High Concentrations Of NH4 Research Articles

Septic system-groundwater-surface water couplings in waterfront communities contribute to harmful algal blooms in Southwest Florida.

As human population growth has expanded in Southwest Florida, water quality has become degraded with an increased occurrence of harmful algal blooms (HABs). Red tide (Karenia brevis) originating offshore, intensifies in nearshore waters along Florida's Gulf Coast, and blue-green algae (Microcystis spp.) originating in Lake Okeechobee is discharged into the Caloosahatchee River. These HABs could be enhanced by anthropogenic nitrogen (N) and phosphorus (P) from adjacent watersheds. North Fort Myers is a heavily developed, low-lying city on the Caloosahatchee River Estuary serviced by septic systems with documented nutrient and bacterial pollution. To identify sources of pollution within North Fort Myers and determine connections with downstream HABs, this multiyear (2017-2020) study examined septic system- groundwater- surface water couplings through the analysis of water table depth, nutrients (N, P), fecal indicator bacteria (FIB), molecular markers (HF183, GFD, Gull2), chemical tracers (sucralose, pharmaceuticals, herbicides, pesticides), stable isotopes of groundwater (δ15N-NH4, δ15N-NO3) and particulate organic matter (POM; δ15N, δ13C), and POM elemental composition (C:N:P). POM samples were also collected during K. brevis and Microcystis spp. HAB events. Most (>80%) water table depth measurements were too shallow to support septic system functioning (<1.07 m). High concentrations of NH4+ and NOx, up to 1094 μM and 482 μM respectively, were found in groundwater and surface water. δ15N values of groundwater (+4.7‰) were similar to septic effluent (+4.9‰), POM (+4.7‰), and downstream HABs (+4.8 to 6.9‰), indicating a human waste N source. In surface water, FIB were elevated and HF183 was detected, while in groundwater and surface water sucralose, carbamazepine, primidone, and acetaminophen were detected. These data suggest that groundwater and surface water in North Fort Myers are coupled and contaminated by septic system effluent, which is negatively affecting water quality and contributing to the maintenance and intensification of downstream HABs.

High-Sensitivity Ammonia Sensors with Carbon Nanowall Active Material via Laser-Induced Transfer.

Ammonia sensors with high sensitivity, reproducible response, and low cost are of paramount importance for medicine, i.e., being a biomarker to diagnose lung and renal conditions, and agriculture, given that fertilizer application and livestock manure account for more than 80% of NH3 emissions. Thus, in this work, we report the fabrication of ultra-sensitive ammonia sensors by a rapid, efficient, and solvent-free laser-based procedure, i.e., laser-induced forward transfer (LIFT). LIFT has been used to transfer carbon nanowalls (CNWs) onto flexible polyimide substrates pre-patterned with metallic electrodes. The feasibility of LIFT is validated by the excellent performance of the laser-printed CNW-based sensors in detecting different concentrations of NH3 in the air, at room temperature. The sensors prepared by LIFT show reversible responses to ammonia when exposed to 20 ppm, whilst at higher NH3 concentrations, the responses are quasi-dosimetric. Furthermore, the laser-printed CNW-based sensors have a detection limit as low as 89 ppb and a response time below 10 min for a 20 ppm exposure. In addition, the laser-printed CNW-based sensors are very robust and can withstand more than 200 bending cycles without loss of performance. This work paves the way for the application and integration of laser-based techniques in device fabrication, overcoming the challenges associated with solvent-assisted chemical functionalization.

Controls of Geochemical and Hydrogeochemical Factors on Arsenic Mobility in the Hetao Basin, China.

High arsenic (As) groundwater is frequently found in inland basins, but little is known about As pools in sediments and their influences on aqueous As distributions. The Hetao Basin is a typical inland basin, where groundwater As concentrations generally increase from alluvial fans to flat plain. Two sites are only 1700 m apart, but groundwater As concentrations at the depth range of 15 to 80 m are quite different, ranging from 7.0 to 31.7 μg/L at site B1 and from 5.2 to 99.8 μg/L at site B2. Sediment geochemistry and groundwater hydrochemistry at two sites were characterized. No distinct differences were observed in the bulk geochemistry of sediments. Sequential extractions of 39 sediments were conducted to determine why As was easily released to groundwater at one site and not the other. Results showed that at site B1 most of solid As was associated with amorphous Fe-(oxyhydr)oxides, whereas at site B2 the strong adsorption pool dominated. Furthermore, higher dissolved Fe2+ and lower ORP in groundwater at site B2 suggested more strongly reducing conditions compared to site B1. High concentrations of NH4 + and HCO3 - at site B2 were consistent with As release coupled to microbially induced reductive dissolution of Fe-(oxyhydr)oxides. Other processes, such as the competitive adsorption of HCO3 - , As desorption under weakly alkaline pH conditions, may also influence the partitioning of As between groundwater and sediments. This study highlights the differences in how As is associated with sediments between high and low As aquifers and the contribution of chemical characteristics to As release.

Secondary PM&amp;lt;sub&amp;gt;2.5&amp;lt;/sub&amp;gt; decreases significantly less than NO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; emission reductions during COVID lockdown in Germany

Abstract. This study estimates the influence of anthropogenic emission reductions on the concentration of particulate matter with a diameter smaller than 2.5 µm (PM2.5) during the 2020 lockdown period in German metropolitan areas. After accounting for meteorological effects, PM2.5 concentrations during the spring 2020 lockdown period were 5 % lower compared to the same time period in 2019. However, during the 2020 pre-lockdown period (winter), PM2.5 concentrations with meteorology accounted for were 19 % lower than in 2019. Meanwhile, NO2 concentrations with meteorology accounted for dropped by 23 % during the 2020 lockdown period compared to an only 9 % drop for the 2020 pre-lockdown period, both compared to 2019. SO2 and CO concentrations with meteorology accounted for show no significant changes during the 2020 lockdown period compared to 2019. GEOS-Chem (GC) simulations with a COVID-19 emission reduction scenario based on the observations (23 % reduction in anthropogenic NOx emission with unchanged anthropogenic volatile organic compounds (VOCs) and SO2) are consistent with the small reductions of PM2.5 during the lockdown and are used to identify the underlying drivers for this. Due to being in a NOx-saturated ozone production regime, GC OH radical and O3 concentrations increased (15 % and 9 %, respectively) during the lockdown compared to a business-as-usual (BAU, no lockdown) scenario. Ox (equal to NO2+O3) analysis implies that the increase in ozone at nighttime is solely due to reduced NO titration. The increased O3 results in increased NO3 radical concentrations, primarily during the night, despite the large reductions in NO2. Thus, the oxidative capacity of the atmosphere is increased in all three important oxidants, OH, O3, and NO3. PM nitrate formation from gas-phase nitric acid (HNO3) is decreased during the lockdown as the increased OH concentration cannot compensate for the strong reductions in NO2, resulting in decreased daytime HNO3 formation from the OH + NO2 reaction. However, nighttime formation of PM nitrate from N2O5 hydrolysis is relatively unchanged. This results from the fact that increased nighttime O3 results in significantly increased NO3, which roughly balances the effect of the strong NO2 reductions on N2O5 formation. Ultimately, the only small observed decrease in lockdown PM2.5 concentrations can be explained by the large contribution of nighttime PM nitrate formation, generally enhanced sulfate formation, and slightly decreased ammonium. This study also suggests that high PM2.5 episodes in early spring are linked to high atmospheric ammonia concentrations combined with favorable meteorological conditions of low temperature and low boundary layer height. Northwest Germany is a hot-spot of NH3 emissions, primarily emitted from livestock farming and intensive agricultural activities (fertilizer application), with high NH3 concentrations in the early spring and summer months. Based on our findings, we suggest that appropriate NOx and VOC emission controls are required to limit ozone, and that should also help reduce PM2.5. Regulation of NH3 emissions, primarily from agricultural sectors, could result in significant reductions in PM2.5 pollution.

Response of bacterial communities and nitrogen-cycling genes in newly reclaimed mudflat paddy soils to nitrogen fertilizer gradients.

Conversion of coastal mudflats into paddy soils is an effective measure to alleviate the pressures on land resources. However, few studies have evaluated the effects of nitrogen (N) fertilizers on bacterial communities in newly reclaimed mudflat paddy soils. We performed a field plot experiment with six N fertilizer rates (0, 210, 255, 300, 345, and 390kgNha-1) in a newly reclaimed mudflat paddy for 2 consecutive years and used Illumina sequencing and qPCR to investigate the effects of N fertilizers on bacterial communities and N-cycling genes. Results showed that high N fertilization (above 300kgNha-1) increased the contents of organic matter (OM), total N (TN), ammonium (NH4+), and nitrate (NO3-) and significantly decreased the diversity and richness of bacteria. Furthermore, high N fertilization had a stronger effect on bacterial communities than low N fertilization, probably due to high concentrations of NH4+, OM, and NO3-. Additionally, in paddy soils with high N fertilizer application, the relative abundances of Bacteroidetes, γ-proteobacteria, and Actinobacteria increased significantly, but the reverse was true for those of Chloroflexi, Firmicutes, δ-proteobacteria, α-proteobacteria, Acidobacteria, and β-proteobacteria. The results of qPCR indicated that high N fertilization significantly increased the relative abundance of nifH genes involved in N fixation and decreased that of amoA-archaea involved in ammonia oxidation, nirS genes involved in nitrite reduction, and nosZ genes involved in nitrous oxide reduction, which suggested that high N fertilization increased the potential of available N retention and reduced the potential of nitrous oxide emission. Overall, N fertilizers with an N fertilizer rate of above 300kgNha-1 significantly altered the bacterial communities and N-cycle of mudflat paddy soils.

A potential linkage between excess silicate-bound nitrogen and N2-rich natural gas in sedimentary reservoirs

Molecular nitrogen (N2) released from sedimentary rocks during metamorphism is an important component of the biogeochemical nitrogen cycles. However, the importance and variability of this metamorphic N2 flux from rock nitrogen to Earth's surface environment remains largely unexplored. Here we present a comprehensive bulk rock C-N and N2 concentration dataset from the lower Cambrian shale across the Yangtze Block. The results reveal a spatial trend of excess silicate-bound nitrogen in the lower Cambrian shale throughout the Yangtze Block, which is interpreted as partial assimilation of ammonium (NH4+) with high concentrations of NH4+ accumulating in the euxinic water column and in sediment pore waters at shelf and slope environments during sedimentation. The remarkable spatial coupling between silicate-bound nitrogen in bulk rock shale and N2 concentration in modern shale reservoirs indicates that the high proportion of silicate-bound nitrogen may act as an important control on the formation of N2-rich gas in shale reservoirs during metamorphism. These N2-rich reservoir rocks may have affected the surface environment through tectonic movement over Earth's history. Our results therefore identify a novel linkage in the nitrogen cycle and provide evidence for the importance of metamorphism on the return of rock nitrogen back to the surface environment. We further reveal that the metamorphic N2 gas flux from the geosphere to the atmosphere is dependent on environmental conditions during sediment deposition.

Nitrate transporter NRT1.1 and anion channel SLAH3 form a functional unit to regulate nitrate-dependent alleviation of ammonium toxicity.

Ammonium (NH4 + ) and nitrate (NO3 - ) are major inorganic nitrogen (N) sources for plants. When serving as the sole or dominant N supply, NH4 + often causes root inhibition and shoot chlorosis in plants, known as ammonium toxicity. NO3 - usually causes no toxicity and can mitigate ammonium toxicity even at low concentrations, referred to as nitrate-dependent alleviation of ammonium toxicity. Our previous studies indicated a NO3 - efflux channel SLAH3 is involved in this process. However, whether additional components contribute to NO3 - -mediated NH4 + detoxification is unknown. Previously, mutations in NO3 - transporter NRT1.1 were shown to cause enhanced resistance to high concentrations of NH4 + . Whereas, in this study, we found when the high-NH4 + medium was supplemented with low concentrations of NO3 - , nrt1.1 mutant plants showed hyper-sensitive phenotype instead. Furthermore, mutation in NRT1.1 caused enhanced medium acidification under high-NH4 + /low-NO3 - condition, suggesting NRT1.1 regulates ammonium toxicity by facilitating H+ uptake. Moreover, NRT1.1 was shown to interact with SLAH3 to form a transporter-channel complex. Interestingly, SLAH3 appeared to affect NO3 - influx while NRT1.1 influenced NO3 - efflux, suggesting NRT1.1 and SLAH3 regulate each other at protein and/or gene expression levels. Our study thus revealed NRT1.1 and SLAH3 form a functional unit to regulate nitrate-dependent alleviation of ammonium toxicity through regulating NO3 - transport and balancing rhizosphere acidification.

Inclusion of Different Level Leucaena in Dairy Ration to Balance Rumen Degradable and Undegradable Protein Ratio

Abstract Sustainability use of expensive protein source in a dairy ration requires ration formulation based on rumen degradable and undegradable protein ratio (RDUP). It improves the efficiency of microbial protein synthesis and less feed residue to the environment. Providing less expensive green protein sources such as leucaena (Leucaena leucocephala) is also an alternative. This study aimed to evaluate the effect of dairy ration based on RDUP with leucaena addition on in vitro fermentability and digestibility. This study was conducted in a 4 x 3 factorial randomized block design. Factor 1 was RDUP levels (R1= 60:40; R2= 55:45; R3= 50:50; R4= 45:55) and factor 2 was Leucaena addition (L1= 10%; L2= 20%; L3= 30%). The data were analyzed using ANOVA and followed by the Duncan test. The result showed that increasing RDUP levels increased NH3 concentration and dry matter digestibility. Treatment L2 resulted in a high NH3 concentration compared to other L treatments. The combination of R1 with L2 and L3 resulted in the highest total VFA concentration than other treatments. Protozoa population increased with increasing leucaena in the ration. It is concluded that dairy ration with 60:40 rumen degradable protein to undegradable protein ratio and 20% leucaena can improve ruminal fermentation and digestibility.

Evaluation of river restoration efforts and a sharp decrease in surface runoff for water quality improvement in North China

Rapid urbanization, population growth, and other intensive human activities have greatly altered natural hydrological conditions and matter cycling, which are the main causes of water quality deterioration in North China’s rivers. With the help of a 15-year (2005–2019) dataset of river water quality (1043 records from nine sites), this study investigated the spatiotemporal water quality patterns in the Yongding River Basin (YRB) in North China using a new water quality index (WQI-DET), which has been customized for China’s water quality classification scheme. Our results showed that the river water quality of the YRB has significantly improved due to the decreased surface runoff and an abrupt change of WQI-DET was observed in 2011. The elimination of anoxic conditions and the mitigation of nitrogen and phosphorus resulting from the construction of wastewater treatment plants and the improvement of treatment capacity are the main reasons for the improvement in river water quality. We also found that eutrophication is still not completely eradicated because of the high concentrations of NH4 + and total phosphorus. Our study suggests that for rivers in which runoff has decreased sharply, the water quality could be improved significantly by wastewater treatment facilities. At present, for the YRB, more effort is needed to eliminate eutrophication and dried-up river sections and thereby finally improve the river ecosystem. We concluded that more attention and effort should be given to river hydrological conditions, specific river ecological characteristics, and the increasingly important non-point source pollutants during the design of river restoration measures in North China.

Nitrogen removal performance of anammox immobilized fillers in response to seasonal temperature variations and different operating modes: Substrate utilization and microbial community analysis

Four anaerobic ammonium oxidation (anammox) immobilized filler reactors (R1: 33 °C-normal, R2: seasonal temperature-normal, R3: seasonal temperature-feast, R4: seasonal temperature-starvation) were established to study the response of anammox immobilized fillers to seasonal temperature changes and different operating modes. The results showed that the anammox immobilized filler could better adapt to the seasonal temperature drop and maintain the activity potential by adjusting the hydraulic retention time (HRT). During the temperature rise phase, R2 activity increased rapidly with the highest nitrogen removal rate reaching 1.26 kgN·(m3·d)−1, which was equivalent to control sample R1 (1.33 kgN·(m3·d)−1). However, feasting and famine conditions severely impaired anammox performance and changed stoichiometric ratios; feasting, in particular, significantly lowered the nitrogen removal potential of R3. The specific anammox activity of R2, R3 and R4 was 92.2%, 52.6% and 67.9%, respectively, that of R1, respectively, where the accumulation of functional bacteria was the reason for the higher activity of R2. Degradation kinetics and NO2−-N inhibition curves showed that R3 was less sensitive to high concentrations of NH4+–N, while R4 responded earlier to low concentrations of NH4+–N, and the reduction of IC50 at low temperature was the reason for the inhibition of R3 activity. Furthermore, seasonal temperature fluctuations had little effect on the microbial community structure but had a considerable impact on bacteria abundance. The anammox functional bacteria Candidatus Kuenenia was found to be the dominant genus in R1-R4; however, the relative abundance of most bacteria, including anammox bacteria, decreased in R3, while the proportion of fermentation bacteria and denitrifying bacteria increased in R4. These findings highlight the necessity of rational regulation of HRT for the adaptation of anammox immobilized fillers to seasonal temperature changes, which could enhance our understanding of the synergistic effect of seasonal temperature changes and different operating modes on nitrogen removal.

Dynamic variations of ammonia in various life spaces and seasons and the influences of human activities

Ammonia (NH3) in occupied indoor environments is significantly higher than those outdoors and poses a serious threat to human health. Here we conducted highly time-resolved measurements of NH3 in three occupied academic offices and a gym using cavity ring-down spectroscopy to explore the sources, sinks and dynamic processes of NH3 in indoor environments. The open-close windows, cooking and cleaning experiments were also performed to investigate the effects of human activities on indoor NH3 levels. Our results showed that the NH3 levels in different offices of the same season did not differ a lot, yet the average concentration in fall was much higher than that in winter due to the increased NH3 emission from more skin exposure. The indoor NH3 presented pronounced diurnal variations and the changes in excess NH3 were highly correlated with CO2 and temperature, demonstrating its dominant source of human activities and the influence of temperature. While the enhanced ventilation reduces indoor NH3 levels, we found that the surfaces can act as an important reservoir to control NH3 concentration by gas-surface equilibrium. Cleaning experiments also showed increases in NH3, yet dominantly from the emissions of occupants under high relative humidity and temperature conditions. Cooking of meat-containing protein quickly releases high concentration of NH3 to the indoor environment. Our results demonstrate the significant impacts of human activities on indoor NH3 concentration and dynamic processes. Future measurements across different indoor spaces and in different seasons are needed to better understand the sources, sinks and dynamic variations of indoor NH3.

Overlooked Nonagricultural and Wintertime Agricultural NH3 Emissions in Quzhou County, North China Plain: Evidence from 15N-Stable Isotopes

Ammonia (NH3) plays a critical role in atmospheric chemistry and can exacerbate haze formation. Agricultural emissions have been known as a primary source of global atmospheric NH3. However, with accelerating urbanization and optimized agricultural production, the dominance of agricultural emissions has become less clear. We investigated the contributions of nonagricultural and agricultural sources to atmospheric NH3 based on measurements of NH3 isotopes at nine sites in Quzhou County, a typical agricultural county in the North China Plain. We found that Quzhou had extremely high NH3 concentrations (annual average across all sites of 40.3 ± 3.3 μg m–3). We compared the sources of seasonal NH3 contributions in rural and urban areas through 15N-stable isotope analyses, which provides new insights into NH3 sources compared with the traditional emission inventories. In rural areas, agricultural sources (fertilizer application and livestock production) make significant contributions (56 ± 3%) to NH3 emissions in the winter, whereas there were larger contributions of nonagricultural sources [fossil fuel, waste, and biomass burning (56 ± 2%)] relative to agricultural sources in urban areas. More effective strategies are still needed for better manure management and vegetable/fruit production in the winter and for controlling nonagricultural sources, even in counties dominated by agriculture.

Effect of rumen degradable protein and sulfur supplementation on in vitro digestibility and ruminal fermentation

The availability of nitrogen and sulfur in the rumen should be synchronized to generate microbial protein synthesis. This study aimed to evaluate rumen degradable protein and sulfur supplementation on in vitro digestibility and ruminal fermentation. The experimental design was a 4 x 3 factorial randomized block design. Factor 1 was RDP levels (%CP) (R1= 60%; R2= 55%; R3= 50%; R4= 45%), and factor 2 was sulfur supplementation (S1= 0%; S2= 0.1%; S3= 0.2%). Data were analyzed with ANOVA followed by the Duncan test. The result showed that sulfur supplementation improved DMD and OMD without changes in rumen pH. NH3 concentration was influenced by RDP levels. Treatment R1 had the highest NH3 concentration (7.03 mM). There was an interaction of two factors on total VFA concentration. The combination of R1 and S2 resulted in the highest total VFA concentration than others. The total bacteria population increased with increasing RDP levels. Protozoa population was affected by RDP levels and sulfur supplementation. This study concluded that a combination of 60% RDP and 0.2% sulfur supplementation resulted in the best ration to improve ruminal fermentation and digestibility.

Synergistic solidification/stabilization of electrolytic manganese residue and carbide slag

Electrolytic manganese residue (EMR) contains high concentrations of NH4+ and heavy metals, such as Mn2+, Zn2+, Cu2+, Pb2+, Ni2+ and Co2+, while carbide slag (CS) contains high amount of OH− and CO32−, both posing a serious threat to the ecosystem. In this study, EMR and CS synergistic stabilization/solidification (S/S) was discussed science CS could stabilize or solidify EMR and simultaneously reduce its corrosive. The results showed that after the synergistic S/S for 24 h when liquid-solid ratio was 17.5% and CS dosage was 7%, Mn2+ and NH4+ leaching concentrations of the S/S EMR were below the detection limits (0.02 mg/L and 0.10 mg/L) with a pH value of 8.8, meeting the requirements of the Chinese integrated wastewater discharge standard (GB 8978–1996). Mn2+ was stabilized as MnFe2O4, Mn2SiO4, CaMnSi2O6, and NH4+ escaped as NH3. Zn2+, Cu2+, Pb2+, Ni2+ and Co2+ in EMR can also be stabilized/solidified because of the react with OH− and CO32− in CS. Chemical cost was only $ 0.54 for per ton of EMR synergistic harmless treatment with CS. This study provided a new idea for EMR cost-effective and environment-friendly harmless treatment.

Ammonia assimilation: A double-edged sword influencing denitrification of Rhodobacter azotoformans and for nitrogen removal of aquaculture wastewater

NO3−-N and NH4+-N are two prevalent nitrogenous pollutants in aquaculture wastewater posing a significant health risk to aquatic animals. R. azotoformans ATCC17025 can rapidly denitrify to remove NO3−-N, assimilating NH4+-N. The study investigated the influence of ammonia assimilation on bacterial denitrification. Results revealed that low concentration of NH4+-N (≤0.3 mM) accelerated denitrification, whereas high concentration inhibited it. RT-qPCR indicated that the inhibition of NO reduction under high concentration of NH4+-N was the primary cause of denitrification depression, whereas low concentration of NH4+-N enhanced the synthesis of practically all enzymes involved in denitrification. Finally, nitrogen-rich aquaculture effluent was effectively treated in lab-scale using a semi-continuous operation that provided an appropriate NH4+-N concentration for denitrification. This semi-continuous operation treated wastewater 2 times faster than the batch operation and the content of nitrogen decreased to effluent standard. The study can provide guidance for nitrogen removal of aquaculture wastewater with bioaugmentation.

Evaluation of global EMEP MSC-W (rv4.34) WRF (v3.9.1.1) model surface concentrations and wet deposition of reactive N and S with measurements

Abstract. Atmospheric pollution has many profound effects on human health, ecosystems, and the climate. Of concern are high concentrations and deposition of reactive nitrogen (Nr) species, especially of reduced N (gaseous NH3, particulate NH4+). Atmospheric chemistry and transport models (ACTMs) are crucial to understanding sources and impacts of Nr chemistry and its potential mitigation. Here we undertake the first evaluation of the global version of the EMEP MSC-W ACTM driven by WRF meteorology (1∘×1∘ resolution), with a focus on surface concentrations and wet deposition of N and S species relevant to investigation of atmospheric Nr and secondary inorganic aerosol (SIA). The model–measurement comparison is conducted both spatially and temporally, covering 10 monitoring networks worldwide. Model simulations for 2010 compared use of both HTAP and ECLIPSEE (ECLIPSE annual total with EDGAR monthly profile) emissions inventories; those for 2015 used ECLIPSEE only. Simulations of primary pollutants are somewhat sensitive to the choice of inventory in places where regional differences in primary emissions between the two inventories are apparent (e.g. China) but are much less sensitive for secondary components. For example, the difference in modelled global annual mean surface NH3 concentration using the two 2010 inventories is 18 % (HTAP: 0.26 µg m−3; ECLIPSEE: 0.31 µg m−3) but is only 3.5 % for NH4+ (HTAP: 0.316 µg m−3; ECLIPSEE: 0.305 µg m−3). Comparisons of 2010 and 2015 surface concentrations between the model and measurements demonstrate that the model captures the overall spatial and seasonal variations well for the major inorganic pollutants NH3, NO2, SO2, HNO3, NH4+, NO3-, and SO42- and their wet deposition in East Asia, Southeast Asia, Europe, and North America. The model shows better correlations with annual average measurements for networks in Southeast Asia (mean R for seven species: R7‾=0.73), Europe (R7‾=0.67), and North America (R7‾=0.63) than in East Asia (R5‾=0.35) (data for 2015), which suggests potential issues with the measurements in the latter network. Temporally, both model and measurements agree on higher NH3 concentrations in spring and summer and lower concentrations in winter. The model slightly underestimates annual total precipitation measurements (by 13 %–45 %) but agrees well with the spatial variations in precipitation in all four world regions (0.65–0.94 R range). High correlations between measured and modelled NH4+ precipitation concentrations are also observed in all regions except East Asia. For annual total wet deposition of reduced N, the greatest consistency is in North America (0.75–0.82 R range), followed by Southeast Asia (R=0.68) and Europe (R=0.61). Model–measurement bias varies between species in different networks; for example, bias for NH4+ and NO3- is largest in Europe and North America and smallest in East Asia and Southeast Asia. The greater uniformity in spatial correlations than in biases suggests that the major driver of model–measurement discrepancies (aside from differing spatial representativeness and uncertainties and biases in measurements) are shortcomings in absolute emissions rather than in modelling the atmospheric processes. The comprehensive evaluations presented in this study support the application of this model framework for global analysis of current and potential future budgets and deposition of Nr and SIA.

Nitrate alleviates ammonium toxicity in wheat (Triticum aestivum L.) by regulating tricarboxylic acid cycle and reducing rhizospheric acidification and oxidative damage

ABSTRACT Ammonium (NH4 +) is one of the most important nutrients required by plants. However, a high concentration of NH4 + as the sole nitrogen source suppresses plant growth. Although nitrate (NO3 −) can alleviate NH4 + toxicity, the mechanisms underlying this ability have not been fully elucidated. In this study, wheat plants were cultivated in hydroponic solution with 7.5 mM NO3 − (control), 7.5 mM NH4 + (sole ammonium, SA) or 7.5 mM NH4 + plus 1.0 mM NO3 − (ammonium and nitrate, AN). The results showed that compared with the control, the SA treatment significantly decreased root growth, protein content and the concentrations of most intermediates and the activity of enzymes from the tricarboxylic acid (TCA) cycle. Moreover, increased the activity of plasma membrane H+-ATPase and the rate of H+ efflux along roots, caused solution acidification, and increased the activity of mitochondrial respiratory chain complexes I–IV and the contents of protein-bound carbonyls and malondialdehyde in roots. SA treatment induced ultrastructure disruption and reduced the viability of root cells. Compared with the SA treatment, the AN treatment increased root growth, protein content, the concentrations of most intermediates and the activity of enzymes from the TCA cycle. Furthermore, AN treatment decreased the rate of H+ efflux, retarded medium acidification, decreased protein carbonylation and lipid peroxidation in roots and relieved ultrastructure disruption and increased the viability of root cells. Taken together, these results indicate that NO3 –-dependent alleviation of NH4 + toxicity in wheat seedlings is closely associated with physiological processes that mediate TCA cycle, relieve rhizospheric acidification and decrease the production of ROS and oxidative damage.

Rumen metabolic activities of cacao (Theobroma cacao L.) pod husk fermented with lingzhi mushroom (Ganoderma lucidum) at different concentration and incubation time

Cacao pod husk is a potential tropical resources that is widely utilized as animal feed. The presented study aimed to investigate rumen metabolic activities of (Theobroma cacao L.) pod husk fermented with lingzhi mushroom (Ganoderma lucidum) at different concentration and incubation time. A completely randomized factorial was applied in this study consisting of two factors; lingzhi mushroom concentration (K1 = 7.5%; K2 = 15%) and incubation time (L1 = 15 d; L2 =30 d; L3 = 45 d) with 3 replicates. All samples of cacao pod husk were analyzed to determine NH3 concentration, volatile fatty acid (VFA) concentration and gas production. Gas production was periodically collected at 2, 4, 6, 8, 10,12, 24, 48 and 72 h after incubation. The result of study indicated that there was significant interaction (P<0.01) between the concentration of G.lucidum and incubation time on NH3 concentration of rumen liquid. The highest concentration of NH3 was found at 7.5% G.lucidum concentration for 45 d incubation (14.70mM). G.lucidum concentration significantly affected (P<0.01) VFA concentration in which samples inoculated with the level of 7.5% G.lucidum was higher compared to that of 15% G.lucidum (125.16 mM vs 113.94 mM). This study concluded that cacao pod husk fermented with lingzhi mushroom at different concentration time influencing metabolic activities of the rumen.

Blueberry Yield and Soil Mineral Nitrogen Response to Nitrogen Fertilizer and Nitrification Inhibitors under Drip-Fertigation Systems

In blueberry plantings, nitrification can result in losses of mineral nitrogen (N) through leaching because blueberries prefer ammonium (NH4+) over nitrate (NO3−). The objective of this study was to assess the effects of two rates of N fertilizer, mixed or not with nitrification inhibitors (NI) and applied through two fertigation systems, on berry yield and the concentrations of NH4+-N and NO3−-N along the soil profile. Thus, nine combinations of treatments including two N fertilizer rates (60 and 120 kg N ha−1), two NI (with DCD + Nitra-pyrin or without) and two fertigation application methods (buried and suspended drip lines) and a control (0 kg N ha−1) were tested over three years (2016–2018) in a long-term blueberry planting. Berry yield was on average 47.32 Mg ha−1 in 2016 and 26.86 Mg ha−1 in 2018. In 2017, berry yield varied between 8.60 Mg ha−1 under the control and 11.66 Mg ha−1 with 120 kg N ha−1 applied through suspended drip lines. Low berry yield in 2017 was due to a heavy pruning to rejuvenate the plants. In 2016, the concentration of NH4+-N in the sawdust mulch layer varied between 13.1 and 27.1 mg kg−1 in the spring, 11.4 and 32.1 mg kg−1 in the summer, and 7.9 and 72.9 mg kg−1 in the fall; the concentration of high NH4+-N along the soil profile did not exceed 5 mg kg−1. High concentrations of NH4+-N in the sawdust mulch layer were associated with NI, but did not translate to high berry yields. The concentration of NO3−-N in the soil profile reached 42.6 mg kg−1 in the summer and 39.0 mg kg−1 in the fall and these high concentrations were associated with NI. In 2017 and 2018, there was no effect of NI on NH4+-N concentrations even in the layer of sawdust mulch which was not consistent with the results obtained in 2016. High concentrations of NO3−-N were measured beneath the sawdust mulch layer with treatments including N fertilizer alone or mixed with NI. It is possible that NH4+ retained in the layer of sawdust mulch and not taken up by plant roots was subsequently oxidized to NO3− at the end of the residence time of NI in the soil. Our results showed that high concentrations of NO3−-N along the soil profile occurred mainly during the summer which could be explained by irrigation water driving NO3− leaching.

Effects of ammonium concentration in the catholyte on electricity and algal biomass generation in a photosynthetic microbial fuel cell treating wastewater

In this study, algal cathodic compartments were integrated to generate oxygen in microbial fuel cells. Chlorella vulgaris and Scenedesmus quadricauda were grown under three NH4+–N concentrations (50, 300, and 900 mg L−1) in the catholyte. With 50 mg L−1 of NH4+–N, the highest maximum power densities of 16.72 and 5.96 mW m−2 were obtained with Chlorella vulgaris and Scenedesmus quadricauda, respectively. Under this condition, dissolved oxygen reached 19.27 and 9.87 mg L−1 for Chlorella vulgaris and Scenedesmus quadricauda respectively, along with 100% removal of NH4+–N within 210 h. Both cultures showed inhibition under higher concentrations of NH4+–N, resulting in decreased photoautotrophic growth that generates oxygen for the cathodic reaction. Under all concentrations, Chlorella vulgaris displayed better tolerance to ammonium. From the results, it can be summarized that 50 mg L−1 of NH4+–N in wastewater is suitable as a microalgal cultivation medium in a cathodic compartment.