NO3-N Accumulation Research Articles

Optimizing roof-harvested rainwater storage: Impact of dissolved oxygen regime on self-purification and quality dynamics

Roof-harvested rainwater presents a promising, unconventional, and sustainable water resource for both potable and non-potable uses. However, there is a significant gap in understanding the quality evolution of stored rainwater under varying dissolved oxygen conditions and its suitability for various applications. This study investigated the evolution of rainwater quality under three distinct storage conditions: aerated, open, and sealed. Additionally, the microbial community and metabolic functions were analyzed to systematically evaluate the self-purification performance over long-term storage durations. The results indicate that aerated storage enhances microbial carbon metabolism, leading to a degradation rate of 54.4 %. Sealed and open storage conditions exhibited primary organic matter degradation during the early and late stages, respectively. Roof-rainwater harvesting (RRWH) systems showed limited denitrification activity across all three dissolved oxygen conditions. The maximum accumulation of NO3-N during the storage period reached 5.23 mg/L. In contrast, sealed storage demonstrated robust self-purification performance, evidenced by a comprehensive coefficient of 15.83 calculated by Streeter-Phelps model. These findings provide valuable insights into the mechanisms governing rainwater quality changes under various storage conditions, emphasizing the necessity for developing effective management strategies for the storage and utilization of roof-harvested rainwater.

Does Nitrogen Fertilization Improve Nitrogen-Use Efficiency in Spring Wheat?

To investigate the effects and mechanism of prolonged inorganic nitrogen (N) fertilization on the N-use efficiency of spring wheat (Triticum aestivum L.), a long-term study initiated in 2003 was conducted. The study analyzed how N fertilization affects dry matter translocation, N translocation, soil NO3-N, and N-use efficiency. Five different N-fertilizer rate treatments were tested: N0, N52.5, N105, N157.5, and N210, corresponding to annual N fertilizer doses of 0, 52.5, 105.0, 157.5, and 210.0 kg N ha−1, respectively. Results showed that increasing N-fertilizer rates significantly enhanced the two-year average dry matter accumulation amount (DMA) at maturity by 22.97–56.25% and pre-flowering crop growth rate (CGR) by 17.11–92.85%, with no significant increase beyond 105 kg N ha−1. However, no significant correlation was observed between the dry matter translocation efficiency (DTE) and wheat grain yield. Both insufficient and excessive N applications resulted in an imbalanced N distribution favoring vegetative growth over reproductive growth, thus negatively impacting N-use efficiency. At maturity, the N-fertilized treatments significantly increased the two-year average N accumulation amount (NAA) by 52.04–129.98%, with no further increase beyond 105 kg N ha−1. N fertilization also improved the two-year average N translocation efficiency (NTE) by 56.89–63.80% and the N contribution proportion (NCP) of wheat vegetative organs by 27.79–57.83%, peaking in the lower-N treatment (N52.5). However, high-N treatment (N210) led to an increase in NO3-N accumulation in the 0–100 cm soil layer, with an increase of 26.27% in 2018 and 122.44% in 2019. This higher soil NO3-N accumulation in the 0–100 cm layer decreased NHI, NUE, NAE, NPFP, and NMB. Additionally, N fertilization significantly reduced the two-year average N harvest index (NHI) by 9.89–12.85% and N utilization efficiency (NUE) by 11.14–20.79%, both decreasing with higher N application rates. The NAA followed the trend of anthesis > maturity > jointing. At the 105 kg N ha−1 rate, the highest N agronomic efficiency (NAE) (9.31 kg kg−1), N recovery efficiency (NRE) (38.32%), and N marginal benefit (NMB) (10.67 kg kg−1) were observed. Higher dry matter translocation amount (DTA) and N translocation amount (NTA) reduced NHI and NUE, whereas higher NTE improved NHI, NUE, and N partial factor productivity (NPFP). Overall, N fertilization enhanced N-use efficiency in spring wheat by improving N translocation rather than dry matter translocation.

Evaluating the suitability of nitrate-nitrogen levels for post-smolt Atlantic salmon Salmo salar production in RAS with assistance from heart rate bio-loggers

Previous onsite research determined that post-smolt Atlantic salmon Salmo salar growth, health, and welfare were unaffected by exposure to 99 mg/L nitrate-nitrogen (NO3-N) in freshwater recirculating aquaculture systems (RAS). A subsequent study was conducted to determine if higher concentrations negatively impact Atlantic salmon within a similar size range. Salmon production metrics were compared in triplicate RAS with NO3-N levels increasing from 100 to 250 mg/L (“high”) vs. 50–100 mg/L NO3-N (“low”). An average feed loading rate of 2.53 kg feed/m3 makeup water/day was maintained to facilitate natural NO3-N accumulation up to 75–100 mg/L, and sodium nitrate was continuously dosed to achieve higher concentrations. All-female diploid and all-female triploid Atlantic salmon were comingled in six replicated RAS, resulting in 227 fish/tank with an initial mean weight of 0.35 kg. Six diploid salmon with surgically implanted heart rate bio-loggers were included in each RAS. Continuously logged heart rates were matched with frequently measured NO3-N levels to determine the onset of a physiological response. At the end of the 6-month study, salmon exposed to the high and low NO3-N conditions weighed 1.84 ± 0.05 and 1.91 ± 0.02 kg, respectively (p > 0.05). Diploid and triploid salmon growth rates, feed conversion ratios, maturation prevalence, survival, fin condition, and cataract scores were unaffected (p > 0.05). However, salmon heart rates were generally higher in the high NO3-N treatment after concentrations exceeded 150 mg/L NO3-N. Higher plasma chloride, hematocrit, and hemoglobin levels (p < 0.05) consistent with an adaptive response to a stressor were also measured in salmon from the high NO3-N RAS during this period. These findings suggest that NO3-N concentrations < 150 mg/L do not affect post-smolt Atlantic salmon under similar operating conditions, including freshwater RAS without denitrification technologies and water hardness >300 mg/L as CaCO3. Additional research is required to determine if higher NO3-N concentrations are suitable for Atlantic salmon production over longer exposure periods and with naturally produced NO3-N levels imparted by reduced water exchange. Feed- and nitrogen-loading rates conducive to maintaining the tested NO3-N levels are reported.

Reducing nitrate and tobacco-specific nitrosamine level in burley tobacco leaves through grafting on flue-cured tobacco rootstock.

Nitrosation of pyridine alkaloids in tobacco generates tobacco-specific nitrosamines (TSNAs), which are notable toxicants in tobacco products and smoke. Burley tobacco, a chloroplast- and nitrogen (N)-deficient phenotype that accumulates high levels of nitrate-nitrogen (NO3-N) in its leaves, is particularly susceptible to TSNAs formation. In this study, reciprocal pot and field grafting experiments were conducted using burley tobacco Eyan No.1 and flue-cured tobacco K326 to investigate whether grafting burley tobacco scions on flue-cured tobacco rootstocks could enhance pigment biosynthesis and photosynthesis, while reducing the NO3-N level in burley tobacco leaves. Grafting burley tobacco scions on flue-cured tobacco rootstocks significantly increased the total pigment content, photosynthetic rate, biomass, nitrate reductase and glutamine synthetase activities, as well as ammonium-nitrogen (NH4-N), total soluble and reducing sugar, and soluble protein levels in burley tobacco leaves compared with burley tobacco self-rooting, while decreasing the NO3-N level and nitrate-N to total N ratio. Transcriptomic analysis revealed that grafting resulted in upregulated expression of genes involved in starch, sucrose, porphyrin, chlorophyll, and N metabolism, as well as carbon fixation and carotenoid biosynthesis. The findings suggest that grafting on high N use efficiency rootstock is an exceptionally promising means of decreasing NO3-N accumulation by improving photosynthesis and N metabolism in the scion, thereby reducing the levels of harmful TSNAs.

Drip fertigation triggered by soil matric potential reduces residual soil nitrate content and improves maize nitrogen uptake and yield stability in an arid area

Effective water and fertilizer management is crucial for enhancing nitrogen (N) use efficiency and ensuring regional food security, especially in arid regions. Drip fertigation can synchronize water and fertilizer supply with crop demand, but its maximum benefits can only be achieved with appropriately designed and well-managed irrigation systems. In this study, we built on our previous work on optimizing the design of drip irrigation systems and evaluated the effect of drip fertigation regimes on soil nitrate nitrogen (NO3-N) supply, crop N uptake, yield, and yield stability. We conducted a five-year field experiment using drip fertigation to grow maize (Zea mays L.) in the Hetao Irrigation District, Northwest China, from 2016 to 2020. We implemented three water levels by controlling soil matric potential (SMP) threshold values [− 10 kPa (S1), − 30 kPa (S3), and − 50 kPa (S5)] under the same N fertilization rate (150 kg N ha−1 broadcast as basal fertilizer, 150 kg N ha−1 applied with drip fertigation). Our results indicated that soil NO3-N in 0–60 cm profile was typically distributed in the non-mulched zone at maturity. Compared with S5, S1 and S3 on average significantly decreased NO3-N accumulation in the 0–60 cm profile by 66% and 47%, and S1 and S3 significantly decreased NO3-N accumulation in the 60–120 cm profile by 31% and 30%. In addition, the S3 significantly decreased NO3-N accumulation in the 120–200 cm profile by 52% and 35% compared with S1 and S5. S3 significantly improved crop grain yield by 45%, sustainable yield index by 26%, N uptake by 28%, and N utilization efficiency by 11% compared with S5. In contrast, S3 decreased the irrigation amount by 40% compared with S1, with no significant differences in grain yield, yield stability, and N uptake in most years. We recommend using an SMP threshold value of − 30 kPa combined with a drip fertigation rate of 150 kg N ha−1 to reduce residual NO3-N and improve yield and yield stability in arid regions. Furthermore, we also recommend using drip fertigation with 208–253 mm irrigation water in wet years and > 253 mm in dry years (irrigation every four days from V6 to R3 stage), with 13.6 kg ha−1 N applied per irrigation (from VT to R3 stage) to facilitate farmer operations. Our research provides valuable technical guidance to promote a stable and sustainable agricultural production in arid regions.

Tillage and N-source affect soil fertility, enzymatic activity, and crop yield in a maize–rice rotation system in the Indian Terai zone

A field experiment (2017–2019) was undertaken to study the short-term effects of tillage [zero tillage (ZT), conventional tillage (CT), and alternate tillage (AT)] and sources of organic and mineral fertilizer N [NS0—control, NS1—recommended doses of fertilizer (160:50:100), NS2—recommended level of fertilizer and crop residue (6 Mg·ha−1), NS3—75% of recommended N as fertilizer (120 kg·ha⁻1) and 25% N (40 kg·ha⁻1) as farm yard manure (FYM), and NS4—75% of recommended N as fertilizer and 25% N as vermicompost] on yield and soil quality under a maize–rice rotation system. Among N sources, NS4 produced the highest maize grain yield (10 Mg·ha⁻1). Residual effects of N sources on mean rice grain yield were evident only in crop residue (NS2)- and vermicompost (NS4)-treated plots. After the harvest of two complete maize–rice crop cycles, higher content of dehydrogenase activity (DHA) and urease activity (UR) were observed in the soil under AT as compared to ZT and CT at 0–10 cm (p &amp;lt; 0.05). Similarly, microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) also recorded positive changes at 0–10 cm soil depth, especially in NS2 and NS4 treatments. AT resulted in the highest total soil carbon (TOC) (8.10 g·kg−1), followed by CT (6.73 g·kg−1) and ZT (5.98 g·kg−1). Fertilizer N treatments, however, influenced the NO3-N accumulation beyond the root zone, where crop residue-based (NS2) fertilizer N treatment resulted in the highest NO3-N (32.52 kg·ha−1), and the lowest NO3-N (14.48 kg·ha−1) was observed in the FYM-based (NS3) treatment. Therefore, the practice of alternate tillage and integration of vermicompost (40 kg·N·ha−1) and chemical fertilizer (total 120 kg·ha−1) sources should be mostly recommended to farmers in the Terai region of India.

Translocation of Nitrate in Rice Rhizosphere and Total Nitrogen Uptake Improvement under Interactive Effect of Water and Nitrogen Supply

ABSTRACT Nitrogen, an essential macronutrient for rice (Oryza sativa L), mineral forms are extremely prone to leaching. In this study, pot experiment in a greenhouse was utilized to investigate the coupling effect of irrigation (W) and fertilizer (N) on nitrate (NO3-N) translocation in the soil-water-plant system, Total Nitrogen (TN) uptake. Three N levels (Low, Medium, High: N1, N2, N3) rated 25, 120, and 250 mg/kg similarly three W levels (Low, Medium, High: W1, W2, W3) 70%-80%, 80%-90% and 100% of field capacity (θf) +0.5 cm submergence depth were applied. Nine treatments (W1N1:T1, W1N2:T2, W1N3:T3, W2N1:T4, W2N2:T5, W2N3:T6, W3N1:T7, W3N2:T8 and W3N3:T9) with four replicates. To understand NO3-N distribution, six soil layers (1 cm width each) per treatment were generated making it 54 in total. T6 (69.2%) revealed the highest increment in NO3-N content followed by T7 (44.2%) and T8 (39%) compared to T1. Generally, Middle layers (3rd-4th) had the least NO3-N content compared to shallow (1st-2nd) and bottom (5th-6th) layers. Concerning TN, the highest was found in T3(63%), T2(45%) and T6(41.5%) and T7(-26%) with the highest decrement. Interacting W and N significantly affected means of NO3-N, TN, moisture content, and root shoot ratio (R/S) at 5% probability level. Results of this study suggested that proper W and N combination result in high rhizosphere NO3-N accumulation in shallow layers leading to high nitrogen uptake by plant thus N leaching reduction.

Yield, nitrogen-use efficiency, and distribution of nitrate-nitrogen in the soil profile as influenced by irrigation and fertilizer nitrogen levels under zero-till wheat in the eastern Indo-Gangetic plains of India

Due to the introduction of zero-till wheat in the Indo-Gangetic plains (IGP) in India, irrigation and fertilizer nitrogen (N) management needs to be modified from that followed under conventionally tilled fields. A field experiment was conducted to study the effect of irrigation and N levels on yield and N uptake by zero-till wheat, fertilizer N-use efficiency, and distribution of nitrate-N (NO3-N) in a soil profile under zero-till conditions in an acidic alluvial soil of the eastern IGP. The experiment was laid out in a split-plot design with four levels of irrigation as main plots (I0-no irrigation, rain-fed, I1-122 mm in one irrigation at 21 days after sowing (DAS), I2-263 mm in two irrigations at 21 and 42 DAS, and I3-386 mm in three irrigations at 21, 42, and 84 DAS) and 4 N levels [0 (N0), 60 (N1), 120 (N2), and 150 (N3) kg N ha−1] as subplots. Grain and straw yields were significantly higher at the irrigation level-I2 and 120 kg N ha−1-N2 over the control (I0 and N0) and were at par with the highest applied levels of irrigation and N (I3 and N3). The nitrogen uptake by wheat followed a trend similar to yield for irrigation levels; however, it increased significantly up to 150 kg N ha−1. After the harvest of wheat crop, more NO3-N was observed in the 60–90 cm subsurface soil layer than in the surface 0–15 cm and/or 15–30 cm and 30–60 cm subsurface soil layers. The highest NO3-N concentration was recorded in the treatment I2N2. Accumulation of NO3-N in the soil increased up to irrigation levels I2 and with increasing doses of fertilizer N application. Combined applications of irrigation and N had a positive and significant influence on agronomic efficiency (AE) and apparent N recovery (ANR) but had no significant effect on physiological efficiency (PE). This study suggests that an appropriate combination of irrigation and N levels in zero-till wheat can lead to not only high-yield levels and N-use efficiency but also adequately control NO3-N leaching under acidic alluvial soils in the eastern IGP.

Using ion-exchange resins to monitor nitrate fluxes in remote semiarid stream beds.

Monitoring in remote areas can represent a real challenge in environmental studies. Numerous techniques have been developed over the last decades to monitor nutrients and other elements in different systems. However, not all of them are suitable for field applications, particularly when the locations are difficult to access or its accessibility depends on seasonal climate conditions. This study was aimed to test the applicability and efficiency of resin samplers and resin bags to monitor nitrates fluxes (NO3-N) in two small semi-arid catchments in Northwestern Mexico. Resin samplers were installed in the hyporheic zone below the river bed in order to monitor the vertical fluxes of NO3-N and remained there for 5 months (during the summer rains). Resin bags were anchored in rock outcrops upstream of the resin samplers before the onset of the summer rainfall season and replaced every 2 weeks during 4 months to capture pulses of NO3-N in ephemeral streams. NO3-N pulses in the stream are a potential source of NO3-N that can infiltrate into the soil. Results of the resin samplers found a difference of up to 12 kg ha-1 season-1 between the two catchments. The resin bags showed a higher accumulation of NO3-N in the catchment with lower vegetation cover (160.3 mg L-1 season-1) compared to the one with higher vegetation (67.8 mg L-1 season-1). Measured nitrate fluxes at both sites responded to rainfall pulses recorded during the monitoring period. Resin samplers and resin bags can be used together, to assess nutrient fluxes on the surface and in the soil and can be tested in any type of ecosystem. In this particular case, these methods demonstrated an efficient way of determining spatio-temporal nitrate fluxes in semi-arid ecosystems in remote areas that are difficult to access, monitor, and collect data.

Evaluating Postharvest Organic Nitrogen Fertilizer Applications in Early Fruiting Northern Highbush Blueberry

Bloom to fruit maturity is a period of rapid growth and nitrogen (N) uptake in northern highbush blueberry (Vaccinium corymbosum L.). Sufficient plant-available N is critical during this time, and growers often accomplish this through fertilizer applications from bloom through fruit development. For organic production in northern climates like Washington State, postharvest applications of N fertilizer are not recommended for northern highbush blueberry because they may stimulate excessive vegetative growth, reduce floral bud set, and increase the risk of winter injury through delayed acclimation. However, early fruiting cultivars with the potential for an extended growing season after harvest may benefit from postharvest N applications because the additional N may promote shoot and root growth that could support fruit production in future years while still allowing plants to form floral buds and acclimate to winter temperatures. The objective of this study was to evaluate the potential impacts of postharvest organic N fertilizer applications on ‘Duke’, an early fruiting northern highbush blueberry cultivar. Specific objectives were to determine the effects of postharvest organic N fertilizer application on plant growth, yield, floral bud set, fruit quality, cold hardiness, tissue macronutrient concentrations, and select soil properties. Four treatments varying in the timing of N application were evaluated in a commercial ‘Duke’ field in eastern Washington using a single fertilizer rate of 130 kg⋅ha−1 N from 2018 to 2020. The organic fertilizer N source was a liquid fertilizer derived from digested plant materials. The experimental design was a randomized complete block design with four replications and treatments included the following: control (100% of N applied preharvest); 80/20 (80% preharvest, 20% postharvest); 70/30 (70% preharvest, 30% postharvest); and 60/40 (60% preharvest, 40% postharvest). Although the year influenced measured variables, including yield, floral bud set, fruit quality, tissue nutrients, and soil properties, few treatment effects were observed across the 3-year study. Cold hardiness was only impacted once (8 Feb. 2020), and floral buds were overall hardy to extreme minimum winter temperatures for the region. This project showed that applying postharvest organic N as a liquid fertilizer had no negative consequences on productivity metrics for an early fruiting blueberry cultivar grown in a region with an extended growing season, thus providing growers with more flexibility when timing their fertilizer applications. Results may differ for other fertilizer sources, and further monitoring of soil NO3-N accumulation should be conducted to gain a better understanding of its dynamics and the potential for risks.

Increasing yields while reducing soil nutrient accumulation by straw strip mulching in the dryland wheat (Triticum aestivum L.) cropping system of Northwest China

Surface mulching is an effective strategy to increase yields in rainfed agroecosystems. The plastic film residue and overuse of chemical fertilizer cause a serious non-point source pollution and high production input cost. With mulching, farmers typically attempt to maintain the balance of soil nutrients and reduce fertilizer use while ensuring high yields. Straw strip mulching (SM) is a new mulching technique, but the effects on nutrient uptake have not been studied yet. Therefore, 19 field comparative experiments were conducted in four growth seasons of winter wheat with three mulching treatments: (1) straw strip mulch (SM), a partial ground mulching using whole corn stalks that alternate with planting strips without mulch; (2) full-field plastic film mulching (PM); and (3) no mulching with wheat sown in rows, as a control (CK). Compared with CK, on average over all experiments, SM increased grain yield by 11.5%, biomass by 19.0%, the total aboveground uptakes of nitrogen (N), phosphorus (P) and potassium (K) by 16.1%, 18.4% and 22.9%. There were no significant differences between SM and CK in N and P requirements, the N, P and K concentrations in grain. The increased total aboveground uptake of each nutrient was closely associated with higher biomass, grain yield and straw yield (r = 0.66 −0.84, P < 0.01). Relative to CK, SM significantly decreased the total accumulation of residual NO3-N in the top 100 cm at maturity stage by 32.3% (22.7 kg ha-1) in typical fertilization (N, 120 kg ha-1; P2O5, 90 kg ha-1) and by 33.8% (45.8 kg ha-1) in high fertilization (N, 150 kg ha-1; P2O5, 120 kg ha-1), and the leaching of NO3-N into the deep soil below 40 cm. When only grain nutrients exported from the field after harvest in typical fertilization, N balance in SM, PM and CK accounted for 43.8%, 38.5% and 48.6% of N input, while P balance for 74.8%, 74.0% and 78.4% of P input, respectively, indicating possible saving potentials in fertilizer costs for all treatment, but the saving potential of P is much greater than that of N. Relative to PM, SM had similar the total aboveground nutrients uptake, similar to or slightly less grain yields, and higher economic benefit. SM is suitable for popularizing in a semiarid rainfed agroecosystem.

Removal of pharmaceutical compounds from municipal wastewater by bioaugmentation with fungi: An emerging strategy using fluidized bed pelleted bioreactor

Fungi have been shown to be good candidates to remove pharmaceuticals. However, the pilot-scale application mainly deals with the strict growth conditions and competition between microbial communities from wastewater. Thus, the bioaugmentation for removing the pharmaceuticals in municipal wastewater by Trametes versicolor and Aspergillus luchuensis using fluidized bed pelleted bioreactor was studied. To find the optimal performance of bioaugmentation by both fungi periodical biomass volume, 10 and 50 g per 1.25 L bioreactor, were tested. The removal of nutrients, pharmaceutical substances, and changes in the pH value, laccase activity, and total cell number of microorganisms were analyzed. The results showed that bioaugmentation has an effect in removing NH4-N and lower accumulation of NO3-N, whereas PO4−3-P and TOC did not show a significant effect on the reduction of nutrient load compared to the control without fungal addition. The results of removal efficiency for diclofenac, carbamazepine, and sulfamethoxazole showed that there was no significant effect on the removal while the highest removal efficiency (> 90 %) for ibuprofen, ketoprofen, and metoprolol was achieved by both fungi with periodical addition with 50 g of biomass after an incubation time of 3 hours. Finally, the data analysis with AI-based experimental design indicated that A. luchuensis can be a useful fungus for pharmaceutical removal and implies a perspective approach for optimization of fluidized bed pelleted bioreactor. Overall, the obtained results and the use of an AI-based platform is a promising approach for the optimization and operation of fluidized bed pelleted bioreactors.

Effect of aquaculture water eutrophication on color development in Biolog EcoPlates

Biolog EcoPlates are useful tools to study the metabolic function of microbial community in water bodies; however, the influence of aquaculture water, which contains complex chemical compositions, on color development in Biolog EcoPlates, has not been clearly illustrated. Previously, we detected a delayed color development in original water samples, comparing to that in the tenfold diluted samples. The objective of this study was to evaluate the differences of average well color development (AWCD) and community-level physiological profiles (CLPP) between the original and tenfold diluted water samples collected from three intensive Litopenaeus vannamei culture ponds, and to explore potential causes of the delayed color development by measuring microbial community structure and physiochemical indexes. Compared with the tenfold diluted samples, the original water samples from all three ponds exhibited delayed color development and reduced microbial metabolic activity. The original water samples exhibited higher utilization of carbohydrates, while significantly higher utilization of amino acids was observed in the corresponding diluted samples. The CLPP of the original water samples was significantly correlated with the microbial community structure at 48 h of incubation, meanwhile both CLPP and community structure were substantially influenced by NO3–N and NO2–N. Therefore, NO2-N and NO3-N accumulation in the intensive Litopenaeus vannamei culture pond might be responsible for the delayed color development in Biolog EcoPlates. In order to minimize the influence of aquaculture water on color development in Biolog EcoPlates, a shorter incubation period is recommended.

A talaj fixált ammónium-ion tartalmának hatása a talajvíz tisztulási folyamataira a szennyezőforrás felszámolását követően települési környezetben

Growing NH4+ content of groundwater results in increasing exchangeable and fixed ammonium ion content of the soil. NH4+ bond in the soil may go again into solution parallel with the dilution of the soil solution but at a slower rate than fixing. This process influences significantly the NH4+ content of the soil. In settlements with no sewerage system the high NH4+ content of sewage flowing out of uninsulated septic tanks may increase the fixed NH4-N content of the soil that could have a significant effect on the quality of groundwater even after the potential disappearance of pollution sources.In this study the effects of the fixed NH4-N content of the soil around an uninsulated residential septic tank on the purification processes of the groundwater were investigated. The septic tank in the study area was dismantled in 2014 after 27 years of operation as a sewerage system was constructed. When the tank was still in operation in 2012 and 2013, very high, 55–75 mg l-1 NH4+ content was measured in the water of the monitoring well 1 metre from the tank in the course of seasonal sampling. When sewage outflow was terminated in 2014 concentrations decreased right away but even 5 years after pollutant supply was stopped, concentrations (35–57 mg l-1) highly exceeding the pollution limit (0.5 mg l-1) were measured. Considering this very high concentration, it can be assumed that great amount of NH4+ is still released into the groundwater.In order to prove this, the exchangeable and fixed NH4-N and NO3-N contents of the soil were determined by 20 cm down to a depth of 4 metres (2019). The measurements indicated the significant accumulation of exchangeable and fixed NH4-N in the zone between 220 and 400 cm. Highest fixed NH4-N concentrations of 457 mg l-1 were found between 220 and 240 cm suggesting that sewage outflow was most intense at this depth. Slow decrease in concentrations can be observed in deeper zones but concentrations higher than 350 mg l-1 were measured between 220 and 380 cm. Based on correlation analyses, the quantity of fixed NH4-N shows no correlation with the soil texture thus it can be stated that the vertical pattern of NH4-N content is determined dominantly by sewage outflow and its depth. In the unsaturated zone of the borehole a significant accumulation of NO3-N was also identified. The maximum of NO3-N was found in the zone between 100 and 140 cm. The peak nitrate calculated for NO3- ion with a value &gt;1300 mg kg-1 is 2.5 times the limit set for the nitrate content of the geological medium.Based on the results, exchangeable and fixed NH4-N contents in the soil are still very high, 5 years after sewage outflow was stopped. The continuous solution of this component still contributes to the high NH4+ content of the groundwater. As a result, the contaminated soil in the immediate environment of the septic tank is still a pollution source.

Simultaneous nitrification-denitrifying phosphorus removal (SNDPR) at low DO for treating carbon-limited municipal wastewater

This study investigated simultaneous nitrification-denitrifying phosphorus removal in a sequencing batch reactor (SBR) activated sludge process. The process consisted of an extended anaerobic period (180 min) followed by a low DO (0.3 ± 0.05 mg/L) simultaneous nitrification-denitrifying phosphorus removal. The reactor was operated within a wide range of COD/N ratio (5–10) without any volatile fatty acids (VFA) supplementation. N and P removal efficiencies were as high as 91% and 96%, respectively. The process was efficient even at a very low COD /N ratio of 5, with N and P removal efficiencies of 70% and 90%, respectively. The N and P removal efficiencies improved to more than 90% at a COD/N ratio 8. It was found that the initial filtered flocculated COD (ffCOD)/[total oxidized Kjeldahl Nitrogen (TKNoxidized) + NOx-Nintitial] ratio in the reactor played a significant role in the process efficiency. It was observed that N-removal efficiency decreased with a decrease of [ffCODinitial/ (TKNoxidized + NOx-Ninitial)] ratio even at high COD/N ratio of 10. Simultaneous nitrification denitrification (SND) efficiencies varied between 60%–88% depending on the influent COD/N ratio and [ffCODinitial/ (TKNoxidized + NOx-Ninitial)] ratio in the reactor. Cyclic studies showed a distinct two step phosphorus release in the extended anaerobic period in contrast to the more conventional single step phosphorus release. During the aerobic period, low DO favored denitrifying P-removal without significant accumulation of NO3-N, and NO2-N until all endogenous carbon was consumed. Denitrifying phosphorus accumulating organisms (DPAOs) played a vital role in simultaneous denitrification and phosphorus removal. Aerobic and anoxic P-removal represented about 55% and 45% of the overall phosphorus removal, respectively. Cycle tests showed that DPAOs have a competitive advantage over NOB for nitrite consumption at low DO. The process was found to be carbon efficient as evidenced by the COD/NOx-N ratio of 4.2 for denitrification. Compared to traditional enhanced biological phosphorus removal (EBPR) coupled with exogenous denitrification, this process reduces carbon and oxygen demand for combined N and P removal from municipal wastewater by about 45%, and 35% respectively.

Removal pathways of benzofluoranthene in a constructed wetland amended with metallic ions embedded carbon

The limited adsorption capacity of the substrate and the concentration of dissolved oxygen in constructed wetlands (CWs) have inhibited their ability to efficiently remove polycyclic aromatic hydrocarbons (PAHs) from wastewater. Presently, biochar and activated carbon modified with Fe3+ and Mn4+ were used as effective sorbents in the removal of benzofluoranthene (BbFA), a typical PAH, in CW microcosms. The addition of metallic ions embedded carbon increased NO3-N accumulation by the reduction of Fe3+ and Mn4+, which led to improved BbFA degradation. Additionally, plant adsorption in root and stem sections were observed separately. The abundance of PAH-degrading microbes in the rhizosphere substrate was higher with the metallic ions embedded carbon than control group. The Fe3+, Mn4+ and NO3-N served as electron acceptors increased BbFA microbial degradation. The removal pathways of BbFA in the modified CWs were proposed which involved settlement in the substrate, plant absorption, and microbial degradation.

Nitrogen source and rate effects on residual soil nitrate and overwinter NO3-N losses for irrigated potatoes on sandy soils

Residual soil NO3-N (RSN) is susceptible to loss during the non-growing season. This 5 yr study investigated the effects of three N fertilizer sources [ammonium nitrate (AN), ammonium sulfate (AS), and polymer-coated urea (PCU)] applied at four rates (60, 120, 200, and 280 kg N ha−1) plus an unfertilized control on RSN following potato production and on overwinter NO3-N changes in an irrigated sandy soil in Quebec, Canada. Composite soil samples were collected at the 0–15, 15–30, 30–60, and 60–90 cm depths immediately after potato harvest in fall and again in the following spring from 2008 to 2012. Residual soil NO3-N content within the 0–30 cm depth (RSN0–30) was highly correlated with the RSN content in the 0–90 cm depth (RSN0–90), indicating that RSN0–30 can be used as an indicator of soil profile NO3-N accumulation. Overall, RSN0–90 increased with fertilizer N application rate, particularly for above the minimum fertilizer N rate required to maximize yield (Nmax), and was generally higher for years with greater pre-plant soil NO3-N. The split application of AN and AS resulted in lower RSN0–90 than the single application of PCU at above Nmax. Overwinter losses of soil NO3-N were generally increased with increasing RSN0–90 in fall. The results suggest that reducing the fertilizer N rate is more important than the choice of N source in managing RSN.

Nitrate Concentration in Leafy Vegetables from the Central Zone of Chile: Sources and Environmental Factors

Leafy vegetables constitute an excellent source of fiber, vitamins, minerals, and phytochemicals, producing many benefits to human health. However, nitrate (NO3-N) accumulation constitutes a risk factor for environment and human health. The present study was focused on the evaluation of concentrations and sources of NO3-N in lettuce and spinach under different production systems, located in the Metropolitan region (Chile). Nitrate concentration was determined in vegetable tissue, soil, water, and organic fertilizers, and compared to Chilean and international standards. Results indicated average, dry matter basis, concentrations of 3065 and 4766 mg kg−1 of NO3-N for summer and winter lettuce, respectively. On the other hand, NO3-N concentration for spinach reached 1686 and 1244 mg kg−1, respectively, for the same seasons. The studied species did not show significant differences in NO3-N content. In addition, there was no correlation between the accumulation of NO3-N in vegetable tissue and soil N availability (average of 75 mg kg−1 NO3-N) or NO3-N concentration in irrigation water (average of 8 mg L−1 of NO3-N). Finally, a nitrogen balance determined that in lettuce production systems 240–430% excess N was applied. On the other hand, organic fertilizers used did not comply with the maturity parameters established by the NCh 2880/04, 2016. There were some lettuce samples with high NO3-N contents, without surpassing the maximum allowable concentration. The nitrogen balance for lettuce determined a large excess N application as organic and/or inorganic fertilizers, which was related to larger NO3-N levels found in their tissues.

The effect of using pig manure as an internal carbon source in a traditional piggery wastewater treatment system for biological denitrification

Due to a low ratio of chemical oxygen demand (COD) to total nitrogen (TN) and poor biodegradability of digested piggery wastewater, lack of a carbon source in subsequent biological treatment limits denitrification, resulting in an accumulation of NO2-N and NO3-N and a low denitrification efficiency. In this project, combined ultrasonication/alkali treatment of pig manure was used to generate a source of pig manure carbon source(PMC). This report mainly discusses the effects of adding the PMC on subsequent biological denitrification and microbial community changes. The experimental results showed that in subsequent biological treatment with the addition of 1.78% PMC, the effluent NO2-N and NO3-N were 0.02 mg·L−1 and 0.90 mg·L−1, respectively. The TN removal percentage was 72.29%, which was 62.29% higher than that obtained without an added carbon source and 36.74% higher than that obtained with added raw wastewater carbon (RWC). High-throughput sequencing revealed that the relative abundances of the dominant microflora Thauera and Thermomonas, which are related to denitrification, increased from 1.13% and 0.55% to 6.19% and 4.69%, respectively, after the addition of PMC. The addition of PMC improved the denitrification of digested piggery wastewater in subsequent biological treatment, and the denitrification effect was obvious and could enable waste resource utilization.

Evaluation of Soil Nitrate Accumulation under Different Fertigation Regimes and Simulation by the Hydrus-1D Model

Nitrate loss is a major reason for non-point source contamination on agricultural lands. The objective of this study was to assess the Hydrus-1D model for simulation of soil nitrate in different irrigation regimes, including 100 (I1), 85 (I2), and 70 (I3) % of the water requirement for sugarcane and different urea fertilization rates with 150 (N1), 250 (N2), and 350 (N3) kg/ha. Van Genuchten (VG) parameters were estimated by the RETC [Retention Curve Program for Unsaturated Soils] program. According to the results, by reducing the amount of irrigation water, the soil nitrate accumulation from the soil surface to the deep soil increased by 17 and 35% under I2 and I3 treatments compared with I1. Results showed that the Hydrus-1D model had fair potential for predicting the NO3-N accumulation in the soil profile over the sampling period (AE: −1.25 to 0.99, RMSE: 0.96 to 2.50, d: 0.78 to 0.98). The coefficient of determination between the field measured and simulated values in the soil layers at depths of 30, 60, 90 and 120 cm were 0.87, 0.88, 0.74, and 0.52, respectively. To reduce nitrogen losses, fertilizer application rates must be considered based on sugarcane needs and soil hydraulic properties.