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Urine deposited by grazing animals is the main source of nitrous oxide (N 2 O) emissions in New Zealand. Recent studies have suggested that certain pasture plants, for example plantain (Plantago lanceolata), can curb N 2 O emissions from livestock systems. This study aimed to i) evaluate the potential of plantain for reducing N 2 O emissions from cattle urine patches; ii) determine the effect of including plantain in animal diets on urine-N loading and its influence on N 2 O emissions; and, iii) evaluate whether any effects on N 2 O emissions reduction could be attributed to a 'urine' or a 'plant' effect. A static chamber method was used to measure N 2 O fluxes from urine collected from cows fed a 0, 15, 30 or 45% plantain mixed with "standard" ryegrass/clover (Lolium perenne / Trifolium repens) diet and applied to plots with the corresponding percentage of plantain in the sward. In addition, we measured N 2 O emissions from different proportions of plantain in the sward (0, 30, 60 and 100%) that received urine collected from cows fed on ryegrass/clover. The urine N loading rates of animals fed plantain, significantly reduced with increasing proportions of plantain in the diet (r2 = 0.987, P < 0.01). There was a trend of lower N 2 O emissions with an increasing proportion of plantain in the diet (r2 = 0.830, P < 0.08). However, there was no significantly difference in the N 2 O emission factors (P > 0.10). Following applications of standard urine, total N 2 O emissions and emission factor reduced linearly as the proportion of plantain in the sward increased (r2 = 0.969, P < 0.05 and 0.974, P < 0.05, respectively). The results suggest that the efficacy of plantain as a N 2 O mitigation option is due to both a reduction in urinary N excretion and a plant effect. The latter could be due to biological nitrification inhibition (BNI) caused by the release of root exudates and/or changes in the soil microclimate. Unlabelled Image • The urine-N loading rates decreased with increasing proportions of Plantain in the animal diet. • EF and total emissions of N 2 O decreased with the increase of Plantain proportions in the sward. • There was a trend of lower N 2 O emissions with increasing proportion of plantain in the diet. • The effect of plantain in the sward on N 2 O emissions may be due to the BNI activity. [ABSTRACT FROM AUTHOR]

A new type of biological folded non-aerated filter (BFNAF) was found to be superior and feasible for the treatment of NH 4 +-N wastewater. It was constructed with the folded structure suitable for the nylon biomass carrier. The advantages of the BFNAF included low energy consumption, long reaction path, large biofilm surface area and non-clogging compared to the traditional biological aerated filter. In this study, the effects of hydraulic retention time (HRT), and the influent NH 4 +-N concentration on the performance of BFNAF were investigated and optimized by the response surface methodology. Under the optimal operating condition (HRT, 10 h; NH 4 +-N concentration, 52 mg/L), the removal efficiency and removal rate were 94.62 ± 0.63% and 0.106 kg-NH 4 + m−3 day−1, respectively. The results showed that the BFNAF reactor could remove NH 4 +-N from wastewater and realized the nitrification process effectively under natural ventilation conditions. Unlabelled Image • Removal of NH 4 +-N by biological folded non-aerated filter reactor was studied. • Reflux can effectively improve the performance of the reactor. • HRT and influent concentration have great influence on the BFNAF reactor. [ABSTRACT FROM AUTHOR]

Terrestrial plant growth is strongly limited by the availability of nitrogen (N). Atmospheric deposition of N has been rapidly increasing since the industrial revolution, associated with fast compositional shifts between ammonium- (NH 4 +) and nitrate-N (NO 3 −) globally. However, whether and how such composition changes of deposition will affect the response of terrestrial plant growth to N deposition remains unclear. To fill the gaps, this study quantified the different responses of terrestrial plants to external NH 4 +-N and NO 3 −-N additions. A meta-analysis was applied to compare the growth responses of 367 plant species to different forms of N addition from 210 N-fertilization experiments. In general, a greater response of plant growth to NH 4 +- N (+6.3% per g N) than NO 3 −-N (+1.0% per g N) addition was detected across all species. The larger response of plant growth to NH 4 +-N than NO 3 −-N addition was found in trees and forbs but not in shrubs and grasses. The NH 4 +-N and NO 3 −-N additions had contrasting effects on biomass allocation. For example, the NO 3 −-N addition increased biomass allocation to above-ground tissues, whereas the NH 4 +-N addition enhanced below- but not above-ground growth. These results generally reveal a higher response of plant growth to NH 4 +- N than NO 3 −-N addition in terrestrial ecosystems. The findings suggest that future predictions on the vegetation response to atmospheric N enrichment could benefit from a better understanding of plant strategies for acquiring different forms of N. Unlabelled Image • Growth of terrestrial plants was enhanced more by NH 4 +-N than NO 3 −-N addition. • Plant allocated more biomass to above- than below-ground parts with NO 3 −-N addition. • NH 4 +-N addition significantly enhanced below- but not above-ground growth. [ABSTRACT FROM AUTHOR]

Abstract Novel muscovite/synthetic zeolitic phillipsite composite (Mu/Ph) was synthesized and inspected by different analytical techniques as a hybrid product of enhanced physicochemical properties and adsorption capacities for phosphate and ammonium. Mu/Ph adsorption systems for phosphate and ammonium were inspected considering the kinetic, equilibrium and thermodynamic studies as well as the controlling mechanisms. The kinetic behaviors of Mu/Ph for both phosphate and ammonium were remarkably described by Pseudo-second order model and the equilibration times were attained after 720 min and 480 min, respectively. The equilibrium curves for both ions were categorized as L-type isotherms which assigned mainly to systems of high affinity between the inspected adsorbents and the target dissolved ions. Additionally, the uptake results of both ions displayed slight preferences to be described by the Langmuir model. The thermodynamic studies revealed endothermic and exothermic nature for phosphate and ammonium, respectively. Moreover, the calculated parameters indicated physisorption of them by spontaneous reaction involved ion exchange processes controlled mainly by electrostatic interactions rather than ionic or covalent binding. The composite showed promising reusability properties to be applied in the reduction of phosphate and ammonium six times. The novel synthetic Mu/Ph exhibits higher capacities than numerous studied adsorbents and was applied in decontamination of phosphate and ammonium from real sewage water achieving exceptional results. Graphical abstract Unlabelled Image Highlights • Mu/Ph composite was prepared as an effective adsorbent for phosphate and ammonium. • It exhibits higher capacities than several adsorbents for both pollutants. • It showed high reusability and used effectively in the purification of raw water. • The results exhibit excellent fitting with pseudo-second-order and Langmuir models. • The system is of endothermic and exothermic nature for phosphate and ammonium, respectively. [ABSTRACT FROM AUTHOR]

Abstract Dramatic changes in soil during opencast coal mine activities inevitably change soil water and solute movement. The objectives of this study were to assess the effects of mining on solute transport in different soil profiles and to find the relationships between solute transport parameters and soil physicochemical characteristics. After taking undisturbed soil columns from the different soil profiles of natural land (NLs) and reclaimed mine land (RLs), ammonium nitrate displacement studies were conducted, and the breakthrough curves (BTCs) of NO 3 − and NH 4 + were obtained. Due to mining and reconstruction, soil texture became coarser, bulk density increased 2.77–15.15%, cation exchange capacity (CEC), soil organic matter (SOM), and total nitrogen (TN) content decreased 19.54–37.25%, 53.66–72.05%, and 42.58–58.55%, respectively. Additionally, the distributions of the physicochemical properties changed. The BTCs of NO 3 − for all soil columns can be well explained by both the convection-dispersion equation (CDE) and the two-region model (T-R). The transport parameters average pore water velocity (v), dispersion coefficient (D), and dispersivity (λ) were lower in RLs, which indicates that solutes became difficult to penetrate after mining. A significantly correlated relationship of bulk density and soil texture with the v , D , and λ parameters only occurred in the RLs samples. This result indicates that transport processes in NLs columns became more complicated and that soil texture and bulk density played an important role in the transport process of RLs columns. The two-site model could well describe NH 4 + transport for both NLs and RLs and provided a slightly better fit in RLs. This finding also gave evidence that RLs became homogeneous after mining and reconstruction. The parameter retardation factor (R) was significantly correlated to CEC, bulk density and soil texture in RLs. These results suggest that soil becomes homogeneous after mining and reconstruction and that high bulk density and fine soil texture could decrease the risk of leaching of solutes. Graphical abstract Unlabelled Image Highlights • Solute transport changed due to the changed physicochemical properties in profiles after mining. • Solute transport models provided a slightly better fit in reclaimed soils. • High bulk density and fine soil texture could decrease the risk of leaching of solutes after mining. [ABSTRACT FROM AUTHOR]

Abstract The knowledge about the impacts of ammonium loading on microbial food webs in biofilms attached to submersed macrophytes is limited. In the present study, Illumina sequencing method was employed to investigate bacterial and eukaryotic communities in biofilms attached to leaves of Vallisneria natans (V. natans) exposed to 1–16 mg L−1 NH 4 +-N for 10 days, and 8 mg L−1 NH 4 +-N for 21 days. Ammonium loading stimulated biofilms growth, enhanced the relative abundance of nitrifying genus Nitrospira and several denitrifying genera. Eukaryotic kingdom Metazoa, Viridiplantae, Chromista, Fungi and super group SARNU (Stramenopiles, Alveolata, Rhizaria, Nucleariidae and Fonticula group and unknown eukaryotes) were obtained. Relative abundance of Metazoa decreased with the increased ammonium concentration and exposure time. Redundancy analysis revealed that ammonium, dissolved oxygen (DO) and pH had a key role in determining microbial community structure. Network analyses revealed that there were complex interactions including feeding, parasitism and predatism among organism in biofilms, and the microbial food webs were disturbed by inhibiting metazoan growth but stimulating bacteria and algae growth. These results suggest that ammonium-disturbed microbial food webs in biofilms may contribute to the growth of biofilms and algae, and thus contribute to the decline of submersed macrophyte and provide "algal seeds" for the algae burst in water column. These data will be helpful in understanding the macrophytic region transform into algal region in water column polluted by ammonium. Graphical abstract Unlabelled Image Highlights • Ammonium increased relative abundances of nitrifiers and denitrifiers in biofilms. • Ammonium decreased relative abundance of Metazoa in biofilms. • Ammonium stimulated the growth of algae in biofilms. • Ammonium altered microbial food web in biofilms attached to leaves of plants. [ABSTRACT FROM AUTHOR]

Abstract Mole (M) and gravel-mole (GM) drainage systems improve the permeability of soils with high clay contents. They collect and carry away infiltrating water during episodic rainfall events. Characterisation of nutrient fluxes (concentration and flows) in overland flow (OF) and in mole drain flow (MF) across sequential rainfall events is important for environmental assessment of such drainage systems. The objective of this study is to assess the impact of drainage systems on soil nutrient losses. Three treatments were imposed on grazed permanent grassland on a clay loam soil in Ireland (52°30′N, 08°12′W) slope 1.48%: undrained control (C), mole drainage (M) and gravel mole drainage (GM). Plots (100 m × 15 m) were arranged in a randomized complete block design with four replicated blocks. Nitrogen (N) and phosphorus (P) concentrations in OF, MF and groundwater (GW) were measured from each plot over 15 consecutive rainfall events. The results showed that M and GM (P < 0.05) deepened the watertable depth and decreased OF. M and GM increased losses of nitrate-N (22%) and ammonium-N (14%) in GW. Nitrate-N concentrations from all the flow pathways (mean and standard error (s.e.): 0.99 s.e. 0.10 mg L−1) were well below the 11.3 mg L−1 threshold for drinking water. Ammonium-N concentrations from all the flow pathways (mean: 0.64 s.e. 0.14 mg L−1) exceeded drinking water quality standards. On the other hand M and GM lowered total P losses (mean annual losses from C, M and GM: 918, 755 and 853 s.e. 14.1 g ha−1 year−1) by enhancing soil P sorption. Hence M and GM can be implemented on farms under similar management to that described in the present study with a minor impact on N (increased concentration on averaged 18% to GW) and P (reduced by on avenged 114 g ha−1 year−1). Graphical abstract Unlabelled Image Highlights • We measured overland, drainage and ground water flows and the associate soil nitrate, ammonium and phosphorus losses following the installation of drainage. • Drainage treatment deepened the water table and decreased the overland flow. • M and gravel GM drainage increased losses of nitrate-N and ammonium-N in drainage flow and also losses to ground water. • M and GM lowered total P losses [ABSTRACT FROM AUTHOR]

Abstract This study presents the financial assessment for implementing an ammonium and phosphate simultaneous recovery process based on the use of calcium activated synthetic zeolites in a large urban Waste Water Treatment Plant (WWTP) located in the Metropolitan Area of Barcelona. A calcium activated synthetic zeolites was selected, after a benchmarking analysis, as it reported capability for simultaneously recover ammonium and phosphate by a combined mechanism of ion exchange for ammonium and formation of insoluble mineral phase for phosphate. The loaded sorbent, rich in ammonium and phosphate, can be used as slow-release fertilizer. Financial indexes such as the net present value, the internal return rate, the return of investment and the payback period were calculated concluding that the integration of a zeolite-based sorption treatment stage in the main stream is economically feasible, with a reasonable payback period. The need, to achieve low-levels of P and N on the discharged waters and the need to develop more sustainable WWTP facilities indicate that the deployment of nutrient recovery solutions will be encouraged. The sensitivity analysis carried out to define the critical parameters of the economic performance of the technology allows concluding that the main variable in the viability of the nutrient recovery unit is related to the nutrients sorbent, both in the cost of purchase and in the market for the sorbent loaded with nutrients. Graphical abstract Unlabelled Image Highlights • The recovery of nutrients in a large wastewater treatment plant has been evaluated. • Simultaneous recovery of N and P is done through the use of calcium zeolites. • Loaded zeolite can be sell as Triple SuperPhosphate fertilizer • Integration of nutrients recovery system is feasible with a reasonable Payback Period. • The key parameters are the cost of the sorbent and sale price of loaded zeolite. [ABSTRACT FROM AUTHOR]

Abstract Wastewater from a fertilizer manufacturing plant requires improvement prior to its environmental disposal. Ammonium is the critical contaminant to be removed. The aim of this study was to evaluate the feasibility of using free water surface wetlands (FWSWs), horizontal subsurface flow wetlands (HSSFWs), and their combination in hybrid wetlands (HWs) for the final treatment of wastewater with high ammonium concentration from a fertilizer manufacturing plant. Substrates and macrophytes were evaluated in microcosm experiments during three months. There were no significant differences in contaminant removal among HSSFWs with LECA or FWSWs planted with Typha domingensis or Canna indica. In a second stage, two configurations of pilot-scale HWs were constructed at the manufacturing facilities. Configuration A: HSSFW(A1)-FWSW(A2) and Configuration B: FWSW(B1)-HSSFW(B2) were evaluated during 12 months. There were no significant differences in contaminant removal (%) between the two configurations of HWs for COD (A: 74.5 ± 12.2/B: 81.5 ± 9.4), ammonium (A: 59.5 ± 17.5/B: 57.9 ± 21.4), nitrite (A: 79.8 ± 24.2/B: 80.6 ± 16.8) and dissolved inorganic nitrogen (DIN) (A: 59.4 ± 17.3/B: 50.3 ± 24.4). However, nitrate concentration (9.83 ± 3.11 mg N L−1) was significantly lower after Configuration A than after Configuration B (18.8 ± 5.2 mg N L−1). Comparing FWSWs and HSSFWs, they did not present significant differences in ammonium removal, while FWSWs presented the highest DIN removal. T. domingensis and C. indica in HSSFWs and T. domingensis in FWSWs tolerated wastewater conditions. T. domingensis presented the highest productivity. In further research, FWSWs in series planted with T. domingensis should be studied. Graphical abstract Unlabelled Image Highlights • Wastewater from a fertilizer manufacturing plant requires final treatment. • Two configurations of HWs (HSSFW-FWSW and FWSW-HSSFW) were compared. • There were no significant differences in contaminant removal between configurations. • There were no significant differences in NH 4 + removal between FWSWs and HSSFWs. • FWSWs presented the highest DIN removal. [ABSTRACT FROM AUTHOR]

Abstract Twenty-six pairs of PM 2.5 and PM 10 samples were collected during haze episodes in Zhengzhou (113°28′ E, 34°37′ N), a highly populated city in North China. The samples were used to examine the inorganic ion chemistry of particulate matter (PM) of local origin at light (PM 2.5 < 60 μg m−3 and PM 10 < 135 μg m−3), medium (PM 2.5 : 60–170 μg m−3 and PM 10 : 135–325 μg m−3), and severe (PM 2.5 > 170 μg m−3 and PM 10 > 325 μg m−3) pollution levels. At the light and severe pollution levels, the increase of PM 10 was accounted for by the increase of PM 2.5 , and the variation of PM 10–2.5 was small. In contrast, the increase of PM 10 at the medium pollution level was caused by the increase in both PM 2.5 and PM 10–2.5. Sulfate (SO 4 2−), nitrate (NO 3 −), ammonium (NH 4 +), and chloride in the form of ammonium chloride (Cl− S) accounted for 47.8% and 60.3% of the PM 2.5 mass at the light and severe levels, respectively. These values indicate a large contribution of secondary inorganic species to the PM 2.5 growth. As the pollution level changed from light to medium, the contribution of SO 4 2− to the growth of PM 2.5 decreased from 49.0% to 15.1%, while those of NO 3 − and Cl− S increased from 25.1% and 0.6% to 32.5% and 2.8%, respectively, indicating the substantial production of nitrate and chloride. At the severe level, the contribution of SO 4 2− was 30.1%, while those of NO 3 − and Cl− S were 5.9% and 0.5%, respectively, suggesting a hindering effect of sulfate on the production of nitrate and chloride. These results indicate that the production of secondary species with the increase of PM 2.5 was dominated by sulfate-associated conversions at the light and severe pollution levels and was substantially influenced by nitrate- and chloride-associated conversions at the medium pollution level. The estimation of carbonate presence in the PM indicates that part of the carbonate in coarse particles (PM 10–2.5) of crustal origin enhanced sulfate production via heterogeneous surface reactions. Quantification of the contribution of primary and secondary species to PM 2.5 showed that it was dominated by both primary and secondary particles at the light pollution level, and it was mainly composed of secondary species at the severe pollution level. Graphical abstract Unlabelled Image Highlights • The particulate pollution at Zhengzhou was divided into three levels: light, medium and severe. • PM 10 increase was dominated by PM 2.5 at the light and severe levels, and by both PM 2.5 and PM 10–2.5 at the medium level. • Secondary aerosol species (inorganic and organic) are major contributors to PM 2.5 elevation. • SO 4 2− hindered NO 3 − formation in PM 2.5 when it constituted >20% of PM 2.5 in mass. [ABSTRACT FROM AUTHOR]

Abstract Landfill leachate is one of the most challenging types of wastewater to treat using constructed wetlands. The objective of this study was to evaluate the effect of two feeding strategies on the treatment efficiency of a landfill leachate using vertical flow wetlands (VFWs) planted with Typha domingensis or Canna indica. The tolerance of these macrophytes to the leachate was also evaluated. Coarse sand and light expanded clay aggregates (LECA) were used as substrates. Two feeding strategies (FS) were applied: FSA = 1 pulse per day of 0.21 m pulse−1, FSB = 3 pulses per day of 0.07 m pulse−1. VFWs planted with T. domingensis presented removal efficiencies of 34/74% (NH 4 +) and 16/48% (TN) for FSA/FSB, respectively. VFWs planted with C. indica presented removal efficiencies of 27/72% (NH 4 +) and 18/46% (TN) for FSA/FSB, respectively. NH 4 + and total nitrogen (TN) removal efficiencies were significantly higher in FSB than in FSA, but there were no significant differences between macrophyte species. COD removal showed no significant differences between FSs or between macrophyte species. T. domingensis and C. indica demonstrated to be tolerant to the leachate studied. VFWs planted with T. domingensis or C. indica are suitable to treat diluted landfill leachate with high ammonium concentrations using a feeding strategy of pulses. However, an anaerobic stage may be added after the VFW to get higher TN and COD removal. Graphical abstract Unlabelled Image Highlights • Diluted landfill leachate presented high pollutant concentrations. • COD showed low removal due to its recalcitrant characteristics. • Removal of NO 3 − and NO 2 − was not achieved due to a lack of anaerobic conditions. • Ammonium and TN showed significantly higher removal in low HLR. • Removal was not significantly different between VFW with the different macrophytes. [ABSTRACT FROM AUTHOR]

Abstract The effects of reduced nitrogen release from sediments were studied using biochar (BC) capping in simulated water–sediment systems. Dried solid waste of Phyllostachys pubescens was used to produce BC, which was then pyrolyzed at 500 °C. Subsequently, 14 sediment cores were collected, including the sediment–water interface and some overlying water, from two sites in Baiyangdian Lake (China). The sediment cores were split into two batches (A and B), and then two each were capped with soil, BC or a BC/soil mixture, and incubated for 30 days. In the BC capped cores, the ammonia nitrogen (NH 4 +-N), nitrate nitrogen (NO 3 −-N) and total nitrogen (TN) concentrations decreased from 0.90 mg·L−1 to 0.05 mg·L−1, 0.88 mg·L−1 to 0.18 mg·L−1, 6.93 mg·L−1 to 2.81 mg·L−1, respectively, in batch A and 3.51 mg·L−1 to 0.11 mg·L−1, 0.92 mg·L−1 to 0.61 mg·L−1, 8.88 mg·L−1 to 3.32 mg·L−1, respectively, in batch B. The sediments to water fluxes of NH 4 +-N, NO 3 −-N and TN were greatly reduced or reversed. Compared with other cappings, the BC layer was shown to absorb more NH 4 +-N from the pore water, thereby breaking the diffusion gradient of NH 4 +-N at the sediment–water interface, and has a good inhibitory effect on the endogenous release of NH 4 +-N from the sediments. Additionally, in the BC capped cores, the redox potential remarkably increased and dissolved oxygen was comparatively high. This study suggests that BC capping can reduce the amount of nitrogen released from polluted sediments because the diffusion of nitrogen to the overlying water is chemically blocked by the cap. Graphical abstract Unlabelled Image Highlights • This study investigates the use of solid waste of Phyllostachys pubescens. • We first propose the idea of using biochar for sediment nitrogen remediation. • Biochar has a good effect on reducing nitrogen release, especially NH 4 +-N. • We propose a good application of biochar capping technology. [ABSTRACT FROM AUTHOR]

This study investigates the effect of anionic surfactant modification on activated carbon (AC) to enhance the adsorption of ammonium ion in aqueous solution. Sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS) or sodium octanoate (SO) was used for the modification. At the initial aqueous concentration of 55 mg NH 4 -N/L and the adsorbent dose of 50 g/L, the SDS-modified AC showed the highest ammonium removal efficiency of 82% among the modified ACs studied. The hydrophobic group of SDS was strongly attached to AC showing almost negligible desorption after the modification. At the same time, the sulfate functional group of SDS provided ion exchange sites favorable for the ammonium ion adsorption. By maximizing SDS loading to the AC, ammonium removal efficiency can further be improved (5% increase). When Na + , K + or Ca 2+ coexisted in the ammonium solution at the concentration of 55 mg/L, the inhibition effect of these cations on ammonium removal efficiency was negligible (<5%). This study shows the potential of anionic surfactant-modified ACs as the excellent adsorbents for ammonium removal from water. [ABSTRACT FROM AUTHOR]

Nitrogen (N) and phosphorus (P) pollution from aquaculture has increased dramatically in recent years, and it is urgent to develop a cost-effective method to clean these polluted waters. The objective of this study is to investigate N and P removal using a two-stage infiltration system based on NaCl modified clinoptilolite (NCLP) and thermally-treated calcium-rich attapulgite (TCAP). Results from a batch study indicated that the maximum ammonium sorption capacity of NCLPs was in the range of 6.64 to 7.27 mg. N/g and decreased slightly among the three particle sizes studied (0.2–0.5 mm, 0.5 mm–1.0 mm and 1–2 mm). A 150-day column experiment indicated that the two-stage infiltration system achieved an average removal efficiency of 99.4% N and 99.0% P, and a removal rate of 50.3 g N/m 3 /d and 8.83 g P/m 3 /d for an influent concentration of 50 mg N/L and 10 mg P/L with a hydraulic retention time (HRT) of 16 h. When the influent concentration increased to 100 mg N/L and 20 mg P/L, the average ammonium removal efficiency decreased to 65.3%, while the system can still keep a high average P removal efficiency of 97.9% for 72 days of the experiment. Longer HRT favored N and P removal efficiency, but short HRTs can oxygenate ammonium sorbed in the NCLP filter and thereby refresh its sorption capacity. The results also indicated that longer wet and dry cycles can enhance the N removal efficiency of the system, but had minor influence on P removal. The sorbed clays contained high N and P content and might have use as a slow-release fertilizer. The results of this study indicate that a reactive clay-based treatment system can be used for dual removal of N and P from aquaculture wastewaters, making possible the development of a sustainable aquaculture model. [ABSTRACT FROM AUTHOR]

The aim of this study was to assess the potential of struvite precipitation to recover nutrients from anaerobically-processed poultry slurry and struvite's interactions with heavy metals (Zn, Cu, Pb, Cr, and Ni) and pathogens (total coliforms and Escherichia coli ). The impacts of pH, Mg, N, and P molar proportion, reaction time, and mixing rate and duration were explored to determine the optimal conditions for nutrient recovery through struvite precipitation. A pH range of 9.5 to 10.5, was ideal for P and N removal and recovery, with a molar ratio of 1:1:1 for Mg:N:P. A mixing rate of 150 rpm for 10 min could allow nutrient recovery with little loss (3.32%) of NH₃ through volatilization, and also achieve an optimal struvite crystal size (50–60 μm). The results of X-ray diffractometry and scanning electron microscopy confirmed that the precipitates generated at pH 9 and 10 were orthorhombic struvite. Moreover, along with the recovery of nutrients, 40, 45, 66, 30, and 20% of Zn, Cu, Pb, Cr, and Ni, respectively, and 70% total coliforms and E. coli were removed by struvite precipitation from poultry slurry. This was observed despite that the levels of contaminants (heavy metals) detected in struvite were well below the permissible limits and free of pathogens. Consequently, it was inferred that the struvite quality was reasonable by virtue of its heavy metal and pathogen content, and therefore appropriate for application in the field. Similarly, struvite precipitation has multiple benefits as it can effectively recover nutrients as well as reducing pathogenic populations. [ABSTRACT FROM AUTHOR]

Low-strength ammonium is still a challenge for the mainstream deammonification because of nitrate over-accumulation. In this study, the threshold of influent ammonium concentration of one-stage deammonification system with granular sludge was investigated, by stepwise decreasing influent ammonium from high concentrations (280 mg/L to 140 mg/L) to the low concentration (70 mg/L) in 108 d at 32 °C without aeration. Results showed that, under 70 mg/L NH 4 + -N, ΔNO 3 − -N/ΔNH 4 + -N ratio increased to 0.2, deviated from the theoretical value of 0.11, with ammonium and TN removal efficiencies of 91% and 71%, respectively. However, under both high ammonium concentrations (280 mg/L and 140 mg/L), nitrate production stabilized at only 13%. Chloroflexi , Planctomycetes and Proteobacteria contributed >70% of the communities under all three ammonium concentrations. As influent ammonium decreasing, the relative abundances of bacteria for anammox, aerobic oxidizing and denitrifying decreased, while NOB (nitrite oxidizing bacteria) abundance increased greatly. So 70 mg/L was the threshold of influent ammonium concentration for stable deammonification without organic influent. It was the decrease of functional bacteria and overgrowth of NOB that worsen the deammonification performance under low-strength ammonium. [ABSTRACT FROM AUTHOR]

Removal of nitrogen from wastewater without using electricity consuming aerators was previously observed in photo-bioreactors with a mixed algal-bacterial biomass. Algammox is the particular process based on algae, ammonium oxidizing organisms and anammox bacteria. In this research the activity of anammox bacteria in such an oxygen-producing environment was tested, as well as the effect of short-duration increase in dissolved oxygen (DO) to values potentially inhibiting anammox activity. Sequencing batch photo-bioreactors were fed with settled domestic wastewater enriched with ammonium (200 mg NH 4 + -N/L) and exposed to light within the photosynthetic active range with intensity of about 500 μmol/m 2 ·s. Each cycle consisted of 12 h illumination and 12 h darkness. A well-settling biomass (10 days solids retention time) developed that carried out nitritation, nitrification and anammox. Ammonium removal rate during the light period was 4.5 mg N-NH 4 + /L·h, equal to 858 mg N-NH 4 + /m 2 ·h or 477 mg N-NH 4 + /(mol photons). When the reactors were aerated for 3 h to temporarily increase the DO, anammox was inhibited at bulk DO values larger than 0.4–1.0 mg/L. For almost oxygen saturated conditions, recovery time was about 9 days. Algammox photo-bioreactors are therefore able to overcome short periods of oxygen stress, provided they occur only occasionally. [ABSTRACT FROM AUTHOR]

Nitrogen (N) stored in deep profiles is important in assessing regional and/or global N stocks and nitrate leaching risk to groundwater. The Chinese Loess Plateau, which is characterized by significantly thick loess deposits, potentially stores immense stocks of mineral N, posing future threats to groundwater quality. In order to determine the vertical distributions of nitrate and ammonium content in the region, as well as to characterize the potential accumulation of nitrate in the deep loess profile, we study loess samples collected at five sites (Yangling, Changwu, Fuxian, An'sai and Shenmu) through a 50 to 200 m loess profile. The estimated storage of mineral N varied significantly among the five sites, ranging from 0.46 to 2.43 × 10 4 kg N ha −1 . Ammonium exhibited fluctuations and dominated mineral N stocks within the whole profile at the sites, except for the upper 20–30 m at Yangling and Changwu. Measured nitrate content in the entire profile at Fuxian, An'sai and Shenmu is low, but significant accumulations were observed to 30–50 m depth at the other two sites. Analysis of δ 15 N and δ 18 O of nitrate indicates different causes for accumulated nitrate at these two sites. Mineralization and nitrification of manure and organic N respectively contribute nitrate to the 0–12 and 12–30 m profile at Changwu; while nitrification of NH 4 + fertilizer, NO 3 − fertilizer and nitrification of organic N control the nitrate distribution in the 0–3, 3–7 and 7–10 m layer at Yangling, respectively. Furthermore, our analysis illustrates the low denitrification potential in the lower part of the vadose zone. The accumulated nitrate introduced by human activities is thus mainly distributed in the upper vadose zone (above 30 m), indicating, currently, a low nitrate leaching risk to groundwater due to a high storage capacity of the thick vadose zone in the region. [ABSTRACT FROM AUTHOR]

Atmospheric deposition nitrogen (ADN) increases the N content in soil and subsequently impacts microbial activity of soil. However, the effects of ADN on paddy soil microbial activity have not been well characterized. In this study, we studied how red paddy soil microbial activity responses to different contents of ADN through a 10-months ADN simulation on well managed pot experiments. Results showed that all tested contents of ADN fluxes (27, 55, and 82 kg N ha −1 when its ratio of NH 4 + /NO 3 − -N ( R N ) was 2:1) enhanced the soil enzyme activity and microbial biomass carbon and nitrogen and 27 kg N ha −1 ADN had maximum effects while comparing with the fertilizer treatment. Generally, increasing of both ADN flux and R N (1:2, 1:1 and 2:1 with the ADN flux of 55 kg N ha −1 ) had similar reduced effects on microbial activity. Furthermore, both ADN flux and R N significantly reduced soil bacterial alpha diversity ( p < 0.05 ) and altered bacterial community structure (e.g., the relative abundances of genera Dyella and Rhodoblastus affiliated to Proteobacteria increased). Redundancy analysis demonstrated that ADN flux and R N were the main drivers in shaping paddy soil bacteria community. Overall, the results have indicated that increasing ADN flux and ammonium reduced soil microbial activity and changed the soil bacterial community. The finding highlights how paddy soil microbial community response to ADN and provides information for N management in paddy soil. [ABSTRACT FROM AUTHOR]

We review data from coastal Pacific Panama and other tropical coasts with two aims. First, we defined inputs and losses of nitrogen (N) mediating connectivity of watersheds, mangrove estuaries, and coastal sea. N entering watersheds—mainly via N fixation (79-86%)—was largely intercepted; N discharges to mangrove estuaries (3-6%), small compared to N inputs to watersheds, nonetheless significantly supplied N to mangrove estuaries. Inputs to mangrove estuaries (including watershed discharges, and marine inputs during flood tides) were matched by losses (mainly denitrification and export during ebb tides). Mangrove estuary subsidies of coastal marine food webs take place by export of forms of N [DON (62.5%), PN (9.1%), and litter N (12.9%)] that provide dissimilative and assimilative subsidies. N fixation, denitrification, and tidal exchanges were major processes, and DON was major form of N involved in connecting fluxes in and out of mangrove estuaries. Second, we assessed effects of watershed forest cover on connectivity. Decreased watershed forest cover lowered N inputs, interception, and discharge into receiving mangrove estuaries. These imprints of forest cover were erased during transit of N through estuaries, owing to internal N cycle transformations, and differences in relative area of watersheds and estuaries. Largest losses of N consisted of water transport of energy-rich compounds, particularly DON. N losses were similar in magnitude to N inputs from sea, calculated without considering contribution by intermittent coastal upwelling, and hence likely under-estimated. Pacific Panama mangrove estuaries are exposed to major inputs of N from land and sea, which emphasizes the high degree of bi-directional connectivity in these coupled ecosystems. Pacific Panama is still lightly affected by human or global changes. Increased deforestation can be expected, as well as changes in ENSO, which will surely raise watershed-derived loads of N, as well as significantly change marine N inputs affecting coastal coupled ecosystems. [ABSTRACT FROM AUTHOR]

The use of low-cost inorganic sorbents as a new sustainable strategy to enhance the valorization of nutrients (N-P-K), from the urban water cycle (e.g., side streams from sewage sludge anaerobic digestion), in agriculture applications is presented. The simultaneous recovery and stabilization of ammonium and phosphate by using a mixture of two reactive sorbents (Na and K zeolites and magnesium oxide) was evaluated. The nutrients stabilization process, favoured at alkaline pH values, is carried out by a) the precipitation of phosphate ions with magnesium and/or ammonium ions and b) the sorption of ammonium by Na- and K-zeolites. MgO(s) promoted the stabilization of phosphate as bobierrite (Mg 3 (PO 4 ) 2 (s)) or struvite (MgNH 4 PO 4 (s)) depending on the applied dose. Doses with the stoichiometric molar ratio of Mg/P promote the formation of bobierrite, while molar ratios higher than 3 favour the formation of struvite. Na zeolites (NaP1-NA, NaP1-IQE) demonstrated efficiency on ammonium stabilization between 60 ± 2 (for 15 gZ/L) to 90 ± 3% (for 50 gZ/L). The ammonium recovery efficiency is limited by the zeolite sorption capacity. If the target of the fertilizing criteria should include K, then the use of a K-zeolite (e.g., 5AH-IQE) provides a good solution. The optimum pH for the precipitation of struvite and bobierrite is 9.5 and the optimum pH for ammonium removal is between 4 and 8.5. N is present in higher concentrations (up 0.7–1 g NH 4 + /L) when pH is ranged between 8.2 and 8.6. The ammonium recovery ratios were better than those previously reported using only magnesium oxide or even a more expensive reagent as newberrite (MgHPO 4 (s)). The recovery mechanisms described generate low-solubility stabilized nutrients forms that potentially can be applied as slow-release fertilizers in agriculture. Thus, the use in agriculture of blends of digested sludge with low-solubility stabilized nutrients forms will improve soils quality properties in terms of organic matter and nutrients availability. [ABSTRACT FROM AUTHOR]

In many developing regions with poor air quality, the use of air filtration devices to clean indoor air is growing rapidly. In this study, we collected indoor, outdoor and personal exposure filter-based samples of fine particulate matter (PM 2.5 ) with both properly operating, and sham air cleaners in six Beijing residences from July 24th to August 17th, 2016. Mass concentrations of PM 2.5 and several health relevant components of PM 2.5 including organic carbon, elemental carbon, sulfate, nitrate, ammonium, and 21 selected metals, were analyzed to evaluate the effectiveness of air cleaners. The effect of air purification on PM 2.5 reactive oxygen species (ROS) activity, a metric of the oxidative potential of the aerosol, was also evaluated. The average indoor PM 2.5 concentration during true filtration was 8.47 μg/m 3 , compared to 49.0 μg/m 3 during sham filtration; thus, air cleaners can significantly reduce the indoor PM 2.5 concentration to well below WHO guideline levels and significantly lower all major components of PM 2.5 . However, the utility of air cleaners in reducing overall personal exposure to PM 2.5 and its components was marginal in this study: the average personal exposure PM 2.5 concentration was 67.8 and 51.1 μg/m 3 during true and sham filtration respectively, and it is likely due to the activity patterns of the subjects. Short-term exposure contributions from environments with high PM 2.5 concentrations, including exposure to traffic related emissions as well as uncharacterized indoor microenvironments, likely add substantially to the total PM 2.5 exposure burden. The toxicity assay indicates that the air cleaners can also significantly reduce ROS activity in the indoor environment; however, this decrease did not translate to a reduction in personal exposure. Elemental carbon, lead, and arsenic were well-correlated with the ROS activity, thus adding to the knowledge base of drivers for ROS activity. [ABSTRACT FROM AUTHOR]

In the past few years, anaerobic ammonium oxidation-based processes have attracted a lot of attention for their implementation at the mainstream line of wastewater treatment plants, due to the possibility of leading to energy autarky if combined with anaerobic digestion. However, little is known about the potential degradation of micropollutants by the microbial groups responsible of these processes and the few results available are inconclusive. This study aimed to assess the degradation capability of biomass withdrawn from a combined nitritation/anaerobic ammonium oxidation (combined N/A) pilot plant towards five pharmaceutically active compounds (ibuprofen, sulfamethoxazole, metoprolol, venlafaxine and carbamazepine). Batch experiments were performed under different conditions by selectively activating or inhibiting different microbial groups: i) regular combined N/A operation, ii) aerobic (optimal for nitrifying bacteria), iii) aerobic with allylthiourea (an inhibitor of ammonia monooxygenase, enzyme of ammonia oxidizing bacteria), iv) anoxic (optimal for anaerobic ammonium oxidizing bacteria), v) aerobic with acetate (optimal for heterotrophic bacteria) and vi) anoxic with acetate (optimal for heterotrophic denitrifying bacteria). Ibuprofen was the most biodegradable compound being significantly degraded (49–100%) under any condition except heterotrophic denitrification. Sulfamethoxazole, exhibited the highest removal (70%) under optimal conditions for nitrifying bacteria but in the rest of the experiments anoxic conditions were found to be slightly more favorable (up to 58%). For metoprolol the highest performance was obtained under anoxic conditions favoring anammox bacteria (62%). Finally, carbamazepine and venlafaxine were hardly removed (≤ 10% in the majority of cases). Taken together, these results suggest the specificity of different microbial groups that in combination with alternating operational parameters can lead to enhanced removal of some micropollutants. [ABSTRACT FROM AUTHOR]

The increasing use of engineered nanoparticles (NPs) in consumer and industrial products raises concerns about their environmental impacts, but their potential influence on anaerobic ammonium oxidation (anammox) process in wastewater treatment remains unknown. In this study, the response of granule-based anammox reactor to different loads of ZnONPs was investigated. The introduction of 1–5 mg L − 1 ZnONPs did not affect reactor performance, but 90% of the nitrogen removal capacity was deprived by a shock of 10 mg L − 1 ZnONPs within 3 days. Anammox activity was significantly inhibited, but no significant stimulation of intracellular reactive oxygen species (ROS) production or extracellular lactate dehydrogenase (LDH) activity was observed. The inhibition was thus mainly due to the accumulation of toxic Zn(II) ions in anammox biomass. However, the resistance and resilience of this anammox reactor to ZnONPs were enhanced by intermittent perturbations in the mode of “shock-recovery”. The up-regulated abundance of Zn(II)-exporter ZntA might contribute to the enhanced resistance. In addition, these repeated transient disturbances improved the functional specificity of the anammox community despite the reduction of its diversity. Overall, these results may provide useful references for evaluating and controlling the risk of NPs to anammox process. [ABSTRACT FROM AUTHOR]

The deposition of reactive nitrogen (N) compounds currently predominates over sulphur (S) deposition in most of the cities in Europe and North America. Acidophytic lichens growing on tree trunks are known to be sensitive to both N and S deposition. Given that tree species and climatic factors affect the composition of epiphytic lichen communities and modify lichen responses to air pollution, this study focused on the impact of urban air pollution on acidophytes growing on boreal conifer trunks. The study was performed in the Helsinki metropolitan area, southern Finland, where annual mean nitrogen dioxide (NO 2 ) concentrations range from 4–5 μg m − 3 to > 50 μg m − 3 . In addition, background forest sites in southern and northern Finland were included. The results demonstrated elevated N contents (≥ 0.7%) in Hypogymnia physodes and Platismatia glauca at all the sites where the species occurred. In the Helsinki metropolitan area, a higher frequency of green algae + Scoliociosporum chlorococcum and reduced numerical frequencies of other indicator lichen species (e.g. Pseudevernia furfuracea , Bryoria spp., Usnea spp.) were associated with elevated atmospheric concentrations of NO 2 and particulate matter containing N, as well as elevated concentrations of inorganic N in bark. The N isotope values (δ 15 N) of lichens supported the uptake of oxidized N mainly originating from road traffic. Sulphur dioxide (SO 2 ) also negatively affected the most sensitive species, despite the current low levels (1–4 μg m − 3 yr − 1 ). Critical levels of 5 μg NO 2 m − 3 yr − 1 and 0.5 μg NH 3 m − 3 yr − 1 , and a critical load of 2–3 kg N ha − 1 yr − 1 are proposed for protecting the diversity of boreal acidophytes. This study calls for measurements of the throughfall of various N fractions in urban forest ecosystems along precipitation and temperature gradients to verify the proposed critical levels and loads. [ABSTRACT FROM AUTHOR]

Lake Taihu Basin, one of the most developed regions in China, has received considerable attention due to its severe pollution. Our study provides a clear understanding of the water quality in the rivers of Lake Taihu Basin based on basin-scale monitoring and a water quality index (WQI) method. From September 2014 to January 2016, four samplings across four seasons were conducted at 96 sites along main rivers. Fifteen parameters, including water temperature, pH, dissolved oxygen (DO), conductivity, turbidity (tur), permanganate index (COD Mn ), total nitrogen, total phosphorus, ammonium (NH 4 -N), nitrite, nitrate (NO 3 -N), calcium, magnesium, chloride, and sulfate, were measured to calculate the WQI. The average WQI value during our study period was 59.33; consequently, the water quality was considered as generally “moderate”. Significant differences in WQI values were detected among the 6 river systems, with better water quality in the Tiaoxi and Nanhe systems. The water quality presented distinct seasonal variation, with the highest WQI values in autumn, followed by spring and summer, and the lowest values in winter. The minimum WQI (WQI min ), which was developed based on a stepwise linear regression analysis, consisted of five parameters: NH 4 -N, COD Mn , NO 3 -N, DO, and tur. The model exhibited excellent performance in representing the water quality in Lake Taihu Basin, especially when weights were fully considered. Our results are beneficial for water quality management and could be used for rapid and low-cost water quality evaluation in Lake Taihu Basin. Additionally, we suggest that weights of environmental parameters should be fully considered in water quality assessments when using the WQI min method. [ABSTRACT FROM AUTHOR]

Nitrogen (N) losses through gaseous emission of ammonia (NH 3 ) and nitrous oxide (N 2 O) can contribute to both economic loss and environmental degradation. This study examined the effect of biochar and a chemical nitrification inhibitor, dicyandiamide (DCD), on N transformation and N losses via gaseous emission of NH 3 and N 2 O from agricultural soils treated with a range of organic and inorganic N sources. The addition of DCD reduced N 2 O emission from both organic and inorganic N sources treated soils by 75%, but increased ammonium (NH 4 + ) concentration and subsequently induced high NH 3 emission from the soils. In contrast, the addition of biochar reduced both N 2 O and NH 3 emissions from organic and inorganic N sources treated soils by 23% and 43%, respectively. The effectiveness of biochar and DCD in reducing NH 3 volatilization and N 2 O emission depends on the nature of the N sources and their initial mineral N concentration. The study demonstrated that biochar can be used to mitigate N losses resulting from NH 3 volatilization and N 2 O emission. [ABSTRACT FROM AUTHOR]

The widespread use of nanoparticles (NPs) has led to their inevitable introduction into environmental systems. How the existence of hydrochars in crop soils will affect the mobility of nanoparticle titanium dioxide (nTiO 2 ), especially in the presence of ammonium (NH 4 + ), remains unknown. Research is needed to study the effects of hydrochars on the transport and retention of nTiO 2 and to uncover the mechanisms of these effects on nTiO 2 transport. Column experiments with nTiO 2 and hydrochars were performed in various electrolyte (NaCl, NH 4 Cl, and CaCl 2 ) solutions under a controlled pH (6.0 and 8.0). Additionally, the size distributions and scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the NPs were observed. The experimental results suggested that the mobility of the hydrochars was much better than that of nTiO 2 . Thus, the mobility of nTiO 2 was improved upon their attachment to the hydrochars. The facilitated transport of nTiO 2 in the presence of hydrochars was stronger at pH 8.0 than at pH 6.0, and facilitated transport was nearly independent of the electrolyte cation at pH 8.0. However, at pH 6.0, the facilitated transport in various electrolytes had the following order: NaCl > NH 4 Cl > CaCl 2 . The conversion from a completely reversible to a partially irreversible deposition of nTiO 2 in sand was induced by the partially irreversible retention of hydrochars, and this phenomenon was more pronounced in the presence of NH 4 + than in the presence of Na + . In particular, the irreversible deposition of nTiO 2 -hydrochars was enhanced as the cation concentration increased. The increased irreversible retention of nTiO 2 was related to the greater k 2 value (irreversible attachment coefficients) on site 2 for hydrochars based on two-site kinetic retention modeling. Thus, there is a potential risk of contaminating crops, soil, and underground water when nTiO 2 exists in a hydrochar-amended environment, especially when associated with NH 4 -N fertilizer. [ABSTRACT FROM AUTHOR]

The removal of nutrients (nitrogen (N), phosphorous (P)) from waste water has become a resource recovery option in recent regulations worldwide, as observed in the European Union. Although both of these nutrients could be recovered from the sludge line, > 70–75% of the N and P is discharged into the water line. Efforts to improve the nutrient recovery ratios have focused on developing low-cost technologies that use sorption processes. In this study, a natural zeolite (clinoptilolite type) in its potassium (K) form was impregnated with hydrated metal oxides and used to prepare natural hybrid reactive sorbents (HRS) for the simultaneous recovery of ammonium (NH 4 + ) and phosphate (PO 4 3 − ) from treated urban waste water. Three unfertile soils (e.g., one acidic and two basic) amended with N-P-K charged HRS were leached with deionized water (e.g. to simulate infiltration in the field) at two- and three-day time intervals over 15 different leaching cycles (equivalent to 15 bed volumes). The N-P-K leaching profiles for the three charged hybrid sorbents exhibited continuous nutrient release, with their values dependent on the composition of minerals in the soils. In the basic soil that is rich in illite and calcite, the release of potassium (K + ) and ammonium (NH 4 + ) is favoured by-ion exchange with calcium (Ca 2 + ) and accordingly diminishes the release of phosphate (PO 4 3 − ) due to its limited solubility in saturated calcite solutions (pH 8 to 9). The opposite is true for sandy soils that are rich in albite (both acidic and basic), whereas the release of NH 4 + and K + was limited and the values of both ions measured in the leaching solutions were below 1 mg/L. Their leaching solutions were poor in Ca 2 + , and the release of PO 4 3 − was higher (up to 12 mg P-PO 4 3 − /L). The nutrient releases necessary for plant growth were provided continuously and were controlled primarily by the soil mineral dissolution rates fixing the soil aqueous solution composition (e.g. pH and ionic composition; in particular, the presence of calcite is a determinant for nutrient release, especially in alkaline soils). The N-P-K charged HRS sorbents that were used for soil amendment may be an alternative for avoiding nutrient leaching and reaching the goals of soil sustainability in agriculture and reducing the nutrient overloading of surface waters. [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]