Total Nitrogen Loss Research Articles

Mechanism of magnetite-assisted aerobic composting on the nitrogen cycle in pig manure

Magnetite affects nitrogen cycle of pig manure (PM) biostabilisation was investigated. Various doses of magnetite (0 % (T1); 2.5 % (T2); 5 % (T3); 7.5 % (T4)) were homogeneously added into PM and wolfberry branch fillings (BF) mixture for a 50-day composting. Compared to T1, total nitrogen (TN) loss in gaseous form increased remarkably by 17.51 %, 56.31 %, and 24.91 %, respectively, in T2–T4. In particular, T3 dramatically increased the cumulative N2O emission but decreased NH3 emissions. However, T2 and T3 enhanced the total nitrogen contents by 7.24 % and 3.09 %. Structural equation models (SEM) analysis indicated that magnetite addition increased the direct and indirect pathways of N2O emission. Further analysis revealed that Ruminofilibacter and N2O emission were significantly correlated, and Pseudomonas played a vital role in nitrogen preservation. Although using 2 % magnetite as an additive could increase the TN content, the obvious increase of N2O emission should be considered in engineering practice.

Sludge composting with self-produced carbon source by phosphate buffer coupled hyperthermophilic pretreatment realizing nitrogen retention

During sludge composting, ammonia emissions is the main pathway of nitrogen loss. In addition to regulating pH, increasing the carbon source is also important for controlling ammonia emissions. Previous studies have focused on additional carbon sources, while this study used phosphate-buffered saline (PBS) and hyperthermophilic pretreatment (HP) to release difficult-to-utilize carbon sources in extracellular polymeric substance (EPS) for composting. The PBS concentration was 0.22 mmol/g total matter (TM), PBS soaking days were 4.74, HP temperature was 149.46 °C, and the soluble chemical oxygen demand (SCOD) was 45.08 g/kg. Compared with the control check, the peak ammonia emission concentration in the pretreated group was reduced by 8.70 % and the total nitrogen loss was reduced by 18.10 %. Changes in EPS, ammonia assimilation activity, and microbial community composition demonstrated that PBS and HP released the carbon source from the sludge, promoted ammonia assimilation, and enriched bacteria related to ammonia assimilation such as Bacillus (16.52 %). HP treatment made Acinetobacter (12.5 %) the dominant genus in the calefactive phase, and the enrichment of Actinobacteriota (27.27 %) promoted the composting maturity. However, total pretreatment reduced the porosity and permeability of the sludge and affected the activity of microorganisms. Considering the cost of energy consumption, partial pretreatment has more practical application prospects.

Runoff, sediment, organic carbon, and nutrient loads from a Canadian prairie micro-watershed under climate variability and land management practices

This study conducted a spatio-temporal analysis of runoff, total suspended sediment, suspended particulate carbon, nitrogen, and phosphorus loadings within the 2.06 km2 Steppler subwatershed in southern Manitoba of Canada based on 11 years of field monitoring data collected at nine stations. Results showed that the nutrient losses were very small because of the implementation of multiple BMPs in the study area. However, a high spatio-temporal variation of runoff and water quality parameters was found for the nine fields within the subwatershed. The average runoff coefficient was 0.19 at the subwatershed outlet with sediment, suspended particulate carbon, total nitrogen, and total phosphorus losses of 73.8, 6.10, 4.54, and 0.76 kg/ha respectively. Spring snowmelt runoff was about 74.5% of the annual runoff at the subwatershed outlet, while for sediment, suspended particulate carbon, total nitrogen, and total phosphorus, the proportions were 61.1%, 63.6%, 74.9%, and 81.2% respectively during the monitoring period, which suggests that BMPs designed for reducing nutrient loadings from snowmelt runoff would be more effective than BMPs designed for reducing pollutant loading from rainfall storms in the study area. Research findings from this study will benefit the enhancement of current BMPs and the development of new BMPs in the region to minimize soil and nutrient losses from agricultural fields and improve water quality in receiving water bodies.

Grazing management impacts on ecosystem services under contrasting climatic conditions in Texas and North Dakota

Grazing management is an important factor affecting the delivery of ecosystem services at the watershed scale. Moreover, characterizing the impacts of climate variation on water resources is essential in managing rangelands. In this study, the effects of alternative grazing management scenarios on provisioning, regulating, and supporting services were assessed in two watersheds with contrasting climates; the Lower Prairie Dog Town Fork Red River (LPDTFR) Watershed in North Texas and the Apple Watershed in South Dakota. The impacts of heavy stocking continuous grazing, light stocking continuous grazing, Adaptive Multi-Paddock (AMP) grazing, and an ungrazed exclosure were compared using the Soil and Water Assessment Tool (SWAT) model. Our results indicate that the quantity of snow and timing of snow melt substantially influenced grazing management effects on ecosystem services in the Apple Watershed. In contrast, precipitation was the main factor influencing these effects in the LPDTFR Watershed because it highly affected the variation in water cycling, streamflow, sediment, and nutrient controls. Simulated results indicated that AMP grazing was the optimal grazing management approach for enhancing water conservation and ecosystem services in both watersheds regardless of climatic conditions. The Apple Watershed, which is a snow-dominated watershed, exhibited greater ecosystem service improvements under AMP grazing (50.6%, 58.7%, 74.4%, 61.5% and 72.6% reduction in surface runoff, streamflow, and sediment, total nitrogen (TN) and total phosphorus (TP) losses, respectively as compared to HC grazing) than the LPDTFR Watershed (46.0%, 22.8%, 34.1%, 18.9% and 38.4% reduction in surface runoff, streamflow, and sediment, TN and TP losses, respectively). Our results suggest that improved grazing management practices enhance ecosystem services and water catchment functions in rangeland-dominated areas, especially in colder climates.

Soluble phenols in litter are reduced during passage through the soil macrofauna gut due to the formation of insoluble complexes with proteins: A case study with isopods and Diptera larvae

Plant litter represents a major source of soil organic matter and hence understanding the pathway of its decomposition and stabilisation is crucial for understanding the soil carbon dynamic. Importantly, more than half of annual litter production is consumed by soil fauna globally. Here we test the hypothesis that soluble phenols can be removed from the litter during gut passage and bound on nitrogen rich compounds, which results in formation of insoluble complexes in the faeces produced by soil fauna. Two invertebrate species, Diptera larvae Bibio marci and terrestrial isopod Armadilidium vulgare, and litter of two tree species, Quercus robur and Alnus glutinosa, were used. Both species of invertebrates were fed by both litter types in full factorial manner. The litter contained significantly more free phenols than the faeces. In opposite, the content of bound phenols was significantly higher in faeces than in the litter. The loss of total nitrogen associated with removal of bound phenolic compounds from faeces was higher than that of the litter. Thus, soil fauna contributes to the stabilisation of soil organic matter by the conversion of soluble phenols to insoluble ones together with nitrogen immobilization. In conclusion, this process of stabilisation likely plays an important role in mature soils where mineral surfaces have reached carbon saturation or in soils with higher organic horizons.

Loss and conservation of soil organic carbon and nutrients in arid and semiarid China during aeolian dust emissions

In this study, based on the application of the integrated wind erosion modeling system (IWEMS), we comprehensively simulated the loss and conservation of soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), and total potassium (TK) during aeolian dust emissions over 2001–2020 in the arid and semiarid areas of China (ASAC). It was found that the past two decades witnessed decreasing trends in nutrient losses over the central-eastern region of Inner Mongolia, most parts of Qinghai Province, the southern part of the Xinjiang Autonomous Region, and the northwestern part of the Tibet Autonomous Region. The results, being model-based estimates, showed that the ecosystems of the ASAC were crucial in preventing annual losses of SOC, TN, TP and TK: approximately 27318.25 Gg, 2311.18 Gg, 1077.28 Gg and 35780.10 Gg, respectively. Both the losses and conservation of SOC, TN, TP and TK were consistently greater in spring and winter than in summer and autumn. The losses of SOC and nutrients during aeolian dust emissions were more serious in the west of the ASAC than in the east, both in the actual situation and the potential degenerative status. The prevention rates of SOC, TN, TP and TK for different land cover types were all greater than 92%. Comparatively speaking, the prevention rates of SOC, TN, TP and TK were the lowest for barren or sparsely vegetated land (∼92.85%−93.12%), open shrublands (∼95.65%−96.10%) and grasslands (∼98.44%−98.50%). For other land cover types, the prevention rates of SOC, TN, TP and TK were all over 99.62%.

Long‐term cultivation drives soil carbon, nitrogen, and bacterial community changes in the black soil region of northeastern China

AbstractThe deteriorating soil carbon, nutrients, and microbial habitat pose a serious threat to crop production. However, the effects of long‐term cultivation with soil erosion on soil carbon, nitrogen, and bacterial communities remain poorly understood. Consequently, this study aims to explore the changes in these soil indicators in the last 110 years and their responses to soil erosion. Luvic Phaeozems in hillslope and Haplic Phaeozems in flat were sampled along 113‐ and 67‐year cultivation chronosequences. The soil organic carbon (SOC), total nitrogen (TN), soil loss rate, the soil bacterial community, and so on were respectively determined using the Walkley–Black, the Kjeldahl, nuclide tracing method, and 16S rRNA amplicon sequencing methods. The comparisons of SOC, TN, and soil bacterial community between Luvic Phaeozems and Haplic Phaeozems were used to differentiate their responses to the soil erosion intensity. The results indicated that SOC and TN decreased negatively and exponentially during long‐term cultivation and took longer to regain stability in Luvic Phaeozems than in Haplic Phaeozems (e.g., SOC: from 55.77 to 23.11 g kg−1 after 152 years vs. from 91.83 to 34.24 g kg−1 after 32 years). The bacterial community transitioned into Proteobacteria‐dominant communities and the quantity of carbon‐fixing and nitrogen‐fixing functional groups decreased. These shifts were mainly driven by the SOC and TN contents (40%) and their loss ratios (44%). In conclusion, soil erosion leads to more severe SOC and TN loss on hillslope than flat under long‐term improper cultivation, ultimately endangering soil bacterial ecological functions, which has important implications for effective soil erosion control and encouraging conservation tillage in this food‐producing region.

Discharge dynamics of agricultural diffuse pollution under different rainfall patterns in the middle Yangtze river

Rainfall plays a crucial role in influencing the loss of agricultural diffuse pollution. The middle Yangtze River region is well-know for its humid climate and numerous agricultural activities. Thus, this study quantitatively analyzed the concentration and distribution of nitrogen (N) and phosphorus (P) load and loss in a major tributary of the middle Yangtze River under different rainfall patterns by using sampling analysis and SWAT model simulation. The total nitrogen (TN) and nitrate-nitrogen (NO3−) concentrations were 1.604–3.574 and 0.830–2.556 mg/L, respectively. The total phosphorous (TP) and Soluble Reactive Phosphorus (SRP) were 2–148 and 2–104 μg/L, respectively. The modeling results demonstrated that higher rainfall intensity led to greater load and loss flux of diffuse pollutant at the outlet. Organic nitrogen (ORGN) is the main nitrogen form transported from the subbasin to the reach, while organic phosphorus (ORGP) and inorganic phosphorus (INORGP) were transported at similar amounts. Under the condition of conventional rainfall, the outlet reaches mainly transported NO3−, and ORGN gradually increased when rainstorm events occurred. The ratio of INORGP to ORGP was relatively stable. During extreme rainfall event, rainfall is the dominant element of agricultural diffuse pollution. A strong positive correlation exists between rainfall intensity and pollution loss during rainstorms. Storm rain events were the main source of TN and TP losses. Few storm rain days generated pollutants that accounted for a large proportion of the total loss, and their impact on TP loss was significantly greater than that of TN. The influence of storm rain on TN is mainly the increase in runoff, while TP is sensitive to the runoff and sediment transport promoted by rainfall. By setting different precipitation scenarios, it was confirmed that under the same rainfall amount, short-term storm rain has the most significant impact on the TN load, whereas TP load may be influenced more by the combined effects of rainfall duration and intensity. Therefore, to reduce the impact of agricultural diffuse pollution, it is important to take targeted measures for the rainstorm days.

Analysis of nitrogen and phosphorus loss of typical economic forests in Zhejiang Province

The quantitative relationship between accumulated rainfall and accumulated total nitrogen and total phosphorus loss was analyzed by setting up economic forest experimental sites in typical regions of Zhejiang Province, and the response efficiency of accumulated total phosphorus and total nitrogen loss in different economic forests to rainfall was compared The results showed that there was a significant linear relationship between accumulated rainfall and accumulated total nitrogen and total phosphorus loss. The total nitrogen and total phosphorus loss rate of Castanea mollissima Blum economic forest was higher than that of Phyllostachys edulis forest and nursery > Morella rubra > Camellia sinensis > Phyllostachys edulis. Man-made disturbance of economic forest will accelerate the loss of total nitrogen and total phosphorus, and its loss rate is 1.5~4 times that of natural economic forest. The total nitrogen loss rate of 28% and total phosphorus loss rate of 47% can be reduced by planting shrubs or herbs under the in the Phyllostachys edulis forest. The purification efficiency of total phosphorus and total nitrogen of different economic forests is affected by economic forest types, ecological restoration, rainfall, and the purification efficiency varies between 30% and 70%.

Interconversion and Removal of Inorganic Nitrogen Compounds via UV Irradiation

Dissolved inorganic nitrogen (DIN) species are key components of the nitrogen cycle and are the main nitrogen pollutants in groundwater. This study investigated the interconversion and removal of the principal DIN compounds (NO3−, NO2− and NH4+) via UV light irradiation using a medium-pressure mercury lamp. The experiments were carried out systematically at relatively low nitrogen concentrations (1.5 mM) at varying pHs in the presence and absence of oxygen to compare the reaction rates and suggest the reaction mechanisms. NO3− was fully converted into NO2− at a pH > 3 in both oxic and anoxic conditions, and the reaction was faster when the pH was increased following a first-order kinetic at pH 11 (k = 0.12 min−1, R2 = 0.9995). NO2− was partially converted into NO3− only at pH 3 and in the presence of oxygen and was stable at an alkaline pH. This interconversion of NO3− and NO2− did not yield nitrogen loss in the solution. The addition of formic acid as an electron donor led to the reduction of NO3− to NH4+. Conversely, NH4+ was converted into NO2−, NO3− and to an unidentified subproduct in the presence of O2 at pH 10. Finally, it was demonstrated that NO2− and NH4+ react via UV irradiation with stoichiometry 1:1 at pH 10 with the total loss of nitrogen in the solution. With these results, a strategy to remove DIN compounds via UV irradiation was proposed with the eventual use of solar light.

Monitoring, Modeling and Planning Best Management Practices (BMPs) in the Atwood and Tappan Lake Watersheds with Stakeholders Engagements

This study was conducted in the Atwood and Tappan Lakes watersheds of the Tuscarawas basin of Ohio. The flow, total nitrogen (TN), and total phosphorus (TP) loadings were monitored with the help of local stakeholders for a few years at various locations of the watershed to develop the Soil and Water Assessment Tool (SWAT). The multi-site SWAT model calibration and validation were accomplished with a reasonable model performance. In the next step, the scenario analysis was conducted in the SWAT model using various BMPs, including vegetative filter strips, grass waterways, fertilizer reduction, crop rotation, and cover crops to evaluate their performance in reducing TN and TP from the watershed. While BMPS in many studies are decided based on researchers’ intuition, these BMPs were selected based on active consultation with the local stakeholders, who were engaged in the reduction of TN and TP loadings from the watersheds. Since the SWAT model calibration for TN and TP was not as good as the hydrologic model calibration, various scenarios of TN and TP reduction using BMPs were investigated for several years using both calibrated and uncalibrated SWAT models. We examined all the BMPs in 12 sub-watersheds of the Atwood and 10 sub-watersheds of the Tappan Lake watershed. The analysis indicated that the management practices of cover crops (rye) in combination with grass waterways with a 10% fertilizer reduction could minimize the TN and TP loading by as much as 88%, without significantly compromising the agricultural yield. However, a 10% fertilizer reduction without any BMPs could reduce TN and TP by just 9%. The cover crop (rye) including 10% fertilizer reduction with grass waterways seemed to be the most effective in reducing TN and TP, whereas the implementation of a filter strip led to a 70% reduction and was the next effective BMPs in reducing TN and TP loadings. In general, TN losses were reduced by 8% to 53%, while TP losses were reduced by 7% to 88%, depending on the BMPs used. By and large, the TN and TP reduction achieved through the calibrated model was not significantly different from the uncalibrated model, even though the reduction using the calibrated model was slightly higher for all scenarios than that of the uncalibrated model. The TN and TP loadings were highly sensitive to cattle grazing. When just 50% of the cattle were permitted to graze, the model predicted that there would be a 40% increase in total nitrogen and a 70% increase in total phosphorus in both watersheds. Our investigation revealed that monitoring the watershed at a small sub-watershed scale and calibrating the SWAT model for nitrogen and phosphorus is delicate.

Feedstock optimization with rice husk chicken manure and mature compost during chicken manure composting: Quality and gaseous emissions

This study investigated the impact of mature compost input on compost quality, greenhouse gases (GHGs, i.e. methane and nitrous oxide) and ammonia emissions during chicken manure and rice husk chicken manure co-composting. The experiment used different volumes of mature compost: 10% (T1), 20% (T2), and 30% (T3) to replace rice husk chicken manure. Results showed that mature compost enhanced compost maturity by promoting the activities of Bacillus, Caldicoprobacter, Thermobifida, Pseudogracilibacillus, Brachybacterium, and Sinibacillus. Compared to CK, T1, T2, and T3 reduced NH3 emission by 32.07%, 33.64%, and 56.12%, and mitigated 14.97%, 16.57%, and 26.18% of total nitrogen loss, respectively. Additionally, T2 and T3 reduced CH4 emission by 40.98% and 62.24%, respectively. The N2O emissions were positive correlation with Lactobacillus, Pseudogracilibacillus and ammonium nitrogen (p < 0.05), while T2 reducing total greenhouse effects. Therefore, replacing rice husk chicken manure with 20% mature compost is an efficient and promising approach for composting.

Extreme rainstorms change organic matter compositions and regulate greenhouse gas production in mangrove sediments

Extreme rainstorms can flush intertidal sediments and drive the transport of large amounts of organic matter from land to sea. Mangrove wetlands, one of the most important “blue carbon” habitats, are located in the intertidal zone and serve as an ecological corridor connecting land and sea. In this study, we investigated the effects of extreme rainstorms on organic carbon compositions, source-sink processes based on the MixSIAR model, and the production of greenhouse gases, including carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), using mangrove sediments. The results showed that in the intertidal zone, the total contents of sediment organic carbon, mineral-bound, and fine-particle organic carbon, humic acid, and humin were improved by the influence of an extreme rainstorm. The contents of coarse sediment organic carbon (SOCcoarse) and fulvic acid were decreased and were exported from intertidal zone to the sea. In tidal creek zones, extreme rainstorms enhanced the mean production rates of CH4 and CO2 by 817.4% and 34.3%, respectively, owing to the increased terrestrial organic matter, including SOCcoarse and humic acid. The N2O production rate was decreased by 72.2% in the creek zone because of the loss of total nitrogen after an extreme rainstorm. These findings provide new insights into SOC components, mechanisms of greenhouse gas production, and their response to extreme rainstorms, which will be helpful for the management of coastal wetlands and our understanding of how frequent extreme weather controls wetland biogeochemical processes.

Nitrogen mass balance and uptake velocity for eutrophic reservoirs in the Brazilian semiarid region.

The nitrogen (N) cycle from the catchment to the downstream reservoir is complex, particularly the quantification of N losses. However, in order to assess the nitrogen impact in a reservoir ecosystem, simplified models may be applicable regarding the TN load production and the magnitude of lake TN removal. This study presented a methodology to perform and validate a TN mass balance to further calibrate a simplified coefficient for TN losses (vf.) in 29 tropical semiarid reservoirs. The study reservoirs were highly productive ecosystems with an average total nitrogen (TN) concentration, accounting for all measurements in all reservoirs, ranging from 0.59 to 3.84 mg L-1. Regarding the production of TN load, the median values ranged from 4.35 to 2,499.43 t year-1 with median of 80.34 t year-1. The TN loads were estimated through an annual mass balance over a 24-year period. The median of the estimates was compared with reference values obtained by using the export modelling coefficient. The correlation between the median estimated and reference loads resulted in satisfactory agreement (r2 0.88) and reinforced the reliability of the mass balance alternative. From the validated TN loads, the TN uptake velocity (vf) was estimated for all reservoirs (44.9 ± 20.1 m year-1) and could be described as a general function of the water residence time. The reservoirs of the study region have demonstrated higher vf than temperate lakes and reservoirs and similar vf with Latin America/Caribbean ones. As expected, reservoirs of warmer climates tend to present intensified N loss processes compared to lakes and reservoirs of temperate regions. The methodology proposed in the present study can be used to potentially improve water quality management in tropical semiarid reservoirs.

Soil erosion and nutrient loss due to changes in rainfall intensity under different wind directions

AbstractIn nature, wind often occurs simultaneously with rainfall, causing nutrient loss in soil and water on slopes. However, the influence of different rainfall intensities combined with different wind directions on soil erosion and nutrient loss remains unclear. This study utilized wind‐driven rainfall laboratory flume experiments to analyse the influence of different wind directions (windward, leeward and crosswind) and rainfall intensities (30, 60 and 90 mm h−1) with constant wind speed (5 m s−1) on slope runoff, sediment yield and the associated losses of different forms of N ( , ) and P ( ‐P). The response of soil erosion, N and P loss to rainfall changes with different wind directions. When the rainfall intensity was constant, runoff, sediment yield and sediment‐associated total nitrogen (TN) and total phosphorus (TP) losses on slopes showed a trend of leeward &gt; crosswind &gt; windless &gt; windward, whereas runoff‐associated TN and TP losses showed a trend of windward &gt; crosswind &gt; windless &gt; leeward. Runoff, sediment yield and sediment‐associated TN and TP losses on leeward slopes were 1.09–1.17, 1.25–1.44, 1.33–1.62, and 1.40–1.66 times than windless slopes. Moreover, with constant wind direction, the runoff, sediment yield and associated N and P losses increased significantly with increasing rainfall intensity. When the rainfall intensity increased from 30 to 60 and 90 mm h−1, the runoff, sediment yield and associated TN and TP losses increased 2.02–2.28, 3.65–5.35, 3.96–34.39 and 4.28–8.45 times, respectively. The effects of rainfall on soil erosion and nutrient loss were significantly greater than those of wind. The loss of different forms of N and P associated with runoff and sediment was consistent with that of TN and TP losses. However, with an increase in rainfall intensity, the growth rates of runoff, sediment yield and associated N and P losses exhibited a gradually weakening trend for all wind directions. An increase in rainfall intensity enhanced the vertical vector force of wind‐driven rainfall, which increasingly decreased the angle between the rain incidence and the normal line of the horizon; therefore, the direction of the rain erosion force gradually approached that of windless conditions.

Nitrogen evolution during membrane-covered aerobic composting: Interconversion between nitrogen forms and migration pathways

Aerobic composting is a promising technology for converting manure into organic fertilizer with low capital investment and easy operation. However, the large nitrogen losses in conventional aerobic composting impede its development. Interconversion of nitrogen species was studied during membrane-covered aerobic composting (MCAC) and conventional aerobic composting, and solid-, liquid-, and gas-phase nitrogen migration pathways were identified by performing nitrogen balance measurements. During the thermophilic phase, nitrogenous organic matter degradation and therefore NH3 production were faster during MCAC than uncovered composting. However, the water films inside and outside the membrane decreased NH3 release by 13.92%–22.91%. The micro-positive pressure environment during MCAC decreased N2O production and emission by 20.35%–27.01%. Less leachate was produced and therefore less nitrogen and other pollutants were released during MCAC than uncovered composting. The nitrogen succession patterns during MCAC and uncovered composting were different and NH4+ storage in organic nitrogen fractions was better facilitated during MCAC than uncovered composting. Overall, MCAC decreased total nitrogen losses by 33.24%–50.07% and effectively decreased environmental pollution and increased the nitrogen content of the produced compost.

The coexisted nitrate and nitrite as a driving force for the aerobic denitrification of Peribacillus sp. EM-C3

A heterotrophic nitrifying and aerobic denitrifying strain was newly isolated from a biogas slurry sample and assigned to be Peribacillus sp. EM-C3 based on phylogenetic and morphological analyses. This strain was capable of removing approximately 95.96% of ▪ , 93.63% of ▪ , and 99.71% of ▪ without nitrite accumulation, with maximum conversion rates of 4.98, 2.73, and 3.17 mg/L/h, respectively. Nitrogen balance analysis showed that high total nitrogen loss (> 50%) was achieved by utilizing ▪ , ▪ , or ▪ as a nitrogen source. Importantly, the maximum ▪ and ▪ removal rates increased to 3.78 and 4.42 mg/L/h when both ▪ and ▪ were present in the system, as this promoted aerobic denitrification by the strain. The key activities of enzymes involved in nitrogen metabolism (ammonia monooxygenase, and nitrate and nitrite reductases) were 0.45, 0.15, and 0.01 U/mg protein, respectively. Taken together, these results show that the coexistence of nitrate and nitrite may promote aerobic denitrification by Peribacillus sp. EM-C3.

Partitioning of the denitrification pathway and other nitrite metabolisms within global oxygen deficient zones

Oxygen deficient zones (ODZs) account for about 30% of total oceanic fixed nitrogen loss via processes including denitrification, a microbially mediated pathway proceeding stepwise from NO3– to N2. This process may be performed entirely by complete denitrifiers capable of all four enzymatic steps, but many organisms possess only partial denitrification pathways, either producing or consuming key intermediates such as the greenhouse gas N2O. Metagenomics and marker gene surveys have revealed a diversity of denitrification genes within ODZs, but whether these genes co-occur within complete or partial denitrifiers and the identities of denitrifying taxa remain open questions. We assemble genomes from metagenomes spanning the ETNP and Arabian Sea, and map these metagenome-assembled genomes (MAGs) to 56 metagenomes from all three major ODZs to reveal the predominance of partial denitrifiers, particularly single-step denitrifiers. We find niche differentiation among nitrogen-cycling organisms, with communities performing each nitrogen transformation distinct in taxonomic identity and motility traits. Our collection of 962 MAGs presents the largest collection of pelagic ODZ microorganisms and reveals a clearer picture of the nitrogen cycling community within this environment.

Carbon‐iron coupling reduced N2O emissions via promoting the conversion to N2 in paddy soils

AbstractThe influence of redox reactions involving carbon‐iron coupling (organic carbon and iron oxides) on nitrous oxide (N2O) production in paddy soils remains poorly understood. In this study, two microcosm experiments were conducted to investigate the effects of carbon‐iron coupling on N2O emissions, and the underlying mechanisms were verified using quantitative denitrification functional genes (nirS, nirK, nosZI and nosZII) and high‐throughput sequencing. The results showed that ferrihydrite (iron) significantly promoted N2O‐N emissions (p &lt; 0.05) after adding ammonium nitrogen, while glucose (carbon) significantly inhibited N2O‐N emissions (p &lt; 0.05). Carbon‐iron coupling significantly decreased N2O‐N emissions (p &lt; 0.05) but did not affect soil total nitrogen loss and increased nitrogen (N2) emissions. After adding high concentrations of acetylene (10% C2H2), the N2O‐N emissions from carbon‐iron coupling treatment increased significantly from 6.4 to 11.9 mg N kg−1 (p &lt; 0.05), which confirmed that the carbon‐iron coupling reduced the N2O emissions by promoting the conversion of N2O to N2. The mechanisms behind carbon‐iron coupling promoting complete denitrification and reducing N2O emissions were attributed to glucose promoting iron reduction and carbon‐iron coupling enhancing the abundance of nosZI (42.7%) and nosZII (16.6%).

Surface Runoff and Diffuse Nitrogen Loss Dynamics in a Mixed Land Use Watershed with a Subtropical Monsoon Climate

The surface hydrology and diffuse pollution loading is hypothesized based on the unique characteristics under different rainfall types in watersheds with a subtropical monsoon climate. This study evaluated the effects of different rainfall event intensity on surface runoff and diffuse nitrogen loss in a subtropical watershed located in the latitude range between 22.5° north and 25° north in southern China by adapting the hydrological model SWAT (Soil and Water Assessment Tool). The rainfall events were classified into four categories including light rainfall (LR), moderate rainfall (MR), intense rainfall (IR), and extreme rainfall (ER). Our results showed that the ER events had the lowest occurrences of 7 days per year, but they contributed the most to total surface runoff (54.29%) and TN losses (57.63%) in the subtropical watershed researched. Although forests and pastures had a better effect on reducing diffuse pollution, their surface runoff and nitrogen loss were still proved to be serious under ER events. As for the nitrogen loss form, water-soluble nitrogen oxides nitrogen (ON-N) loss was the dominant form of total nitrogen (TN) loss, which accounted for 90% of the total loss in the simulated watershed in the subtropical monsoon climate region. Under LR events, however, nitrate nitrogen (NO3-N) accounted for 74.54% and 55.59% of TN losses from paddy fields and dry lands, respectively. The effects of antecedent soil water content (ASW) on surface runoff and TN loss were higher under ER events. The surface runoff and TN loss in the high-ASW condition were 1.17–3.86 times and 1.34–1.76 times higher, respectively, than in the low-ASW condition. These findings highlighted the important influence of ER events on diffuse pollution and have significant implications for controlling diffuse pollution under different rainfall types. This conclusion proved that extra attention and efforts are required in handling non-point-source pollution in subtropical monsoon watersheds than the watersheds in cooler regions because the natural systems including forest and pastures are no longer effective enough in controlling surface runoff and TN loss during ER.