on one type of pollution can increase the quantity of another type of pollution if farm inputs are substitutes. However, if one of the pollutions is controlled by a local emissions trading scheme, and another pollution type is taxed, then the pollution type which is taxed becomes less responsive to a change in its own tax levels. This policy scenario results in inefficient levels of environmental pollution outcomes unless the cap for the local emissions trading scheme is constantly being shifted in response to the tax. [ABSTRACT FROM AUTHOR]

Abstract An anaerobic incubation was launched with varying nitrate (1, 5, 10 and 20 mM exogenous NaNO 3) and molybdate (20 mM Na 2 MoO 4 , a sulfate-reducing inhibitor) additions to investigate the characteristics of PCP dechlorination, as well as the reduction of natural co-occurring electron acceptors, including NO 3 −, Fe(III) and SO 4 2−, and the responses of microbial community structures under a unique reductive mangrove soil. Regardless of exogenous addition, nitrate was rapidly eliminated in the first 12 days. The reduction process of Fe(III) was inhibited, while that of SO 4 2− reduction depended on addition concentration as compared to the control. PCP was mainly degraded from orth -position, forming the only intermediate 2,3,4,5-TeCP by anaerobic microbes, with the highest PCP removal rate of average 21.9% achieved in 1 and 5 mM NaNO 3 as well as 20 mM Na 2 MoO 4 treatments and the lowest of 7.5% in 20 mM NaNO 3 treatment. The effects of nitrate on PCP dechlorination depended on addition concentration, while molybdate promoted PCP attenuation significantly. Analyses of the Illumina sequencing data and the relative abundance of dominant microorganisms indicated that the core functional groups regulated PCP removal at genera level likely included Bacillus , Pesudomonas, Dethiobacter , Desulfoporosinus and Desulfovbrio in the nitrate treatments; while that was likely Sedimentibacter and Geosporobacter_Thermotalea in the molybdate treatment. Nitrate supplement but not over supplement, or addition of molybdate are suggested as alternative strategies for better remediation in the nitrate-deficient and sulfur-accumulated soil ecosystem contaminated by PCP, through regulating the growth of core functional groups and thereby coordinating the interaction between dechlorination and its coupled soil redox processes due to shifts of more available electrons to dechlorination. Our results broadened the knowledge regarding microbial PCP degradation and their interactions with natural soil redox processes under anaerobic soil ecosystems. Graphical abstract Image 1 Highlights • Effects of N and Fe/S status on PCP removal was studied in a flooded mangrove soil. • Moderate not over supply of NO 3 − and SO 4 2--reducing suppression facilitated PCP removal. • Various mechanisms operated in facilitated PCP removal. • Synergistic microbes but not typical dechlorinators mediated the facilitated PCP removal. • Coordinating electron transfer of microbial respiration improved PCP remediation. Coordinating electron transfer of microbial respiration improved PCP remediation through moderate not over supply of NO 3 − and SO 4 2--reducing suppression. [ABSTRACT FROM AUTHOR]

Abstract Nitrate pollution has emerged as a problem of great importance because in recent years, the levels of nitrate in soil and groundwater have increased, mainly through anthropogenic activities, such as the use of fertilizers in agriculture, domestic wastewater and septic tanks, industrial waste and deforestation. In animals, nitrate reduction to nitrite (NO 2) and nitric oxide (NO) promote the formation of methemoglobin in the blood and the generation of highly reactive intermediates that induce oxidative stress in target organs. Exposition to nitrates has been associated with methemoglobinemia, reproductive toxicity, metabolic and endocrine alterations and cancer. This study analyzed acute intoxication with sodium nitrate (NaNO 3) in male Wistar rats, aged 12–16 weeks. Four groups with n = 10 rats each were formed: group 1 was the control, and group 2, group 3 and group 4 were treated for 10 days with intragastric doses of 19, 66 and 150 mg/kg/d NaNO 3 , respectively. Hematological, metabolic and histological biomarkers in the liver were analyzed. The results showed high percentages of methemoglobin, an increase in NO 2 in the plasma and an accumulation in the liver. Moreover, there were high counts of white blood cells and platelets in all treated groups. Additionally, there was an increase in the spleen weight in group 4. High levels of glucose, triglycerides, lactate dehydrogenase (LDH), alanine aminotransferase (ALT), and aspartate aminotransferase (AST) were observed and were significantly increased in groups 3 and 4. For oxidative stress biomarkers, there were increases in Thiobarbituric Acid Reactive Substances (TBARS), total GSH and SOD activity, mainly in group 4. Changes in mitochondrial activity were not significant. Histopathological analyses of the liver showed inflammation, infiltration of mononuclear cells, steatosis, ischemia and necrosis, and these findings were more evident at high doses of NaNO 3 in which high of S-nitrosylation were found. In conclusion, NaNO 3 was reduced to NO 2 , thereby inducing methemoglobinemia, whereas other reactive species generated oxidative stress, causing hematological and metabolic alterations and injury to the liver. Graphical abstract fx1 Highlights • Subacute intoxication with NaNO 3 increases the level of NO 2 in the plasma and the percentage of methemoglobin in Wistar rats. • Short term exposition to NaNO 3 causes alterations in white blood cell and platelet counts. • An increase in the dose of NaNO 3 also increases the TBARS and S-nitrosylation levels and triggers the antioxidant response. • Inflammation, steatosis, ischemia and necrosis in the liver were found at a high dose, namely, 150 m/kg/d NaNO 3. [ABSTRACT FROM AUTHOR]

Abstract The generation of HONO and NO 2 by the photolysis of nitrates in the presence of humic acids (HA) was measured under various conditions. The photolysis experiments of HA, KNO 3 and KNO 3 /HA under simulated sunlight was carried out by a flow tube reactor at ambient temperature and pressure. HONO and NO 2 were major products by the photolysis of KNO 3. By contrast, the photolysis of HA and KNO 3 /HA mainly generated HONO. HA significantly enhanced the formation of HONO during the photolysis process of KNO 3. With increasing the KNO 3 mass, the HONO formation rate (R HONO) on KNO 3 /HA increased while the photolysis rate normalized by the KNO 3 mass exhibited an opposite trend. R HONO on KNO 3 /HA linearly increased with irradiation intensity (88–262 W/m2) and relative humidity (7–70%), whereas it linearly decreased with the pH (pH = 2–12). In addition, the reaction paths of the HONO formation by the photolysis of nitrates in the presence of HA were proposed according to experimental results. Finally, atmospheric implications of the enhanced HONO formation by the photolysis of nitrates in the presence of HA were discussed. Graphical abstract Image 1 Highlights • HA significantly enhanced the formation of HONO by the photolysis of nitrates. • The HONO formation rate was investigated under various environmental conditions. • Mechanism of the photoenhanced HONO formation on nitrates and HA was proposed. • Implications of the HONO formation by the photolysis of nitrates were discussed. HONO was significantly produced on the mixtures of KNO 3 and humic acids under irradiation, and the HONO formation rate depended on the environmental conditions. [ABSTRACT FROM AUTHOR]

The impact of climate change on agricultural systems is a major concern as it can have a significant effect on the world food supply. The objective of this study was to evaluate climate change impacts on crop production and nitrate leaching in two distinct climatic zones in Canada. Spring wheat (Triticum aestivum L.) was selected for the semiarid regions of Western Canada (Swift Current, SK) and maize (Zea mays L.) was chosen for the more humid regions of central Canada (Woodslee, ON). Climate scenarios were based upon simulations from a Canadian Regional Climate Model (CanRCM4) under two Representative Concentration Pathways (RCP4.5 and RCP8.5) and crop simulations were conducted using the Decision Support System for Agrotechnology Transfer (DSSAT) model. Compared to the baseline climate scenario, wheat yields increased by 8, 8, 11, 15%, whereas maize yields decreased by 15, 25, 22, 41% under RCP4.5 2050s (2041–2070), RCP4.5 2080s (2071–2100), RCP8.5 2050s and RCP8.5 2080s scenarios, respectively. Annual nitrate leaching increased by 19, 57, 73, 129% at Swift Current and by 84, 117, 208, 317% at Woodslee under the four scenarios, respectively. Adaptation measures suggested that fertilizer N rate for spring wheat should be increased to 80–100 kg N ha-1 to obtain optimal yields although this will result in an additional risk of 5–8 kg N ha-1 nitrate leaching at Swift Current. The fertilizer N rate of 150 kg N ha-1 was found to be suitable for high maize yields at Woodslee. New wheat and maize cultivars with long growing seasons would enable crop growth to match the phenological stage and hence maintain high crop yields to adapt to increased temperatures in the future. [ABSTRACT FROM AUTHOR]

PM 2.5 -bound nitrated polycyclic aromatic hydrocarbons (nPAHs) and oxygenated polycyclic aromatic hydrocarbons (oPAHs) in ambient air were analysed in Langfang during periods with and without traffic restriction. During traffic restriction periods, 20% of gasoline vehicles and all diesel vehicles were restricted to travel within downtown. The 2-nitrofluoranthene/1-nitropyrene ratios obtained during the sampling periods implied that direct emission, especially from diesel vehicles, is the main source for the nPAHs in Langfang. The primary sources of nPAHs and oPAHs, including diesel vehicle emissions and gasoline vehicle emissions, were reduced in the P2 period. Thus, the concentrations of 1-nitropyrene, 3-nitrobenzanthrone, 9-nitrophenanthrene, 2-nitrofluorene, 7-nitrobenz[ a ]anthracene, 9,10-anthraquinone and benzanthrone were reduced up to 73.3% under this traffic restriction policy. However, the concentrations of 2-nitrofluoranthene and 9-fluorenone formed from gas phase reactions increased slightly. Meanwhile, the chemical profiles of nPAHs and oPAHs changed with traffic fleet variation, and cancer risk levels decreased under the traffic restriction policy. Hence, the traffic restriction policy did effect the ambient concentrations of nPAHs and oPAHs. [ABSTRACT FROM AUTHOR]

Abstract Background Prenatal particulate air pollution exposure may alter lung growth and development in utero in a time-sensitive and sex-specific manner, resulting in reduced lung function in childhood. Such relationships have not been examined for nitrate (NO 3 -). Methods We implemented Bayesian distributed lag interaction models (BDLIMs) to identify sensitive prenatal windows for the influence of NO 3 - on lung function at age 7 years, assessing effect modification by fetal sex. Analyses included 191 mother-child dyads. Daily ambient NO 3 - exposure over pregnancy was estimated using a hybrid chemical transport (Geos-Chem)/land-use regression model. Spirometry was performed at mean (SD) age of 6.99 (0.89) years, with forced expiratory volume in one second (FEV 1) and forced vital capacity (FVC) z-scores accounting for child age, sex, height and race/ethnicity. Results Most mothers were Hispanic (65%) or Black (22%), had ≤ high school education (67%), and never smoked (71%); 17% children had asthma. BDILMs adjusted for maternal age and education and child's asthma identified an early sensitive window of 6–12 weeks gestation, during which increased NO 3 - was significantly associated with reduced FEV 1 z-scores specifically among boys. BDLIM analyses demonstrated similar sex-specific patterns for FVC. Conclusion Early gestational NO 3 - exposure is associated with reduced child lung function, especially in boys. Highlights • Prenatal nitrate exposure is associated with reduced lung function at age 7 years • Link between prenatal nitrate exposure and lung function deficits is male-specific • Significant effects occur during early sensitive window of 6-12 weeks gestation [ABSTRACT FROM AUTHOR]

Highlights • The first study was carried out to show how setting WF benchmarks may help alleviate groundwater scarcity and pollution. • Iran's groundwater will be saved by 32% when reducing WFs of crops to 25th percentile benchmark levels. • Nitrogen-related grey ground WF will be lowered by 23% through setting WF benchmarks. • A significant increase in economic groundwater productivity is acheived when setting benchmark levels at 25th percentile. • The introduced methodology here is a promising way to alleviate overexploitation of aquifers and increase national food security. Abstract The formulation of water footprint (WF) benchmarks in crop production – i.e. identifying reference levels of reasonable amounts of water consumption and pollution per tonne of crop produced – has been suggested as a promising strategy to counter inefficient water use and pollution. The current study is the first to show how setting WF benchmarks may help alleviate groundwater scarcity and pollution, in a case study for Iran. We advance the field of WF assessment by developing WF benchmark levels for crop production, which we successively use to assess potential groundwater saving, quality improvement and economic water productivity gains. First, we calculate climate-specific WF benchmark levels for both total blue water footprints and nitrogen-related grey groundwater footprints for 26 crops, for all years in the period 1980–2010, at 5 × 5′ spatial resolution. Second, we estimate the water saving potential for total blue water resources and for groundwater resources specifically, as well as the grey groundwater footprint reduction potential. Finally, we compare mean economic water productivities of crop production in the past with productivities if WFs are reduced to benchmark levels. We find that groundwater comprises up to 83% of total blue water consumption of irrigated crops, with the highest share in arid areas and in cereals. Aquifers are under significant to severe stress, except in the dry sub-humid zone, where irrigation mainly relies on surface water. Reducing WFs of crops to 25th percentile benchmark levels can save 32% of groundwater compared to the reference year 2010, and lower the nitrogen-related grey groundwater footprint by 23%. Moreover, it would increase average economic groundwater productivity in Iran by 20% for cereals, and 59% for nuts. We conclude that reducing WFs to climate-specific benchmark levels in a water-stressed country is a promising way to alleviate overexploitation of aquifers and increase national food security. [ABSTRACT FROM AUTHOR]

Excess accumulation of nitrate in vegetable crops is normally related to the excessive use of nitrogen fertilizers applied in agricultural fields. This study was performed to evaluate the level of nitrate concentration in onion production in Isfahan province of Iran and the potential health risks associated with high level of nitrate in this crop, as an example of a case-study . The risk was estimated by using the United States Environmental Protection Agency (USEPA) method and presented as risk maps. Additionally, the impact of an improved fertilizer management practice in selected vulnerable fields for reducing nitrate concentration in onion production was evaluated. For this assessment, four different onion fields in which onion bulb nitrate concentration was higher than the safety level (70 mg kg −1 FW), provided by Welch (2003) in a survey study, were chosen. The risk maps showed that despite higher risk possibility in adults, in comparison with children, all values were lower than the acceptable level. Further, the split application of nitrogen fertilizers in all fields significantly reduced plant nitrate concentration with no reduction in yield and even observed increase in the overall economic yield production. Therefore, considering crop yields and nitrate accumulation impacts, improved nitrogen management could provide an opportunity to promote onion crop production while reducing negative health effects in high-risk regions in Isfahan province of Iran. [ABSTRACT FROM AUTHOR]

Organic nitrate chemistry is the primary control over the lifetime of nitrogen oxides (NOx ) in rural and remote continental locations. As NOx emissions decrease, organic nitrate chemistry becomes increasingly important to urban air quality. However, the lifetime of individual organic nitrates and the reactions that lead to their production and removal remain relatively poorly constrained, causing organic nitrates to be poorly represented by models. Guided by recent laboratory and field studies, we developed a detailed gas-phase chemical mechanism representing most of the important individual organic nitrates. We use this mechanism within the Weather Research and Forecasting (WRF) model coupled with Chemistry (WRF-Chem) to describe the role of organic nitrates in nitrogen oxide chemistry and in comparisons to observations. We find the daytime lifetime of total organic nitrates with respect to all loss mechanisms to be 2.6 h in the model. This is consistent with analyses of observations at a rural site in central Alabama during the Southern Oxidant and Aerosol Study (SOAS) in summer 2013. The lifetime of the first-generation organic nitrates is ~ 2 h versus the 3.2 h lifetime of secondary nitrates produced by oxidation of the first-generation nitrates. The different generations are subject to different losses, with dry deposition to the surface being the dominant loss process for the secondgeneration organic nitrates and chemical loss being dominant for the first-generation organic nitrates. Removal by hydrolysis is found to be responsible for the loss of ~ 30 % of the total organic nitrate pool. [ABSTRACT FROM AUTHOR]

Denitrification has documented as a promising pathway to permanently remove nitrate from a system. Numerous studies have used the isotope fractionation technique (IFT) to evaluate the denitrification rate in the constructed wetlands (CWs), but the potential of IFT method to quantify the denitrification rate in hyporheic zone (saturated sediments beneath a stream) is still challenging. Thus, more studies are required to investigate that if measurements of the natural abundance of δ 15 N-NO 3 - and δ 18 O-NO 3 - (IFT) can be employed to calculate the fate of nitrate in hyporheic zone. Therefore, in this study, the possibility of the IFT to quantify the hyporheic-denitrification rate was investigated. Then, the results were verified by the combined application of the pre-established net Sediment N 2 flux and multi-linear regression analysis ( p  < 0.01). Finally, the groundwater bacterial groups ( Fecal coliform (FC) and Escherichia coli (EC)), and the mass balance isotope mixing model were used to investigate the dominant sources of hyporheic-nitrate. The IFT reveals that denitrification contributes 74.1% and 29.1% of the hyporheic-nitrate removal during dry and wet seasons, respectively. The multi-linear regression analysis, considering at 99% confidence interval (R 2  = 92.1%; n = 44; p < 0.01), slightly overestimates the rate and the percent contribution of denitrification in the dry season (475.15 ± 101.18 μmol/m2d; 80.7%) and underestimates it during the wet season (205.072 ± 35.39 μmol/m2d; 24.01%). The analysis of EC and FC demonstrates that manure (41.9 ± 4.2%) and sewage (54.1 ± 8.9%) are the dominant contributors of the hyporheic-nitrate load. In addition, the results achieved by the analysis of the fecal bacterial indicators (EC and FC) were confirmed by NO 3 − /Cl − vs Cl − diagram. This study provides an alternative-initiative framework to accurately quantify the spatio-seasonal variations in the hyporheic-nitrate sources and hyporheic-denitrification rate that enables decision-makers to apply appropriate and targeted strategies to regulate nitrate load in river-aquifer systems. [ABSTRACT FROM AUTHOR]

The church of San Diego de Alcalá, located in Pitiquito, Sonora, in Mexico, lies on a missionary road founded by the Jesuit Eusebio F. Kino, which, with the expulsion of the Jesuit order in 1767, passed into the care of the Franciscans. It contains wallpaintings which presented deterioration problems whose cause was not easy to determine, since the damage appeared to be inconsistent with the techniques used and the environmental conditions. With an interdisciplinary team, a methodology was designed for a combined study of the environment of the church and its wallpaintings. Thermal imaging of the exterior and interior walls indicated that the building was made up of different materials, and the junctions between them explained the different deterioration pathologies between one zone and another. Hydrological maps for groundwater in the locality were studied, to elucidate the presence of water in a desert zone; abundant sources of water in the subsoil were identified, which, because of overexploitation of the land, have been diminishing over time. This allowed the elaboration of a plan for site management, through the identification of those deterioration factors that can be mitigated by simple maintenance actions that are inherent to the environment and the materials, which enabled a scheduled maintenance scheme to be implemented. This improved the condition of the building and its wallpaintings, while reducing the resource invested to achieve this goal. [ABSTRACT FROM AUTHOR]

Nitrate has been recognized as a global threat to environmental health. In this regard, the hyporheic zone (saturated media beneath and adjacent to the stream bed) plays a crucial role in attenuating groundwater nitrate, prior to discharge into surface water. While different nitrate removal pathways have been investigated over recent decades, the adsorption capacity of hyporheic sediments under natural conditions has not yet been identified. In this study, the natural attenuation capacity of the hyporheic-sediments of the Ghezel-Ozan River, located in the north-west of Iran, was determined. The sampled sediments (from 1 m below the stream bed) were characterized via XRD, FT-IR, BET, SEM, BJH, and Zeta potential. Nitrate adsorption was evaluated using a batch experiment with hyporheic pore-water from each study site. The study was performed in the hyporheic sediments of two morphologically different zones, including Z 1 located in the parafluvial zone having the clay sediment texture (57.8% clay) with smectite/Illite mixed layer clay type and Z 2 located in the river confluence area containing silty clay sediment texture (47.6% clay) with smectite/kaolinite mixed layer clay type. Data obtained from the batch experiment were subjected to pseudo-first order, pseudo-second order, intra-particle diffusion, and Elovich mass transfer kinetic models to characterize the nitrate adsorption mechanism. Furthermore, to replicate nitrate removal efficiencies of the hyporheic sediments under natural conditions, the sampled hyporheic pore-waters were applied as initial solutions to run the batch experiment. The results of the artificial nitrate solution correlated well with pseudo-second order (R 2 >95%; in both Z 1 and Z 2 ) and maximum removal efficiencies of 85.3% and 71.2% (adsorbent dosage 90 g/L, pH = 5.5, initial adsorbate concentration of 90 mg/L) were achieved in Z 1 and Z 2 , respectively. The results of the nitrate adsorption analysis revealed that the nitrate removal efficiencies varied from 17.24 ± 1.86% in Z 1 during the wet season to 28.13 ± 0.89% in Z 2 during the dry season. The results obtained by this study yielded strong evidence of the potential of hyporheic sediments to remove nitrate from an aqueous environment with great efficiency. [ABSTRACT FROM AUTHOR]

Nitrate is a widespread contaminant of aquatic ecosystems and drinking water. It is also broadly active in organismal physiology, and as such, has the potential to both enhance and disrupt normal physiological function. In animals, nitrate is a proposed endocrine disrupter that is converted in vivo to nitrite and nitric oxide. Nitric oxide, in particular, is a potent cell signaling molecule that participates in diverse biological pathways and events. Here, we review in vivo nitrate cycling and downstream mechanistic physiology, with an emphasis on reproductive outcomes. However, in many cases, the research produces contradictory results, in part because there is good evidence that nitrate follows a non-monotonic dose-response curve. This conundrum highlights an array of opportunities for scientists from different fields to collaborate for a full understanding of nitrate physiology. Opposing conclusions are especially likely when in vivo/in vitro, long term/short term , high dose/low dose, or hypoxia/normoxia studies are compared. We conclude that in vivo studies are most appropriate for testing an organism’s integrated endocrine response to nitrate. Based on the limited available studies, there is a generalized trend that shorter term studies (less than 1 month) or studies involving low doses (≤5 mg/L NO 3 -N) cause steroid hormone levels to decline. Studies that last more than a month and/or involve higher, but still environmentally relevant, exposures (>50–100 mg/L NO 3 -N) cause steroid hormone levels to increase. Very high nitrate doses (>500 mg/L NO 3 -N) are cytotoxic in many species. Hypoxia and acidity are likely to intensify the effects of nitrate. For study design, degree of study animal reproductive maturity or activity is important, with immature/reproductively quiescent animals responding to nitrate differently, compared with reproductively active animals. A detailed table of studies is presented. [ABSTRACT FROM AUTHOR]

Ionic liquids (ILs), which are alternatives to traditional organic solvents, have the potential to enter soil and cause negative effects on the soil micro-environment, especially soil organisms. The objective of this study was to determine the “alkyl chain effect” and “cut-off effect” mechanisms underlying the toxicity of ILs. The assessment for subchronic toxicity toward earthworms ( Eisenia fetida ) by five common imidazole nitrate ILs ([C n mim]NO 3 (n = 4, 6, 8, 10, and 12)) was conducted on day 28 after exposure to five concentrations (0, 5, 10, 20, and 40 mg kg −1 ) of ILs. Earthworms showed oxidative stress and oxidative damage, and both “alkyl chain effect” and “cut-off effect” (occurred in C 10 ) were observed. In addition, the toxicity of ILs increased with the increase in concentration. Analysis of imidazolium ILs in artificial soil at the end of the experiment indicated that these selected ILs remained relatively stable, with a rate of change of less than 7.39%. The present study provides theoretical support for decisions regarding IL use and helps to establish a friendly IL structure database. [ABSTRACT FROM AUTHOR]

The EU directive has addressed ambitious targets concerning the quality of water bodies. Predicting water quality as affected by land use and management requires using dynamic agro-hydrogeological models. In this study, an agronomic model (STICS) and a hydrogeological model (MODCOU) have been associated in order to simulate nitrogen fluxes in the Seine-Normandie Basin, which is affected by nitrate pollution of groundwater due to intensive farming systems. This modeling platform was used to predict and understand the spatial and temporal evolution of water quality over the 1971-2013 period. A quality assurance protocol (Refsgaard et al. Environ Model Softw 20: 1201-1215, 2005) was used to qualify the reliability of STICS outputs. Four iterative runs of the model were carried out with improved parameterization of soils and crop management without any change in the model. Improving model inputs changed much more the spatial distribution of simulated N losses than their mean values. STICS slightly underestimated the crop yields compared to the observed values at the administrative district scale. The platform also slightly underestimated the nitrate concentration at the outlet level with a mean difference ranging from −1.4 to −9.2 mg NO3 L−1 according to the aquifer during the last decade. This outcome should help the stakeholders in decision-making to prevent nitrate pollution and provide new specifications for STICS development. [ABSTRACT FROM AUTHOR]

This study examines the role of grid resolution on particulate nitrate predictions over the Eastern US during the summer using the three-dimensional chemical transport model (CTM) PMCAMx. The Base Case simulation with coarse resolution (36 × 36 km) often predicts high nighttime nitrate production rates thus leading to overprediction of aerosol nitrate levels. This overprediction is due to the artificial mixing of NO x -rich plumes from major point and area sources with the background atmosphere. Three different horizontal grid resolutions were tested (12 × 12 km, 4 × 4 km and telescoping 12x12/4 × 4 km) for parts of the northeastern US. The bias for PM 2.5 nitrate decreased by 65% when the grid resolution was increased to 4 × 4 km. However, the remaining discrepancies between nitrate predictions and measurements indicate the need for additional improvements including better simulation of the total emissions of ammonia and their temporal evolution, improved description of nighttime chemistry and mixing etc. [ABSTRACT FROM AUTHOR]

Nitrogen (N) stored in deep profiles is important in assessing regional and/or global N stocks and nitrate leaching risk to groundwater. The Chinese Loess Plateau, which is characterized by significantly thick loess deposits, potentially stores immense stocks of mineral N, posing future threats to groundwater quality. In order to determine the vertical distributions of nitrate and ammonium content in the region, as well as to characterize the potential accumulation of nitrate in the deep loess profile, we study loess samples collected at five sites (Yangling, Changwu, Fuxian, An'sai and Shenmu) through a 50 to 200 m loess profile. The estimated storage of mineral N varied significantly among the five sites, ranging from 0.46 to 2.43 × 10 4 kg N ha −1 . Ammonium exhibited fluctuations and dominated mineral N stocks within the whole profile at the sites, except for the upper 20–30 m at Yangling and Changwu. Measured nitrate content in the entire profile at Fuxian, An'sai and Shenmu is low, but significant accumulations were observed to 30–50 m depth at the other two sites. Analysis of δ 15 N and δ 18 O of nitrate indicates different causes for accumulated nitrate at these two sites. Mineralization and nitrification of manure and organic N respectively contribute nitrate to the 0–12 and 12–30 m profile at Changwu; while nitrification of NH 4 + fertilizer, NO 3 − fertilizer and nitrification of organic N control the nitrate distribution in the 0–3, 3–7 and 7–10 m layer at Yangling, respectively. Furthermore, our analysis illustrates the low denitrification potential in the lower part of the vadose zone. The accumulated nitrate introduced by human activities is thus mainly distributed in the upper vadose zone (above 30 m), indicating, currently, a low nitrate leaching risk to groundwater due to a high storage capacity of the thick vadose zone in the region. [ABSTRACT FROM AUTHOR]

Nitrate has become the most important hydrophilic chemical component in PM 2.5 during serious air pollution periods in urban areas of the Pearl River Delta (PRD) region of south China, but there is a lack of fully understanding of its formation mechanisms and controlling factors, especially during daytime nitrate episodes. To fill the knowledge gap, water-soluble inorganic ions in PM 2.5 and trace gases including SO 2 , HNO 3 , NH 3 , NOx and O 3 , particle size distribution, vertical profile of aerosol backscatter density, and ground-level and vertical profiles of key meteorological variables were simultaneously measured at high time resolution in urban Guangzhou of the PRD. The remarkably enhanced nitrate mass concentrations observed at the surface-level during daytime were identified to be caused by strong boundary-layer turbulent mixing of residual aerosols produced from evaporation of low-level shallow stratocumulus clouds. This finding may have important implications on the sources of secondary inorganic aerosols in this and other similar cloudy regions. [ABSTRACT FROM AUTHOR]

Nitrate-dependent anaerobic iron oxidation (NAIO) is a chemolithotrophic bioprocess that converts nitrate to nitrogen gas using zero-valent/ferrous iron, making it valuable for autotrophic denitrification. Seeding sludge is vital for the application of NAIO process, but scarce information is available about the capability of active sludge. In this work, activated sludge (AS) and anaerobic granular sludge (AGS) were investigated for their NAIO performance, and AGS was preferred as inocula after systematic evaluation on three aspects. AGS demonstrated higher nitrogen removal performance with nitrate removal rate of 0.20 ± 0.02 kg-N/(m 3 ·d) and removal efficiency of 95.58 ± 2.29%. The AGS system showed robustness facing NAIO operation conditions, exhibiting stable sludge characteristics (e.g. particle size and shape factors) with variation range of −14.75% to +26.43%. The AGS system demonstrated high economical efficiency with lower iron consumption for nitrate removal and higher iron content for resource recycling. 16S rRNA gene high-throughput sequencing was applied to investigate the microbial community. Nitrosomonadales_unclassified , Geothrix in AS and Nitrosomonadales_unclassified , Desulforhabdus in AGS were supposed to play important roles in NAIO process. The present work clarifies about the choice of seeding sludge for the application of the chemolithotrophic NAIO process and for the development of biotechnology. [ABSTRACT FROM AUTHOR]

Nitrate that originates from agriculture is linked to a series of deleterious environmental consequences that are closely related to human health. Therefore, it is vital to design cropping systems that can produce acceptable crop yields while minimizing the impact of surplus soil nitrate. To develop quantitative estimations, data from 2008 to 2016 were evaluated using multiple regression models. A split-plot field experiment was conducted, with the main treatments of growing Huai bean, soybean and mung bean in summer as leguminous green manure (LGM) while fallow as the control. Four synthetic N rates (0, 108, 135 and 162 kg ha −1 ) were applied as sub-treatments at wheat seeding. The N accumulation for LGMs ranged from 61 to 90 kg ha −1 , and that of Huai bean was 46% higher than the average value of soybean and mung bean ( P < 0.05). The threshold of total N for wheat to produce the highest yields was 141 kg ha −1 . For the LGM treatments, residual nitrate accumulated below the root-zone soil was not significantly increased even when their total N inputs were higher than that of fallow with 162 kg ha −1 of synthetic N. The estimated nitrate-holding capacity of the root-zone soil for the LGM treatments ranged from 104 to 117 kg ha −1 , and the corresponding synthetic N limits were 97–130 kg ha −1 . Considering the target of producing high wheat yields while keeping the residual nitrate in the root-zone soil, the optimal synthetic N rates for LGM treatments were 52–80 kg ha −1 . In conclusion, growing LGMs can maintain high crop yield and mitigate the environmental impact of residual nitrate by substantially replacing the synthetic N to avoid nitrate leaching to deeper soils. [ABSTRACT FROM AUTHOR]

Nitrate aerosol makes up a significant fraction of fine particles and plays a key role in regional air quality and climate. The North China Plain (NCP) is one of the most industrialized and polluted regions in China. To obtain a holistic understanding of the nitrate pollution and its formation mechanisms over the NCP region, intensive field observations were conducted at three sites during summertime in 2014-2015. The measurement sites include an urban site in downtown Jinan -- the capital city of Shandong Province --, a rural site downwind of Jinan city, and a remote mountain site at Mt. Tai (1534 ma.s.l.). Elevated nitrate concentrations were observed at all three sites despite distinct temporal and spatial variations. Using historical observations, the nitrate / PM2:5 and nitrate / sulfate ratios have statistically significantly increased in Jinan (2005-2015) and at Mt. Tai (from 2007 to 2014), indicating the worsening situation of regional nitrate pollution. A multiphase chemical box model (RACM-CAPRAM) was deployed and constrained by observations to elucidate the nitrate formation mechanisms. The principal formation route is the partitioning of gaseous HNO3 to the aerosol phase during the day, whilst the nocturnal nitrate formation is dominated by the heterogeneous hydrolysis of N2O5. The daytime nitrate production in the NCP region is mainly limited by the availability of NO2 and to a lesser extent by O3 and NH3. In comparison, the nighttime formation is controlled by both NO2 and O3. The presence of NH3 contributes to the formation of nitrate aerosol during the day, while there is slightly decreasing nitrate formation at night. Our analyses suggest that controlling NOx and O3 is an efficient way, at the moment, to mitigate nitrate pollution in the NCP region, where NH3 is usually in excess in summer. This study provides observational evidence of a rising trend of nitrate aerosol as well as scientific support for formulating effective control strategies for regional haze in China. [ABSTRACT FROM AUTHOR]

Recent field studies have suggested that sea-salt particulate nitrate (NITs) photolysis may act as a significant local source of nitrogen oxides (NOx ) over oceans. We present a study of the global impact of this process on oxidant concentrations in the marine boundary layer (MBL) using the GEOS-Chem model, after first updating the model to better simulate observed gas--particle phase partitioning of nitrate in the marine boundary layer. Model comparisons with long-term measurements of NOx from the Cape Verde Atmospheric Observatory (CVAO) in the eastern tropical North Atlantic provide support for an in situ source of NOx from NITs photolysis, with NITs photolysis coefficients about 25-50 times larger than corresponding HNO3 photolysis coefficients. Short-term measurements of nitrous acid (HONO) at this location show a clear daytime peak, with average peak mixing ratios ranging from 3 to 6 pptv. The model reproduces the general shape of the diurnal HONO profile only when NITs photolysis is included, but the magnitude of the daytime peak mixing ratio is under-predicted. This underprediction is somewhat reduced if HONO yields from NITs photolysis are assumed to be close to unity. The combined NOx and HONO analysis suggests that the upper limit of the ratio of NITs V HNO3 photolysis coefficients is about 100. The largest simulated relative impact of NITs photolysis is in the tropical and subtropical marine boundary layer, with peak local enhancements ranging from factors of 5 to 20 for NOx, 1.2 to 1.6 for OH, and 1.1 to 1.3 for ozone. Since the spatial extent of the sea-salt aerosol (SSA) impact is limited, global impacts on NOx, ozone, and OH mass burdens are small (~1-3 %). We also present preliminary analysis showing that particulate nitrate photolysis in accumulation-mode aerosols (predominantly over continental regions) could lead to ppbv-level increases in ozone in the continental boundary layer. Our results highlight the need for more comprehensive long-term measurements of NOx, and related species like HONO and sea-salt particulate nitrate, to better constrain the impact of particulate nitrate photolysis on marine boundary layer oxidant chemistry. Further field and laboratory studies on particulate nitrate photolysis in other aerosol types are also needed to better understand the impact of this process on continental boundary layer oxidant chemistry. [ABSTRACT FROM AUTHOR]

This study employed an open external circuit, rather than a closed circuit applied in previous studies, to operate an microbial fuel cell (MFC) sensor for real-time nitrate monitoring, and achieved surprisingly greater sensitivity (4.42 ± 0.3–6.66 ± 0.4 mV/(mg/L)) when the nitrate was at a concentration of 10–40 mg/L, compared to that of the MFC sensor with a closed circuit (0.8 ± 0.05–1.6 ± 0.1 mV/(mg/L)). The MFC sensor operated in open circuit (O-MFC sensor) delivered much more stable performance than that operated in closed circuit (C-MFC sensor) when affected by organic matter (NaAc). The sensitivity of O-MFC sensor was twice that of C-MFC sensor at a low background concentration of organic matter. When organic matter reached a high concentration, the sensitivity of O-MFC sensor remained at an acceptable level, while that of C-MFC sensor dropped to almost zero. Challenged by a combined shock of organic matter and nitrate, O-MFC sensor delivered evident electrical signals for nitrate warning, while C-MFC failed. Another novel feature of this study lies in a new mathematical model to examine the bioanode process of nitrate monitoring. It revealed that lower capacitance of the bioanode in O-MFC was the major contributor to the improved sensitivity of the device. [ABSTRACT FROM AUTHOR]

Peroxy and peroxyacyl nitrates (PNs and PANs) are important trace gas constituents of the troposphere which are challenging to quantify by differential thermal dissociation with NO2 detection in polluted (i.e., high-NOx) environments. In this paper, a thermal dissociation peroxy radical chemical amplification cavity ring-down spectrometer (TD-PERCA-CRDS) for sensitive and selective quantification of total peroxynitrates (ΣPN = ΣRO2NO2) and of total peroxyacyl nitrates (ΣPAN = ΣRC(O)O2NO2) is described. The instrument features multiple detection channels to monitor the NO2 background and the ROx (= HO2+RO2+ΣRO2) radicals generated by TD of ΣPN and/or ΣPAN. Chemical amplification is achieved through the addition of 0.6ppm NO and 1.6% C2H6 to the inlet. The instrument's performance was evaluated using peroxynitric acid (PNA) and peroxyacetic or peroxypropionic nitric anhydride (PAN or PPN) as representative examples of ΣPN and ΣPAN, respectively, whose abundances were verified by iodide chemical ionization mass spectrometry (CIMS). The amplification factor or chain length increases with temperature up to 69±5 and decreases with analyte concentration and relative humidity (RH). At inlet temperatures above 120 and 250°C, respectively, PNA and ΣPAN fully dissociated, though their TD profiles partially overlap. Furthermore, interference from ozone (O3) was observed at temperatures above 150°C, rationalized by its partial dissociation to O atoms which react with C2H6 to form C2H5 and OH radicals. Quantification of PNA and ΣPAN in laboratory-generated mixtures containing O3 was achieved by simultaneously monitoring the TD-PERCA responses in multiple parallel CRDS channels set to different temperatures in the 60 to 130°C range. The (1s, 2Σ) limit of detection (LOD) of TD-PERCA-CRDS is 6.8pptv for PNA and 2.6pptv for ΣPAN and significantly lower than TD-CRDS without chemical amplification. The feasibility of TD-PERCA-CRDS for ambient air measurements is discussed. [ABSTRACT FROM AUTHOR]

Nitrate leaching is a pressing environmental problem in intensive agriculture. Especially after the crop harvest, leaching risk is greatest due to decomposing plant residues, and low plant nutrient uptake and evapotranspiration. The specific crop also matters: grain legumes and canola commonly result in more leftover N than the following winter crop can take up before spring. Addition of a high carbon amendment (HCA) could potentially immobilize N after harvest. We set up a 2-year mesocosm experiment to test the effects of N fertilization (40 or 160 kg N/ha), HCA addition (no HCA, wheat straw, or sawdust), and precrop plant functional group identity on winter barley yield and soil C/N ratio. Four spring precrops were sown before winter barley (white lupine, faba bean, spring canola, spring barley), which were selected based on a functional group approach (colonization by arbuscular mycorrhizal fungi [AMF] and/or N2-fixing bacteria). We also measured a subset of faba bean and spring barley for leaching over winter after harvest. As expected, N fertilization had the largest effect on winter barley yield, but precrop functional identity also significantly affected the outcome. The non-AMF precrops white lupine and canola had on average a positive effect on yield compared to the AMF precrops spring barley and faba bean under high N (23% increase). Under low N, we found only a small precrop effect. Sawdust significantly reduced the yield compared to the control or wheat straw under either N level. HCAs reduced nitrate leaching over winter, but only when faba bean was sown as a precrop. In our setup, short-term immobilization of N by HCA addition after harvest seems difficult to achieve. However, other effects such as an increase in SOM or nutrient retention could play a positive role in the long term. Contrary to the commonly found positive effect of AMF colonization, winter barley showed a greater yield when it followed a non-AMF precrop under high fertilization. This could be due to shifts of the agricultural AMF community toward parasitism. [ABSTRACT FROM AUTHOR]

Surface snow and atmospheric samples collected along a traverse from the coast to the ice sheet summit (Dome A) are used to investigate summertime atmospheric production of nitrate (NO 3 – ) across East Antarctica. The strong relationship observed between δ 15 N and δ 18 O of nitrate in the surface snow suggests a large (lesser) extent of nitrate photolysis in the interior (coastal) region. A linear correlation between the oxygen isotopes of nitrate (δ 18 O and Δ 17 O) indicates mixing of various oxidants that react with NO x (NO x  = NO + NO 2 ) to produce atmospheric nitrate. On the plateau, the isotopes of snow nitrate are best explained by local reoxidation chemistry of NO x , possibly occurring in both condensed and gas phases. Nitrate photolysis results in redistribution of snow nitrate, and the plateau snow is a net exporter of nitrate and its precursors. Our results suggest that while snow-sourced NO x from the plateau due to photolysis is a significant input to the nitrate budget in coastal snow (up to ∼35%), tropospheric transport from mid-low latitudes dominates (∼65%) coastal snow nitrate. The linear relationship of δ 18 O vs. Δ 17 O of the snow nitrate suggests a predominant role of hydroxyl radical (OH) and ozone (O 3 ) in nitrate production, although a high Δ 17 O(O 3 ) is required to explain the observations. Across Antarctica the oxygen isotope composition of OH appears to be dominated by exchange with water vapor, despite the very dry environment. One of the largest uncertainties in quantifying nitrate production pathways is the limited knowledge of atmospheric oxidant isotopic compositions. [ABSTRACT FROM AUTHOR]

Dual (oxygen and nitrogen) isotopic composition of the museum archived nitrates from the United States of America, South Africa and Australia was studied. The analyzed specimens were collected in middle 19th to early 20th centuries, and represent world-wide acquisition of the Smithsonian Institution Natural Museum of Natural History (Washington, D. C., USA) and the Natural History Museum (London, UK). The samples consist of transparent to semi-transparent aggregates of minute nitrate, euhedral crystallites which imply precipitation from percolating fluids under ample space and dry regimes. The major nitrate chemistry is saltpetre (KNO 3 ) with minor nitratine (NaNO 3 ). A binary plot of δ 15 N vs. δ 18 O of almost all nitrates indicates a trend, reflecting microbial origin through nitrification of ammonium. The diagram excludes the contribution of meteoric origin formed by mass-independent, photochemical reaction of NO with ozone in stratosphere. Calculated paleo-ambient fluid compositions responsible for microbial nitrification imply extreme evaporative concentration of relevant fluids under dry climatic regimes in the Northern Cape Province (South Africa) and in the Northern Territory (central Australia), and even throughout the United States of America. The dual isotopic characterization provides direct evidence to the origin of the museum archived nitrates. [ABSTRACT FROM AUTHOR]