High Nitrogen Loading Research Articles

Estimating the impact of temperature and streamflow change on river nitrogen pollution using the land-river integrated modeling system

The high nitrogen load in most rivers across the globe causes various environmental issues. Non-point source (NPS) pollution within a watershed has a significant impact on water quality management and prediction accuracy in rivers. Temperature and streamflow, as the most important environmental indicators, significantly affect water pollution management. This study takes the Rappahannock River Basins (RRB) as a case and adopts the method of coupling land and river models to improve the simulation accuracy of river pollution, outputs and analyzes the temporal and spatial distributions of nitrogen pollution in RRB, assesses the impact of temperature and streamflow changes on nitrogen pollution in water bodies. The results show that NPS pollution is mainly affected by topography and land use, and the annual output is more correlated with the watershed area. Temperature is negatively correlated with NH4-N and NO3-N in the Rappahannock River. Nitrogen is more susceptible to streamflow in winter; but in summer, it was stable and even showed the opposite changing tendency to winter. Changes in temperature of 1.5 ∼ 2℃ and streamflow of 20 ∼ 50% have similar effects on NH4-N, while increasing streamflow can significantly increase the concentration of NO3-N, and most of these changes are very evident. NH4-N and NO3-N concentrations will increase in RRB when the summer temperature is below the long-term average. NH4-N concentration will increase when upstream streamflow (such as the amount of mountain snowmelt) decreases in winter, while NO3-N concentration will decrease. The establishment of the integrated model can provide the nitrogen pollution load of each sub-watershed and each segment, which can be used to develop the TMDL for the Rappahannock River.

Balancing Water Ecosystem Services: Assessing Water Yield and Purification in Shanxi

Water yield and purification are important aspects of water ecosystem services, and achieving a balanced development of the two is necessary for the development of aquatic ecosystems. Using the InVEST model, the spatiotemporal variations of regional water yield and purification services in Shanxi, China, from 2000 to 2020 were analyzed. Three future scenarios (natural development, urban development, and ecological protection) were assessed for 2030 using the PLUS model. The results showed that in 2000–2020, the water yield of Shanxi Province in terms of space was generally low in the middle and northwest and high in the southeast, and it was affected by land-use change and climatic change. From 2000 to 2020, the water yield of Shanxi Province changed by 78.8 mm. In 2030, water yield will be highest under the urban development scenario (380.53 mm) and lowest in the ecological protection scenario (368.22 mm). Moreover, the water quality purification capacity improved, with nitrogen loading high in the center and low in the east and west. Due to the implementation of environmental protection policies and the improvement of the technical level, the nitrogen load was the highest in 2000 (0.97 kg/hm2) and lowest in 2015 (0.94 kg/hm2). By 2030, because of the high nitrogen loadings of cultivation and construction land and low nitrogen loadings of forests and grasslands, the nitrogen load was lowest under the scenario of urban development (0.94 kg/hm2) and highest under ecological protection (0.85 kg/hm2).

Low discharge intensifies nitrogen retention in rivers – A case study in the Elbe River

Eutrophication due to excessive nutrient inputs is a major threat to coastal ecosystems worldwide, causing harmful algae blooms, seagrass loss and hypoxia. Decisions to combat eutrophication in the North Sea were made in the 1980s. Despite significant improvements during recent decades, high nitrogen loads and resulting eutrophication problems remain. In this study, long-term changes in nitrogen inputs to the Elbe Estuary (Germany) were characterized based on nitrogen data provided by the Elbe River Basin Community from 1985 to 2019. Additionally, surface water samples were taken at the weir separating the river from the estuary from 2011 to 2021 to characterize dissolved inorganic nitrogen concentrations and nitrate stable isotope composition. The findings suggest a close coupling of river discharge with the riverine nitrogen cycle. Nitrogen loads decreased disproportionately with decreasing discharge. This decrease is due to intensified nitrogen retention in the Elbe catchment, which can double nitrogen retention compared to average discharge conditions. Phytoplankton growth was enhanced by long residence times and high light availability at low water levels. This suggests that the recent decreases in nitrogen loads in the Elbe River were not only a result of management measures in the catchment but were also amplified by a recent long-lasting drought in the catchment. Based on projections from the Intergovernmental Panel on Climate Change, more frequent and extensive droughts are anticipated, which may lead to future seasonal shifts to nitrate limitation in the lower Elbe River.

Start‐up and operation of anammox biofilter in treating low‐strength ammonia wastewater prepared by tail water from a municipal wastewater treatment plant

AbstractBACKGROUNDEconomic technology of advanced nitrogen removal of municipal wastewater is urgently needed. In this study, anammox biofilter (A‐BF) as a carbon‐ and energy‐saving advanced nitrogen removal process was tested under the conditions of sewage secondary effluent.RESULTSThe results showed that A‐BF could be successfully started up under total nitrogen (TN) of both 25 and 75 mg L−1 within 30 days at 25 °C. It achieved a nitrogen removal rate of 0.62 ± 0.08 kg‐N m−3 d−1 with nitrogen loading rate of 1.35 kg‐N m−3 d−1 at TN of 17 mg L−1. The ceramsite bed was conducive to the formation of biofilm and enrichment of functional microorganisms. The volatile suspended solid reached 1.39–7.33 g L−1, in which the abundance of the typical anammox bacteria Candidatus_Brocadia and Candidatus_Kuenenia occupied 0.96–1.35% and 0.29–0.92%, respectively.CONCLUSIONSOverall, under low TN concentration and high nitrogen load, A‐BF could be a candidate technique for advanced nitrogen removal of municipal sewage. © 2023 Society of Chemical Industry.

Deammonification Potential of Pig Slurries and Vapor Condensates from Sewage Sludge Drying-Substrate Quality and Inhibition.

Deammonification is a well-established process for sludge liquor treatment and promising for wastewaters with high nitrogen loads because of its low energy demand compared to nitrification/denitrification. Two wastewaters with high NH4-N concentrations and a rising significance in Germany-pig slurry (12 samples) and condensates from sewage sludge drying (6 samples)-were studied for their deammonification potential. Furthermore, a comprehensive quality assessment is presented. Both wastewaters show a wide range in terms of CODt, CODs, TN and NH4-N, whereby condensates show a greater variability with no direct relation to dryer type or temperature. In the slurries, CODt shows a relative standard deviation of 106% (mean 21.1 g/L) and NH4-N of 33% (mean 2.29 g/L), while in condensates it reaches 148% for CODt (mean 2.0 g/L) and 122% for NH4-N (mean 0.7 g/L). No inhibition of ammonium-oxidizing-bacteria was detected in the slurries, while two out of five condensates showed an inhibition of >40%, one of >10% and two showed no inhibition at all. Since the inhibition could be avoided by mixing, deammonification can be recommended for condensate treatment. For slurry treatment, the importance of employing some form of solid-liquid-separation as a pretreatment was noted due to the associated COD.

1561-P: Dietary Proteins Impact Glucose Tolerance and Hepatic Insulin Resistance in Mice through Modulation of the Urea Cycle

We recently reported that dietary proteins (DP) modulate diet-induced obesity and insulin resistance in mice (Nat Commun 12: 3377, 2021). We posit that these metabolic alterations are caused by differential activation of the hepatic urea cycle in response to different amino acid (AA) compositions and total nitrogen load. Objective: To test whether DP sources alter hepatic metabolism and insulin resistance through the urea cycle. Methods: Metabolic phenotypes, hepatic urea cycle and insulin resistance were measured in mice fed low-fat, low-sucrose (LFLS) or high-fat, high-sucrose (HFHS) diets containing either pork (PP), soy (SP) or casein (CP) protein for 12 weeks. Based on their AA composition, PP had the highest nitrogen load, followed by SP and CP. Results: When compared to SP and CP, feeding PP to HFHS mice induced more glucose intolerance which was correlated with higher post-prandial AA-derived nitrogen load in the portal vein. PP feeding in HFHS mice induced hepatic insulin resistance, revealed by impaired insulin-induced Akt phosphorylation on Ser473. Mice fed the LFLS diet were, however, protected from PP-induced glucose intolerance and insulin resistance, and this was associated with robust increase in the protein levels of urea cycle enzymes (CPS1, OTC) in the liver. In starked contrast, induction of urea cycle enzymes was blunted in the liver of PP-fed HFHS mice. PP feeding also increased the expression of inducible nitric oxide synthase (iNOS) and reactive oxygen species (ROS) as showed by DHE staining of liver sections. Conclusion: Dietary PP increases total nitrogen load activating the urea cycle, which may protect against metabolic dysfunction and hepatic insulin resistance in LFLS mice. This protective mechanism is lost in PP-fed HFHS mice, likely by downregulation of urea cycle activity, when the liver is overloaded with dietary fat. iNOS induction could be acting as an alternative nitrogen handling pathway, causing a build-up of mitochondrial ROS. Disclosure F.Bégin: None. A.Caron: None. A.Marette: Advisory Panel; Valbiotis, Amancia, Plexus, Acasti.

Introducing molasses as an alternative feedstock into itaconate production using Ustilago sp

In this work, we established an efficient process for the production of itaconate from the regionally sourced industrial side-stream molasses using Ustilago cynodontis and Ustilago maydis. While being relatively cheap and more environmentally friendly than refined sugars, there are some major challenges to overcome when working with molasses. Some of those challenges are a high nitrogen load, unknown impurities in the feedstock, and high amounts of ill-favoured carbon sources, such as sucrose or lactate. We could show that the activity of the sucrose-hydrolysing enzyme invertase plays a crucial role in the efficiency of the process and that the fructose utilisation differs between the two strains used in this work. Thus, with a higher invertase activity, the ability to convert fructose into the desired product itaconate, and an overall higher tolerance towards undesired substances in molasses, U. maydis is better equipped for the process on the alternative feedstock molasses than U. cynodontis. The established process with U. maydis reached competitive yields of up to 0.38 g g−1 and a titre of more than 37 g L−1. This shows that an efficient and cost-effective itaconate production process is generally feasible using U. maydis, which has the potential to greatly increase the sustainability of industrial itaconate production.

Implication of dissolved nitrogen dynamics of urban rivers using multivariate regression and structural equation modeling

AbstractThe river's functional balance varies according to flow regimes and nutrient distribution. Watercourses can receive water from different point and nonpoint sources, which discharge high nitrogen load in rivers generated from domestic and industrial effluents and agricultural runoff. The excessive concentration of nitrogen load affects the riverine ecosystem by attenuating dissolved oxygen balance and disturbing the water quality. A study has been conducted to determine the nitrogen dynamics and their impact on the water quality of the Delhi stretch of Yamuna River, India, which is highly influenced by anthropogenic activities. Multivariate linear regression (MLR) was performed to gain insight into nitrogen dynamics, and structural equation modeling was applied to determine the direct (primary) and indirect (secondary) relation between the water quality parameters and the subsequent impact on water quality. Dissolved inorganic nitrogen (DIN) was measured using ammonia, nitrate, and nitrite, and total Kjeldahl nitrogen was estimated to reflect the dissolved organic nitrogen (DON). The variation in dissolved nitrogen (organic and inorganic) signifies high negative flux on the river's organic content, causing further degradation of river water quality. MLR predicted a high correlation between predicted and observed DIN at the Income Tax Office (ITO) (92.5%) and Nizamuddin (94.37%) and DON at ITO (93.49%) and Nizamuddin (95.28%). The high concentration during the lean period deteriorates the water quality tremendously and suggests that the variation in dissolved nitrogen content should be monitored carefully to maintain the river's water quality dominated by the organic load.

Coastal acidification alters estuarine sediment nitrous oxide and methane fluxes

AbstractThe impact of coastal acidification on sediment nitrous oxide (N2O) and methane (CH4) fluxes is largely unknown. We exposed temperate estuarine sediments to moderate (pH 7.3) and extreme (pH 6.3) acidification. Sediments were collected from two sites—one exposed to high and the other to low nitrogen loading. We demonstrate that low pH has a strong effect on greenhouse gas fluxes. The response, in terms of both magnitude and direction, was site specific. Sediments from the high nitrogen loading site exhibited increased N2O fluxes and decreased CH4 fluxes under moderate and extreme acidification. In contrast, sediments from the low nitrogen loading site exhibited decreased N2O fluxes under moderate and extreme acidification while CH4 fluxes both decreased (moderate) and increased (extreme). This study highlights the dynamic response of sediment N2O and CH4 fluxes to low pH and emphasizes the need for deeper understanding of ofcoastal acidification impacts on sediment biogeochemistry.

Enhancing anammox nitrogen removal by static magnetic field exposure: Performance, microbial community and symbiotic relationship analysis

Anammox batch reactors were operated with different static magnetic field (SMF) intensities (0 mT, 40 mT, and 100 mT). The impacts of SMF and the influent nitrogen concentration on nitrogen removal were analyzed. Sludge characteristics, microbial community structure, and metabolism pathways were explored. The results show that a high nitrogen load greatly decreased the nitrogen removal efficiency. Still, applying SMF with appropriate intensity enhanced the nitrogen removal performance, especially under high nitrogen loading conditions. Systems with 40 mT SMF at normal nitrogen loading conditions had the highest total nitrogen removal efficiency. In contrast, a higher SMF intensity was conducive to the anammox process with a high nitrogen load. Candidatus Kuenenia was fast enriched under high nitrogen loading conditions in the control systems. However, Candidatus Brocadia was more abundant than Ca. Kuenenia in the systems with SMF application. SMF was the main factor affecting the microbial metabolism, enhancing the metabolic pathways related to bacterial growth and resistance to environmental stress. The metabolic interactions between the anammox bacteria and other bacteria were enhanced by applying SMF to the anammox process, especially for the cross-feeding of cofactors and vitamins in the anammox consortia.

Integration of environmental signatures and omics-based approaches on the European flounder to assist with health assessment of estuarine ecosystems in Brittany, France

This study aimed to develop a multidisciplinary approach to assess the ecological status of six moderate-sized French estuaries. For each estuary, we gathered geographical information, hydrobiological data, chemistry of pollutants and fish biology, including integration of proteomics and transcriptomics data. This integrative study covered the entire hydrological system studied, from the watershed to the estuary, and considered all the anthropogenic factors that can impact this environment.To reach this goal, European flounder (Platichthys flesus) were collected from six estuaries in September, which ensures a minimum residence time of five months within an estuary. Geographical metrics are used to characterize land use in each watershed. The concentrations of nitrite, nitrate, organic pollutants, and trace elements were measured in water, sediments and biota. All of these environmental parameters allowed to set up a typology of estuaries.Classical fish biomarkers, coupled with molecular data from transcriptomics and shotgun proteomics, highlighted the flounder's responses to stressors in its environment. We analysed the protein abundances and gene expression levels in the liver of fish from the different estuaries. We showed clear positive deregulation of proteins associated with xenobiotic detoxification in a system characterized by a large population density and industrial activity, as well as in a predominantly agricultural catchment area (mostly cultures of vegetables and pig breeding) mainly impacted by pesticides. Fish from the latter estuary also displayed strong deregulation of the urea cycle, most probably related to high nitrogen load. Proteomic and transcriptomic data also revealed a deregulation of proteins and genes related to the response to hypoxia, and a probable endocrine disruption in some estuaries. Coupling these data allowed the precise identification of the main stressors interacting within each hydrosystem.

Chronic sleep loss sensitizes Drosophila melanogaster to nitrogen stress

Chronic sleep loss profoundly impacts metabolic health and shortens lifespan, but studies of the mechanisms involved have focused largely on acute sleep deprivation.1,2 To identify metabolic consequences of chronically reduced sleep, we conducted unbiased metabolomics on heads of three adult Drosophila short-sleeping mutants with very different mechanisms of sleep loss: fumin (fmn), redeye (rye), and sleepless (sss).3,4,5,6,7 Common features included elevated ornithine and polyamines, with lipid, acyl-carnitine, and TCA cycle changes suggesting mitochondrial dysfunction. Studies of excretion demonstrate inefficient nitrogen elimination in adult sleep mutants, likely contributing to their polyamine accumulation. Increasing levels of polyamines, particularly putrescine, promote sleep in control flies but poison sleep mutants. This parallels the broadly enhanced toxicity of high dietary nitrogen load from protein in chronically sleep-restricted Drosophila, including both sleep mutants and flies with hyper-activated wake-promoting neurons. Together, our results implicate nitrogen stress as a novel mechanism linking chronic sleep loss to adverse health outcomes-and perhaps for linking food and sleep homeostasis at the cellular level in healthy organisms.

A method for researching the eutrophication and N/P loads of plateau lakes: Lugu Lake as a case

Lugu Lake is one of the best plateau lakes in China in terms of water quality, but in recent years the eutrophication of Lugu Lake has accelerated due to high nitrogen and phosphorus loads. This study aimed to determine the eutrophication state of Lugu Lake. Specifically, the spatio-temporal variations of nitrogen and phosphorus pollution during the wet and dry seasons were investigated in Lianghai and Caohai, and the primary environmental effect factors were defined. Adopting the endogenous static release experiments and the exogenous improved export coefficient model, a novel approach (a combination of internal and external sources) was developed for the estimation of nitrogen and phosphorus pollution loads in Lugu Lake. It was indicated that the order of nitrogen and phosphorus pollution in Lugu Lake was Caohai > Lianghai and dry season > wet season. Dissolved oxygen (DO) and chemical oxygen demand (CODMn) were the main environmental factors causing nitrogen and phosphorus pollution. Endogenous nitrogen and phosphorus release rates in Lugu Lake were 668.7 and 42.0 t/a, respectively, and exogenous nitrogen and phosphorus input rates were 372.7 and 30.8 t/a, respectively. The contributions of pollution sources, in descending order, were sediment > land-use categories > residents and livestock breeding > plant decay, of which sediment nitrogen and phosphorus loads accounted for 64.3 % and 57.4 %, respectively. Regulating the endogenous release of sediment and obstructing the exogenous input from shrubland and woodland are emphasized for the management of nitrogen and phosphorus contamination in Lugu Lake. Thus, this study can serve as a theoretical foundation and technical guide for eutrophication control in plateau lakes.

Nitrogen removal performance and bacterial community analysis of a multistage step-feeding tidal flow constructed wetland

A multistage mesocosm vertical flow constructed wetland system was designed to treat synthetic domestic wastewater with a high nitrogen (N) load. The study aim was to determine the impact of design and operational variables on N removal efficiency in such systems. A tidal flow operational strategy enhanced aeration and was coupled with a step-feeding approach to promote N removal. Over the 420-day running period N removal rates were between 70 and 77 gN/m3/d, for a step-feeding ratio range of 60:40 to 80:20. The system was able to remove 91–95% of chemical oxygen demand, 74–91% of ammonium and 66–81% of total-N. Tidal flow and step-feeding strategies significantly impacted nitrogen removal with the best performance at a step-feeding ratio of 80:20 providing a carbon to nitrogen (COD/N) ratio of 4–5. The bacterial diversity increased at each stage throughout the system with dominating phyla Proteobacteria, Firmicutes, Planctomycetes, Bacteroidetes, Chloroflexi, Verrucomicrobia and Acidobacteria. Dominant bacteria at the genus level were Thiothrix, Planctomyces, Azonexus, Pseudoxanthomonas, Hydrogenophaga, Gemmobacter and other genera suggesting that N removal was accomplished via diverse metabolic pathways, including autotrophic nitrification, heterotrophic denitrification, autotrophic denitrification, and possibly anammox. This study shows benefits of step-feeding strategies in tidal flow constructed wetlands as a cost-effective solution for minimizing external carbon input to achieve effective N removal.

Watershed urbanization dominated the spatiotemporal pattern of riverine methane emissions: Evidence from montanic streams that drain different landscapes in Southwest China

Methane (CH4) emissions from streams are an important component of the global carbon budget of freshwater ecosystems, but these emissions are highly variable and uncertain at the temporal and spatial scales associated with watershed urbanization. In this study, we conducted investigations of dissolved CH4 concentrations and fluxes and related environmental parameters at high spatiotemporal resolution in three montanic streams that drain different landscapes in Southwest China. We found that the average CH4 concentrations and fluxes in the highly urbanized stream (2049 ± 2164 nmol L−1 and 11.95 ± 11.75 mmol·m−2·d−1) were much higher than those in the suburban stream (1021 ± 1183 nmol L−1 and 3.29 ± 3.66 mmol·m−2·d−1) and were approximately 12.3 and 27.8 times those in the rural stream, respectively. It provides powerful evidence that watershed urbanization strongly enhances riverine CH4 emission potential. Temporal patterns of CH4 concentrations and fluxes and their controls were not consistent among the three streams. Seasonal CH4 concentrations in the urbanized streams had negative exponential relationships with monthly precipitation and demonstrated greater sensitivity to rainfall dilution than to the temperature priming effect. Additionally, the CH4 concentrations in the urban and semiurban streams showed strong, but opposite, longitudinal patterns, which were closely related to urban distribution patterns and the HAILS (human activity intensity of the land surface) within the watersheds. High carbon and nitrogen loads from sewage discharge in urban areas and the spatial arrangement of the sewage drainage contributed to the different spatial patterns of the CH4 emissions in different urbanized streams. Moreover, CH4 concentrations in the rural stream were mainly controlled by pH and inorganic nitrogen (NH4+ and NO3−), while urban and semiurban streams were dominated by total organic carbon and nitrogen. We highlighted that rapid urban expansion in montanic small catchments will substantially enhance riverine CH4 concentrations and fluxes and dominate their spatiotemporal pattern and regulatory mechanisms. Future work should consider the spatiotemporal patterns of such urban-disturbed riverine CH4 emissions and focus on the relationship between urban activities with aquatic carbon emissions.

Influence of plants on anammox process in constructed Wetland: Irrelevance, inhibition or enhancement

Anaerobic ammonia oxidation (anammox) can become the dominant process of nitrogen removal in constructed wetland, yet whether plants that are signature composition of wetland play a significant role in this process is still unknown. Therefore, this study investigated the influence of plants (Phragmites) on the anammox-driven wetlands by comparing the differences between plant group and non-plant group. The results indicated that the proportion range of anammox process in nitrogen metabolism of both groups was estimated to be 45 %–63 % according to the detected abundance of functional genes, and there was a significant positive relationship between anammox proportion and total nitrogen removal efficiency (R = 0.81, P < 0.05), which confirmed anammox process dominating the nitrogen transformation in all systems. The average total nitrogen removal efficiencies in the systems with plants addition (84–85 %) were significantly superior than those in the corresponding control systems (74–82 %), respectively (P < 0.05). The presence of plants significantly contributed to the increase in the anammox proportion of nitrogen metabolism and the total absolute abundances of anammox bacteria (P < 0.05). Partial Least Squares Path Analysis Model (PLSPM) furtherly revealed that the estimated weight coefficients of plants to anammox process (R = 1.24) showed the larger level than denitrification process (R = 0.25). Overall, plants played an enhancing role in the anammox process of anammox-driven wetlands, rather than irrelevant or potential inhibiting role. The reason was mainly related to the plant role for improving biofilm formation by extracellular polymeric substances (EPS), and a significant positive relationship between EPS concentrations (7–224 μg·g−1) and anammox bacteria abundances (1.63–7.66 × 108 cells·g−1) was found (R = 0.44, P < 0.05). Besides, the subsidiary reasons also lie in the minimal role of plant roots under higher nitrogen loading and the appropriate nitrogen component of wastewater.

Responses of anammox and sulfur/pyrite autotrophic denitrification in one-stage system to high nitrogen load: Performance, metabolic and bacterial community

To remove residual nitrate from anammox process and achieve efficient nitrogen removal, a two-stage system (TAS) with the two individual reactors and a one-stage system (OAS) with the spatial functional areas in one reactor were established via anammox coupling sulfur autotrophic denitrification. The total nitrogen removal efficiency (TNRE) of OAS system (97.85 ± 1.92%) was higher than that of TAS system (93.63 ± 1.87%) under the influent NH4+-N and NO2−-N of 227 and 300 mg/L. Meanwhile, the responses of microbial metabolism to high nitrogen load were investigated in term of microbial metabolites, electron transfer and metabolic activity. Microbial metabolites characteristics demonstrated that the OAS system secreted more EPS with lower protein (PN)/polysaccharide (PS) ratio than that in the TAS system, which was beneficial to protect bacteria from high nitrogen load. Electrochemical analysis suggested that the secretion of electron conductive substance (such as PN, PS) and redox active substances (such as flavin mononucleotide, the binding of flavins and cytochrome c on the outer membrane) were increased in the OAS system, which promoted the electron transfer efficiency. Moreover, the electron transport system activity (ETSA) values and ATP contents in OAS system were higher than that in the TAS system, which indicated that metabolic activity was improved in OAS system under the stimulation of high nitrogen load. Additionally, the bacterial community analysis indicated that the functional bacteria of Candidatus_Kuenenia and Armatimonadetes_gp5 had higher abundance in the OAS system than that in the TAS system, which was beneficial to realize the stable nitrogen removal performance. Overall, the responses mechanism of the OAS system was established to explain the resistant to high nitrogen load.

Nitrous oxide emission and its influencing factors at the cyanobacteria-dominated lake

湖泊等内陆水体是大气N₂O潜在的重要排放源,也是全球N₂O收支估算的重要组成部分。目前全球湖泊普遍面临富营养化和蓝藻暴发等问题,明晰藻型湖泊N₂O排放强度及其环境影响因子对准确估算湖泊N₂O排放和预测其未来变化至关重要。本研究选择太湖藻型湖区为研究对象,同时选取人为活动影响较小的湖心区作为对比区域,基于2011年8月至2013年8月为期2年的逐月连续观测,探讨藻型湖区N₂O排放特征及其影响因素。结果表明,藻型湖区呈现极强的N₂O排放,其排放通量为(4.88±3.05) mmol/(m²·d),是参考区域(湖心: (2.10±4.31) mmol/(m²·d))的2倍多。此外,在藻型湖区中不同点位N₂O排放差异显著,受河流外源输入影响,近岸区是N₂O的热点排放区,其年均排放通量高达10.93 mmol/(m²·d)。连续观测表明N₂O排放具有显著的季节变化模式,但在不同区域调控N₂O排放时间变化的因子有所不同。其中,近岸区N₂O排放主要受氮负荷影响,其他区域N₂O排放变化受水温和氮负荷等多因子影响。氮素富集是藻型湖区N₂O高排放的直接原因,水体氮负荷可以作为N₂O排放热点的重要指示因子。但藻型湖泊N₂O排放极其显著的时空变异等在未来研究中应得到更多关注。;Inland lakes potential emit large nitrous oxide (N₂O) to atmosphere and play significant role in global N₂O budget estimation. Widespread global increase in lake phytoplankton blooms have been found, identifying the N₂O flux and its influencing factors at the cyanobacteria-dominated lake is essential to being able to accurate estimate the N₂O emissions from lakes and predict future change. In order to identify N₂O flux characteristics and its influencing factors in the cyanobacteria-dominated zone of Lake Taihu, the N₂O emission was observed based on the two-year field measurements. Results showed the annual mean N₂O flux from the cyanobacteria-dominated zone ((4.88±3.05) mmol/(m²·d)) was about twice higher than that in the central zone with less cyanobacteria blooms ((2.10±4.31) mmol/(m²·d)). Meanwhile, the N₂O emissions varies spatially within the cyanobacteria-dominated zone, peak N₂O emission (10.93 mmol/(m²·d)) occurred in littoral zone due to the large external loadings input via river discharge. Continuous filed measurement showed that the N₂O emission varied seasonally, but the factors influencing the seasonal patterns varied among sub-zones. Generally, the temporal variation of N₂O emission were regulated by N loadings in littoral zone, and were regulated by multiple environment variables, such as temperature and N loadings, in Meiliang Bay and the central zone. High nitrogen loadings contributed to large N₂O emission from cyanobacteria-dominated zone, indicating that N loadings can be used as proxy of N₂O emission from lakes. Considering significant temporal and spatial variation of N₂O emission from cyanobacteria-dominated zones, more attention should be paid in future research.

Stormwater biofilter response to high nitrogen loading under transient flow conditions: Ammonium and nitrate fates, and nitrous oxide emissions

Nitrogen (N) in urban runoff is often treated with green infrastructure including biofilters. However, N fates across biofilters are insufficiently understood because prior studies emphasize low N loading under laboratory conditions, or use “steady-state” flow regimes over short time scales. Here, we tested field scale biofilter N fates during simulated storms delivering realistic transient flows with high N loading. Biofilter outflow ammonium (NH4+-N) was 60.7 to 92.3% lower than that of the inflow. Yet the characteristic times for nitrification (days to weeks) and denitrification (days) relative to N residence times (7 to 30 h) suggested low N transformation across the biofilters. Still, across 7 successive storms, total outflow nitrate (NO3−-N) greatly exceeded (3100 to 3900%) inflow nitrate, a result only explainable by biofilter soil N nitrification occurring between storms. Archaeal, and bacterial amoA gene copies (2.1 × 105 to 1.2 × 106 gc g soil−1), nitrifier presence by16S rRNA gene sequencing, and outflow δ18O-NO3− values (-3.0 to 17.1 ‰) reinforced that nitrification was occurring. A ratio of δ18O-NO3− to δ15N-NO3− of 1.83 for soil eluates indicated additional processes: N assimilation, and N mineralization. Denitrification potential was suggested by enzyme activities and soil denitrifying gene copies (nirK + nirS: 3.0 × 106 to 1.8 × 107; nosZ: 5.0 × 105 to 2.2 × 106 gc g soil−1). However, nitrous oxide (N2O-N) emissions (13.5 to 84.3 μg N m − 2 h − 1) and N2O export (0.014 g N) were low, and soil nitrification enzyme activities (0.45 to 1.63 mg N kg soil−1day−1) exceeded those for denitrification (0.17 to 0.49 mg N kg soil−1 day−1). Taken together, chemical, bacterial, and isotopic metrics evidenced that storm inflow NH4+sorbs and, along with mineralized soil N, nitrifies during biofilter dry-down; little denitrification and associated N2O emissions ensue, and thus subsequent storms export copious NO3−-N. As such, pulsed pass-through biofilters require redesign to promote plant assimilation and/or denitrification of mineralized and nitrified N, to minimize NO3−-N generation and export.

The Summary of Nitritation Process in Mainstream Wastewater Treatment

The application of the mainstream partial nitritation/anammox (PN/A) process is promising due to the huge cost reduction compared to traditional biological nitrogen removal. However, the nitrite production rate (NPR) of a biological nitritation pre-treatment process is relatively lower than the nitrite consumption rate in a pure anammox reactor with a high nitrogen loading rate (NLR). Thus, the NPR is the rate-limiting step for operating the PN/A process with a higher NLR. Various studies have attempted to improve mainstream NPR. A comprehensive review of these processes is needed for the actual application of the PN/A process. This study focuses on: (1) various nitrite production processes that have emerged in recent years; (2) the main microbial species and characteristics involved in biological nitritation; (3) the existing problems and the N2O emission problem of these processes; and (4) a proposed novel and promising PN/A process facilitated with photocatalyst oxidation. This review is expected to provide references and a basis for the research on the nitritation step of the application of the mainstream PN/A process.