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Ambient nitrate has been of increasing concern in PM2.5, while there are still large uncertainties in quantifying the formation of nitrate aerosol. The formation pathways of nitrate aerosol at an urban site and a suburban site in the Pearl River Delta (PRD) are investigated using an observation-constrained box model. Throughout the campaigns, aerosol pollution episodes were constantly accompanied with the increase in nitrate concentrations and fractions at both urban and suburban sites. The simulations demonstrate that chemical reactions in the daytime and at night both contributed significantly to formation of nitrate in the boundary layer at the two sites. However, nighttime reactions predominantly occurred aloft in the residual layer at the urban site, and downward transport from the residual layer in the morning is an important source (53 %) for surface nitrate at the urban site, whereas similar amounts of nitrate were produced in the nocturnal boundary layer and residual layer at the suburban site, which results in little downward transport of nitrate from the residual layer to the ground at the suburban site. We show that nitrate formation was in the volatile-organic-compound-limited (VOC-limited) regime at the urban site, and in the transition regime at the suburban site, identical to the response of ozone at both sites. The reduction of VOC emissions can be an efficient approach to mitigate nitrate in both urban and suburban areas through influencing hydroxyl radical (OH) and N2O5 production, which will also be beneficial for the synergistic control of regional ozone pollution. The results highlight that the relative importance of nitrate formation pathways and ozone can be site-specific, and the quantitative understanding of various pathways of nitrate formation will provide insights for developing nitrate and ozone mitigation strategies.

Nitrate pollution in water environments is a ubiquitous problem. Solid-phase denitrification (SPD) is a technology that has attracted in recent years increasing attention due to its significant advantage suitability over the aqueous-based denitrification for

Particulate nitrate (pNO3-) has often been found to be the major component of fine particles in urban air-sheds in China, the United States, and Europe during winter haze episodes in recent years. However, there is a lack of knowledge regarding the experimentally determined contribution of different chemical pathways to the formation of pNO3-. Here, for the first time, we combine ground and tall-tower observations to quantify the chemical formation of pNO3- using observationally constrained model approach based on direct observations of OH and N2O5 for the urban air-shed. We find that the gas-phase oxidation pathway (OH+NO2) during the daytime is the dominant channel over the nocturnal uptake of N2O5 during pollution episodes, with percentages of 74% in urban areas and 76% in suburban areas. This is quite different from previous studies in some regions of the US, in which the uptake of N2O5 was concluded to account for a larger contribution in winter. These results indicate that the driving factor of nitrate pollution in Beijing and different regions of the US is different, as are the mitigation strategies for particulate nitrate.

The heterogeneous hydrolysis of dinitrogen pentoxide (N2O5) plays an important role in regulating NOx. The N2O5 uptake coefficient, γ(N2O5), was determined using an iterative box model that was constrained to observational data obtained in suburban Beijing from February to March 2016. The box model determined 2289 individual γ(N2O5) values that varied from

Nitrate monitoring is commonly conducted with low‐spatial resolution, only at the outlet or at a small number of selected locations. As a result, the information about spatial variations in nitrate export and its drivers is scarce. In this study, we present results of high‐spatial resolution monitoring conducted between 2012 and 2017 in 65 sub‐catchments in an Alpine mesoscale river catchment characterized by a land‐use gradient. We combined stable isotope techniques with Bayesian mixing models and geostatistical methods to investigate nitrate export and its main drivers, namely, microbial N turnover processes, land use and hydrological conditions. In the investigated sub‐catchments, mean values of NO3− concentrations and its isotope signatures (δ15NNO3 and δ18ONO3) varied from 2.6 to 26.7 mg L−1, from −1.3‰ to 13.1‰, and from −0.4‰ to 10.1‰, respectively. In this study, land use was an important driver for nitrate export. Very strong and strong positive correlations were found between percentages of agricultural land cover and δ15NNO3, and NO3− concentration, respectively. Mean proportional contributions of NO3− sources varied spatially and seasonally, and followed land‐use patterns. The mean contribution of manure and sewage was much higher in the catchments characterized by a high percentage of agricultural and urban land cover comparing to forested sub‐catchments. Specific NO3− loads were strongly correlated with specific discharge and moderately correlated with NO3− concentrations. The nitrate isotope and concentration analysis results suggest that nitrate from external sources is stored and accumulated in soil storage pools. Nitrification of reduced nitrogen species in those pools plays the most important role for the N‐dynamics in the Erlauf river catchment. Consequently, nitrification of reduced N sources was the main nitrate source except for a number of sub‐catchments dominated by agricultural land use. In the Erlauf catchment, denitrification plays only a minor role in controlling NO3− export on a regional scale., We integrated results of the BMM with informative priors and top‐kriging. Reduced N stored in soil is an important source for stream N in a mesoscale catchment. Manure and sewage is the main NO3− source in agricultural sub‐catchments. Denitrification played only a minor role in controlling regional scale NO3− export.

The hydrochemistry and quality of local shallow groundwater was assessed within the Xinzhou basin in Shanxi, North China. Piper diagrams, correlation analysis, principal component analysis, chloro-alkaline indices, ion proportion diagrams, and Gibbs diagrams were used to reveal the hydrochemical characteristics and evolution mechanisms of groundwater. Besides, two indicators of sodium adsorption ratio and soluble sodium percentage, USSL and Wilcox diagrams, and water quality index models were used to evaluate the groundwater quality for irrigation and drinking. In general, groundwater in most areas of the basin is fresh water with total dissolved solid lower than 1000 mg/L. But there are salt water in some parts of the southern basin, with total dissolved solid higher than 1000 mg/L, due to industrial and domestic pollution. The hydrochemical facies of groundwater in most areas are HCO3-Ca and mixed HCO3-Ca·Mg·Na types, while it is HCO3·SO4·Cl-Na type in a small part of the basin. Nitrate pollution widely occurred in the basin because of the use of nitrogenous fertilizers. The dominant mechanism controlling the evolution of groundwater chemistry compositions was the weathering of rock minerals. It mainly reflected in the dissolution of carbonate minerals. And the carbonate dissolution is the major origins of HCO3−, Ca2+, and Mg2+ in groundwater. However, Na-Ca exchange is the important source of Na+. Shallow groundwater was suitable for irrigation and drinking except for some southern parts of the basin. These results will be helpful for the protection and efficient management of groundwater in the Xinzhou basin.

Nitrate is a prominent pollutant in surface and groundwater bodies worldwide. Isotopes in nitrate provide a powerful approach for tracing nitrate sources and transformations in waters. Given that analytical techniques for determining isotopic compositions are generally time-consuming, laborious and expensive, alternative methods are warranted to supplement and enhance existing approaches. Hence, we developed a support vector regression (SVR) model and explored its feasibility to predict nitrogen isotopic composition of nitrate (δ15N-NO3-) in a rural-urban river system in Southeastern China. A total of 16 easily obtained hydro-chemical variables were measured in the wet season (September 2019) and dry season (January 2020) and used to develop the SVR prediction model. The grading method utilized ~75% (35) of the samples for model building while the remaining 11 samples assessed model performance. Principal component analysis (PCA) extracted 7 principal components for SVR model inputs as PCA reduces superfluous variables. We optimized tuning parameters in the SVR model using a grid search technique coupled with V-fold cross-validation. The optimized SVR model provided accurate δ15N-NO3- predictions with a determination coefficient (R2) of 0.88, Nash-Sutcliffe (NS) of 0.87, and mean square error (MSE) of 0.53‰ in the testing step, and performed much better than the corresponding multivariate linear regression model (R2=0.60, NS=0.58 and MSE=1.76‰) and general regression neural network model (R2=0.66, NS=0.65 and MSE=1.45‰). Overall, the SVR model provides a potential indirect method to predict environmental isotope values for water quality management that will complement and enhance the interpretation of direct measurements of δ15N-NO3-.

High concentrations of nitrate in groundwater pose a threat to human health. To quantify groundwater nitrate pollution in China's Changchun New District and evaluate its human health risks, 98 grou...

In this study, Bayesian technique was applied in order to estimate export coefficients for the Melen Watershed. Furthermore, instead of calculating the contributions of subwatersheds individually, the whole watershed was considered for the estimation of the total load at the outlet of the Melen Watershed using the calculated nitrate export coefficient. The Bayesian approach has the goal of combining prior knowledge with data to optimally use both sources of information. Success of the Bayesian approach is directly proportional to sufficiency of data for acquiring the prior information about estimands. Bayesian analysis was conducted through Structural Equation Model (SEM) using AMOS software and posterior information about land use based export coefficients was obtained through Markov Chain Monte Carlo (MCMC) method. Estimated land use based nitrate export coefficients are in kg/km2/day unit. In addition, monthly river retention value of nitrogen in all subwatersheds of the Melen Watershed were estimated. This information was used in order to predict nitrate export coefficients appropriately. This study is aimed to be an important precedent for other basins that are determined as in priority in terms of pollution by The Ministry of Forest and Water Works of Turkey. Keywords: AMOS, Bayesian approach, Melen Watershed, MCMC, nitrate export coefficient, Structural Equation Model

The main purpose of this study was to model nitrate and its spatial and temporal variations under hydrological tensions. For this purpose, the hydrodynamic characteristics and transmission of Varamin plain groundwater were modeled after collecting and organizing the field data. Qualitative data were imported to the quantitative GMS model constructed by using the MODLFLOW code. Then, quantitative and qualitative models were calibrated. Measured and model predicted values were compared and relatively acceptable results were obtained. The most important factor in deteriorating the groundwater quality was nitrate pollution related to the agricultural areas which will exceed the permissible limits of drinking water during a 10-year period. Also, according to the model maps of the unconfined aquifer, the highest content of nitrate was related to downstream areas of the big cities. Since the confined aquifer is overlaid by an impermeable layer, it is less affected by nitrate pollution and contains high-quality drinking water. However, population growth and subsequent increase in agricultural activities and human sewage disposal may lead to further pollution of the unconfined aquifer by nitrate.

Water pollution by excessive amounts of nitrate (NO3−) has become a global issue. Technologies to clean up nitrate-contaminated water bodies include phytoremediation. In this context, this research aimed to evaluate four tree species (Salix alba L., Populus alba L., Corylus avellana L. and Sambucus nigra L.) to remediate nitrate-contaminated waters (100 and 300 mg L−1). Some physiological parameters showed that S. alba L. and P. alba L. increased particularly photosynthetic activity, chlorophyll content, dry weight, and transpired water, following the treatments with the above NO3− concentrations. Furthermore, these species were more efficient than the others studied in the phytodepuration of water contaminated by the two NO3− levels. In particular, within 15 days of treatment, S. alba L. and P. alba L. removed nitrate quantities ranging from 39 to 78%. Differently, C. avellana L. and S. nigra L. did not show particular responses regarding the physiological traits studied. Nonetheless, these species removed up to 30% of nitrate from water. In conclusion, these data provide exciting indications on the chance of using S. alba L. and P. alba L. to populate buffer strips to avoid NO3− environmental dispersion in agricultural areas.

Nitrate pollution in groundwater is a serious problem in Shimabara Peninsula, Nagasaki, Japan. A better understanding of the hydrogeochemical evolution of groundwater in vulnerable aquifers is important for health and environment. In this study, groundwater samples were collected at 12 residential and 57 municipal water supply wells and springs in July and August 2018. Nitrate (NO3-N) concentration at eight sampling sites (12%) exceeded Japanese drinking water standard for NO3 + NO2-N (10 mg L-1). The highest nitrate concentration was 19.9 mg L-1. Polluted groundwater is distributed in northeastern, northwestern, and southwestern areas, where land is used for intensive agriculture. Correlation analysis suggests that nitrate sources are agricultural fertilizers and livestock waste. Dominant groundwater chemistry is (Ca+Mg)-HCO3 or (Ca+Mg)-(SO4+NO3) type. Groundwater with higher nitrate concentration is of (Ca+Mg)-(SO4+NO3) type, indicating nitrate pollution affecting water chemistry. Principal component analysis extracted two important factors controlling water chemistry. The first principal component explained dissolved ions through water-rock interaction and agricultural activities. The second principal component explained cation exchange and dominant agricultural effects from fertilizers. Hierarchical cluster analysis classified groundwater into four groups. One of these is related to the dissolution of major ions. The other three represent nitrate pollution., Water, 13(4), art.no.426; 2021

Globally occurring nitrate pollution in groundwater is harming the environment and human health. In situ hydrogen addition to stimulate denitrification has been proposed as a remediation strategy. However, observed nitrite accumulation and incomplete denitrification are severe drawbacks that possibly stem from the specific microbial community composition. We set up a microcosm experiment comprising sediment and groundwater from a nitrate polluted oxic oligotrophic aquifer. After the microcosms were sparged with hydrogen gas, samples were taken regularly within 122 h for nitrate and nitrite measurements, community composition analysis via 16S rRNA gene amplicon sequencing and gene and transcript quantification via qPCR of reductase genes essential for complete denitrification. The highest nitrate reduction rates and greatest increase in bacterial abundance coincided with a 15.3-fold increase in relative abundance of Rhodocyclaceae, specifically six ASVs that are closely related to the genus Dechloromonas. The denitrification reductase genes napA, nirS and clade I nosZ also increased significantly over the observation period. We conclude that taxa of the genus Dechloromonas are the prevailing hydrogenotrophic denitrifiers in this nitrate polluted aquifer and the ability of hydrogenotrophic denitrification under the given conditions is species-specific.

Nitrate pollution is considered to be one of the most common environmental problems in groundwater, especially in areas affected by human mining, such as the arid region of northern China. However, the human health risk assessment of nitrate pollution in this area has not yet been carried out. In this study, groundwater samples were taken in the Selian mining area in Inner Mongolia to conduct a full analysis of water quality. On this basis, the groundwater quality, the distribution range of nitrate pollution, and human health risks were evaluated. The results show that the groundwater in the Selian mining area is neutral to alkaline, with high salinity and hardness. The concentration of nitrate ions in groundwater generally exceeds the standard, and the maximum exceeds 5.48 times the value specified in the Chinese national standard, indicating that groundwater nitrate pollution needs to be controlled urgently. Groundwater is polluted by large amounts of nitrogen fertilizer used by humans in agricultural activities. At the same time, mining activities have accelerated the severity and spread of pollution. Groundwater is not recommended for direct human life and irrigation use in the study area unless purification measures are taken. Nitrate pollution is more harmful to children through groundwater, about 1.54 times that of adults. Excess nitrate is transported into the body through drinking groundwater, so proper drinking water control will reduce the health risks of nitrate, such as centralized water supply. This study will provide a scientific basis for the rational use of groundwater and nitrate pollution control in the area.

Denitrification in floodplain soils is one key process that determines the buffering capacity of riparian zones in terms of diffuse nitrate pollution. One widely used approach to measure the denitrification potential is the acetylene inhibition technique that requires fresh soil samples. We conducted experiments with air-dried soils using a time series analysis to determine the optimal rewetting period. Thus, air-dried soil samples from six different floodplain areas in Germany were rewetted for 1 to 13days to 100% water-filled pore space. We analyzed nitrogen accumulated as N2O in the top of anaerobic flasks with and without acetylene by gas chromatography after four hours of incubation. We observed an overall optimal rewetting of at least seven days for complete denitrification. We also saw the strong influence of pH and field capacity on the denitrification product ratio, in soils with pH &lt, 7, we hardly assumed complete denitrification, whereas the treatments with pH &gt, 7 achieved stable values after seven days of rewetting. This advanced method provides the opportunity to carry out campaigns with large soil sample sizes on the landscape scale, as samples can be stored dry until measurements are taken.

To achieve the objectives of the Water Framework Directive’s, the identification and reversal of significant upward trends in pollutant concentrations in groundwater is crucial. A statistically significant increase in a pollutant, groups of pollutants or pollution indicators in groundwater bodies, means an upward trend in concentration values, calculated using a recognized statistical method, at least 90% significant. Following this aim, we focused on a groundwater body of southern Italy, with high concentration of nitrate and, therefore, defined “at risk”, on the basis of its bad quality status. In this area, we calculated the trends of the time series of nitrate concentrations in groundwater. We described the adopted procedure for trend analysis, following the guidelines proposed by the Italian Institute for Environmental Protection and Research (ISPRA). We used the Mann–Kendall method for calculating the statistical significance of the upward trend of time series and, successively, the Sen method for estimating the value of the trend (angular coefficient). We applied these methods also to forecast nitrate concentrations in groundwater in 2021 and in 2027. We found differences in the sampling stations in terms of groundwater quality and trends, as a result of different environmental factors. Peculiarly, the location of the wells presenting upward trends seems to be in areas with high population density and intensive agriculture.

The aim of this work is to evaluate the nitrate content and its impact on groundwater quality used for supply in dairy farms in a sector of the Pampas Plain in relation to specific point sources of pollution. Samples were collected in nine dairy farms during the months of June, August and November 2017 and April 2018. In all the samples, electrical conductivity and pH were measured in situ with a portable multiparameter equipment and water samples were collected to determine nitrates content. In the April 2018 sampling, carbonates, bicarbonates, chlorides, sulphates, nitrates, sodium, calcium, magnesium, and potassium were also determined. Results show that groundwater is mainly sodium bicarbonate to magnesium calcium bicarbonate type with variable pH and salinity. Nitrates and hardness were above the limits for human and animal consumption. Nitrate contents are significantly correlated with pH, electrical conductivity and hardness, and tend to decrease in wells which are more distant from point sources of pollution. In turn, the incorporation of other ions into the aquifer is evidenced by the increase of chlorides and EC and their correlation with nitrates. It is interpreted that the nitrification process acidifies the medium, triggering the dissolution of carbonates present in the aquifer matrix which increases groundwater hardness. Water quality deterioration could not only put at risk farmers’ health but it also conditions animal production and the dairy farm machinery. This study is the first contribution to defining local guidelines to set a proper water management plan as well as to provide tools to address the problem in other dairy farms in this sector of the Pampas Plain and in other regions., Facultad de Ciencias Naturales y Museo, Centro de Investigaciones Geológicas, Facultad de Ciencias Agrarias y Forestales

Although representing a paramount mechanism against nitrogen excess in agricultural landscapes, soil denitrification is still a largely unknown term in nitrogen balances at the watershed scale. In the present work, a comprehensive investigation of nitrogen sources and sinks in agricultural soils and waters was performed with the aim of gaining insights into the relevance of soil denitrification in a highly farmed sub-basin of the Po River delta (Northern Italy). Agricultural statistics, water quality datasets, and results of laboratory experiments targeting nitrogen fluxes in soils were combined to set up a detailed nitrogen budget along the terrestrial&ndash, freshwater continuum. The soil nitrogen budget was not closed, with inputs exceeding outputs by 72 kg N&middot, ha&minus, 1&middot, year&minus, 1, highlighting a potential high risk of nitrate contamination. However, extensive monitoring showed a general scarcity of mineral nitrogen forms in both shallow aquifers and soils. The present study confirmed the importance of denitrification, representing ~37% of the total nitrogen inputs, as the leading process of nitrate removal in heavily fertilized fine-texture soils prone to waterlogged conditions.

Shallow aquifers of coastal and internal alluvial plains of developed countries are commonly characterized by the challenging management of groundwater resources due to the intense agricultural and industrial activities that determine a high risk of groundwater contamination. Among the principal origins of pollution in these areas are agricultural practices based on the amendment of soils by nitrate fertilizers, which have been recognized as one of the most severe environmental emergencies for which specific policies and regulations have been issued (e.g., EU Directive 2006/118/EC). In such a framework, the results of research aimed at assessing the specific vulnerability of shallow alluvial aquifers to nitrate fertilizer pollutants by coupled process-based and empirical approaches are here proposed. The research focused on assessing the specific vulnerability to nitrate pollution of a shallow alluvial aquifer of the Campania region (southern Italy), which was selected due to its representativeness to other recurrent hydrogeological settings occurring in alluvial plains of the region and worldwide. In this area, 1D hydro-stratigraphic models of the unsaturated zone were reconstructed and applied for simulating the transport of nitrate pollutants at the water table and estimating the associated travel times. Numerical modeling was carried out by the finite differences VS2TDI code and considered a 10-year time series of rainfall and evapotranspiration as well as typical local farming practices of nitrate fertilizer input. Results of the travel time calculated for the 1D hydro-stratigraphic models considered and at different depths were recognized as a proxy to assess the specific vulnerability to nitrate fertilizer pollution. Among the principal outcomes is an empirical multiple correlation between the travel time of the nitrate fertilizer pollutant, water table depth, and equivalent saturated hydraulic conductivity of the unsaturated zone or hydraulic resistance, which was used to assess the travel time at the distributed scale over the whole area studied as well as the related specific vulnerability. Given such results, the coupled process-based and empirical approach is proposed as generally applicable for assessing and mapping groundwater vulnerability in shallow aquifers, for which detailed stratigraphic and piezometric data are available.

The shift from rainfed to irrigated agriculture is associated with a change in the fertilization rates due to increases in expected production and the fact of growing more N demanding crops. In addition, the circulation of irrigation return flows (IRF) mobilizes soluble salts stored in soils or geological materials. As a consequence, it implies severe modifications in the dynamics and total amount of soluble salts and nitrogen exported, especially in semi-arid watersheds. In this study, long-term data collected by the regional authorities was used to assess the effects of irrigation implementation on salinity (using electrical conductivity, EC, as a proxy) and nitrate concentration (NO3 −) after the transformation of ca. 77 km2 from rainfed to irrigated agriculture in the Cidacos River (CR) watershed. The results indicate that water quality in the lower reaches of the CR was significantly modified after the diffuse incorporation of IRF. In contrast, neither EC nor NO3 − were different in those monitoring stations whose contributing watersheds did not include transformed area. In addition, the temporal dynamics in the analysed variables shifted from a rainfed land signal typical in the region to an irrigated land signal, and the hydrochemical type of the CR shifted from mixed-to-Na+-mixed-to-HCO3 – to mostly Na+-mixed type, typical of waters affected by IRF in the region. Groundwater EC and NO3 − also increased in those wells located within the irrigated area. Although there are great uncertainties in the actual amount of salt and N reaching the CR via IRF, the expected contribution of waste water spilled into the CR is minor in comparison to other sources, mostly agricultural sources in the case of N. The observed changes have promoted the designation of the lower reaches of the CR as 'affected' by NO3 − pollution, and the whole CR watershed as a Nitrate Vulnerable Zone, with the emergent question about whether irrigation implementation as carried out currently in Spain is against the environmental objectives of the Water Framework Directive. This work received funding from 'Ministerio de Economía y Competitividad' (Government of Spain) via the Research Project CGL2015-64284-C2-1-R and support to D. Merchán ('Juan de la Cierva - Formación' program, FJCI-2015-24920 ) and I. Hernández-García (FPI program, BES-2016-078786 ). It also benefited from the LIFE-Nitrates Project (LIFE+10 ENV/ES/478 ; www.life-nitratos.eu).

High nitrate concentration of fresh groundwater of a coastal karstic aquifer, not far from the Apulian regional capital (Southern Italy), caused public concern and alarm from the authorities. The attention of local communities focused on the effect of a group of landfills, the use of which started from 1975, using improved technological and safety devices to reduce groundwater pollution risks.

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 m a.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.

Global change effects, such as warming and increases in nitrogen loading, alter vulnerable Mediterranean aquatic systems, and charophytes can be one of the most affected groups. We addressed the possible interaction between these factors on two populations of the cosmopolitan charophytes Chara hispida and Chara vulgaris. Populations were taken from two different environments, a nitrate-poor mountain lake and a nitrate-rich Mediterranean coastal spring. The laboratory experiment had a 2 × 2 factorial design based on two nitrate levels (similar to and double the local conditions) and two temperatures. Increased temperatures favoured the growth of the four populations, but an increase in nitrate did not have any effect on their growth or architecture. Both species took up and stored more nitrogen (measured as %N in plant tissue) when more nitrate was supplied, and warming favoured this increase in %N and, consequently, in N:P ratio. The effects of both factors depended on the local conditions where the populations originated and on the species. Chara vulgaris, a pioneer species, exhibited more phenotypic plasticity than C. hispida, and its ecotype from the coastal spring was better adapted to changes in temperature and nitrate level. These differential responses to warming conditions and nitrate pollution may modify charophyte diversity, which might be reflected in ecosystem performance, a matter of concern in vulnerable Mediterranean water bodies where these species co-occur., This study was supported by the Spanish Ministry of Economy and Competitiveness for research project CGL2014-54502-C2-1-P (including EC FEDER funding). Eric Puche is the holder of a grant (UV-INV-PREDOC16F1-383810) funded by the University of Valencia.

In recent years, nitrate plays an increasingly important role in haze pollution and strict emission control seems ineffective in reducing nitrate pollution in China. In this study, observations of gaseous and particulate pollutants during the COVID-19 lockdown, as well as numerical modelling were integrated to explore the underlying causes of the nonlinear response of nitrate mitigation to nitric oxides (NOx) reduction. We found that, due to less NOx titration effect and the transition of ozone (O3) formation regime caused by NOx emissions reduction, a significant increase of O3 (by ∼ 69%) was observed during the lockdown period, leading to higher atmospheric oxidizing capacity and facilitating the conversion from NOx to oxidation products like nitric acid (HNO3). It is proven by the fact that 26–61% reduction of NOx emissions only lowered surface HNO3 by 2–3% in Hebi and Nanjing, eastern China. In addition, ammonia concentration in Hebi and Nanjing increased by 10% and 40% during the lockdown, respectively. Model results suggested that the increasing ammonia can promote the gas-particle partition and thus enhance the nitrate formation by up to 20%. The enhanced atmospheric oxidizing capacity together with increasing ammonia availability jointly promotes the nitrate formation, thereby partly offsetting the drop of NOx. This work sheds more lights on the side effects of a sharp NOx reduction and highlights the importance of a coordinated control strategy., Graphical abstract Image 1

Decreasing nitrate concentrations is one of the most relevant Water Framework Directive (WFD) goals, which today is still unreached in several European countries. Vegetated canals have been recognized as effective filters to mitigate nitrate pollution, although rarely included in restoration programs aimed at improving water quality in agricultural watersheds. The Po di Volano basin (713 km2, Northern Italy) is a deltaic territory crossed by an extensive network of agricultural canals (~1300 km). The effectiveness in buffering nitrate loads via denitrification was assessed for different levels of in-stream emergent vegetation maintenance by employing an upscale model based on extensive datasets of field measurements. The scenarios differed for the canal network length (5%, 20%, 40%, and 60%) where conservative management practices were adopted by postponing the mowing operations from the middle of summer, as nowadays, to the early autumn, i.e., the vegetative season end. The scenario simulations demonstrated that the capacity to mitigate diffuse nitrate pollution would increase up to four times, compared to the current condition (5% scenario), by postponing the vegetation mowing to the end of the vegetative season in 60% of the canal network length. By preserving the in-stream vegetation in 20% of the canal network, its denitrification capacity would equal the nitrate load reduction target required for achieving, from May to September, the good ecological status according to the WFD in waters delivered to the coastal areas. Changing the timing of vegetation mowing may create a large potential for permanent nitrate removal via denitrification in agricultural landscapes, thus protecting the coastal areas when the eutrophication risk is higher. Conservative management practices of in-stream vegetation might be promoted as an effective low-cost tool to be included in the WFD implementation strategies.

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.

Currently a debate exists about whether the reduced growth of macrophytes with increased nitrogen loading in shallow ecosystems is determined by ecological or physiological factors. To discover whe...

Investigation of contaminant sources is indispensable for developing effective countermeasures against nitrate (NO3 ?) pollution in groundwater. Known major nitrogen (N) sources are chemical fertilizers, livestock waste, and domestic wastewater. In general, scatter diagrams of δ18O and δ15N from NO3 ? can be used to identify these pollution sources. However, this method can be difficult to use for chemical fertilizers and livestock waste sources due to the overlap of δ18O and δ15N ranges. In this study, we propose to use coprostanol as an indicator for the source of pollution. Coprostanol can be used as a fecal contamination indicator because it is a major fecal sterol formed by the conversion of cholesterol by intestinal bacteria in the gut of higher animals. The proposed method was applied to investigate NO3 ? pollution sources for groundwater in Shimabara, Nagasaki, Japan. Groundwater samples were collected at 33 locations from March 2013 to November 2015. These data were used to quantify relationships between NO3-N, δ15N-NO3 ?, δ18O-NO3 ?, and coprostanol. The results show that coprostanol has a potential for source identification of nitrate pollution. For lower coprostanol concentrations (, Journal of Hydrology, 550, pp.663-668; 2017

Wetlands remove nitrate pollution from water effectively. An analysis shows that this effect is constrained in the United States by the distribution of wetlands, and could be increased by targeting wetland restoration to nitrate sources. US wetlands are not well placed to remove nitrate from the environment.

Deterioration of groundwater quality due to the introduction of pollutants from natural and anthropic sources has become a major environmental issue. We tested three methodologies in assessing groundwater quality and intrinsic aquifer vulnerability in the Agro-Aversano area (Southern Italy). A geographic information system (GIS)-based groundwater quality index (GQI) was realized to assess groundwater quality for drinking and irrigation use and, in parallel, standard SINTACS was applied to evaluate the intrinsic vulnerability of the aquifer. Nitrate concentrations and sodium absorption ratio (SAR) in groundwater samples were used to verify the reliability of vulnerability data. GQI analysis pointed to a general poor quality of groundwater both for drinking and irrigation use, especially in sub-urban areas. The spatial pattern of water quality from GQI analysis was positively related to nitrate and fluoride concentrations for drinking use and to bicarbonate and sodium concentrations for irrigation use, whose levels exceeded the WHO and FAO recommended thresholds, respectively. Standard SINTACS was found to be inadequate for describing the aquifer state, its results showing no correlation with nitrate concentration or SAR. Because of this inconsistency, we tested a novel approach combining GQI with SINTACS analysis. Results showed positive correlation with nitrate (r = 0.63) and SAR (r = 0.64) contents, thus pointing to combined SINTACS-GQI as a more reliable approach than standard methodologies.

Although ubiquitous elements of agricultural landscapes, the interest on ditches and canals as effective filters to buffer nitrate pollution has been raised only recently. The aim of the present study was to investigate the importance of in-ditch denitrification supported by emergent aquatic vegetation in the context of N budget in agricultural lands of a worldwide hotspot of nitrate contamination and eutrophication, i.e. the lowlands of the Po River basin (Northern Italy). The effectiveness of N abatement in the ditch network (>18,500 km) was evaluated by extrapolating up to the watershed reach-scale denitrification rates measured in a wide range of environmental conditions. Scenarios of variable extents of vegetation maintenance were simulated (25%, 50% and 90%), and compared to the current situation when the natural development occurs in only 5% of the ditch network length, subjected to mechanical mowing in summer. Along the typical range of nitrate availability in the Po River lowlands waterways (0.5–8 mg N L−1), the current N removal performed by the ditch network was estimated in 3300–4900 t N yr−1, accounting for at most 11% of the N excess from agriculture. The predicted nitrate mitigation potential would increase up to 4000–33,600 t N yr−1 in case of vegetation maintenance in 90% of the total ditch length. Moreover, a further significant enhancement (57% on average) of this key ecosystem function would be achieved by postponing the mowing of vegetation at the end of the growing season. The simulated outcomes suggest that vegetated ditches may offer new agricultural landscape management opportunities for effectively decreasing nitrate loads in surface waters, with potential improved water quality at the watershed level and in the coastal zones. In conclusion, ditches and canals may act as metabolic regulators and providers of ecosystem services if conservative management practices of in-stream vegetation are properly implemented and coupled to hydraulic needs.

Nitrate pollution has become a serious global problem, threatening human health and ecosystems. The electrochemical reduction has emerged as an energy-efficient and environmental-friendly technology to remove nitrate from water. Recently, non-noble metal electrocatalysts have attracted increasing attention in nitrate reduction due to their great advantages in terms of low cost, high activity, and large-scale application potential. This review highlights the latest research progress in the area of non-noble metal materials for electrochemical nitrate reduction. The mechanistic insight into the electrochemical reduction of nitrate is briefly discussed. Meanwhile, numerous examples in this field are collected and analyzed. Some strategies employed to improve the performance of nitrate electroreduction are also presented. Finally, the challenges and prospects in this field are discussed. This review hopes to guide the design and development of efficient non-noble metal electrocatalysts for nitrate reduction on a large scale.

WOS: 000399797600003 Geostatistical approaches (ordinary kriging (OK) and indicator kriging (IK)) were used in this study to investigate the spatial and temporal variations in groundwater nitrate concentrations in Caramba plain of Turkey. Groundwater samples were taken in April 2012, July 2012, September 2012 and March 2013 from 78 groundwater wells. The experimental semivariograms were often fitted well by a Gauss model for April 2012 and September 2012, whereas a spherical model was fitted to experimental semivariograms for July 2012 and March 2013. Spatial distribution maps revealed that groundwater nitrate concentrations were above the threshold value of 50mgL(-1) specified for drinking water in 4.3% of the study area in April 2012, 40.8% in July 2012, 32.8% in September 2012 and 19.1% in March 2013. Probability maps created with IK showed that 3.1% and 3.2% of the total area had very strong probability (0.8-1.0) of exceeding the threshold nitrate concentration in July 2012 and September 2012, respectively. Current findings revealed that groundwater nitrate concentrations changed seasonally and increased much more in summer. It was concluded that OK and IK may yield significant outcomes for groundwater management, identification of risky sites for potential pollution and identification of the sites with excessive fertilizer uses. Ondokuz Mayis University, Scientific Research ProgramsOndokuz Mayis University [PYO. ZRT. 1901.12.005] This study was supported by Ondokuz Mayis University, Scientific Research Programs under the project no. PYO. ZRT. 1901.12.005. The authors are also grateful to the the Seventh regional Directorate of State Hydraulic Works (DSI), Samsun, Turkey, for data analysis.

Nitrate is a worldwide pollutant in aquifers. Shallow aquifer nitrate concentrations generally display vertical stratification, with a maximum concentration immediately below the water level. The concentration then gradually decreases with depth. Different techniques can be used to highlight this stratification. The paper aims at comparing the advantages and limitations of three open hole multilevel sampling techniques (packer system, dialysis membrane samplers and bailer), chosen on the base of a literary review, to highlight a nitrate vertical stratification under the assumption of (sub)horizontal flow in the aquifer. The sampling systems were employed at three different times of the year in a shallow aquifer piezometer in northern Italy. The optimal purge time, equilibration time and water volume losses during the time in the piezometer were evaluated. Multilevel techniques highlighted a similar vertical nitrate stratification, present throughout the year. Indeed, nitrate concentrations generally decreased with depth downwards, but with significantly different levels in the sampling campaigns. Moreover, the sampling techniques produced different degrees of accuracy. More specifically, the dialysis membrane samplers provided the most accurate hydrochemical profile of the shallow aquifer and they appear to be necessary when the objective is to detect the discontinuities in the nitrate profile. Bailer and packer system showed the same nitrate profile with little differences of concentration. However, the bailer resulted much more easier to use.

Contamination of groundwater with nitrate poses a major health risk to millions of people around Africa. Assessing the space–time distribution of this contamination, as well as understanding the factors that explain this contamination, is important for managing sustainable drinking water at the regional scale. This study aims to assess the variables that contribute to nitrate pollution in groundwater at the African scale by statistical modelling. We compiled a literature database of nitrate concentration in groundwater (around 250 studies) and combined it with digital maps of physical attributes such as soil, geology, climate, hydrogeology, and anthropogenic data for statistical model development. The maximum, medium, and minimum observed nitrate concentrations were analysed. In total, 13 explanatory variables were screened to explain observed nitrate pollution in groundwater. For the mean nitrate concentration, four variables are retained in the statistical explanatory model: (1) depth to groundwater (shallow groundwater, typically

The study of NO3 (-) contamination in groundwater is becoming increasingly significant as high concentrations of NO3 (-) in groundwater can do damage to public health. Nitrate pollution in the shallow, middle-deep and deep aquifers in the urban district of Zhanjiang was studied using the ordinary Kriging interpolation method combined with hydrochemical and correlation analyses in 2011. The results showed NO3 (-) pollution was present in the shallow groundwater, with average concentrations of 47.43 mg/L and standard deviation of 50.92. Nitrate concentrations were lower in middle-deep and deep aquifers, with average concentrations of 2.36, 0.80 mg/L, and standard deviation of 6.23, 0.93, respectively. Nitrate was correlated with Na(+) + K(+), Mg(2+), Cl(-) and SO4 (2-) in the shallow aquifer, and the spatial distributions of NO3 (-) exhibited a same pattern with TDS in the shallow aquifer, the NO3 (-) pollution in the middle-deep and deep aquifers is less serious.

The Gaza Strip is in a chronic state of water shortage and the coastal aquifer as the only freshwater source is increasingly depleted and polluted, especially by nitrate. Assessment of groundwater vulnerability to pollution is essential for adequate protection and management. In this study, the assessment of the aquifer vulnerability to contamination is derived by applying the DRASTIC procedure, firstly with original default weights and ratings and, secondly, improved by estimating rating values by multiple linear regression of observed log-transformed nitrate concentration in groundwater, with DRASTIC factors extended to land-use. The results are very different because high and low vulnerability areas shift considerably. Subsequently, a geostatistical analysis of the spatial distribution of the nitrate concentration is performed, firstly by ordinary kriging interpolation of the observed nitrate concentration and secondly by regression kriging using DRASTIC factors and land-use as indicators of the spatial variation in nitrate occurrence. These maps differ because the map obtained by regression kriging interpolation shows much more details of environmental factors such as dunes, ridges, soil types and built-up areas that affect the presence of nitrate in groundwater. The results of this study can be used by the Palestinian authorities concerned with sustainable groundwater management in the Gaza Strip.

Nitrate in drinking water may cause serious health problems for consumers. Agricultural activities are known to be the main source of groundwater nitrate contaminating rural domestic and urban public water supply wells in farming regions. Management practices have been proposed to reduce the amount of nitrate in groundwater, including improved nutrient management practices and "pump and fertilize" with nitrate-affected irrigation wells. Here, we evaluate the feasibility and long-term impacts of agricultural managed aquifer recharge (Ag-MAR) in the source area of public water supply wells. A numerical model of nitrate fate and transport was developed for the Modesto basin, part of California's Central Valley aquifer system. The basin is representative of semi-arid agricultural regions around the world with a diversity of crop types, overlying an unconsolidated sedimentary aquifer system. A local public supply well in an economically disadvantaged community surrounded by farmland was the focus of this study. Model scenarios implemented include business as usual, alternative low-impact crops, and Ag-MAR in the source area of the public supply well. Alternative nutrient management and recharge practices act as remediation tools in the area between farmland and the public supply well. Improved agricultural source area management practices are shown to be an effective tool to maintain or even enhance groundwater quality in the targeted supply well while remediating ambient groundwater. Best results are obtained when lowering nitrate load while also increasing recharge in the source area simultaneously. This scenario reduced nitrate in the supply well's drinking water by 80% relative to the business as usual scenario. It also remediated ambient groundwater used by domestic wells between the source area farmlands and the supply well and showed 60% more reduction of nitrate after 60 years of application. Increasing recharge led to shorter initial response time (five years) and showed the most sustainable impact. Our analysis further suggests that Ag-MAR in a highly discontinuous, wide-spread pattern leads to slow water quality response and may not yield sufficient water quality improvements.

Shahre-Kord aquifer is located at the east part of Karoon basin. The water of Shahre-Kord aquifer has acceptable to unsuitable quality for drinking and also suitable and useful for the agricultural utilities. In this research, sampling from the studied aquifer was performed at spring and autumn. The obtained results of analysis performed on autumn samples revealed that the concentration of nitrate in the two wells was higher than its allowable limit in the drinking water. In the measurements of the samples at the end of spring, the highest concentration of nitrate from 16 samples belongs to the drinking water of Taghanak municipality which also has more than the allowable limit within the drinking water range, whereas the concentration of phosphate in all samples lies in the allowable limit. The samples were prepared through treatment by plant materials and different values of nanoscale zero-valent iron (NZVI) during 7 days. The measuring of nitrate concentration of samples illustrated that the south of aquifer have higher concentration in autumn than spring because N-fertilizers usually are used in autumn and the spring precipitation of nitrates. The results derived by several treatment methods in this study indicate that the combination of NZVI with fine pieces of corn for a period of 7 days is the best treatment, which has the highest efficiency for nitrate removal from an aquifer.

12 pages, 14 figures, 3 tables, supplementary data https://doi.org/10.1016/j.scitotenv.2018.10.426, Agricultural practices have raised the level of nutrients reaching aquifers. In Europe, nitrate pollution is considered as one of the main threats for the quality of groundwater in agricultural areas. Treatment wetlands (TWs), also known as Constructed Wetlands, are used for groundwater treatment in areas with an important concentration of nitrogen compounds; total nitrogen removal depends on the type and operation scheme. Cork by-product from the industry has shown clear adsorbent properties to remove organic pollutants. The work is focused on the characterization of microbial communities involved in the nitrate‑nitrogen removal process in groundwater polluted from agricultural activities. The experimental design allowed the comparison of nitrate removal efficiency depending on the filter media material, cork by-product or gravel, used in two hybrid TWs (a vertical flow cell followed by a horizontal subsurface flow cell), installed in areas close to two irrigated agricultural plots at the Lleida plain area (Spain). Both physicochemical and microbial results were consistent and confirm the nitrate removal efficiency using cork as a filter media. A significant (p = 0.0025) higher removal in Bellvís TW using cork compared with the Vilanova de la Barca gravel system was observed, achieving a removal rate from 80 to 99% compared to the 5–46%, respectively. Regarding the community composition of the two different TWs, microorganisms were mainly related to the phylum Proteobacteria, and included members found to be key players in the nitrogen cycle, such as ammonia and nitrite oxidizers, as well as denitrifiers. Also, the group Bacteroidetes turns to be another abundant phylum from our bacterial dataset, whose members are suggested to be strongly involved in denitrification processes. Some groups showed to prevail depending on the type of media (cork or gravel); Firmicutes and Delta and Epsilonproteobacteria had a significant higher abundance in the TW with cork, while Acidobacteria and Planctomyces were prevalent in gravel. Therefore, cork could be an alternative material used by treatment wetlands to minimize the impact in the environment caused by nitrogen pollution in groundwater bodies, To LIFE Programme, the EU's financial instrument supporting environmental, nature conservation and climate action projects throughout the EU, that supports REAGRITECH LIFE 11 ENV/ES/579