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1.
Chemosphere ; 262: 128015, 2021 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-33182116

RESUMO

The important role of reactive chlorine species (RCS) in electrochemical system has been widely concerned for water disinfection recently. In this study, we built an electrochemical system using carbon nanotube as cathode and oxide precursor (Ti/SnO2-Sb2O5-IrO2) as anode, where RCS was produced from Cl-. This system was used to degrade nitrogen contaminants, i.e. NO3- and 4-nitrophenol. Optimization of the reaction conditions was carried out by a treatment of inorganic nitrogen contaminant NO3- and the optimal condition of the electrochemical system was determined at U = 5.5 V, and pH = 10 with a Cl- concentration of 2000 mg L-1, and the removal efficiency of NO3- can reach up to 60.6% in 150 min. Under the optimal condition, a common nitrogenous organic pollutant, 4-nitrophenol was treated and a removal efficiency of nearly 100% in 90 min. To investigate the detailed degradation mechanism in the applied electrochemical system, a combined method of products identification and density functional theory (DFT) calculation was employed. It concluded that Cl radicals' generation was stimulated was stimulated by the OH radicals after adding Cl- into the electrochemical system. These two radicals jointly promoted the transformation of 4-nitrophenol resulting in the formation of more toxic organic and inorganic substances. In addition, a conversion of organic nitro group to amino group leading to the formation of 4-aminophenol was found and explained by the indirect reduction theory.


Assuntos
Cloro/química , Técnicas Eletroquímicas/métodos , Modelos Teóricos , Nitrofenóis/análise , Poluentes Químicos da Água/análise , Purificação da Água/métodos , Catálise , Eletrodos , Nitratos/análise , Oxirredução
2.
J Water Health ; 18(5): 681-691, 2020 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-33095192

RESUMO

The presence of nitrate in sources of drinking water is a matter of concern because of its potential risk for human health. In many countries like Argentina, an increasing proportion of the population chooses to consume bottled water, among other reasons, for lack of water access. The present study was conducted (a) to evaluate the quality of bottled waters by determining nitrate concentration, (b) to relate bottled water quality with water access, (c) to analyze public awareness about bottled water quality and consumption habits of the population in the urban area of Buenos Aires. Two locations were selected, Ciudad Autónoma de Buenos Aires (C.A.B.A.) and Malvinas Argentinas in Buenos Aires Province (PBA), with percentages of water access of 99.6% and 8.8%, respectively. Random samples from both locations (n = 100) were analyzed. A survey was conducted in order to inquire about perception of population on bottled water quality and their consumption habits. In C.A.B.A., no sample exceeded the 45 mg/L limit value in force in Argentina, while in Malvinas Argentinas, 34% of the brands analyzed showed values above it. The survey revealed that 71.7% of people consume bottled water. While people in C.A.B.A. do so mainly out of habit, safety is the priority in PBA.


Assuntos
Água Potável , Argentina , Água Potável/análise , Humanos , Nitratos/análise , Inquéritos e Questionários , Abastecimento de Água
3.
Huan Jing Ke Xue ; 41(11): 4936-4947, 2020 Nov 08.
Artigo em Chinês | MEDLINE | ID: mdl-33124237

RESUMO

The multi-environment media of water, surface soil and vadose zone soil samples were collected in the upstream of Miyun Reservoir, in the Luanping Basin of Chengde City, Hebei Province. The aim was to identify the pollution source, ratio, spatial distribution, migration, and transformation characteristics of nitrogen in groundwater. Hydrogeochemistry, soil total nitrogen, and dissolved nitrate nitrogen of vadose zone soil analysis and a multi isotope tracer technique of δ15 N-NO3 and δ18O-NO3, δ34S-SO4 and δ18O-SO4, δ14 C, combined with land-use type analysis and geostatistics, were used in the study. The results showed that nitrate was the main form of nitrogen in the groundwater of the Luanping Basin. The NO3- concentration of groundwater was significantly correlated with the land-use types of residential land and cultivated land where the nitrate pollution of shallow groundwater was mainly distributed. Of the groundwater samples, 13.79% exceeded the National Standard Ⅲ for Groundwater (GB/T 14848-2017) of NO3- concentration value, while the excess multiple was 1.04-3.86, and 37.93% of the groundwater samples exceeded the World Health Organization NO3- concentration standard value. The excess multiple was 1.08-6.83. The spatial variation of groundwater NO3- concentration, soil total nitrogen and surface soil dissolved nitrate nitrogen of vadose zone was affected by the combination of natural structural factors and anthropogenic factors. The source of groundwater nitrate was mainly from livestock manure and domestic sewage, followed by chemical fertilizer leaching. The nitrogen cycle in the aeration zone-groundwater-dominated nitrogen circulation in the groundwater runoff area of the piedmont basin was nitrification. These findings are highly significant for the prevention and remediation of groundwater pollution when viewing the basin system as an independent unit, and for studying the sources and fate of nitrate pollution in the water environment.


Assuntos
Água Subterrânea , Poluentes Químicos da Água , Monitoramento Ambiental , Nitratos/análise , Isótopos de Nitrogênio/análise , Poluentes Químicos da Água/análise
4.
Huan Jing Ke Xue ; 41(9): 4333-4344, 2020 Sep 08.
Artigo em Chinês | MEDLINE | ID: mdl-33124315

RESUMO

Nitrogen plays a vital role in biological activities as the basic element of organic molecules and the main nutrient of soil. In the study of nitrogen pollution, the first step is to understand the transformation mechanism of various nitrogen forms. Based on the transformation process and the mechanism of nitrogen in the ecosystem, this review summarizes the research methods of nitrogen source analysis and nitrogen isotope fractionation in soil and water, and categorically reviews the applications of nitrogen source identification in surface water and groundwater. We showed that it is more effective to identify the sources of soil and water nitrogen pollution by combining hydrochemical methods with the multi-isotope approach. The importance of primary nitrogen sources should also be quantified to study groundwater pollution. A new approach to determine the source of oxygen atoms during nitrosation was also presented, and the enrichment principle of δ18O-NO3- during secondary oxidation was explained. Finally, the contribution of primary ammonium nitrogen to groundwater pollution was discussed, and innovative research ideas were provided.


Assuntos
Água Subterrânea , Poluentes Químicos da Água , Ecossistema , Monitoramento Ambiental , Nitratos/análise , Nitrogênio/análise , Isótopos de Nitrogênio/análise , Solo , Água , Poluentes Químicos da Água/análise
5.
Huan Jing Ke Xue ; 41(8): 3637-3645, 2020 Aug 08.
Artigo em Chinês | MEDLINE | ID: mdl-33124337

RESUMO

Due to the vulnerability of karst hydrological systems, nitrate pollution in karst groundwater has become a global common and serious environmental problem. In order to ensure drinking water safety, it is very important to accurately identify groundwater nitrate sources. The groundwater hydrochemistry and δ15N-NO3- and δ18O-NO3- isotopes were analyzed in samples taken from a suburb of Chongqing:the Longfeng karst trough-valley, which is mainly affected by agricultural activities, and the Longche karst trough-valley, which is primarily affected by urbanization. The IsoSource model was then used to quantify the groundwater nitrate sources. The results showed that:① The NO3- concentration in groundwater ranged from 19.31 mg·L-1 to 37.01 mg·L-1(mean of 28.21 mg·L-1) in the Longfeng karst trough-valley, and from 2.15 mg·L-1 to 27.69 mg·L-1(mean of 10.31 mg·L-1) in the Longche karst trough-valley. The groundwater NO3- concentration exhibited an obvious seasonal variation in both valleys. ② The δ15N-NO3- and δ18O-NO3- isotopes in groundwater in the Longfeng karst trough-valley ranged from 3.29‰ to 11.03‰ (mean of 6.74‰) and 0.88‰ to 7.51‰ (mean of 3.18‰), respectively. In contrast, groundwater in the Longche karst trough-valley presented higher δ15N-NO3- and δ18O-NO3- values that ranged from 5.25‰ to 11.40‰ (mean of 7.95‰) and 2.90‰ to 19.94‰ (mean of 11.18‰), respectively. The lower values of δ15N-NO3- and δ18O-NO3- in groundwater in the Longfeng karst trough-valley suggest that groundwater NO3- was mainly sourced from agricultural N fertilizer, while the higher values of δ15N-NO3- and δ18O-NO3- in groundwater in the Longche karst trough-valley indicate that groundwater NO3- was primarily sourced from domestic sewage. Moreover, such δ15N-NO3- and δ18O-NO3- values in groundwater indicate that nitrification was the primary process for nitrogen conversion in both valleys. Meanwhile, significant seasonal differences in groundwater δ15N-NO3- and δ18O-NO3- were observed in both valleys; the δ15N-NO3- and δ18O-NO3- values were higher during the dry season (means of 8.83‰ and 2.79‰, respectively) than during the rainy season (means of 4.64‰ and 3.58‰, respectively) in the Longfeng karst trough-valley, whereas the δ15N-NO3- and δ18O-NO3- values were lower during the dry season (means of 9.79‰ and 14.56‰, respectively) than during the rainy season (means of 5.12‰ and 7.8‰, respectively) in the Longche trough-valley. This suggests that there were differences in the seasonal NO3- sources to groundwater in both valleys. During the rainy season, the groundwater NO3- concentration in the Longfeng karst trough-valley was mainly due to the nitrification of NH4+ in precipitation and fertilizer as well as organic nitrogen in soil, whereas during the dry season, the groundwater NO3- concentration primarily originated from domestic sewage. In contrast, the groundwater NO3- concentration in the Longche karst trough-valley primarily originated from domestic sewage in both seasons. ③ The results of the IsoSource model indicated that the nitrification of NH4+ from fertilizer and rainwater was the primary NO3- source to groundwater (44.63% of the total) in the Longfeng trough valley, and was followed by domestic sewage (29.5%), soil organic nitrogen (22.38%), and NO3- from rainwater and fertilizer (<10%). During the rainy season, the groundwater NO3- concentration was mainly due to the nitrification of NH4+ from fertilizer and rainwater (52.25% of the total) in Longfeng trough-valley, while groundwater NO3- concentration primarily originated from domestic sewage during the dry season (41% of the total). In contrast, the groundwater NO3- concentration was mainly from domestic sewage (36.17%) in Longche karst trough-valley, and was followed by the nitrification of NH4+ from fertilizer and rainwater (23.5%), soil organic nitrogen (22.5%), and NO3- from rainwater and fertilizer (<10%). The groundwater NO3- concentration in the Longche karst trough-valley primarily originated from domestic sewage in both seasons, and accounted for 47% and 25% during the rainy season and dry season, respectively.


Assuntos
Água Subterrânea , Poluentes Químicos da Água , Monitoramento Ambiental , Nitratos/análise , Isótopos de Nitrogênio/análise , Poluentes Químicos da Água/análise
6.
Huan Jing Ke Xue ; 41(10): 4539-4546, 2020 Oct 08.
Artigo em Chinês | MEDLINE | ID: mdl-33124385

RESUMO

Shallow groundwater is the main drinking water supply for the mountainous area in the upper reaches of the Yangtze River, while its quality is often degraded by nitrate (NO3--N) pollution due to intensive agricultural production activities. In the present study, we selected a mountainous agricultural watershed in the upper reaches of the Yangtze River to investigate the land use, management, and hydrogeological conditions, aiming to clarify the spatial-temporal variations in NO3--N concentration of shallow groundwater, thereby exploring the key regulators. The results showed that the NO3--N concentrations of the groundwater ranged from 0.40 to 12.51 mg ·L-1in the study area, and the exceeding ratio was nearly 30%. On an average, NO3--N concentrations for the wet season were higher than that for the dry season, indicating great variations in NO3--N concentration across different seasons. In addition, the spatial variations of NO3--N concentration in groundwater were also significant among different sub-catchment, which was mainly due to variations in the groundwater table depth and land uses. Furthermore, the significant correlations between the NO3--N concentrations and concentrations of Cl-, NH4+-N, DOC, and SO42- in the shallow groundwater were also explored in this study, suggesting that the NO3--N concentrations were likely to depend on the chemical factors of the shallow groundwater in the study area. Overall, our current study highlights that the characterization of spatial-temporal variations of NO3--N status in shallow groundwater and illustration of key regulators are essential to mitigate NO3--N pollution and prevent quality degradation of shallow groundwater in mountainous rural areas of the upper Yangtze River watershed.


Assuntos
Água Subterrânea , Poluentes Químicos da Água , Monitoramento Ambiental , Nitratos/análise , Rios , Poluentes Químicos da Água/análise
7.
J Environ Qual ; 49(2): 392-403, 2020 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-33016417

RESUMO

Numerous studies have documented the linkages between agricultural nitrogen loads and surface water degradation. In contrast, potential water quality improvements due to agricultural best management practices are difficult to detect because of the confounding effect of background nitrate removal rates, as well as the groundwater-driven delay between land surface action and stream response. To characterize background controls on nitrate removal in two agricultural catchments, we calibrated groundwater travel time distributions with subsurface environmental tracer data to quantify the lag time between historic agricultural inputs and measured baseflow nitrate. We then estimated spatially distributed loading to the water table from nitrate measurements at monitoring wells, using machine learning techniques to extrapolate the loading to unmonitored portions of the catchment to subsequently estimate catchment removal controls. Multiple models agree that in-stream processes remove as much as 75% of incoming loads for one subcatchment while removing <20% of incoming loads for the other. The use of a spatially variable loading field did not result in meaningfully different optimized parameter estimates or model performance when compared with spatially constant loading derived directly from a county-scale agricultural nitrogen budget. Although previous studies using individual well measurements have shown that subsurface denitrification due to contact with a reducing argillaceous confining unit plays an important role in nitrate removal, the catchment-scale contribution of this process is difficult to quantify given the available data. Nonetheless, the study provides a baseline characterization of nitrate transport timescales and removal mechanisms that will support future efforts to detect water quality benefits from ongoing best management practice implementation.


Assuntos
Monitoramento Ambiental , Água Subterrânea , Agricultura , Nitratos/análise , Rios
8.
J Environ Qual ; 49(2): 440-449, 2020 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-33016427

RESUMO

The use of suctions cups is a common practice for estimating nitrate (NO3 -N) leaching under agricultural systems despite the various uncertainties associated with the approach. One major uncertainty is water flux, which is required for calculating NO3 -N leaching loads from measured concentrations. Another problem is the interpolation of NO3 -N concentrations between measurement days. We investigated how differences in water flux, obtained from two different models (EVACROP and APSIM), affect NO3 -N leaching loads. The effect of interpolation of NO3 -N concentrations based on days or drainage was also addressed. The models were set up according to a 2-yr field experiment with spring barley (Hordeum vulgare L. Quinch) with different levels of N fertilization rates on a loamy soil at Flakkebjerg, Denmark. Due to small differences in measured NO3 -N concentrations between sequential samplings, the method of interpolation did not significantly affect NO3 -N leaching in the two periods investigated. Although there is no standard against which leaching losses from different approaches can be tested, results highlight that the modeling of water uptake as affected by N supply influences the amount of drainage and thus calculated NO3 -N leaching. Therefore, for experiments with varying N fertilization levels, the APSIM model, which accounts for N nutrition on crop water use, is likely more accurate. For common fertilization rates, the simpler EVACROP seems appropriate. Thus, when using suction cup data for testing models or for evaluating mitigation options for nitrate leaching, the use of an appropriate model for estimating water fluxes is important.


Assuntos
Fertilizantes/análise , Nitratos/análise , Agricultura , Solo , Sucção
9.
Environ Monit Assess ; 192(11): 724, 2020 Oct 23.
Artigo em Inglês | MEDLINE | ID: mdl-33095309

RESUMO

Nitrate contamination of drinking water, common in agricultural areas, increases the risk of certain cancers and impacts fetal development during pregnancy. Building on previously published methodology, this study evaluates nitrate-attributable disease cases and adverse birth outcomes as well as their economic costs for Wisconsin, USA. Nitrate is the most common contaminant in groundwater in Wisconsin. Two-thirds of the state's residents use groundwater as the primary source of drinking water. Here, we analyze nitrate exposure from drinking water in Wisconsin based on nitrate test results for community water systems for the period of 2010-2017 and a novel methodology for estimating nitrate exposure for the 28% of state's residents who use private wells. We estimate that annually, 111-298 combined cases of colorectal, ovarian, thyroid, bladder, and kidney cancer in Wisconsin may be due to nitrate contamination of drinking water. Each year, up to 137-149 cases of very low birth weight, 72-79 cases of very preterm birth, and two cases of neural tube defects could be due to nitrate exposure from drinking water. The direct medical cost estimates for all nitrate-attributable adverse health outcomes range between $23 and $80 million annually. Simulating targeted reductions in the counties with the highest current drinking water nitrate concentrations resulted in similar reductions in adverse health outcomes as statewide reduction efforts, up to nitrate reductions of 20%. Time trend analysis suggests that groundwater nitrate concentrations are overall increasing. Thus, nitrate contamination of water supplies in Wisconsin is a public health problem that needs to be addressed.


Assuntos
Água Potável , Nascimento Prematuro , Monitoramento Ambiental , Feminino , Humanos , Nitratos/análise , Gravidez , Wisconsin
10.
J Environ Qual ; 49(5): 1347-1358, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-33016459

RESUMO

Fertilizer management practices that focus on applying N fertilizer at the right rate and time have been proposed as a practical option to reduce NO3 -N losses from subsurface drained agricultural fields. In this study, regression equations were developed to predict NO3 -N losses for a corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] rotation in southern Minnesota, using fertilizer application timing and rate and growing season precipitation as inputs. The equations were developed using the results of the field-scale hydrologic and N simulation model DRAINMOD-NII, first calibrated and validated for three sites in southern Minnesota, and then run with different combinations of N fertilizer application rates and timings. Fertilizer timing treatments included a single application in the fall or spring and a split-spring application (half applied preplant and the remaining applied as sidedress). The predictive regression equations showed that the split fertilizer application timing could reduce regional N loads by 28% compared with spring or fall applications. Greater reductions were predicted when the split timing was combined with lower N fertilizer rates. Utilizing the split application timing and reducing the fertilizer rate by 10 and 30% showed 33 and 41% reductions in N loads, respectively, compared with current fertilizer management practices. Such reductions in fertilizer application rates could be achieved through the use of variable-rate nitrogen (VRN) fertilizer technologies. Results of this modeling study indicate that synchronizing fertilizer application with crop requirements and utilizing VRN technologies could significantly reduce N loads to surface waters in southern Minnesota.


Assuntos
Fertilizantes , Nitrogênio , Agricultura , Minnesota , Nitratos/análise
11.
Environ Monit Assess ; 192(11): 687, 2020 Oct 08.
Artigo em Inglês | MEDLINE | ID: mdl-33029661

RESUMO

Agricultural subsurface drainage can be an important conduit of nitrate from agricultural fields to streams. This study focused on understanding the variability in nitrate concentrations and loads, exported by subsurface drains, into a small, north-central Iowa stream. Ninety-three subsurface drains in this watershed were sampled up to 5 times between 2006 and 2008. Additionally, 2 subsurface drains and the stream draining the study area (South Fork Iowa River near Blairsburg, IA, USA) were sampled frequently during the growing seasons in 2007 and 2008. Spatial variability analysis revealed no distinct spatial pattern in nitrate concentrations. The median nitrate concentrations were not significantly different when the drain outlets were characterized by diameter (17-23 cm, 27-48 cm, 60-108 cm). The eight large subsurface drains (part of the public drainage network) had less variability in nitrate concentration than the smaller drain sizes and generally contributed 70-87% of the total water and nitrate loads exported by subsurface drains to the stream. During high-discharge events, the medium-sized (27-48 cm) subsurface drains discharging to the stream became more important by contributing a higher discharge and nitrate load. The temporal variability examined in this study found that discharge and nitrate loads were influenced by the amount of precipitation that had occurred over the previous months. This paper demonstrates the spatial and within-season homogeneity of nitrate delivery to a stream from an intensely agricultural landscape that has subsurface drainage.


Assuntos
Monitoramento Ambiental , Nitratos , Iowa , Nitratos/análise , Óxidos de Nitrogênio , Rios
12.
Sci Total Environ ; 740: 140169, 2020 Oct 20.
Artigo em Inglês | MEDLINE | ID: mdl-32927550

RESUMO

Hydrological extremes of unusually high or low river discharge may deeply affect the biogeochemistry of coastal lagoons, but the effects are poorly explored. In this study, microbial nitrogen processes were analyzed through intact core incubations and 15N-isotope addition at three sites in the eutrophic Sacca di Goro lagoon (Northern Adriatic Sea) both under high discharge (spring) and after prolonged low discharge (late-summer) of the main freshwater inputs. Under high discharge/nitrate load, denitrification was the leading process and there was no internal recycling. The site located at the mouth of the main freshwater input and characterized by low salinity exhibited the highest denitrification rate (up to 1150 ± 81 µmol N m-2 h-1), mostly sustained by nitrification stimulated by burrowing macrofauna. In contrast, we recorded high internal recycling under low discharge, when denitrification dropped at all sites due to low nitrate concentrations, reduced bioturbation and nitrification. The highest recycling was measured at the sites close to the sea entrance and characterized by high salinity and particularly at the clams cultivated area (up to 1003 ± 70 µmol N m-2 h-1). At this site, internal recycling was sustained by ammonification of biodeposits, bivalve excretion and dissimilatory nitrate reduction to ammonium (DNRA), which represented 30% of nitrate reduction. Flash floods and high nitrate loads may overwhelm the denitrification capacity of the lagoon due to the reduced residence time and to the saturation of microbial enzymatic activity, resulting in high transport of nitrate to the sea. Prolonged dry periods favor large internal recycling, due to a combination of high temperatures, low oxygen solubility and low bioturbation, which may prolong the extent of algal blooms with negative effects on lagoon biogeochemical services. We conclude that hydrological extremes, which are expected to become more frequent under climate change scenarios, strongly alter N cycling in coastal sediments.


Assuntos
Compostos de Amônio/análise , Animais , Desnitrificação , Sedimentos Geológicos , Hidrologia , Nitratos/análise , Nitrogênio/análise
13.
Environ Monit Assess ; 192(10): 620, 2020 Sep 05.
Artigo em Inglês | MEDLINE | ID: mdl-32888049

RESUMO

Groundwater in Delhi Metropolitan Region (DMR) is suffering from multiple catastrophes, viz., asymptotic increases in groundwater withdrawal, reduced recharge due to erratic rainfall, and variable soil type. In this study, we examined long-term trends in groundwater levels across the DMR from 1996 to 2018. Station level data collected by the Central Groundwater Board for 258 stations at the seasonal scale were visualized and interpreted using geospatial analysis. The spatial patterns of the trends in groundwater levels revealed increasing depths of groundwater levels, except the Yamuna River floodplains. The main cause for the decline is related to the rapid growth in population accompanied with high-density impervious urban land uses, leading to lower levels of recharge vs unlimited withdrawal of groundwater for daily needs. In addition, the local geology in the form of clayey soils in northwest DMR also contributed to the lower levels of recharge. The results of the analysis enabled us to establish the trend and delineate the zones of differential recharge. Furthermore, the level of contaminants were analyzed at the district level for fluorides and nitrates. The presence of fluoride contamination was mostly concentrated in the northwestern district, while the nitrate exceedance was more widespread. These findings will help in achieving the 6th Sustainable Development Goal (SDG) of United Nations by 2030 as well as goals identified in Delhi's master plan of 2041.


Assuntos
Monitoramento Ambiental , Água Subterrânea , Índia , Nitratos/análise , Rios
14.
Chemosphere ; 258: 127310, 2020 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-32947673

RESUMO

We characterized the aerosol composition and sources of particulate matter (PM) in Sanmenxia, a polluted city located in the Fen-Wei Plain region of Central China. The PM2.5 concentration decreased by 18% from 72 µg m-3 in 2014 to 59 µg m-3 in 2019. All chemical species presented pronounced seasonal variations, with their highest concentrations in winter due to enhanced emissions and the frequent stagnant meteorological conditions. Nitrate was the major fraction of PM2.5 during all seasons (35-41%) except summer (25%), while sulfate was a dominant species in summer (29%) compared to other seasons (16-18%) from July 2018 to June 2019. The detailed analysis of a wintertime severe haze episode that lasted for approximately half a month demonstrated that secondary aerosols, including secondary organic aerosol, sulfate, nitrate, and ammonium, contributed 89% to non-refractory PM1 (NR-PM1), indicating the remarkable role of secondary aerosol formation in air pollution in Sanmenxia. Positive matrix factorization analysis further showed considerably enhanced low-volatility oxygenated organic aerosol (OA) and hydrocarbon-like OA during severe haze episodes, while significant contributions in semi-volatile oxygenated OA and coal combustion OA during clean periods. Severe pollution events in the city were generally associated with air masses from the southwest, and we also found that aerosol species, especially secondary aerosol species, showed distinct forenoon increases that were caused by the subsidence of air pollutants aloft. Our results highlight that future air quality improvement would benefit substantially from a more efficient control of gaseous precursors, particularly the NOx emissions from industry and vehicle emissions.


Assuntos
Aerossóis/análise , Poluentes Atmosféricos/análise , Poluição do Ar/estatística & dados numéricos , Poluição do Ar/análise , China , Cidades , Carvão Mineral/análise , Monitoramento Ambiental/métodos , Poluentes Ambientais/análise , Poluição Ambiental/análise , Hidrocarbonetos/química , Nitratos/análise , Óxidos de Nitrogênio/análise , Material Particulado/análise , Estações do Ano , Emissões de Veículos/análise
15.
Environ Pollut ; 267: 115274, 2020 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-32891045

RESUMO

Inorganic particulate nitrate (p-NO3-), gaseous nitric acid (HNO3(g)) and nitrogen oxides (NOx = NO + NO2), as main atmospheric pollutants, have detrimental effects on human health and aquatic/terrestrial ecosystems. Referred to as the 'Third Pole' and the 'Water Tower of Asia', the Tibetan Plateau (TP) has attracted wide attention on its environmental changes. Here, we evaluated the oxidation processes of atmospheric nitrate as well as traced its potential sources by analyzing the isotopic compositions of nitrate (δ15N, δ18O, and Δ17O) in the aerosols collected from the Mt. Everest region during April to September 2018. Over the entire sampling campaigns, the average of δ15N(NO3-), δ18O(NO3-), and Δ17O(NO3-) was -5.1 ± 2.3‰, 66.7 ± 10.2‰, and 24.1 ± 3.9‰, respectively. The seasonal variation in Δ17O(NO3-) indicates the relative importance of O3 and HO2/RO2/OH in NOx oxidation processes among different seasons. A significant correlation between NO3- and Ca2+ and frequent dust storms in the Mt. Everest region indicate that initially, the atmospheric nitrate in this region might have undergone a process of settling; subsequently, it got re-suspended in the dust. Compared with the Δ17O(NO3-) values in the northern TP, our observed significantly higher values suggest that spatial variations in atmospheric Δ17O(NO3-) exist within the TP, and this might result from the spatial variations of the atmospheric O3 levels, especially the stratospheric O3, over the TP. The observed δ15N(NO3-) values predicted remarkably low δ15N values in the NOx of the sources and the N isotopic fractionation plays a crucial role in the seasonal changes of δ15N(NO3-). Combined with the results from the backward trajectory analysis of air mass, we suggest that the vehicle exhausts and agricultural activities in South Asia play a dominant role in determining the nitrate levels in the Mt. Everest region.


Assuntos
Monitoramento Ambiental , Poluentes Químicos da Água , Ásia , Ecossistema , Nitratos/análise , Isótopos de Nitrogênio/análise , Óxidos de Nitrogênio/análise , Poluentes Químicos da Água/análise
16.
Water Res ; 186: 116355, 2020 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-32890809

RESUMO

Climate change can have substantial impacts on nitrogen runoff, which is a major cause of eutrophication, harmful algal blooms, and hypoxia in freshwaters and coastal regions. We examined responses of nitrate loading to climate change in the Upper Mississippi River Basin (UMRB) with an enhanced Soil and Water Assessment Tool with physically based Freeze-Thaw cycle representation (SWAT-FT), as compared with the original SWAT model that employs an empirical equation. Driven by future climate projections from five General Circulation Models (GCMs) from 1960 to 2099 under the Representative Concentrations Pathways (RCP) 8.5 scenario, we analyzed changes in riverine nitrate loadings, as well as terrestrial surface and subsurface contributions of the UMRB in the 21st century relative to the baseline period of 1960-1999. By the end of the 21st century, the original SWAT model predicted about a 50% increase in riverine nitrate loadings which is nearly twice as much as that estimated by SWAT-FT (ca. 25%). Such a large difference in projected nitrate changes can potentially mislead mitigation strategies that aim to reduce nitrogen runoff from the UMRB. Further analysis shows that the difference between the original SWAT model and SWAT-FT led to substantial discrepancies in the spatial distribution of surface and subsurface nitrate loadings in the UMRB. In general, SWAT-FT predicted more nitrate leaching for northwestern parts of the UMRB which are more sensitive to freeze-thaw cycle, mainly because SWAT-FT simulated less frequent frozen soils. This study highlights the importance of using physically based freeze-thaw cycle representation in water quality modeling. Design of future nitrogen runoff reduction strategies should include careful assessment of effects that land management has on the freeze-thaw cycles to provide reliable projection of water quality under climate change.


Assuntos
Modelos Teóricos , Rios , Mississippi , Nitratos/análise , Qualidade da Água
17.
Water Res ; 186: 116388, 2020 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-32916623

RESUMO

Understanding where nitrate is mobilized from and under what conditions is required to reduce nitrate loss and protect water quality. Low frequency sampling may inadequately capture hydrological and biogeochemical processes that will influence nitrate behavior. We used high-frequency isotope sampling and in-situ nitrate sensing to explore nitrate export and transformation in a karst critical zone. Nitrate was mobilised during light rainfall, and transferred from soil layers to the karst matrix, where some nitrate was retained and denitrified. Nitrate isotopic composition changed rapidly during the rising limb of events and slowly during the falling limb. The main nitrate source was synthetic fertiliser (up to 80% during event flow), transported by conduit flow following high rainfall events, and this contribution increased significantly as discharge increased. Soil organic nitrogen contribution remained constant indicating at baseflow this is the primary source. Isotope source appointment of nitrate export revealed that synthetic fertilizer accounted for more than half of the total nitrate export, which is double that of the secondary source (soil organic nitrogen), providing valuable information to inform catchment management to reduce nitrate losses and fluvial loading. Careful land management and fertilizer use are necessary to avoid nitrate pollution in the karst agroecosystem, for example by timing fertilizer applications to allow for plant uptake of nitrate before rainfall can flush it from the soils into the karst and ultimately into catchment drainage.


Assuntos
Monitoramento Ambiental , Nitratos , Agricultura , Isótopos , Nitratos/análise , Nitrogênio/análise
18.
J Environ Manage ; 272: 111067, 2020 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-32736232

RESUMO

Subsurface denitrification plays a key role in the reduction or 'attenuation' of nitrate contamination of groundwater and surface waters. We investigated subsurface denitrification characteristics in the vadose zone and shallow groundwater at four sites under pastoral farming in the Manawatu River catchment, located in the lower part of North Island, New Zealand. The denitrification potential of the vadose zone was determined by the laboratory incubation assays measuring the denitrifying enzyme activity (DEA) in soil samples collected from different soil horizons (up to 2.1 m below ground surface), whereas denitrification rates in shallow groundwaters were measured in situ by single-well, push-pull tests conducted in piezometers installed at multiple depths at the study sites. Soils and underlying geology, defining hydrogeologic settings, appear to influence the spatial variability of subsurface denitrification characteristics at the study sites. Where the vadose zone is thin and composed of coarse-textured soils, percolation of nitrate was evident in observed high nitrate-nitrogen concentrations (>5 mg L-1) in oxic and young shallow groundwaters, but low nitrate-nitrogen concentrations (<0.05 mg L-1) were observed in the reduced shallow groundwater found underneath the fine textured soils and/or a thick vadose zone. This was confirmed by the push-pull tests measuring denitrification rates from 0.08 to 1.07 mg N L-1 h-1 in the reduced shallow groundwaters (dissolved oxygen or DO < 0.5 mg L-1), while negligible in the oxic groundwaters (DO > 5 mg L-1) found at the study sites. These contrasting subsurface denitrification characteristics determine the ultimate delivery of nitrate losses from agricultural soils to receiving waters, where the fine textured thick vadose zone and reducing groundwater conditions offer nitrate reduction in the subsurface environment.


Assuntos
Água Subterrânea , Poluentes Químicos da Água/análise , Agricultura , Desnitrificação , Monitoramento Ambiental , Nova Zelândia , Nitratos/análise , Nutrientes
19.
J Environ Manage ; 272: 110996, 2020 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-32854899

RESUMO

Woodchip bioreactors are a practical, low-cost technology for reducing nitrate (NO3) loads discharged from agriculture. Traditional methods of quantifying their performance in the field mostly rely on low-frequency, time-based (weekly to monthly sampling interval) or flow-weighted sample collection at the inlet and outlet, creating uncertainty in their performance and design by providing incomplete information on flow and water chemistry. To address this uncertainty, two field bioreactors were monitored in the US and New Zealand using high-frequency, multipoint sampling for in situ monitoring of NO3-N concentrations. High-frequency monitoring (sub hourly interval) at the inlet and outlet of both bioreactors revealed significant variability in volumetric removal rates and percent reduction, with percent reduction varying by up to 25 percentage points within a single flow event. Time series of inlet and outlet NO3 showed significant lag in peak concentrations of 1-3 days due to high hydraulic residence time, where calculations from instantaneous measurements produced erroneous estimates of performance and misleading relationships between residence time and removal. Internal porewater sampling wells showed differences in NO3 concentration between shallow and deep zones, and "hot spot" zones where peak NO3 removal co-occurred with dissolved oxygen depletion and dissolved organic carbon production. Tracking NO3 movement through the profile showed preferential flow occurring with slower flow in deeper woodchips, and slower flow further from the most direct flowpath from inlet to outlet. High-frequency, in situ data on inlet and outlet time series and internal porewater solute profiles of this initial work highlight several key areas for future research.


Assuntos
Reatores Biológicos , Desnitrificação , Nova Zelândia , Nitratos/análise , Viés de Seleção
20.
Environ Monit Assess ; 192(9): 568, 2020 Aug 07.
Artigo em Inglês | MEDLINE | ID: mdl-32767118

RESUMO

Anthropogenic atmospheric emission and subsequent deposition of sulfur (S) has been linked to disrupted watershed biogeochemical processes through soil and surface water acidification. We investigated watershed-scale impacts of acidic deposition on tributary concentrations and watershed exports of major nutrients and ions for the Kitimat River Watershed, British Columbia. Since the 1950s, the Kitimat watershed had an aluminum smelting facility with substantial emissions at the river estuary. Emissions load the airshed overlying the watershed and potentially impact western tributaries leaving eastern tributaries available as reference. We assessed concentrations and export of key compounds in three reference and six potentially impacted tributaries and watersheds in 2015 and 2016. Sulfate (SO4), fluoride (F), nitrate (NO3), and chloride (Cl) were significantly higher in impacted tributaries. F concentrations exceeded the Canadian Council of Ministers of the Environment guideline for aquatic life in 83% of samples collected from impacted streams. Watershed export and associated uncertainty were determined by bootstrapped flow-stratified Beale's unbiased estimator. Impact of emissions on watershed export was modeled in a Bayesian approach to include variance in the export estimate to inform the uncertainty of model parameters. Export of SO4 and Ca increased significantly within 16 km and 8 km, respectively, toward the smelter emissions. The corresponding impacted area for SO4 and Ca was approximately 100 km2 and 45 km2, respectively. SO4 export is likely due to direct impacts of S deposition, with excess S being flushed from the watersheds. Ca export patterns likely result from indirect impacts of S deposition on soil chemistry and flushing of Ca. These impacts may contribute to effects within tributaries on benthic stream communities and regionally important juvenile Pacific salmon.


Assuntos
Monitoramento Ambiental , Rios , Teorema de Bayes , Canadá , Nitratos/análise
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