NO3-N Concentrations Research Articles

Effects of an oil-based substrate (The Water Cleanser\u2122) and bacterial additives on nitrogen and phosphorous dynamics in freshwater crayfish (Cherax cainii, Austin and\xa0Ryan 2002) aquaculture

Two experiments were conducted to evaluate the efficacy of an oil-based substrate, The Water Cleanser™ (TWC). The first experiment studied the effects two substrates of different oil composition (TWC, TWC +), and a commercial bacterial additive (Bio-Aid) on concentrations of nitrogen and phosphorous in indoor aquaria. The second experiment studied the effects of TWC, a bacterial additive, and a combination (TWC + B) on concentrations of nitrogen and phosphorous, phytoplankton abundance and diversity in outdoor freshwater crayfish (Cherax cainii, Austin and Ryan, Invertebr Syst 16:357–367, 2002) tanks. In the first experiment, the concentration of TAN decreased more rapidly with Bio-Aid, whilst the maximum concentrations of NO2-N and NO3-N were reduced with the substrates. The concentration of orthophosphate was reduced in aquaria with TWC + . In the second experiment, concentrations of TAN, NO2-N, NO3-N and total phosphate were not significantly affected by TWC. After addition of TWC + B, there was a significant decrease in the concentrations of nitrate and total phosphate, and a higher abundance of phytoplankton was maintained than with other treatments. Additionally, a population Bacillus sp. was found on the substrate surface. TWC had no adverse effects on phytoplankton abundance or diversity, or C. cainii physiology, weight gain or survival. TWC and TWC + were effective bioremediators of eutrophic water, whilst a combination of TWC + B was effective in short term bioremediation and in promoting phytoplankton abundance in C. cainii tank culture.

Fruits-Based Critical Nitrogen Dilution Curve for Diagnosing Nitrogen Status in Cotton.

Estimating the precise nutritional status of crop nitrogen (N) after flowering period is not only important to predict deficiency but the excess that could be revised by fertilization in future crops. Critical N dilution curves describing the critical N concentration ([N]c) in plant tissues during crop growth have been used to estimate the N status of whole plants in cotton. Little is known, however, about the critical N dilution curve for specific plant organs such as cotton fruits. The objective of this study was to verify the feasibility of fruits-based critical N dilution curve as a useful diagnostic tool for diagnosing the N status of cotton crops. A 3-year field experiment was conducted with seven N application rates (0–360 kg N ha–1) using the high-yielding cultivars Jimian 228 and Lumian 28, which differ in maturity. The relationship between fruits dry mass (DM) and N concentration ([N]) was analyzed, and a model of [N]c for cotton fruits was constructed and validated. The results showed that fruits [N]c decreased with increasing fruits DM. The critical N dilution curve based on cotton fruits was described by the equation [N]c = 2.49 × DM–0.12 (R2 = 0.649, P < 0.0001) across cultivar-years. The N nutrition index (NNI) of the fruits (NNIf) with the N dilution curve was significantly related to the NNI of shoot DM, relative yield (RY), and boll density at most sampling dates. For an NNIf of approximately 1, the RY was nearly 95%, while it decreased with a decreasing NNIf below 1. The petiole nitrate-N (NO3-N) concentration was also linearly related to the NNIf, suggesting that the NO3-N concentration in the petiole was a good predictor of the NNIf. Therefore, fruits-based critical N dilution curve and the derived NNIf values will serve as a useful diagnostic tool for diagnosing N status in cotton crops.

Factors influencing the spatial and temporal distributions of green algae micro-propagules in the coastal waters of Jinmenghaiwan, Qinhuangdao, China

Since 2015, green tides have impacted the coastal waters of Qinhuangdao, particularly at Jinmenghaiwan bath. Micro-propagules are considered the “seed bank” of algal blooms and play an important role in the formation of green tides. To investigate the spatial and temporal distributions of micro-propagules of green algae and associated environmental factors, a field survey was carried out in the coastal waters of Jinmenghaiwan, Qinhuangdao, China. The results showed that the NO3-N concentration was the most important impact factor of the abundance of micro-propagules and explained 42.9% of the total variance. Furthermore, the number of micro-propagules was significantly and positively correlated with the biomass of attached and floating macroalgae. Therefore, reducing the NO3-N concentration by controlling the NO3-N input from Tang River is expected to be an effective measure to prevent and control green tides in the coastal waters of Qinhuangdao.

Management-intensive grazing impacts on total Escherichia coli, E. coli O157:H7, and antibiotic resistance genes in a riparian stream

The impacts of management-intensive grazing (MIG) of cattle on concentrations of total Escherichia coli, total suspended solids (TSS), and nitrate-nitrite nitrogen (NO3 + NO2-N), and occurrence of E. coli O157:H7 and selected antibiotic resistance genes (ARGs) in stream water and/or sediments were evaluated. Cattle were grazed for two-week periods in May in each of three years. Overall, grazing increased total E. coli in downstream water by 0.89 log10 MPN/100 mL (p < 0.0001), and downstream total E. coli concentrations were higher than upstream over all sampling intervals. Downstream TSS levels also increased (p ≤ 0.0294) during grazing. In contrast, there was a main effect of treatment for downstream NO3 + NO2-N to be lower than upstream (3.59 versus 3.70 mg/L; p = 0.0323). Overwintering mallard ducks increased total E. coli and TSS concentrations in January and February (p < 0.05). For precipitation events during the 24 h before sampling, each increase of 1.00 cm of rainfall increased total E. coli by 0.49 log10 MPN/100 mL (p = 0.0005). In contrast, there was no association of previous 24 h precipitation volume on TSS (p = 0.1540), and there was a negative linear effect on NO3 + NO2-N (p = 0.0002). E. coli O157:H7 prevalence was low, but the pathogen was detected downstream up to 2½ months after grazing. Examination of ARGs sul1, ermB, blactx-m-32, and intI1 identified the need for additional research to understand the impact of grazing on the ecology of these resistance determinants in pasture-based cattle production. While E. coli remained higher in downstream water compared to upstream, MIG may reduce the magnitude of the downstream E. coli concentrations. Likewise, the MIG strategy may prevent large increases in TSS and NO3 + NO2-N concentrations during heavy rain events. Results indicate that MIG can limit the negative effects of cattle grazing on stream water quality.

Subsurface Nitrate Processing Beneath Drainageways: Are They Landscape Opportunities for Subsurface Drainage Remediation?

HighlightsDrainageways contain fine-textured and nutrient rich alluvial soils conducive for denitrification.NO3-N concentrations in drainageway groundwater were 70% lower than observed in cropped fields.A new grass waterway design connects subsurface water from upland cropped fields to the drainageway deposits for NO3-N remediation.Abstract. Efforts to reduce nutrient export from agricultural crop production in the U.S. Midwest are leading to development of new conservation practices. In this study our objectives were to: (1) characterize subsurface soils and hydrogeology found in two main drainageway areas in eastern Iowa, (2) compare groundwater quality to upland agricultural fields, and (3) utilize a groundwater flow model to assess the capacity of drainageways to provide additional NO3-N processing in agricultural watersheds. Using data obtained from a network of 12 shallow wells installed across six different waterways, we found that the waterways contained fine-textured and nutrient rich alluvial soils derived from erosion and deposition of upland loess and till. Concentrations of NO3-N in waterway groundwater (3.1 mg/l) were 70% lower compared to groundwater beneath nearby cropped fields (10.5 mg/l). A shallow water table in the organic-rich drainageway soils provides the requisite organic carbon, anaerobic soil conditions, and nitrogen supply for denitrification to occur. Numerical modeling suggested that groundwater from the surrounding catchment discharges approximately 53 m3/day into the waterways and reduces NO3-N mass by 144.3 kg/yr, or 7.8 kg/ha. Results suggest that drainageways could be better exploited for additional NO3-N reductions from subsurface drainage if the flow could be diverted into these areas. Keywords: Denitrification, Grass waterway, Nitrate-nitrogen, Saturated buffer.

Nitrogen distribution in apple orchard soil profile under fertilization with different water and fertilizer coupling techniques

Optimization of water and fertilizer coupling management approaches could not only increase apple yield and quality, but also reduce the potential negative impacts of such management activities on the environment. The aim of the present study was to determine the optimal water-nitrogen (WN) coupling management strategy in an apple orchard in the Weibei Dryland, Shaanxi Province, China, under limited irrigation. A randomized complete block design was adopted to test the effects of three drip irrigation levels (W1, 300 m3/hm2; W2, 600 m3/hm2; W3, 900 m3/hm2) and four N application levels (N0, 0 kg/hm2; N1, 200 kg/hm2; N2, 400 kg/hm2; and N3, 600 kg/hm2) on N distribution in the 0-100 cm soil profile. Apple yield and economic benefits under different treatments were also evaluated over a three-year period (2012-2014). Compared with the N0W1 treatment, soil N contents were higher and exhibited distinct trends in the soil profile under other treatments. Overall, total N contents exhibited a downward trend from the surface to the subsurface layers (0.11-2.34 g/kg); however, the total N contents of the lower soil layer increased with an increase in irrigation amount. NO3-N contents were the lowest in the 40- 60 cm soil layer and then increased with an increase in soil depth. The highest NO3-N contents of different soil layers were observed under the N3W3 treatment, ranging from 124.7 mg/kg (0-20 cm) to 90.9 mg/kg (80-100 cm). NH4+-N contents were low ( 20 cm. Different water-N coupling treatments also increased apple yield by 7.30%-41.62% when compared with the N0W1 treatment. The highest apple yield (three-year mean: 41.01 t/hm2) was observed under the N2W2 treatment, with an output value of 237 900 RMB yuan/hm2 and a net income of 232 000 RMB yuan/hm2. Considering fruit yield, partial productivity of N fertilizer, and economic and environmental benefits, the N2W2 treatment is the optimal water-N fertilizer coupling drip irrigation scheme for apple production in the study area and other similar dryland areas. Keywords: apple orchard, water-nitrogen coupling, nitrogen fertilization, soil profile, yield DOI: 10.25165/j.ijabe.20221505.7257 Citation: Zhao Z P, Yan S, Hu S Y, Qu K J, Tong Y A. Nitrogen distribution in apple orchard soil profile under fertilization with different water and fertilizer coupling techniques. Int J Agric & Biol Eng, 2022; 15(5): 146–154.

Engineered Urea-Doped Hydroxyapatite Nanomaterials as Nitrogen and Phosphorus Fertilizers for Rice

The application of nanomaterials as nanofertilizers is one of the advanced solutions to overcome the excessive use of conventional fertilizers without compromising the yield. In this study, the synthesized urea-doped hydroxyapatite nanomaterials (UHN) at recommended (UHN_RD) and half-recommended (UHN_HRD) doses were compared with a recommended dose of commercial bulk urea fertilizer (BUF) and control (CNT) treatment for nutrient availability in soil and yield of rice crops. Rice was grown in 12 field columns (four treatments × three replications) by applying the fertilizer treatments at four growth stages and irrigating the columns conventionally. The crop growth parameters such as plant height, biomass, and yield were measured for all columns. The depths of ponding water and drainage were measured daily, and the water samples collected from ponding water and drainage were analyzed for ammonium (NH4-N), nitrate (NO3-N), and ortho phosphorus (PO4-P) concentrations. The grain yield was increased by 61, 60, and 65% in BUF, UHN_HRD, and UHN_RD, respectively, compared to the CNT treatment, which indicates that the UHN can result in a yield at par with commercial fertilizers. The concentrations of NH4-N, NO3-N, and PO4-P in the leachate were reduced by 69.11, 16.3, and 87%, respectively, under UHN_HRD and by 60, 10.6, and 66.3%, respectively, under UHN_RD compared to BUF. The nutrient use efficiency was the highest in UHN_HRD for nitrogen (76.5%) and phosphorus (14.27%) nutrients. The application of UHN as nitrogen and phosphorus sources revealed yield improvement and reduced leaching of nutrients. Therefore, UHN could be used both as a nitrogen and phosphorus supplement to rice crops at a reduced application rate.

Assessing and modeling nitrite inhibition in microalgae-bacteria consortia for wastewater treatment by means of photo-respirometric and chlorophyll fluorescence techniques

Total nitrite (TNO2 = HNO2 + NO−2) accumulation due to the activity of ammonia-oxidizing bacteria (AOB) was monitored in microalgae-bacteria consortia, and the inhibitory effect of nitrite/free nitrous acid (NO2-N/FNA) on microalgae photosynthesis and inhibition mechanism was studied. A culture of Scenedesmus was used to run two sets of batch reactors at different pH and TNO2 concentrations to evaluate the toxic potential of NO2-N and FNA. Photo-respirometric tests showed that NO2-N accumulation has a negative impact on net oxygen production rate (OPRNET). Chlorophyll a fluorescence analysis was used to examine the biochemical effects of NO2-N stress and the mechanism of NO2-N inhibition. The electron transport rate (ETR), non-photochemical quenching (NPQ), and JIP-test revealed that the electron transport chain between Photosystems II and I (PS II and PS I) was hindered at NO2-N concentrations above 25 g N m−3. Electron acceptor QA was not able to reoxidize and could not transfer electrons to the next electron acceptor, QB, accumulating P680+ (excited PS II reaction center) and limiting oxygen production.A semi-continuous reactor containing a Scenedesmus culture was monitored by photo-respirometry tests and Chlorophyll a fluorescence to calibrate NO2-N inhibition (5–35 g N m−3). Non-competitive inhibition and Hill-type models were compared to select the best-fitting inhibition equations. Inhibition was correctly modeled by the Hill-type model and a half inhibition constant (KI) for OPRNET, NPQ, maximum photosynthetic rate (ETRMAX) and the performance index PIABS was 23.7 ± 1.2, 26.36 ± 1.10, 39 ± 2 and 26.5 ± 0.4, respectively.

Long-term water quality assessments under changing land use in a large semi-arid catchment in South Africa

Increasing nutrient loads from land use and land cover (LULC) change degrade water quality through eutrophication of aquatic ecosystems globally. The Vaal River Catchment in South Africa is an agriculturally and economically important area where eutrophication has been a problem for decades. Effective mitigation strategies of eutrophication in this region require an understanding of the relationship between LULC change and water quality. This study assessed the long-term impacts of LULC changes on nitrate (NO3-N) and orthophosphate (PO4-P) pollution in the lower Vaal River Catchment between 1980 and 2018. Multi-year LULC was mapped from Landsat imagery and changes were determined. Long-term trends in NO3-N and PO4-P loads and concentrations in river water samples were analysed, while multi-year LULC data were ingested into the Soil and Water Assessment Tool (SWAT) to simulate the impacts of LULC changes in NO3-N and PO4-P loads. Main LULC changes included an increase in the irrigated area by 262% and in built-up area by 33%. This occurred at the expense of cultivated dryland fields and rangelands. In situ data analysis showed that at the catchment inlet, PO4-P concentration and loads significantly increased, while NO3-N concentration and loads decreased between 1980 and 2018. At the catchment outlet, only PO4-P loads increased, while NO3-N loads and concentrations remained the same. SWAT simulations at the Hydrologic Response Unit scale showed that irrigated land was the largest contributor to NO3-N leaching per ha. Aggregation of nutrient loads by LULC type showed increased nutrient loads from irrigated and built-up areas over time, while loads from dryland areas decreased. At catchment scale, dryland remained an important contributor of the annual nutrient loads total because of its large area. In future, research efforts should focus on crop management practices to reduce nutrient loads.

Effects of carbon input quality and timing on soil microbe mediated processes

Compost application is viewed as an eco-friendly and sustainable method to improve agricultural soil fertility. However, composts vary in lability and recalcitrance, which drives energy supply for microbial biomass formation and microbial processes such as soil respiration, nitrogen mineralization, and enzyme production. To provide further insights into the issue, this study aimed to elucidate how microbial activities are affected by substrate quality, amendment volume, and frequency. We proposed three hypotheses: i) microbial biomass and microbial activities increase as soon as C substrate is amended compared to control soil; ii) microbe-mediated processes are affected by substrate lability as incubation progresses; iii) repeated amendment of smaller split C source sustains a more gradual increase of microbial activities as compared to a single input. To test these hypotheses, we incubated an agricultural soil at 25 °C, adding substrates of various assimilability (glucose, cellulose and lignin) once or in 2–3 split additions. Soil respiration was determined every 2–3 days throughout incubation, while microbial biomass (MBC, MBN), inorganic N (NO3-N and NH4-N) concentration, and potential enzyme activities were assayed at day 4, 32, 82, and 186 following substrate amendment. Regardless of C source amendments, soil respiration increased twofold in amended soils while microbial biomass C (MBC) was 1.5 times higher compared to control soil, indicating that microbial growth was C-limited in this agricultural soil. The association between high NO3-N concentration and low microbial biomass at the end of the incubation, regardless of amended substrate, suggested increased microbial C turnover due to C exhaustion. The addition of cellulose mostly enhanced enzyme activities of β-1,4-glucosidase (BG), β-1,4-N-acetyl glucosaminidase (NAG) and tyrosine amino peptidase (TAP) while the additions of glucose and lignin either reduced or did not affect enzyme activities compared to control at respective measuring time. Based on the result, we supposed that the selective synthesis of different enzymes by microbial community was C-source lability dependent. In conclusion, substrate quality rather than substrate amendment volume and timing had greater impacts on soil microbial activities, and hence indirectly influenced soil fertility.

Cultivation of Chlorella sp. for biodiesel production using two farming wastewaters in eastern Colombia

The production of biofuels using wastewater as a microalgae culture medium is a little explored technology, but with potential for success. In order to contribute to the knowledge of these technologies and their technical feasibility for microalgae growth, in this work the Chlorella sp. strain was cultivated in two types of effluents generated in an experimental farm located in eastern Colombia, before and after a biological treatment process. The consumption of the main nutrients that regulate growth and lipid production was evaluated, in order to extract, quantify, characterize and convert them into biodiesel. The results showed that Chlorella sp. growth and lipid production is more favourable in R2 medium of treated water than in R1 medium of raw water, mainly due to phosphorus limitation and higher N-NO3 concentration in R2 compared to R1. In the R2 medium culture, a percentage of 42.54% of long-chain fatty acids was found, which is necessary to obtain a high quality biodiesel. Finally, the best transesterification experiment allowed reaching a fatty acid methyl esters (FAME) percentage of 90.1 ± 2.7%. In general, the results demonstrated the potential viability of using the wastewater generated in the San Pablo farm to produce biomass with lipid content to obtain biodiesel, finding that where the concentration of nutrients, mainly nitrogen, has a great influence on the microalgal metabolism for lipid accumulation.

Erratum to: Analysis of differences in nutrients chemistry in seamount seawaters in the Kocebu and M5 seamounts in Western Pacific Ocean

Comprehensive surveys were conducted in the Kocebu deep seamount and the M4 shallow seamount in the Western Pacific Ocean in March 2018 and May 2019, respectively. The distributions of nutrients in euphotic zone of the two seamount-areas were revealed, and the causative controlling factors were analyzed. Results show that the vertical distribution of nutrients in the two seamount-areas accorded with the general law of the oligotrophic ocean. The concentrations of NO3-N, PO4-P, and SiO3-Si generally increased gradually with the increase of water depth, and they were extremely low in water layers within 100 m. The area of high NO2-N concentration well agreed with the Deep Chlorophyll Maximum Layer. On the other hand, the distribution of water masses and phytoplankton and hydrological conditions in the two seamount-areas were different, resulting in lower concentrations of NO3-N, PO4-P, and SiO3-Si in the water layers below 100 m in the Kocebu seamount area than those in the M4 seamount area. In addition, NO2-N was affected by the distribution of phytoplankton, and distributed mainly in the water layers of 150 and 100 m. There was upwelling in the euphotic zone of M4 seamount area, causing accumulations of nutrients and phytoplankton around the seamount, forming a “seamount effect”; however, no such an effect was found in Kocebu seamount area. Affected by the composition of biological community and the “seamount effect”, the nitrogen limitation in the M4 seamount area was not significant, and the dissolved inorganic nitrogen (DIN):PO4-P and SiO3-Si:DIN were closer to the Redfield ratios.

황금 비단잉어를 이용한 Hybrid 바이오플락 아쿠아포닉 시스템과 수경재배 시스템의 엽채류 생산성 비교 연구

Aquaponics is a cultivation system that combines aquaculture and agricultural hydroponics. This study investigated the productivity of leafy vegetables cultivated in the hybrid biofloc technology-aquaponics (HBFT-AP) and hydroponics (HP). Yellow koi fish (Cyprinus carpio) were fed an EP diet containing 3% MKP (monobasic potassium phosphate, KH₂PO₄) for 10 weeks in the HBFT-AP. Leafy vegetables of 2 cultivar (ovired lettuce, volare lettuce) were employed in the experiment and water quality [dissolved oxygen (DO, mg/L), pH, water temperature (℃), electrical conductivity (EC; μs/cm), turbidity (NTU), TAN (NH₃ + NH₄SUP+/SUP) (mg/L), NO₂-N (mg/L), NO₃-N (mg/L) and PO₄-P (mg/L)] was measured 6 times a week. Leafy vegetables in HBFT-AP using yellow koi fish fed the EP with MKP 3.0% had a productivity somewhat higher (2 kinds of cultivar) compared to those in HP, and the pH in the HBFT-AP was maintained at the range around 6.0 for 7-10 week. During the 10-week feeding trial, concentration of NO₂-N was kept low in variability while total TAN, NO₃-N and PO₄-P levels increased with time in HBFT-AP. Higher values in hematocrit (PCV, %), hemoglobin (Hb, g/dL) and inorganic phosphorus (mg/dL) were found (P0.05) in fish at the end of the experiment compared to the fish at the beginning of the experiment (initial fish: 27.45%, 12.19 g/dL and 6.39 mg/dL; final fish: 36.26%, 14.52 g/dL and 11.21 mg/dL).

Crop Field Level Estimation of Nitrogen Input from Fertilizer Use in Jeju Island, South Korea: Management Methods to Prevent Groundwater NO3-N Contamination

The application of synthetic nitrogen (N) fertilizers has boosted crop yields globally. However, it has also imposed on environmental pollution problems. An estimation of actual fertilizer N inputs at the crop field level is needed to establish effective N management plans to control groundwater NO3-N contamination. Here, a survey to collect the types of cultivated crop and fertilizer application rate was conducted during 2016–2018, covering 44,253 small crop fields (7730 ha) in the western part (Hanrim and Hankyung regions) of Jeju Island, South Korea. Foreign vegetables, citrus fruits, and bulb vegetables are the major crop types grown in the total cultivated areas of 2165.6 ha, 1718.7 ha, and 944.9 ha, respectively. For several crops (green garlic, potato, and chives), the over-use of N fertilizers is observed, the amount of which is 1.73–4.95 times greater than the standard fertilizer application rate. The highest level of fertilizer N input is observed for bulb vegetables in both the regions (Hanrim: 500.5 kg/ha, Hankyung: 487.1 kg/ha), with nearly 80% of the N fertilizer input turned into surplus N loading. A comparison between a spatial interpolation map of the fertilizer N input and that of the groundwater NO3-N concentration implies that the excessive use of synthetic fertilizer results in the degradation of groundwater quality by NO3-N. N management plans for the study area are suggested based on the N fertilizer input at the crop field level. This study highlights that sustainable N management plans should be arranged at the crop field level, considering the spatial heterogeneity of N fertilizer use.

Spatial Pattern of Dissolved Nitrogen in the Water on Receiving Agricultural Drainage in the Sanhuanpao Wetland in China

The total nitrogen (TN) increases and the water quality deteriorates when a large amount of nitrogen-containing water is discharged from farmlands into wetlands. This research on the relationship between the TN, ammonia nitrogen (NH4-N), and nitrate nitrogen (NO3-N) concentrations in water has a certain reference significance for understanding the spatial pattern of nitrogen removal in wetlands. Taking the Sanhuanpao wetland in northeast China as the research object, 24 sampling plots in the study area were sampled in the spring and summer of 2017 to test the concentrations of TN, NH4-N, and NO3-N. Based on the calculations of the change rates of the TN, NH4-N, and NO3-N in spring and summer, a step-by-step elimination analysis was carried out and the spatial pattern of the TN, NH4-N, and NO3-N removals were revealed by gradual buffer extrapolations, combined with stepwise fitting functions. The results show that the removal capacity of NH4-N is strong within the range of 14.55 km–20 km and 26.93 km–35.96 km from the wetland inlet, and the removal capacity of NO3-N is relatively strong within the range of 26.93 km–35.96 km. The strong NH4-N and NO3-N removal areas in the wetland are not in the geometric center of the wetland, but in separate narrow areas around the center. The TN removal along water channel direction is only 0.25 times higher than that direction perpendicular to the channel, indicating that regardless of whether wetlands are expanded along the water channel or perpendicular to the water channel, the difference to the TN removal is small. Effectively monitoring and managing the reception of agricultural drainage is extremely important for maintaining the water-purification function of wetlands. The aim of the research is to reveal a spatial law of nitrogen removal in wetland water, and provide a framework for studying the mechanism of spatial difference of nitrogen.

Nitrogen availability under conventional and conservation tillage in semiarid Inceptisol

The present experiment was conducted to study the spatio-temporal variation of available nitrogen fraction in cotton (Gossypium hirsutum L.) in conservation agricultural based long term experiment (since 2010) during 2019-20. The treatment comprises two distinct practices, i.e. conventional tillage (CT) and zero tillage (ZT). Under ZT, permanent narrow bed without (PNB) and with residue of previous crops (PNB+R); permanent broad bed without (PBB) and with residues (PBB+R); flat bed (FB) and FB with residues (FB+R). Soil samples were collected (0-15 and 15-30 cm) at pre-flowering, flowering, boll formation and harvest stages. Adoption of CA practices increased the NH4-N, NO3-N and mineral-N fractions of nitrogen at different crop growth stages. Highest NH4-N, NO3-N and mineral-N were recorded at flowering and boll formation stage respectively. The effect of crop residue retention and crop establishment methods on available N fractions was prominent up to 15 cm soil depth. Crop residue retained plots recorded significantly higher N fraction compared to respective without residue and CT plots. Residue retained plots of FB, PBB, PNB recorded 50, 25 and 36% higher NO3-N concentration as compared to respective without residues plots at pre-flowering stage. At flowering stage, maximum NH4-N was recorded in PBB+R (17.9 mg/kg) and FB+R plots (17.5 mg/kg), which was approximately 68 and 16% higher over CT and PNB+R plots. The results revealed that zero tillage together with PBB+R could be a viable option over conventional practice for maintaining nitrogen availability to plants under cotton-wheat (Triticum aestivum L.) cropping system in semiarid climate.

Riparian Land Use and Hydrological Connectivity Influence Nutrient Retention in Tropical Rivers Receiving Wastewater Treatment Plant Discharge

Riparian areas are recognized for their buffering capacity regarding phosphorus and nitrogen from agricultural and urban runoff. However, their role in attenuating nutrient loads of rivers receiving point source nutrient inputs (e.g., from wastewater treatment plants, WWTPs) is still little understood. Here, we investigated whether ammonium (NH4-N), nitrate (NO3-N), and soluble reactive phosphorus (SRP) retention were influenced by the riparian land use in three Brazilian rivers receiving WWTP effluents. We hypothesized that nutrient attenuation would be potentially influenced by the hydrological connectivity between the main channel and riparian areas with native vegetation. We estimated retention from longitudinal patterns of dilution-corrected nutrient concentrations below the WWTPs. We assessed nutrient retention during periods with high (i.e., the wet) and low connectivity (i.e., the dry season). Relationships between non-conservative (nutrients) and conservative (chloride) solutes in both seasons were used to identify potential changes in the river chemistry due to the hydrological connectivity with the riparian areas. We also evaluated the relationship between net uptake velocities (Vf-net) and the accumulated percent native vegetation cover in the 100-m buffer using linear regressions, comparing the response for each nutrient between seasons with Analysis of Covariance. Slopes of regressions between nutrients and chloride significantly differed between seasons for NO3-N and SRP but not for NH4-N. The relationships between Vf-net and accumulated native vegetation in the riparian buffer presented steeper slopes for SRP in the wet than in the dry season. No significant relationships between NO3-N Vf-net and native vegetation cover were observed in either season. In contrast, increases in Vf-net with increasing vegetation cover were observed for NH4-N in the dry season. In periods with expected higher connectivity, NO3-N and SRP concentrations tended to be lower relative to chloride concentrations, with a potential effect of native vegetation in the riparian area on SRP retention. Our results suggest that seasonal connectivity between nutrient-rich river water and riparian areas is likely to induce changes in the predominant nutrient transformation processes, thereby favoring either nutrient retention or export in such rivers.

Evaluating the effects of biodegradable film mulching and topdressing nitrogen on nitrogen dynamic and utilization in the arid cornfield

The residual film and nitrate nitrogen (NO3-N) leaching are the main sources of non-point pollution in arid fields. To solve the above problems, the DNDC model was first calibrated and validated based on data obtained from plastic film mulching (PM), biodegradable film mulching (BM), and no film mulching (NM) studies performed during 2016 and 2017. The NO3-N content in 0–50 cm soil layer, leaching, uptake, balance and use efficiency (NUE) under PM, BM, and NM with topdressing nitrogen (N) amount of 280 kg ha−1 (PM280, BM280, and NM280) were evaluated using observed and simulated data. Additionally, scenario simulation and prediction tests were carried out using the DNDC model to explore the critical topdressing N amount for BM, PM, and NM. These factors were compared for BM with topdressing N amount of 160 kg ha−1 (BM160) and 220 kg ha−1 (BM220). DNDC model showed remarkably high accuracy in simulating the NO3-N content, leaching, uptake, and yield, with R2 and NSE (Nash-Sutcliffe efficiency) of 0.88–0.99 and 0.77–0.99, respectively, during validation studies. During the late growth stage, the corn yield, NO3-N uptake, content, cumulative NO3-N leaching (cum.NL), and NUE for BM280 showed an average decrease of 4%, 1.44%, 8.81%, 0.75%, and 2.04% than PM280, respectively. NO3-N content and cum.NL increased markedly with increasing concentration of topdressing N. NO3-N content and cum.NL was increased by 149.03% and 87.33% for BM280 and 46.71% and 40.7% for BM220, respectively, as compared to BM160. The NUE for BM280 decreased by 30.56% and 18.25% compared to BM160 and BM220, respectively. The scenario simulations showed that 200 kg ha−1 is a critical topdressing N application amount for the arid cornfields, with corn yield of 11,132.1 kg ha−1, cum.NL of 121.33 kg ha−1, and NUE of 42.54%, respectively.

Transport and sources of nitrogen in stormwater runoff at the urban catchment scale

Revealing the transport and sources of nitrate in urban stormwater runoff can effectively manage nitrate pollution in urban areas. This study used the chemical properties of stormwater along with δ15N-NO3− and δ18O-NO3− isotopes to identify the transport and sources of nitrate within an urban catchment. The results showed that the NO3-N concentration and total dissolved nitrogen (TDN) composition differed among roof runoff, road runoff, and drainage runoff. The highest NO3−N concentration was found in roof runoff and NH3-N dominated the TDN composition. However, the erosion of pervious surfaces and litter may have led to higher DON/TDN values in road runoff. The TDN composition of drainage runoff was consistent with that of roof runoff. Furthermore, among the various rainfall characteristics, the depth and intensity of rainfall were significantly correlated with the NO3-N concentrations in roof runoff and road runoff, while antecedent dry days had little effect. According to a Bayesian mixing model, the average contributions of the nitrate load in drainage runoff were ranked as road runoff (51.6%) > rainwater (29.2%) > and roof runoff (15%), which is consistent with the results of previous studies. Rainwater nitrate may have ranked second due to the confluence time, pollution level, and other factors that made rainwater reduce the pollution characteristics of roof runoff. The dominant contribution of road runoff to the NO3−N concentration of drainage runoff could be attributed to the large runoff volume. Hence, effective measures should be taken to minimize the NO3-N concentration in roof runoff, while runoff volume reduction should be the primary concern for controlling road runoff pollution. This work is helpful for obtaining a better understanding of the transport and sources of nitrate that vary dynamically within different hydrological flow pathways, and the outcomes are expected to enhance targeted measures to mitigate nitrate pollution in urban water systems.

Nitrate-Nitrogen (N-NO3-) in Ground Waters of Agricultural Zones in Tabasco, México; Risks for Aquatic Life and Human Health

Nitrate nitrogen (N-NO3-), the most common pollutant in groundwater, is a result of the effect of diffuse sources of pollution like agriculture and animal husbandry intensive. The land use for these economic activities is very common in the Los Ríos sub-region in the state of Tabasco, Mexico, where the Los Ríos and Boca del Cerro aquifers are located. The aim of this research was to assess the concentrations of nitrate-nitrogen (N-NO3-) in groundwater, determine the quality in agreement with the maximum permissible limits established by national and international regulations, and the risks to the public health and aquatic life. The spatial distribution of N-NO3- was determined using the inverse distance weighted (IDW) interpolation technique. The average nitrate-nitrogen concentration was 0.76 mg.L-1, while the maximum concentration observed was 3.98 mg.L1. This does not exceed the maximum permissible limit (MPL) established in the national and international normativity for drinking water. However, in 50% of the sampling sites, the concentrations of N-NO3- exceed the MPL established in Mexico for the protection of the life of seawater. Relatively low concentrations of N-NO3- have shown to be toxic to certain aquatic organisms, and the aquifers studied discharge a third of the water to the rivers in the area, which flow into the Laguna de Términos Campeche and the Gulf of Mexico. Laguna de Términos Campeche is one of the most diverse and rich environmental systems on earth, where numerous ecosystems converge such as coastal lagoons, wetlands, mangroves, seagrasses, and coral reefs.