Large Seasonal Variation in Nitrogen Isotopic Abundances of Ammonia Volatilized from a Cropland Ecosystem and Implications for Regional NH3 Source Partitioning.

Ammonia (NH3) volatilization from agricultural lands is a main source of atmospheric reduced nitrogen species (NHx). Accurately quantifying its contribution to regional atmospheric NHx deposition is critical for controlling regional air nitrogen pollution. The stable nitrogen isotope composition (expressed by δ15N) is a promising indicator to trace atmospheric NHx sources, presupposing a reliable nitrogen isotopic signature of NH3 emission sources. To obtain more specific seasonal δ15N values of soil NH3 volatilization for reliable regional seasonal NH3 source partitioning, we utilized an active dynamic sampling technique to measure the δ15N-NH3 values volatilized from maize cropping land in northeast China. These values varied from -38.0 to -0.2‰, with a significantly lower rate-weighted value observed in the early period (May-June, -30.5 ± 6.7‰) as compared with the late period (July-October, -8.5 ± 4.3‰). Seasonal δ15N-NH3 variations were related to the main NH3 production pathway, degree of soil ammonium consumption, and soil environment. Bayesian isotope mixing model analysis revealed that without considering the seasonal δ15N variation in soil-volatilized NH3 could result in an overestimate by up to absolute 38% for agricultural volatile NH3 to regional atmospheric bulk ammonium deposition during July-October, further demonstrating that it is essential to distinguish seasonal δ15N profile of agricultural volatile NH3 in regional source apportionment.

Asynchronous characteristics of Feammox and iron reduction from paddy soils in Southern China.

Recently, the newly discovered anaerobic ammonium oxidation coupled with iron reduction (i.e., Feammox) has been proven to be a widespread nitrogen (N) loss pathway in ecosystems and has an essential contribution to gaseous N loss in paddy soil. However, the mechanism of iron-nitrogen coupling transformation and the role of iron-reducing bacteria (IRB) in Feammox were poorly understood. This study investigated the Feammox and iron reduction changes and microbial community evolution in a long-term anaerobic incubation by 15N isotope labeling combined with molecular biological techniques. The average rates of Feammox and iron reduction during the whole incubation were 0.25 ± 0.04 µg N g-1 d-1 and 40.58 ± 3.28 µg Fe g-1 d-1, respectively. High iron oxide content increased the Feammox rate, but decreased the proportion of Feammox-N2 in three Feammox pathways. RBG-13-54-9, Brevundimonas, and Pelomonas played a vital role in the evolution of microbial communities. The characteristics of asynchronous changes between Feammox and iron reduction were found through long-term incubation. IRB might not be the key species directly driving Feammox, and it is necessary to reevaluate the role of IRB in Feammox process.

Removal of PAHs, TSS, oils and fats from ammonium-rich coke wastewater by granular filtration.

Coke wastewater is a complex industrial wastewater due to its high content of toxic compounds such as cyanides, thiocyanates, phenols, tar, oils, and fats. After a series of treatments, wastewater with a high ammonium content is obtained (around 4,150 mg·L-1). A stripping process is used to reduce it. Certain pollutants in the influent, such as tar, polycyclic aromatic hydrocarbons (PAHs), oils, fats and total suspended solids (TSS), interfere with stripping and therefore must be previously removed. In this study, the performance of a pilot-scale airlift sand filter was evaluated under real conditions for the reduction of the concentration of tar, PAHs, oils, fats and TSS, before stripping. Prior to the sand filter, a cationic flocculant was added to the influent (2 ppm). High (10 mm.min-1), medium (7.5 mm.min-1) and low sand speeds (1.9-2.6 mm.min-1) were assessed. The latter conditions gave the best results: a decrease of 98.2% in TSS, 99.7% in oils, fats and grease and 97.6% in PAHs. The final effluent (≤ 1.6 mg PAHs·L-1, ≤ 5 mg TSS·L-1 and ≤ 0.05 mg·L-1 of fats, oils and grease) was suitable for the stripping process.

Global soil nitrogen cycle pattern and nitrogen enrichment effects: Tropical versus subtropical forests.

Tropical and subtropical forest biomes are a main hotspot for the global nitrogen (N) cycle. Yet, our understanding of global soil N cycle patterns and drivers and their response to N deposition in these biomes remains elusive. By a meta-analysis of 2426-single and 161-paired observations from 89 published 15 N pool dilution and tracing studies, we found that gross N mineralization (GNM), immobilization of ammonium ( I NH 4 ) and nitrate ( I NO 3 ), and dissimilatory nitrate reduction to ammonium (DNRA) were significantly higher in tropical forests than in subtropical forests. Soil N cycle was conservative in tropical forests with ratios of gross nitrification (GN) to I NH 4 (GN/ I NH 4 ) and of soil nitrate to ammonium (NO3 - /NH4 + ) less than one, but was leaky in subtropical forests with GN/ I NH 4 and NO3 - /NH4 + higher than one. Soil NH4 + dynamics were mainly controlled by soil substrate (e.g., total N), but climatic factors (e.g., precipitation and/or temperature) were more important in controlling soil NO3 - dynamics. Soil texture played a role, as GNM and I NH 4 were positively correlated with silt and clay contents, while I NO 3 and DNRA were positively correlated with sand and clay contents, respectively. The soil N cycle was more sensitive to N deposition in tropical forests than in subtropical forests. Nitrogen deposition leads to a leaky N cycle in tropical forests, as evidenced by the increase in GN/ I NH 4 , NO3 - /NH4 + , and nitrous oxide emissions and the decrease in I NO 3 and DNRA, mainly due to the decrease in soil microbial biomass and pH. Dominant tree species can also influence soil N cycle pattern, which has changed from conservative in deciduous forests to leaky in coniferous forests. We provide global evidence that tropical, but not subtropical, forests are characterized by soil N dynamics sustaining N availability and that N deposition inhibits soil N retention and stimulates N losses in these biomes.

Paleo-Geomorphology Determines Spatial Variability of Geogenic Ammonium Concentration in Quaternary Aquifers.

Naturally occurring (i.e., geogenic) ammonium in groundwater has been widely detected globally, but the major controls on its regional distribution have been poorly characterized. Here, we identified the dominant role of paleo-geomorphology driven by paleo-climate in controlling the spatial variability of geogenic ammonium in groundwater using random forest algorithm and revealed the underlying mechanisms based on borehole sediment analysis of data obtained from the Dongting Lake Plain of the central Yangtze River basins in China. In the paleo-channel (PC) area, the aquifer depth-matched sediments were deposited during the last deglaciation when warm climate resulted in rapid filling into incised valleys, and terrestrial organic matter (OM) mainly as lignin experienced less degradation prior to sedimentation and had lower humification, higher N abundance, and nominal oxidation state of carbon (NOSC). In the paleo-interfluve (PI) area, the depth-matched sediments were deposited during the last glaciation, followed by intensive erosion in the surface during the last glacial maximum, and terrestrial OM mainly as lignin had been partly degraded into aliphatics prior to sedimentation and had higher humification, lower N abundance, and NOSC. As a result, under the present anaerobic conditions, less-humic and N-rich OM with more oxidized C tends to be more intensively mineralized into ammonium in the PC area than those in the PI area. These findings highlight the importance of paleo-geomorphology with paleo-climate in controlling the enrichment of geogenic ammonium in groundwater, which has a universal significance for understanding the genesis and distribution of high N loads in the aquatic environment worldwide.

Toward Energy Neutrality: Novel Wastewater Treatment Incorporating Acidophilic Ammonia Oxidation.

Chemically enhanced primary treatment (CEPT) followed by partial nitritation and anammox (PN/A) and anaerobic digestion (AD) is a promising roadmap to achieve energy-neutral wastewater treatment. However, the acidification of wastewater caused by ferric hydrolysis in CEPT and how to achieve stable suppression of nitrite-oxidizing bacteria (NOB) in PN/A challenge this paradigm in practice. This study proposes a novel wastewater treatment scheme to overcome these challenges. Results showed that, by dosing FeCl3 at 50 mg Fe/L, the CEPT process removed 61.8% of COD and 90.1% of phosphate and reduced the alkalinity as well. Feeding by low alkalinity wastewater, stable nitrite accumulation was achieved in an aerobic reactor operated at pH 4.35 aided by a novel acid-tolerant ammonium-oxidizing bacteria (AOB), namely, Candidatus Nitrosoglobus. After polishing in a following anoxic reactor (anammox), a satisfactory effluent, containing COD at 41.9 ± 11.2 mg/L, total nitrogen at 5.1 ± 1.8 mg N/L, and phosphate at 0.3 ± 0.2 mg P/L, was achieved. Moreover, the stable performances of this integration were well maintained at an operating temperature of 12 °C, and 10 investigated micropollutants were removed from the wastewater. An energy balance assessment indicated that the integrated system could achieve energy self-sufficiency in domestic wastewater treatment.

Constituents of fine particulate matter and asthma in 6 low- and middle-income countries.

BACKGROUND: Evidence concerning the effects of different chemical components of particulate matter with an aerodynamic diameter of 2.5 µm or less (PM2.5) on asthma is limited, and the methodology to compare the relative importance of different PM2.5 components is lacking. OBJECTIVE: Our aim was to examine the associations between PM2.5 components and asthma and investigate which constituent of PM2.5 possessed the most harmful effect on asthma. METHODS: A total of 45,690 subjects in 6 countries were surveyed from 2007 to 2010. We geocoded the residential community addresses of the participants and used satellite remote sensing and chemical transport modeling to estimate their annual average concentrations of PM2.5 constituents. Mixed-effects generalized additive models were utilized to examine the associations between PM2.5 constituents and prevalence of asthma. We further used counterfactual analyses to determine the potential number of asthma cases. RESULTS: We identified 6178 patients with asthma among the participants, producing an asthma prevalence of 13.5%. The odds ratio for asthma associated with per-SD increment was 1.12 for PM2.5 mass, 1.12 for organic carbon, 1.18 for black carbon, 1.19 for sulfate, 1.28 for ammonium, and 1.21 for nitrate after controlling for potential confounders. Our counterfactual analyses suggested that ammonium was responsible for a substantial decline in asthma cases (by 1382 cases, corresponding to 22.37% of overall cases) if the concentration was reduced to the 5th percentile of the current level. CONCLUSIONS: Our study suggests that some chemical components of PM2.5 (including black carbon, organic carbon, sulfate, ammonium, and nitrate) might be hazardous constituents contributing to the prevalence of asthma; among them, ammonium might be responsible for a substantial proportion of asthma cases if reduced to a certain level.

Dynamic elution of residual ammonium leaching agent from weathered crust elution-deposited rare earth tailings by magnesium chloride.

The release of residual ammonium (RA) leaching agent from weathered crust elution-deposited rare earth tailings would cause serious environmental pollution, and it was necessary to efficiently remove it from the ore body before the mine closure. In this study, occurrence states of the RA were determined and dynamic elution of RA from rare earth tailings by using magnesium chloride as eluent was investigated. Effects of initial concentration, pH, flow rate, and particle size on the ammonium removal efficiency were investigated, and variations of ammonium occurrence states before and after elution were determined. Lastly, elution mechanism was discussed. Results showed that removal efficiency of RA by magnesium chloride was significantly higher than that by deionized water, and elution efficiency of RA could reach about 95.7% at the optimum laboratory experiment conditions. Energy dispersive spectrometer (EDS) analysis illustrated that the residual ammonium was replaced by Mg2+ during the elution process, and occurrence state experimental results showed that 94.0% of water-soluble and adsorbable ammonium was eluted. The empirical kinetic equation of eluting RA by magnesium chloride was established as 1-2/3α-(1-α)2/3= 0.02*C00.6t. This study provided a valuable method for reducing environmental pollution caused by the release of the residual ammonium from the rare earth tailings.

Enhancement of desulfurization by hydroxyl ammonium ionic liquid supported on active carbon.

Power plants emit sulfur dioxide (SO2) during combustion, which is typically removed via wet flue gas desulfurization, but this process produces numerous secondary pollutants. Ionic liquids (ILs) can potentially be used to remove SO2, but they suffer from poor mass transfer rates. Hydroxyl ammonium ILs are classical cheap ILs that contain electron-rich O and N sites that favor high absorption capacities. To accelerate mass transfer, two hydroxyl ammonium ILs, triethanolamine citrate and triethanolamine lactate, were immobilized on activated carbon (SILs) and used to capture SO2 from simulated flue gas. They exhibited excellent adsorption at low SO2 partial pressures due to the presence of a large gas-liquid interface. The molar adsorption ratios reached 7.65 and 2.40 mol/mol at 10 kPa SO2. The SILs possessed good SO2 selectivity in SO2/CO2 and SO2/O2 mixtures, because of the only 8% reduction in the total adsorption of SILs at 60 °C. And they exhibited excellent reversibility in which their total adsorption capacities were unaffected after 5 adsorption-desorption cycles. The mechanism analysis revealed that chemical adsorption was the major adsorption route, although physical adsorption also occurred. The main reactive sites included C-O and N-H groups in the ionic liquid. These SILs may potentially replace traditional chemical absorption materials for the separation of SO2 from flue gas.

Long-term exposure to PM2.5 constituents in relation to glucose levels and diabetes in middle-aged and older Chinese.

BACKGROUND: Previous studies have indicated the associations between fine particulate matter (PM2.5) exposure and diabetes or glucose levels. However, evidence linking PM2.5 constituents and diabetes or glucose levels was extensively scarce, particularly in developing countries. This study aimed to investigate the associations of exposure to PM2.5 and its five constituents (black carbon [BC], organic matter [OM], nitrate [NO3-], sulfate [SO42-], and ammonium [NH4+]) with diabetes and glucose levels among the middle-aged and elderly Chinese populations. METHODS: A national cross-sectional sample of participants aged 45+ years was enrolled from 28 provinces across China's mainland. Health examination and questionnaire survey for each respondent were performed during 2011-2012. Diabetes was determined by alternative definitions, and the main definition (MD) was self-report diabetes or antidiabetic medicine use or HbA1c ≥6.5 or fasting glucose ≥7 mmol/L or random glucose ≥11.1 mmol/L. Monthly exposure to PM2.5 mass and its five constituents (BC, OM, NO3-, SO42-, and NH4+) for each participant at residence were estimated using satellite-based spatiotemporal prediction models. Generalized linear models and linear mixed-effects models were used to assess the effects of exposure to PM2.5 and its constituents on diabetes or glucose levels, respectively. Stratification analyses were done by sex and age. RESULTS: We included a total of 17,326 adults over 45 years in this study. The 3-year mean (interquartile range [IQR]) concentrations of PM2.5, BC, OM, NO3-, SO42-, and NH4+ were 47.9 (27.4) µg/m3, 2.9 (2.2) µg/m3, 9.2 (6.6) µg/m3, 10.2 (9.4) µg/m3, 11.0 (5.2) µg/m3, and 7.1 (4.4) µg/m3, respectively. Per IQR rise in exposure to PM2.5 was significantly associated with an increase of 0.133 mmol/L (95% confidence interval, 0.048-0.219) in glucose concentrations. Similar positive associations were observed for BC (0.097 mmol/L [0.012-0.181]), OM (0.160 mmol/L [0.065-0.256]), NO3- (0.145 mmol/L [0.039-0.251]), SO42- (0.111 mmol/L [0.026-0.196]), and NH4+ (0.135 mmol/L [0.041-0.230]). Under different diabetes definitions, PM2.5 mass and selected constituents with the exception of SO42- were all associated with a higher risk of prevalent diabetes. In MD-based analysis, similar positive associations were observed for four constituents, with corresponding odds ratios of 1.180 (1.097-1.270) for PM2.5, 1.154 (1.079-1.235) for BC, 1.170 (1.079-1.270) for OM, 1.200 (1.098-1.312) for NO3-, and 1.123 (1.037-1.215) for NH4+. Stratified analyses showed a significantly higher risk of diabetes in males (1.225 [1.064-1.411]) than females (1.024 [0.923-1.136]) when exposed to PM2.5. Participants under 65 years were generally more vulnerable to diabetes hazards related to PM2.5 constituents exposure. CONCLUSIONS: Exposures to PM2.5 and its constituents (i.e., BC, OM, NO3-, and NH4+) were positively associated with increased risks of prevalent diabetes and elevated glucose levels in middle-aged and older adults.

Using Biological Responses to Monitor Freshwater Post-Spill Conditions over 3 years in Blacktail Creek, North Dakota, USA.

A pipeline carrying unconventional oil and gas (OG) wastewater spilled approximately 11 million liters of wastewater into Blacktail Creek, North Dakota, USA. Flow of the mix of stream water and wastewater down the channel resulted in storage of contaminants in the hyporheic zone and along the banks, providing a long-term source of wastewater constituents to the stream. A multi-level investigation was used to assess the potential effects of oil and brine spills on aquatic life. In this study, we used a combination of experiments using a native fish species, Fathead Minnow (Pimephales promelas), field sampling of the microbial community structure, and measures of estrogenicity. The fish investigation included in situ experiments and experiments with collected site water. Estrogenicity was measured in collected site water samples, and microbial community analyses were conducted on collected sediments. During the initial post-spill investigation, February 2015, performing in situ fish bioassays was impossible because of ice conditions. However, microbial community (e.g., the presence of members of the Halomonadaceae, a family that is indicative of elevated salinity) and estrogenicity differences were compared to reference sites and point to early biological effects of the spill. We noted water column effects on in situ fish survival 6 months post-spill during June 2015. At that time, total dissolved ammonium (sum of ammonium and ammonia, TAN) was 4.41 mg NH4/L with an associated NH3 of 1.09 mg/L, a concentration greater than the water quality criteria established to protect aquatic life. Biological measurements in the sediment defined early and long-lasting effects of the spill on aquatic resources. The microbial community structure was affected during all sampling events. Therefore, sediment may act as a sink for constituents spilled and as such provide an indication of continued and cumulative effects post-spill. However, lack of later water column effects may reflect pulse hyporheic flow of ammonia from shallow ground water. Combining fish toxicological, microbial community structure and estrogenicity information provides a complete ecological investigation that defines potential influences of contaminants at organismal, population, and community levels. In general, in situ bioassays have implications for the individual survival and changes at the population level, microbial community structure defines potential changes at the community level, and estrogenicity measurements define changes at the individual and molecular level. By understanding effects at these various levels of biological organization, natural resource managers can interpret how a course of action, especially for remediation/restoration, might affect a larger group of organisms in the system. The current work also reviews potential effects of additional constituents defined during chemistry investigations on aquatic resources.

Using Canadian Water Quality Index method to evaluate the spatio-variation of water quality and the impacts of quality parameters: a case study of Amasya's surface water (Northern Turkey).

In this study, the spatial variation of water quality in Yesilirmak River passing through Amasya was investigated using the Canadian Water Quality Index (CWQI). For this aim, the measured 15 parameters in 3-month periods between the years 2008 and 2015 were used at 11 sample points from the Yesilirmak River and its tributaries. The calculated CWQI scores using parameters of pH, Dissolved Oxygen (DO), Chemical Oxygen Demand (COD), ammonia, ammonium, nitrite, nitrate, phosphate, iron, copper, zinc, potassium, sulfate, sulfite and chlorine range from 33 to 64. These scores indicate that the surface waters in the studied area are poor to marginal in quality. The effect of each parameter on the CWQI scores by excluding each parameter, one by one, considering the water quality of the Yesilirmak River was investigated using the Hierarchical Cluster Analysis (HCA) method. It was determined that the presence and/or absence of the parameters, which caused an increase or decrease in CWQI scores, were ammonia, phosphate, COD, sulfide, iron, ammonium, nitrite, DO. On the other hand, the parameters having positive effects on CWQI are nitrate, chlorine and potassium. The HCA statistical analysis method is suitable for interpreting complex water quality datasets and understanding time/location dependent changes in water quality. HCA can be used effectively to group parameters in river water quality monitoring programs.

Chemometric and risk assessment of nitrogen composition of atmospheric rainwater from diverse surfaces in Rivers State, Nigeria.

Organic and inorganic nitrogen ions in the environment play important role across environmental matrices. Rainwater samples collected from ambient and different roofing surfaces (zinc, aluminium, asbestos and stone-coated roofing sheets) from selected locations at Ogale, Rumuodomaya/Rumuodome, Diobu and Chokocho within Rivers State, Niger Delta, Nigeria, from April to June, July to August and September to October depicting three regiments of early, mid and late rains. The samples were analysed for Kjeldahl nitrogen, ammonium, nitrate and nitrite using APHA methodology. Quantitative assessment showed that Kjeldahl nitrogen were in range of 0.11 to 28.05 mg/L; ammonium 0.50 to 20.22 mg/L, nitrate from 0.12 to 22.69 mg/L and nitrite from 0.15 to 3.90 mg/L. Parameters decreased from early to late rain, which can be attributed to rain dilution factor potential, wind pattern and emission from anthropogenic sources that influenced the rainwater quality across surfaces. Nitrogen results showed that dry and wet deposition has great impact; atmospheric aerosols and biogeochemical interactions can affect water quality. Monthly variation showed that Ogale had high regression compared to other locations due to close proximity to oil and gas emission and marine contribution. Neutralization factor showed that nitrate-nitrite compounds have strong correlation with ammonium ion. Non-carcinogenic risk assessment using US EPA model showed hazard index less than one (1), thus no associated health effect of nitrate and nitrite in rainwater. In conclusion, it is evident that nitrate/nitrite levels and other nitrogen derivatives in rainwater in crude oil-producing Niger Delta and its continuous consumption can cause negative health outcome.

Year-round observation of atmospheric inorganic aerosols in urban Beijing: Size distribution, source analysis, and reduction mechanism.

To investigate particle characteristics and find an effective measure to control severe particle pollution, year-round observation of size-segregated inorganic aerosols was conducted in Beijing from January to December, 2016. The sampled atmospheric particles all presented bimodal size distribution at four pollution levels (clear, slight pollution, moderate pollution and severe pollution), and peak values appeared at the size range of 0.7-2.1 µm and >9.0 µm, respectively. As dominant particle compositions, NO3-, SO42-, and NH4+ in four pollution levels all showed significant peaks in fine mode, especially at the size range of 1.1-2.1 µm. Secondary inorganic aerosols accounted for about 67.6% (36.3% (secondary sulfates) + 31.3% (secondary nitrates)) of the total sources of fine particles in urban Beijing. Severe pollution of fine particles was mainly caused by the air masses transported from nearby western and southern areas, which are industrial and densely populated region, respectively. Sensitivity tests further revealed that the control measures focusing on ammonium emission reduction was the most effective for particle pollution mitigation, and fine particles all showed nonlinear responses after reducing ammonium, nitrate, and sulfate concentrations, with the fitting curves of y = -120.8x - 306.1x2 + 290.2x3, y = -43.5x - 67.8x2, and y = -25.8x - 110.4x2 + 7.6x3, respectively (y and x present fine particle mass variation (µg/m3) and concentration reduction ratio (CRR)/100 (dimensionless)). Overall, our study presents useful information for understanding the characteristics of atmospheric inorganic aerosols in urban Beijing, as well as offers policy makers with effective measure for mitigating particle pollution.

Nitrogen isotope analysis of aqueous ammonium and nitrate by membrane inlet isotope ratio mass spectrometry (MIRMS) at natural abundance levels.

RATIONALE: Existing methods for the measurement of the 15 N/14 N isotopic composition of ammonium and nitrate are either only suitable for labelled samples or require considerable sample preparation efforts (or both). Our goal was to modify an existing analytical approach to allow for natural abundance precision levels. METHODS: Published reaction protocols were used to convert ammonium into N2 by NaOBr and nitrate into N2 O by TiCl3 . A membrane inlet system was developed and coupled to an isotope ratio mass spectrometer to allow precise determination of the analytes. RESULTS: Concentrations of ≥35 µmol/L N for both ammonium or nitrate could be analysed for δ15 N values with precisions of better than 0.9 mUr. While ammonium analyses exhibited a small concentration dependency and an offset of 2.7 mUr at high ammonium concentrations irrespective of the standard isotopic composition, nitrate analysis showed no offset but a blank contribution visible at very low concentrations. CONCLUSIONS: The presented method is capable of fast measurement of δ15 N values in ammonium and nitrate from aqueous samples with reasonable accuracy at natural abundance levels. It will thus facilitate the application of isotopic methods to studies of nitrogen cycling in ecosystems.

Dissolved organic matter characterization in high and low ammonium groundwater of Dongting Plain, central China.

High levels of ammonium in groundwater is a potential threat to drinking water security and ecological status. The role of dissolved organic matter (DOM) in mobilization of natural ammonium in groundwater is crucial but the intrinsic link between them has still been poorly understood. This study used high-pressure size exclusion chromatography (HPSEC) and fluorescence excitataion-emission-matrix spectra (EEMs) with parallel factor analysis (PARAFAC) to elucidate the influence of DOM characteristics in groundwater systems having contrastive ammonium levels in Dongting Plain, central Yangtze River. The results indicate that NH4+-N concentration in groundwater of western plain (0-16.75 mg/L) are much higher compared with southern plain (0-1.5 mg/L). The groundwater in western plain is in a more reductive environment and characterized by larger molecular weight (MW) of DOM and lower polydispersity (ρ), whereas DOM with relatively small molecular weight and high polydispersity is detected in the south with a more oxidative condition. The groundwater in western plain is characterized by lower fluorescence index (f450/500) and biological index (BIX), and dominated by the high molecular weight terrestrial humic-like component and larger amounts of microbial humic-like components. Protein-like is the main component in groundwater of southern plain with higher f450/500 and BIX. The ammonium concentration in groundwater correlates well with molecular weight and increases significantly with the content of high molecular weight terrestrial humic-like component, indicating that mobilization of ammonium is more closely associated with the terrestrial organic matter of high molecular weight. This study further enriches the theory on mobilization of ammonium in Quaternary alluvial-lacustrine aquifer systems and provides theoretical basis for the local water supply security.

The influence of soil particle size distribution and clay minerals on ammonium nitrogen in weathered crust elution-deposited rare earth tailing.

Even after being abandoned for many years, a large number of weathered crust elution-deposited rare earth (WCED-RE) tailings continue to release ammonia nitrogen (AN) pollution into their surrounding environments. However, the influences of particle size distribution and clay minerals on AN pollution caused by these tailings have been insufficiently studied, and its causes are poorly understood. In this study, soil samples at different depths (5, 7, 9, 11 and 14 m) were collected from a rare earth tailing in Ganzhou City, Jiangxi Province, China. Particles were screened by size into six groups (2-1, 1-0.5, 0.5-0.25, 0.25-0.1, 0.1-0.075 and < 0.075 mm), and AN forms were extracted. The results showed that as soil particle size decreases, both soil specific surface area and clay content increase, leading to stronger AN enrichment ability. With increased sampling depth, the distribution of clay across the six particle fractions became more uniform, such that the accumulation of AN in soil with fine particle size was less obvious. Clay minerals with different capacities for AN enrichment vary with sampling depth. This variation is responsible for the profile of AN distribution in the mine, where AN first increases and then decreases as vertical depth is increased. Although AN content was highest at 11 m, water soluble AN content was higher in the upper part of the completely weathered layer (5 and 7 m), which poses a higher environmental risk. This study provides significant information to deepen our understanding of the distribution characteristics of AN and its main influencing factors, as well as a foundation for the prevention and remediation of nitrogen pollution from WCED-RE tailings.

Amino acids, betaines and related ammonium compounds in Neapolitan limmo, a Mediterranean sweet lime, also known as lemoncetta Locrese.

BACKGROUND: The so-called 'Neapolitan limmo' or 'lemoncetta Locrese' is an old and now rare Mediterranean sweet lime, similar to lemon but smaller. It is a fruit distinguished from orange, lemon, mandarin, and lime for its sweeter, watery, and non-acidic taste, with a pH between 5.6 and 5.9. No compositional studies are currently available for this citrus fruit. Here we report, for the first time, the distribution in the limmo juice of free amino acids and their main derivatives such as betaines and related ammonium compounds. RESULTS: Seven proteinogenic amino acids (proline, asparagine, serine, aspartic acid, glutamine, alanine, and threonine) and a non-protein amino acid (γ-aminobutyric acid) characterize Neapolitan limmo juice. Proline betaine is the predominant betaine. The data were compared with those of other important citrus juices. CONCLUSION: The specific 'taste quality' of Neapolitan limmo juice can be attributed to its peculiar composition in amino acids. The species-specific presence of the ammonium compound derivatives of the amino acid proline, with proline betaine as the predominant betaine, characterize the non-acidic varieties of Mediterranean sweet lime. Our study constitutes an important step towards the repopulation of this ancient plant and its exploitation in food industry. © 2020 Society of Chemical Industry.

Differences in nitrification and ammonium-oxidising prokaryotes in the process of wetland restoration.

Ammonia-oxidising archaea (AOA) and ammonia-oxidising bacteria (AOB) are ammonium oxidising prokaryotes that can drive soil nitrification in wetlands. During the restoration of wetlands, different types of land use soils (agricultural soil [AS], restored wetland soil [RS], and natural wetland soil [NWS]) are present. However, studies on the effects of changes in the types of land use in wetlands during restoration on nitrification and the community composition of AOA and AOB are still not well understood. In this study, the differences in the potential nitrification rate (PNR) and community composition of AOA and AOB in AS, RS, and NWS were compared and discussed. The results indicated that the PNRs in the AS, RS, and NWS were on the same order of magnitude. Nitrification was mainly driven by AOB. High-throughput sequencing results showed that the genus Nitrososphaera of AOA and unclassified_o_Nitrosomonadales of AOB were only detected in the AS. Redundancy analysis (RDA) results indicated that the community composition of AOA was mostly influenced by pH, while TC was the most influential variable on the community composition of AOB. Our study provides a basis for distinguishing the roles of ammonium-oxidising prokaryotes in nitrification and further understanding the changes in nitrifying activity in wetlands during restoration.

Marine aquaculture regulates dissimilatory nitrate reduction processes in a typical semi-enclosed bay of southeastern China.

Marine aquaculture in semi-enclosed bays can significantly influence nutrient cycling in coastal ecosystems. However, the impact of marine aquaculture on the dynamics of dissimilatory nitrate reduction processes (DNRPs) and the fate of reactive nitrogen remain poorly understood. In this study, the rates of DNRPs and the abundances of related functional genes were investigated in aquaculture and non-aquaculture areas. The results showed that marine aquaculture significantly increased the denitrification (DNF) and dissimilatory nitrate reduction to ammonium (DNRA) rates and decreased the rate of anaerobic ammonium oxidation (ANA), as compared with non-aquaculture sites. DNF was the dominant pathway contributing to the total nitrate reduction, and its contribution to the total nitrate reduction significantly increased from 66.72% at non-aquaculture sites to 78.50% at aquaculture sites. Marine aquaculture can significantly affect the physicochemical characteristics of sediment and the abundances of related functional genes, leading to variations in the nitrate reduction rates. Although nitrate removal rates increased in the marine aquaculture area, ammonification rates and the nitrogen retention index in the aquaculture areas were 2.19 and 1.24 times, respectively, higher than those at non-aquaculture sites. Net reactive nitrogen retention exceeded nitrogen removal in the aquaculture area, and the retained reactive nitrogen could diffuse with the tidal current to the entire bay, thereby aggravating N pollution in the entire study area. These results show that marine aquaculture is the dominant source of nitrogen pollution in semi-enclosed bays. This study can provide insights into nitrogen pollution control in semi-enclosed bays with well-developed marine aquaculture.