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Anammox has received increased attention due to its enhanced and cost-efficient approach to nitrogen removal. However, its practical application is complicated by strict influent NO 2 - -N ratio demands and an 11% nitrate production from the anammox process. This study was the first known research to propose and verify a system of zeolite integrated with partial denitrification and anammox (Z-PDA) in an up-flow anaerobic sludge bed (UASB) reactor. The enhanced and robust nitrogen removal resulted in an ultra-high nitrogen removal efficiency (NRE, 93.0 ± 2.0%). Zeolite adsorption and biological desorption of ammonium contributed to robust nitrogen removal with fluctuating influent NO 4 + -N ratios. Applying 16S rRNA gene sequencing found that Candidatus Brocadia and Thauera were the key bacteria responsible for anammox and partial denitrification (PD), respectively. Zeolite also acted as a biological carrier. This significantly enriched anammox bacteria with a higher relative abundance of Candidatus Brocadia, reaching 49.2%. Metagenomic analysis demonstrated that the multiple functional genes related to nitrogen removal (nrfA/H, narG/H/I) and the metabolic pathways (Biosynthesis of cofactors, the Two-component system, the Biosynthesis of nucleotide sugars, and Purine metabolism) ensured the resilience of the Z-PDA system despite influent fluctuations. Overall, this study provided novel insights into the impacts of zeolite in the PDA system. It described the fundamental mechanism of zeolite based on adsorption and biological desorption, and demonstrated a meaningful application of the anammox process in sewage treatment.2 - -N to NH 4 + -N ratios. Applying 16S rRNA gene sequencing found that Candidatus Brocadia and Thauera were the key bacteria responsible for anammox and partial denitrification (PD), respectively. Zeolite also acted as a biological carrier. This significantly enriched anammox bacteria with a higher relative abundance of Candidatus Brocadia, reaching 49.2%. Metagenomic analysis demonstrated that the multiple functional genes related to nitrogen removal (nrfA/H, narG/H/I) and the metabolic pathways (Biosynthesis of cofactors, the Two-component system, the Biosynthesis of nucleotide sugars, and Purine metabolism) ensured the resilience of the Z-PDA system despite influent fluctuations. Overall, this study provided novel insights into the impacts of zeolite in the PDA system. It described the fundamental mechanism of zeolite based on adsorption and biological desorption, and demonstrated a meaningful application of the anammox process in sewage treatment., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Nitrogen is an essential nutrient in the environment that exists in multiple oxidation states in nature. Numerous microbial processes are involved in its transformation. Knowledge about very complex N cycling has been growing rapidly in recent years, with new information about associated isotope effects and about the microbes involved in particular processes. Furthermore, molecular methods that are able to detect and quantify particular processes are being developed, applied and combined with other analytical approaches, which opens up new opportunities to enhance understanding of nitrogen transformation pathways. This review presents a summary of the microbial nitrogen transformation, including the respective isotope effects of nitrogen and oxygen on different nitrogen-bearing compounds (including nitrates, nitrites, ammonia and nitrous oxide), and the microbiological characteristics of these processes. It is supplemented by an overview of molecular methods applied for detecting and quantifying the activity of particular enzymes involved in N transformation pathways. This summary should help in the planning and interpretation of complex research studies applying isotope analyses of different N compounds and combining microbiological and isotopic methods in tracking complex N cycling, and in the integration of these results in modelling approaches., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Dominika Lewicka-Szczebak reports financial support was provided by Polish National Agency for Academic Exchange. Dominika Lewicka-Szczebak reports financial support was provided by National Science Centre Poland. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

The California current system (CCS) hosts one of the largest oxygen minimum zones (OMZs) in the world: the Eastern North Pacific (ENP) OMZ, which is dissociated into a subtropical and tropical region (i.e., the ESTNP and ETNP). In the modern ENP OMZ, bioavailable nitrogen (N) is lost via denitrification and anaerobic ammonium oxidation (anammox). Even so, paleo-reconstructions of N-loss have focused solely on denitrification. Fluctuations in bulk sedimentary δ15N over glacial-interglacial cycles have been interpreted to reflect variations in denitrification rates in response to ETNP OMZ intensity changes. This δ15N signal is thought to be transported northwards to the ESTNP OMZ. Here, we present the first CCS sedimentary record of ladderane lipids, biomarkers for anammox, located within the ESTNP OMZ (32° N; 118° W). Over the last two glacial terminations (~160 cal ka BP), ladderane concentrations were analysed in combination with the index of ladderanes with five cyclobutane moieties (NL5), short-chain (SC) ladderane degradation products, and productivity proxies. This shows that: 1) ladderanes derived from anammox bacteria living within the ESTNP OMZ water column; 2) ladderanes were continuously present, with relatively high concentrations during both glacial- and interglacial-periods, showcasing the ESTNP OMZ must have retained an anoxic core in which N-loss occurred; and 3) anammox abundance appears to have been driven both by OM-remineralization and advection changes, which regulated nutrient and oxygen levels. Our study shows that anammox was an important feature in the CCS and provides a more holistic picture of N-loss dynamics and the development of the ESTNP OMZ over glacial-interglacial cycles. Lastly, ladderanes were also detected in 160–500 cal ka BP sediments (15.7–37.5 mbsf; analysed at a low temporal resolution), highlighting their potential as anammox biomarkers in relatively deeper buried sediments for future studies. [ABSTRACT FROM AUTHOR]

The California current system (CCS) hosts one of the largest oxygen minimum zones (OMZs) in the world: the Eastern North Pacific (ENP) OMZ, which is dissociated into a subtropical and tropical region (i.e., the ESTNP and ETNP). In the modern ENP OMZ, bioavailable nitrogen (N) is lost via denitrification and anaerobic ammonium oxidation (anammox). Even so, paleo-reconstructions of N-loss have focused solely on denitrification. Fluctuations in bulk sedimentary δ15N over glacial-interglacial cycles have been interpreted to reflect variations in denitrification rates in response to ETNP OMZ intensity changes. This δ15N signal is thought to be transported northwards to the ESTNP OMZ. Here, we present the first CCS sedimentary record of ladderane lipids, biomarkers for anammox, located within the ESTNP OMZ (32°N; 118°W). Over the last two glacial terminations (~160 cal ka BP), ladderane concentrations were analysed in combination with the index of ladderanes with five cyclobutane moieties (NL5), short-chain (SC) ladderane degradation products, and productivity proxies. This shows that: 1) ladderanes derived from anammox bacteria living within the ESTNP OMZ water column; 2) ladderanes were continuously present, with relatively high concentrations during both glacial- and interglacial-periods, showcasing the ESTNP OMZ must have retained an anoxic core in which N-loss occurred; and 3) anammox abundance appears to have been driven both by OM-remineralization and advection changes, which regulated nutrient and oxygen levels. Our study shows that anammox was an important feature in the CCS and provides a more holistic picture of N-loss dynamics and the development of the ESTNP OMZ over glacial-interglacial cycles. Lastly, ladderanes were also detected in 160-500 cal ka BP sediments (15.7-37.5 mbsf; analysed at a low temporal resolution), highlighting their potential as anammox biomarkers in relatively deeper buried sediments for future studies. [ABSTRACT FROM AUTHOR]

Anaerobic ammonium oxidation (anammox) has shown success in past years for the treatment of municipal and industrial wastewater containing inorganic nutrients (i.e., nitrogen). However, the increase in polycyclic aromatic hydrocarbon (PAH)-contaminated matrices calls for new strategies for efficient and environmentally sustainable remediation. Therefore, the present review examined the literature on the connection between the anammox process and PAHs using VOSviewer to shed light on the mechanisms involved during PAH biodegradation and the key factors affecting anammox bacteria. The scientific literature thoroughly discussed here shows that PAHs can be involved in nitrogen removal by acting as electron donors, and their presence does not adversely affect the anammox bacteria. Anammox activity can be improved by regulating the operating parameters (e.g., organic load, dissolved oxygen, carbon-to-nitrogen ratio) and external supplementation (i.e., calcium nitrate) that promote changes in the microbial community (e.g., Candidatus Jettenia), favoring PAH degradation. The onset of a synergistic dissimilatory nitrate reduction to ammonium and partial denitrification can be beneficial for PAH and nitrogen removal. [ABSTRACT FROM AUTHOR]

Realizing the smallest nitrogen loss is a challenge in the nitrate reduction process. Dissimilatory nitrate reduction to ammonium (DNRA) and nitrate assimilation play crucial roles in nitrogen retention. In this study, the effects of the carbon source, C/N ratio, pH, and dissolved oxygen on the multiple nitrate reduction pathways conducted by Pseudomonas putida Y-9 are explored. Strain Y-9 efficiently removed nitrate (up to 89.79%) with glucose as the sole carbon source, and the nitrogen loss in this system was 15.43%. The total nitrogen decrease and ammonium accumulation at a C/N ratio of 9 were lower than that at 12 and higher than that at 15, respectively (P < 0.05). Besides, neutral and alkaline conditions (pH 7–9) favored nitrate reduction. Largest nitrate removal (81.78%) and minimum nitrogen loss (10.63%) were observed at pH 7. The nitrate removal and ammonium production efficiencies of strain Y-9 increased due to an increased shaking speed. The expression patterns of nirBD (the gene that controls nitrate assimilation and DNRA) in strain Y-9 were similar to ammonium patterns of the tested incubation conditions. In summary, the following conditions facilitated nitrate assimilation and DNRA by strain Y-9, while reducing the denitrification: glucose as the carbon source, a C/N ratio of 9, a pH of 7, and a shaking speed of 150 rpm. Under these conditions, nitrate removal was substantial, and nitrogen loss from the system was minimal. [ABSTRACT FROM AUTHOR]

A new bacterium capable of heterotrophic nitrogen removal was isolated and identified as Oligella sp. XS68. The strain exhibited efficient heterotrophic nitrogen removal capabilities, with a low accumulation of nitrification products. Single-factor experiments indicated that efficient nitrogen removal and growth of the strain XS68 occurred with sodium succinate as the carbon source, C/N ratio 15, pH 6.0-9.0, temperature 30-37 °C, and shaking speed 160-200 rpm. The removal efficiency of ammonium nitrogen could achieve 98 % within 96 h when the initial nitrogen concentration was 421.3 mg L-1. These findings demonstrate that XS68 is a promising candidate for nitrogen removal in wastewater treatments. [ABSTRACT FROM AUTHOR]

Anaerobic ammonium oxidation (anammox), a promising technology for bio-nitrogen removal, has been a research hotspot in the field of leachate treatment. However, the inhibitory effect of organic matter and high-strength nitrogen on anammox bacteria and the limitation of the theoretical total nitrogen removal efficiency of anammox (<90%) are obstacles to its wider application. The mechanisms of the inhibitory effects of organic matter, ammonium, and nitrite on anammox bacteria, and the corresponding control strategies are summaries. The anammox-based processes developed for advanced nitrogen removal (ANR) in recent years, including anammox-based heterotrophic denitrification, anammox-based partial denitrification, and anammox-based constructed wetlands are systematically discussed. An integrated anaerobic system of simultaneous denitrification and methanogenesis (anaerobic membrane bioreactor) + anammox-based processes was proposed for the ANR and optimal energy recovery from leachate. This process showed a 16% increase in biogas yield, a 64% decrease in aeration energy consumption, and the decrease in the external carbon source is expected to be 100% compared to conventional leachate treatment processes such as anoxic/oxic-membrane bioreactors. Finally, a few research perspectives on leachate treatment using anammox-based processes are reviewed. The conclusions drawn from the studies presented herein provide guidance for further research and engineering applications in the field of leachate treatment. AnMBR pretreatment is proposed for energy recovery and elimination of inhibition of anammox bacteria by organics. Anammox-based heterotrophic denitrification, partial denitrification, and anammox-based constructed wetlands are discussed for ANR. SDM is proposed for ANR from leachate via anammox effluent recirculation. An SDM(AnMBR)+anammox based process is proposed for energy saving and recovery. [ABSTRACT FROM AUTHOR]

• Denitrification alone does not govern N removal in woodchip and coconut husk bioreactors. • Substantial N removal can be achieved via the anammox pathway. • Relative contributions of denitrification and anammox vary between media types used. • Anammox becomes more dominant when denitrification is carbon limited. Denitrification has been considered the main pathway converting nitrate (NO 3 –) to dinitrogen gas (N 2) in denitrifying bioreactors. Here, the importance of an alternative nitrogen (N) removal process, namely anaerobic ammonium oxidation (anammox), was assessed by monitoring the removal of N species from partially nitrified municipal wastewater passing through fifteen mesocosm scale (∼700 L) bioreactors containing woodchip, coconut husk or gravel during their initial and eighth year of operation. Additionally, lab experiments using a 15N isotope-pairing technique were performed to partition production of N 2 to these different microbial processes. The effective removal of both NO 3 – and ammonium (NH 4 +) and the formation of hybrid N 2 (i.e. 29N 2) observed in this study demonstrated that, along with denitrification, anammox was an effective pathway for N removal when both NO 3 – and NH 4 + were present. Anammox removal rates ranged from 0.6 to 3.8 g N per m3 per day, while denitrification rates ranged from 0.7 to 2.6 g N per m3 per day. The contributions of anammox to N removal was dependent on media, with anammox becoming more dominant in bioreactors where denitrification was carbon limited. Designing denitrifying bioreactors to support both denitrification and anammox expands the utility of these passive approaches for improving treatment of wastewater. [ABSTRACT FROM AUTHOR]

Thiocyanate (SCN−)-based autotrophic denitrification (AD) has recently been demonstrated as a promising technology that could be integrated with anaerobic ammonium oxidation (Anammox) to achieve simultaneous removal of nitrogen and SCN−. However, there is still a lack of a complete SCN−-based AD model, and the potential microbial competition/synergy between AD bacteria and Anammox bacteria under different operating conditions remains unknown, which significantly hinders the possible application of coupling SCN−-based AD with Anammox. To this end, a complete SCN−-based AD model was firstly developed and reliably calibrated/validated using experimental datasets. The obtained SCN−-based AD model was then integrated with the well-established Anammox model and satisfactorily verified with experimental data from a system coupling AD with Anammox. The integrated model was lastly applied to investigate the impacts of influent NH 4 +-N/NO 2 −-N ratio and SCN− concentration on the steady-state microbial composition as well as the removal of nitrogen and SCN−. The results showed that the NH 4 +-N/NO 2 −-N ratio in the presence of a certain SCN− level should be controlled at a proper value so that the maximum synergy between AD bacteria and Anammox bacteria could be achieved while their competition for NO 2 − would be minimized. For the simultaneous maximum removal (>95%) of nitrogen and SCN−, there existed a negative relationship between the influent SCN− concentration and the optimal NH 4 +-N/NO 2 −-N ratio needed. Image 1 • A complete thiocyanate-based autotrophic denitrification (AD) model was developed. • Thiocyanate-based AD model was evaluated with integration of Anammox model. • Relationship between thiocyanate and NH 4 +-N/NO 2 −-N for maximum removal was studied. High-level (>95%) simultaneous removal of nitrogen and thiocyanate could be achieved through combining thiocyanate-based autotrophic denitrification and Anammox. [ABSTRACT FROM AUTHOR]

A dynamic analysis approach for determining nitrite production and consumption rates was established to systematically investigate the characteristics of nitrogen transformation and N 2 O emission of the completely autotrophic nitrogen removal over nitrite (CANON) process coupled with denitrification using a sequencing batch biofilm reactor (SBBR). The results indicate that anaerobic ammonium-oxidizing bacteria was not inhibited significantly by low C/N ratios. There were no obvious differences in the nitrite production rate, nitrite consumption rate or nitrogen removal among reactors operated with C/N ratios of 0, 0.67 and 1.00, which suggested that the certain carbon source did not significantly affect the nitrite conversion and nitrogen removal in the process. More than 60% of total N 2 O emission is generated during the initial phase of each period in the SBBR. More than 94.5% of N 2 O was generated by NO 2 −-N consumption via denitrification in the process. Interestingly, total N 2 O production drops by 16.7%, when the C/N ratio increases from 0 to 1. This phenomenon may be caused by the inhibition of N 2 O production via AOB denitrification. Therefore, an appropriate carbon source (C/N = 1.00) has the beneficial effect of reducing N 2 O emission by CANON coupled with denitrification. The results of this study provide an important empirical foundation for the mitigation of N 2 O emission in the CANON process coupled with denitrification. Image 1 • N conversion and N 2 O emission were investigated in a CANON coupled with DN process. • AOB and AnAOB were not inhibited significantly by low C/N ratios. • Low C/N ratios did not evidently affect nitrite conversion and nitrogen removal. • More than 94.5% of N 2 O was generated by NO 2 −-N consumption via denitrification. • The C/N ratio should be maintained at 1.00 for the N 2 O emission reduction. [ABSTRACT FROM AUTHOR]

• Both SMX and N-SMX exposure inhibited denitrification and DNRA rates in a short time. • Denitrification and DNRA rates recovered under SMX/N-SMX exposure in a long time. • The removal of nitrogen, SMX, and N-SMX can be achieved simultaneously. • Nitrogen-reducing bacteria that also degrade antibiotics were detected. Constructed wetlands (CWs) are increasingly used to treat complex pollution such as nitrogen and emerging organic micropollutants from anthropogenic sources. In this study, the denitrification, anaerobic ammonium oxidation, dissimilatory nitrate reduction to ammonium, and nitrous oxide release rates following exposure to the frequently detected sulfonamides sulfamethoxazole (SMX) and its human metabolite, N-acetylsulfamethoxazole (N-SMX), were investigated in lab-scale CWs. Over a period of 190 d, the denitrification rates were noticeably inhibited in the SMX and N-SMX groups at week 5. Subsequently, the denitrification rates recovered, accompanied by an increase in the relevant nitrogen reduction and antibiotic resistance genes (ARGs). The composition of the microbial community also changed during this process. After the denitrification rates recovered, Burkholderia _ Paraburkholderia and Gordonia exhibited a significant positive correlation with SMX exposure, which simultaneously reduced nitrate concentrations and degraded antibiotics. Burkholderia _ Paraburkholderia is a key carrier of ARGs. Finally, nitrogen reduction (> 90%) and antibiotic removal (> 80%) also recovered in both SMX- and N-SMX-exposed lab-scale CWs during the operation, which revealed the interaction of SMX or N-SMX removal and nitrogen reduction. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Isolated a bacterial consortium to enable P recovery. • Nitrate is participate in phosphorus bio-recovery process. • Different N species has little influence on the characteristics of products. • Acinetobacter genus dominates phosphorus recovery in different nitrogen species. Recovering finite and non-substitutable phosphorus from liquid waste streams through bio-mediated techniques has attracted increasing interest, but current approaches are incredibly dependent on ammonium. Herein, a process to recover phosphorus from wastewater under multiple nitrogen species conditions was developed. This study compared the effects of nitrogen species on the recovery of phosphorus resources by a bacterial consortium. It found that the consortium could not only efficiently utilize ammonium to enable phosphorus recovery but also utilize nitrate via dissimilatory nitrate reduction to ammonium (DNRA) to recover phosphorus. The characteristics of the generated phosphorus-bearing minerals, including magnesium phosphate and struvite, were evaluated. Furthermore, nitrogen loading positively influenced the stability of the bacterial community structure. The genus Acinetobacter was dominant under nitrate and ammonium conditions, with a relatively stable abundance of 89.01% and 88.54%, respectively. The finding may provide new insights into nutrient biorecovery from phosphorus-containing wastewater contaminated with multiple nitrogen species. [ABSTRACT FROM AUTHOR]

Dissimilatory nitrate reduction to ammonium (DNRA), denitrification, anaerobic ammonium oxidation (anammox) and biological N2 fixation (BNF) can influence the nitrogen (N) use efficiency of rice production. Whilst the effect of N application on BNF is known, little is known about its effect on NO3 - partitioning between DNRA, denitrification and anammox. Here, we investigated the effect of N application on DNRA, denitrification, anammox and BNF, and on the abundance of relevant genes in three paddy soils in Australia. Rice was grown in the glasshouse with (150 kg N ha-1 ) and without N-fertiliser for 75 days, and the rhizosphere and bulk soils were collected separately for laboratory incubation and quantitative PCR analysis. Nitrogen application reduced DNRA rates by >16% in all the soils regardless of the rhizospheric zone but it did not affect the nrfA gene abundance. Without N, the amount and proportion of NO3 - reduced by DNRA (0.42-0.52 µg g-1 soil day-1 , 45-55%) was similar or higher than that by denitrification. However, with N the amount of NO3 - reduced by DNRA (0.32-0.40 µg g-1 soil day-1 ) was 40-50% lower than the NO3 - reduced by denitrification. Denitrification loss increased by >20% with N addition, and was affected by the rhizospheric zones. Nitrogen loss was minimal through anammox, while BNF added 0.02-0.25 µg N g-1 soil day-1. We found that DNRA plays significant positive role in paddy soil N retention as it accounts for up to 55% of the total NO3 - reduction, but this is reduced by N application. [ABSTRACT FROM AUTHOR]

The fate of the enormous amount of reactive nitrogen released to the environment by human activities in India is unknown. Here we show occurrence of seasonal stratification and generally low concentrations of dissolved inorganic combined nitrogen, and high molecular nitrogen (N2) to argon ratio, thus suggesting seasonal loss to N2 in anoxic hypolimnia of several dam-reservoirs. However, 15N-experiments yielded low rates of denitrification, anaerobic ammonium oxidation and dissimilatory nitrate reduction to ammonium--except in the presence of methane (CH4) that caused ~12-fold increase in denitrification. While nitrite-dependent anaerobic methanotrophs belonging to the NC10 phylum were present, previously considered aerobic methanotrophs were far more abundant (up to 13.9%) in anoxic hypolimnion. Methane accumulation in anoxic freshwater systems seems to facilitate rapid loss of reactive nitrogen, with generally low production of nitrous oxide (N2O), through widespread coupling between methanotrophy and denitrification, potentially mitigating eutrophication and emissions of CH4 and N2O to the atmosphere. [ABSTRACT FROM AUTHOR]

Abstract: BACKGROUND: High SO42‐, COD, and nitrogen‐containing wastewater treatment requires different bacterial groups and environmental conditions, which can be achieved by sequential separate processes. This study examined the simultaneous removal of SO42‐, COD and nitrogen in a four‐compartment ABR, which allowed enrichment of different group of bacteria in each compartment. Feed COD and SO42‐ concentrations were kept constant at 1200 and 1500 mg L‐1, corresponding to COD/SO4‐2 ratio of 0.8. Initially, ABR was tested at varying influent ammonium concentrations (25–1500 mg NH4+‐N/L). Further, the third compartment of ABR was supplemented with nitrate under varying loading rates (60–300 mgNO3‐N L‐1 d‐1) for autotrophic denitrification with the sulfide produced in the previous compartments. This kind of application mimicked the internal recirculation of nitrate, which can be generated via nitrification of ABR effluent. RESULTS: High sulfate reduction efficiencies (over 86%) were observed up to 1000 mg L‐1 NH4+‐N, however, 1500 mg L‐1 NH4+‐N caused decrease in reduction efficiency. Optimum nitrate loading rate was determined as 146 mgNO3‐N L‐1 d‐1 at molar N/S ratio of 0.42, corresponding with 100% nitrate, 83% sulfate, and 79% COD removals. Nitrate removal decreased at higher nitrate loadings and high sulfate generation arising from sulfide oxidation was observed. CONCLUSION: Sulfate and COD removals together with efficient sulfide‐based autotrophic denitrification succeeded in a single reactor configuration at S/N ratio of 0.42. The developed process has the potential to be used in lab‐scale applications. © 2017 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

The availability of nitrogen (N) can alter vegetation species composition and diversity in degraded ecosystems. A comprehensive understanding of the dynamic fate of ammonium (NH 4 + -N) and nitrate (NO 3 − -N) processing and the underlying mechanisms are still lacking, particularly in arid to semi-arid degraded ecosystems. We compared and quantified the changes in the rates of net ammonification (R a ), nitrification (R n ) and total mineralization (R m ) and the abundance of bacteria, archaea, and microbial genes related to N transformation on the northern Loess Plateau of China across a 40-year chronosequence of farmland undergoing spontaneous restoration. We found that R a , R n , and R m decreased in grassland soils (0–30-y sites) of different ages and exhibited significant increases at the 40-y sites. The capabilities of the soil to deliver NH 4 + -N and NO 3 − -N were not a limiting factor during the growing season after 40 years of vegetation recovery. Soil mineral nitrogen may be not suitable for predicting and assessing the long-term (approximately 40 years) restoration success and progress. The abundance of functional N genes showed differences in sensitivity to natural vegetation recovery of abandoned farmland, which likely reflects the fact that the multi-pathways driven by N functional microbial communities had a large influence on the dynamic fate of NH 4 + -N and NO 3 − -N. Quantitative response relationships between net N transformation rates and microbial genes related to N transformation were established, and these relationships confirmed that different N transformation processes were strongly linked with certain N functional genes, and collaboratively contributed to N transformation as vegetation recovery progressed. Specifically, R a was controlled by AOA- amoA , AOB- amoA , and nxrA ; R n was governed by napA , narG , nirK , nirS , and nosZ ; and R m was controlled by nifH , apr , AOA- amoA , AOB- amoA , nirS , and nirK . [ABSTRACT FROM AUTHOR]

Mechanisms through which microorganisms are impacted by surface application of ground cover and nutrient source in organic orchard management are not fully understood. Twelve ground cover (compost, wood chips, paper mulch, or mow-and-blow) by fertilizer (poultry litter, organic commercial, or a no-fertilizer control) treatment combinations were applied annually in April beginning in 2006, with soil collected in March 2007 and 2013 to determine the 1-year and 7-year effects of treatments on soil chemical and biological properties. Organic matter (OM) increased through time regardless of ground cover treatment averaged across fertilizers, with the greatest increase occurring with compost addition. Soil water content, microbial biomass N, ammonium-N, and nitrate-N were greater in 2013 than in 2007 at the 0–10 cm depth. Denaturing gradient gel electrophoresis analysis of denitrifying ( nirK) communities revealed that fertilizers did not have a significant main effect or interaction with ground covers. Greater nirK richness and diversity coincided with clustering of the nirK community composition within compost treatments, and greater dissolved organic carbon concentrations with compost compared to wood chip or mow-and-blow treatments in 2007. By 2013 nirK communities in wood chip and compost ground covers tended to cluster together. Furthermore, soil nirK richness increased significantly from 2007 to 2013 in compost and wood chip treatments and was greatest in 2013 under those two ground covers. Diversity with wood chip addition increased from among the least in 2007 to among the greatest in 2013. Greater richness and diversity and community composition in the nirK community within a year of compost additions and gradually over time with wood chip addition indicate potential for enhanced denitrification in low OM, organic apple orchard soil receiving compost and wood chips mulches. [ABSTRACT FROM AUTHOR]

Salinity intrusion caused by land subsidence resulting from increasing groundwater abstraction, decreasing river sediment loads and increasing sea level because of climate change has caused widespread soil salinization in coastal ecosystems. Soil salinization may greatly alter nitrogen (N) cycling in coastal ecosystems. However, a comprehensive understanding of the effects of soil salinization on ecosystem N pools, cycling processes and fluxes is not available for coastal ecosystems. Therefore, we compiled data from 551 observations from 21 peer-reviewed papers and conducted a meta-analysis of experimental soil salinization effects on 19 variables related to N pools, cycling processes and fluxes in coastal ecosystems. Our results showed that the effects of soil salinization varied across different ecosystem types and salinity levels. Soil salinization increased plant N content (18%), soil NH4+ (12%) and soil total N (210%), although it decreased soil NO3− (2%) and soil microbial biomass N (74%). Increasing soil salinity stimulated soil N2O fluxes as well as hydrological NH4+ and NO2− fluxes more than threefold, although it decreased the hydrological dissolved organic nitrogen ( DON) flux (59%). Soil salinization also increased the net N mineralization by 70%, although salinization effects were not observed on the net nitrification, denitrification and dissimilatory nitrate reduction to ammonium in this meta-analysis. Overall, this meta-analysis improves our understanding of the responses of ecosystem N cycling to soil salinization, identifies knowledge gaps and highlights the urgent need for studies on the effects of soil salinization on coastal agro-ecosystem and microbial N immobilization. Additional increases in knowledge are critical for designing sustainable adaptation measures to the predicted intrusion of salinity intrusion so that the productivity of coastal agro-ecosystems can be maintained or improved and the N losses and pollution of the natural environment can be minimized. [ABSTRACT FROM AUTHOR]

Removal of biologically available nitrogen (N) by the microbially mediated processes denitrification and anaerobic ammonium oxidation (anammox) affects ecosystem N availability. Although few studies have examined temperature responses of denitrification and anammox, previous work suggests that denitrification could become more important than anammox in response to climate warming. To test this hypothesis, we determined whether temperature responses of denitrification and anammox differed in shelf and estuarine sediments from coastal Rhode Island over a seasonal cycle. The influence of temperature and organic C availability was further assessed in a 12-week laboratory microcosm experiment. Temperature responses, as characterized by thermal optima ( Topt) and apparent activation energy ( Ea), were determined by measuring potential rates of denitrification and anammox at 31 discrete temperatures ranging from 3 to 59 °C. With a few exceptions, Topt and Ea of denitrification and anammox did not differ in Rhode Island sediments over the seasonal cycle. In microcosm sediments, Ea was somewhat lower for anammox compared to denitrification across all treatments. However, Topt did not differ between processes, and neither Ea nor Topt changed with warming or carbon addition. Thus, the two processes behaved similarly in terms of temperature responses, and these responses were not influenced by warming. This led us to reject the hypothesis that anammox is more cold-adapted than denitrification in our study system. Overall, our study suggests that temperature responses of both processes can be accurately modeled for temperate regions in the future using a single set of parameters, which are likely not to change over the next century as a result of predicted climate warming. We further conclude that climate warming will not directly alter the partitioning of N flow through anammox and denitrification. [ABSTRACT FROM AUTHOR]

[Display omitted] • An aerobic-heterotrophic nitrogen removal strain was isolated from saltern sediment. • The strain removed nitrogen from high-salinity (2–10% (w/v) NaCl) wastewater. • Nitrogen removal occurred via ammonium assimilation and HN-AD processes. • The complete genome of the strain was sequenced. • A complex nitrogen metabolism network was proposed. Nitrogen (N) removal from high-salinity wastewater is a major challenge. The aerobic-heterotrophic nitrogen removal (AHNR) process has been demonstrated to be feasible for treating hypersaline wastewater. In this study, Halomonas venusta SND-01, a halophilic strain capable of performing AHNR, was isolated from saltern sediment. The strain achieved ammonium, nitrite, and nitrate removal efficiencies of 98%, 81%, and 100%, respectively. The N balance experiment suggests that this isolate removes N mainly via assimilation. Various functional genes related to N metabolism were found in the genome of the strain, establishing a complex AHNR pathway that includes ammonium assimilation, heterotrophic nitrification-aerobic denitrification, and assimilatory nitrate reduction. Four key enzymes in the N removal process were successfully expressed. The strain exhibited high-adaptability under C/N ratios of 5–15, salinities of 2%−10% (m/v), and pH of 6.5–9.5. Therefore, the strain shows high potential for treating saline wastewater with different inorganic N compositions. [ABSTRACT FROM AUTHOR]

High organic loadings to constructed wetlands can result in water quality issues such as low dissolved oxygen and high ammonium concentrations, with artificial aeration a potential mitigation option. This study compared baseline (no aeration – NA), continuous aeration (CA), and intermittent aeration (IA) conditions to improve water quality in a tertiary treatment free water surface constructed wetland (FWS CW) with night time hypoxia/anoxia, and high nutrient concentrations. The response variables included dissolved oxygen (DO), total nitrogen (TN), ammonium nitrogen (NH 4 +-N), nitrate nitrogen (NO 3 −-N), total phosphorus (TP), phosphate (PO 4 3–-P), and dissolved organic carbon (DOC). In situ aeration and monitoring was performed from April to June 2021 in a large, field-scale FWS CW, the Laratinga wetlands Mount Barker, South Australia. The results demonstrated that DO increased by an average 2.11 mg L−1 from NA to CA during the night and 1.26 mg L−1 and 1.84 mg L−1 from NA to IA during the night and day respectively when averaging over the basins. The C/N ratio was very low and there was no significant influence of DO on DOC concentrations. There was no significant difference in TN concentrations with the application of aeration aside from a decrease in the channel at night from NA to IA, and an increase in NH 4 +-N resulted under IA compared with NA in Basin 1 and 2 during the day. This implies that the N loadings exceeded the wetland's ability to complete nutrient conversions at a rate that aligns with input rate. The concentrations of NO 3 −-N increased at night under CA and IA treatments suggesting that some nitrification was promoted, or there was inhibition of dissimilatory nitrate reduction to ammonium. The concentrations of TP and PO 4 3–-P significantly increased with the aeration compared with no aeration, however there was no difference between the aeration treatments. This suggested that increased sediment resuspension during aeration increased P in the water. There was no change in DOC with the application of aeration. Overall, the DO increased with aeration application and may be able to better support the wetland ecology; however, the Laratinga wetland is overloaded and the capacity of the wetland to effectively transform and remove nutrients is inhibited, even with the application of artificial aeration. • Dissolved oxygen increased with the application of continuous and intermittent aeration. • There was no change in total nitrogen with aeration and ammonium levels remained high. • There was a small increase in nitrate, and total and soluble phosphorus with aeration. • Despite near-neutral pH values, unionised ammonia was calculated to be at toxic levels. • Using aeration to manage systems with high nutrient loadings is challenging. [ABSTRACT FROM AUTHOR]

Ammonium (NH 4 +) enrichment of riverbank filtration (RBF) systems is gaining popularity. However, most previous research has concentrated on NO 3 − removal efficiencies, while the mechanisms of NH 4 + enrichment remain unknown. A nitrogen biogeochemical process model was developed for the quantitative analysis of NH 4 + enrichment in the Kaladian well field in northwest Songyuan City, NE China. Data from laboratory experiments and in-situ monitoring were used to determine initial values and calibrate the thermodynamic/kinetic parameters representing nitrogen (N) biogeochemical reactions. (1) The NO 3 − from river was subjected to denitrification (DNF) and dissimilatory nitrate reduction to ammonium (DNRA) within 10–14 m of the shore, whereas the NH 4 + in groundwater was caused by DNRA, organic nitrogen mineralization (MIN), and mixing with laterally recharged high NH 4 + groundwater. (2) DNF and DNRA were regulated by hydrodynamic processes, with the ranges of these processes being more significant in the wet season due to a higher hydraulic gradient. MIN occurred widely throughout the water flow path, with temperature primarily controlling the rates of the three reactions. (3) DNRA activity was relatively higher in the wet season when the water temperature was higher within 10–14 m of the shore. In the wet season, DNRA contributed 25%–30% to NO 3 − reduction, which was higher than in the dry season (5%–10%). DNRA contributed at least 40% and 15% to NH 4 + enrichment in the wet and dry seasons, respectively. (4). Organic N in media gradually released NH 4 + into groundwater via MIN and desorption across the entire flow path, with contributions to NH 4 + enrichment reaching 75% and 85%, respectively, in the wet and dry seasons. • Spatiotemporal variations of N biogeochemical reactions in RBF were identified. • Conditions for denitrification, DNRA, and mineralization in RBF were identified. • Simulation parameters were refined through multi-environmental N experiments. • Contributions of DNRA to NO 3 − reduction and NH 4 + enrichment were quantified. • Introduction. [ABSTRACT FROM AUTHOR]

The oxidation of ammonium (NH 4 + ) under iron reducing conditions, also referred to as Feammox, has been described in recent years by several investigators. The environmental characteristics in which the Feammox process occurs need to be understood in order to determine its contribution to the nitrogen cycle. In this study, through extensive field sampling at various locations in the US (mostly New Jersey) and South China, soil chemical analyses, serial incubation experiments, analysis of microbial communities, and using canonical correspondence analyses, it was determined that the soil pH, as well as its Fe(III) and NH 4 + concentration were the most important factors controlling the distribution of Acidimicrobiaceae , which have been linked to the Feammox reaction. Under the conditions that favored the presence of Feammox bacteria and their oxidation of NH 4 + under iron reducing conditions, denitrification bacteria were also abundant. However, the presence of known nitrous oxide (N 2 O) reducers was limited under these conditions, implying that at locations where the Feammox process is active, conditions might favor a higher N 2 O:N 2 ratio for the nitrogen (N) end products. To determine the effect of dissolved oxygen (DO) on NH 4 + oxidation under iron reducing conditions, incubations were conducted at two different DO levels. In incubations with DO < 0.02 mg/L, and when NH 4 + oxidation was noticeable, the proportion of Acidimicrobiaceae with respect to total bacteria increased, while the proportion of other known NH 4 + oxidizing bacteria (aerobic ammonia-oxidizing bacteria and anammox bacteria) decreased. In incubations of the same soil but with DO = 0.8–1.0 mg/L the opposite trend was observed, indicating that Feammox favored very low or no DO in these incubations. [ABSTRACT FROM AUTHOR]