Nitrate Release Research Articles

Amonium and Nitrate Of Soil In Relation To Water Table Fluctuation At The Tidal Rice Fields

The reclaimed lowlands of Indonesia with the respective of 256 hectares of secondary block consist of 16 hectares of tertiary blocks, were used for rice plant production. Paddy was planted during the rainy season of November to February. It was followed by water melon plant in March to May. Then corn was growed in the dry season of June to September finally. Fluctuations of water table in the farm is very crucial in determining the cropping calender. Water management with free drainage approach is influenced by tidal water movement into the tertiary canals bordering the farmers fields. A constant water retention -10 cm below the canal bank has increased the water table in the farm from -10 cm to +20 cm. Water retention (controlled drainage) mode was applied by the farmers especially during the rice growing period. The release of water in the canal to a depth of -50 cm below the canal bank had lowered the water table level to -20 cm. During almost 200 days of experimental work, soil and water samples were taken by 11 times. The content of NO 3 - , NH 4 + and pH of the soil sample and be analyzed in relation to the water table fluctuation. Groundwater level does not show the effect on nitrate release on the urea application stocked. however, on the high ground water level it appears to be more in control of ammonium release compared to the ground water level of -20 cm.

Controlled Release of Nitrate and Molybdate Intercalated in Zn-Al-Layered Double Hydroxide Nanocontainers towards Marine Anticorrosion Applications

Zn-Al layered double hydroxides (LDHs) intercalating with molybdate anions was developed to inhibit the corrosion of mild steel in neutral chloride conditions. The LDH compounds were prepared by a method involving co-precipitation and anion-exchange and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR), respectively. The anticorrosion capabilities of the LDHs hybrids were analyzed by using open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curve. A significant reduction of the corrosion rate is observed in the presence of a 2 g/L concentration of the LDHs hybrids in the corrosive media. The mechanism is that the intercalated molybdate anion can slowly diffuse out of the inner structure of LDHs in a controllable way and result in a relatively long-term effect of corrosion inhibition. The result presented here underlines the great potential of the controlled release mechanism for marine anticorrosion applications.

Effects of Azorhizophilus paspali and Paenibacillus mucilaginosus as Biofertilizer and Determination of Nutritional Efficiency by Sensors

The benefits of nitrogen-fixing and potassium-solubilizing microorganisms in plant growth were investigated by using micro-sized ion-selective sensors developed in our laboratory. Azorhizophilus paspali (ATCC 23367) having nitrogen-fixing capability and Paenibacillus mucilaginosus (DSM 24461) having potassium-solubilizing capability were used in media. The microorganisms grown in aseptic conditions were mixed with soil and compost in order to improve plant nutrition, and samples taken from growth medium were examined for 23 days by ammonium- and potassium-selective PVC membrane sensors exhibiting almost Nernstian response. The highest nitrate release were obtained on the 14th day of inoculation in samples using A. paspali. The highest potassium release was obtained on 18th day of inoculation in samples using P. mucilaginosus. The results showed that bacterial inoculation had a more stimulating effect on assimilation of N and K in compost than in soil. In addition, the effect of microbial strains on shoot and root growth and nutrient uptake of tomato was tested in pot experiments using compost. A. paspali and P. mucilaginosus inoculation increased the shoot and root dry weight of tomato seedlings, respectively, 7–14 and 12–19% when compared with the control. The results showed that addition of the microorganisms into compost would be beneficial in plant nutrition. Application of these microorganisms as biofertilizers in barren areas will protect soil from the harmful effects of chemical fertilizers with an environmentally friendly approach.

Organ uptake and release of inorganic nitrate and nitrite in the pig

Numerous studies have shown beneficial cardiovascular and metabolic effects of dietary nitrate but the release or uptake of these anions on an organ level is still poorly elucidated. Here we administered sodium nitrate in the pig and measured acute changes in release/uptake of nitrate and nitrite across several organs as well as cardiovascular and metabolic functions.In 17 anesthetized pigs multiple venous catheters and arterial ultrasonic blood flow probes were positioned. After pretreatment with the NO synthase (NOS) inhibitor l-NAME to minimize involvement of NOS-dependent nitrate/nitrite generation, the animals received bolus injections of either sodium nitrate or sodium chloride. Organ blood flows and release/uptake of nitrate and nitrite were measured in the pulmonary, splanchnic, hepatic and renal circulations for up to two hours. In addition, small intestinal luminal NO, gut secretion of nitrate, as well as hepatic and renal NADPH oxidase activity were measured.At baseline there was a significant uptake of nitrite in the liver and kidneys together with a release of nitrite from the lungs. In the control pigs, arterial plasma nitrite progressively declined during the observation period (−54%) but was stable in the nitrate group, indicating conversion of nitrate to nitrite. Sodium nitrate led to a marked accumulation of nitrate in the small intestinal lumen with a parallel increase in luminal nitrite. This was coupled with release of nitrite in the portal vein and a concomitant uptake of this anion in the liver. There was a trend towards reduced NADPH oxidase-dependent superoxide generation in the liver but an increase in the kidney. Nitrate had no acute effects on cardiovascular parameters or regional and systemic oxygen consumption.In conclusion, we found a notable difference in release and uptake of nitrate and nitrite between the organs investigated. Our findings indicate an acute conversion of nitrate to nitrite, most likely independent of oral bacteria but by a mammalian nitrate reductase and/or gut bacteria.

Use of Biogenic Silica in Porous Alginate Matrices for Sustainable Fertilization with Tailored Nutrient Delivery

Population growth coupled with significant pressure for clean agricultural practices puts a heavy burden on conventional crop treatments that target high yields with minimal cropland expansion. Optimization of fertilization systems is required as part of the solutions to current megatrends. Herein, we present a sustainable strategy to achieve controlled release formulations for nitrogen fertilization. Specifically, we used interfacial engineering to design alginate-based matrices that incorporated biogenic silica particles to achieve increased interfacial area for dynamic entrapment and release of ammonium nitrate. The incorporation of biogenic silica in the alginate matrix provided a porous architecture spanning length scales from the micro- (within particles) to the macrosize (within the polymeric matrix) levels, leading to tunable patterns of nitrogen release. Alginate–biogenic silica granules approached the European requirements of “slow-release” compositions. At optimized silica content, 15% of the n...

Environmental Effect of Hydroxyapatite Urea Application on Optimizing Urea Fertilizers for Wheat Plant

This study was intended gradually release of nitrogen into the soil through the covering of urea pellets with hydroxyapatite and increase the wheat yield using zero valent iron spraying. Incubation trial was planed under different conditions (saturated and field capacity) for soil samples to study the performance of the use Hydroxyapatite urea on ammonium ionrelease for 63 days. A field trial was aimed to examine of hydroxyapatite urea and zero valent iron spraying on improved N-use efficiency, minimize nitrate leaching, and wheat productivity. Urea was used at two rates 80 and 100 % from recommended dose. Data of incubation trial observed that an increase of ammonium ion release with increase in time of incubation by using hydroxyapatite urea. Data of field trial observed that the release of nitrate was slower from hydroxyapatite urea soil than pellets urea, which reached 20 mg L-1 for urea pellets and 150 mg L-1 for hydroxyapatite urea at two weeks, respectively. Hydroxyapatite urea leads to minimize nitrate leaching into ground water. Also the results showed that the using of hydroxyapatite urea and zero valent iron individually or combined lead to increment in the yield of wheat compared to urea pellets. Yield of treatments was in the following order: urea100+Fe (11%) < hydroxyapatite urea100 (20%) < hydroxyapatite urea100+Fe (27%) compared to urea100 while urea80+Fe (10%) < hydroxyapatite urea 80 (23%) < hydroxyapatite urea 80+Fe (30%) compared to Urea 80. It is concluded from these data that controlled released urea fertilizer improved yield by 27%, and grain protein percentage 50% as compared to urea pellets. The highest increase for nitrogen uptake by wheat plant was observed by using hydroxyapatite urea with zero valent iron spraying. From the results obtained it can summarize that, the efficiency of the use of urea fertilizer can be improved by covering with hydroxyapatite, as well as increasing the productivity of wheat yield by spraying of zero valent iron to reduce the cost price.

Tracking the Release of Soil Nitrate and Labile C in A Legume-Maize Rotation in Zimbabwe

This study compared the effect of a weedy fallow (5.2 t/ha biomass), a velvet bean (Mucuna pruriens) cut for hay (7.2 t/ha biomass) and a green-manured M. pruriens (6.49 t/ha biomass) on the dynamics of soil N and C in a maize crop. An on-farm, farmer participatory experiment was established on a farmer’s field in Wedza District, Zimbabwe. Soil mineral N and labile carbon were determined at intervals upto 120 cm depth, at maize planting and at 1 and 2 weeks after planting. Before planting, the soil mineral N content ranged from 28 kg N/ha after weed fallow to 107 kgN/ha following M. pruriens. Total nitrate concentration was highest in the 0-15 cm depth of the M. pruriens treatments in the pre-planting sampling, but following rainfall and maize planting, nitrate concentration declined rapidly. By 2 weeks after planting, 7.5 and 13.5 kg N/ha remained in the 0-120 cm soil depth of the weedy fallow and green-manured M. pruriens, respectively. Improving synchrony of nutrient release and uptake is critical when applying high quality residues which breakdown relatively slowly. This could result in significant inputs of C, release nutrients more slowly and reduce soil nutrient losses.

Swelling behavior of poly (N-hydroxymethylacrylamide-co-acrylic acid) hydrogels and release of potassium nitrate as fertilizer

Abstract Poly (N-hydroxymethylacrylamide-co-acrylic acid) [P(NHMA-AAx)] hydrogels were prepared by free-radical polymerization in aqueous solution at 56°C, using N,N′-methylenebisacrylamide as the cross-linking agent. The synthesized hydrogels were subsequently investigated by a series of characterization techniques including Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis and differential scanning calorimetry analysis. The effects of comonomer composition in the feed, pH, temperature and ionic strength on the swelling behavior were studied. Results indicated that the swelling capabilities of P(NHMA-AAx) hydrogels decreased with the increase in N-hydroxymethylacrylamide (NHMA) content in the polymeric matrix and ionic strength of the medium. Additionally, the hydrogels showed both temperature and pH responses. The dynamic swelling behaviors of hydrogels at different pH values followed a non-Fickian type. The P(NHMA-AAx) hydrogels were also loaded with potassium nitrate (KNO3) as a model agrochemical, and the release kinetics of fertilizer from the hydrogels was studied as a function of KNO3 and NHMA concentrations. Moreover, various kinetic parameters, such as release exponents and diffusion coefficients, were calculated.

Novel mixed vesicles containing lactobacilli biosurfactant for vaginal delivery of an anti-Candida agent

The purpose of this work was to prepare and characterize an innovative formulation for vaginal delivery of econazole nitrate, commonly used for the treatment of Candida infections. A novel biosurfactant isolated from a vaginal Lactobacillus strain was used to prepare phosphatidylcholine based mixed vesicles. Biosurfactant was produced by Lactobacillus gasseri BC9, isolated from the vagina of a healthy premenopausal woman, and was chemically characterized by FT-IR and ESI-MS. Mixed vesicles, obtained through film rehydration and extrusion method, were characterized in terms of size, zeta potential, encapsulation efficiency, mucoadhesion properties and econazole release. Moreover, the antimicrobial activity of the mixed vesicles was tested towards both planktonic cultures and biofilms of Candida albicans. Biosurfactant produced by L. gasseri BC9 was composed by peptide-like molecules containing hydrocarbon chains and possessed a high surface activity together with a low critical micelle concentration. All the mixed vesicles presented optimal diameter range (226–337nm) for topical vaginal administration. Econazole-loaded mixed vesicles containing biosurfactant showed higher encapsulation efficiency and mucoadhesion ability with respect to vesicles containing Tween 80. Further, they allowed a sustained release of econazole nitrate, maintaining the antifungal activity against C. albicans planktonic culture. Notably, biosurfactant-based vesicles were significantly more active than free econazole in the eradication of Candida biofilm. In conclusion, mixed vesicles are promising new vaginal delivery systems for the potential employment in the treatment of chronic infections.

Microstructural and associated chemical changes during the composting of a high temperature biochar: Mechanisms for nitrate, phosphate and other nutrient retention and release

Recent studies have demonstrated the importance of the nutrient status of biochar and soils prior to its inclusion in particular agricultural systems. Pre-treatment of nutrient-reactive biochar, where nutrients are loaded into pores and onto surfaces, gives improved yield outcomes compared to untreated biochar. In this study we have used a wide selection of spectroscopic and microscopic techniques to investigate the mechanisms of nutrient retention in a high temperature wood biochar, which had negative effects on Chenopodium quinoa above ground biomass yield when applied to the system without prior nutrient loading, but positive effects when applied after composting. We have compared non-composted biochar (BC) with composted biochar (BCC) to elucidate the differences which may have led to these results. The results of our investigation provide evidence for a complex series of reactions during composting, where dissolved nutrients are first taken up into biochar pores along a concentration gradient and through capillary action, followed by surface sorption and retention processes which block biochar pores and result in deposition of a nutrient-rich organomineral (plaque) layer. The lack of such pretreatment in the BC samples would render it reactive towards nutrients in a soil-fertilizer system, making it a competitor for, rather than provider of, nutrients for plant growth.

Fabrication of smart magnetic nanocomposite asymmetric membrane capsules for the controlled release of nitrate

Nitrate contamination of water resources due to excessive use of nitrogen-based fertilizers has become a global health issue. In this work, a recyclable and environmentally sensitive magnetic Fe2O3/PES (Polyethersulfone) nanocomposite asymmetric membrane like capsules (NAMCs) were prepared such that release nitrate in a controlled manner. Different characterization techniques such as SEM, EDAX, DSC, and surface energy measurement were used to systematically characterize the NAMCs. It was observed that the incorporation of only 0.5wt.% Fe2O3 nanoparticles into NAMC provided a slow and steady release rate of nitrate. A further addition of nanoparticles (from 0.5wt.% to 1.5wt.%) into the capsules matrix resulted in an increase in the initial-release rate (IRR, from 3.17 to 4.17μS/cmmin) and maximum release level (MRL, from 36 to 52μS/cm). The designed capsules also showed recyclability and the ability to respond to the environmental conditions. For instance, IRR increased from 3.17 to 5.31μS/cmmin for NAMCs when temperature increased only by 10°C. These findings could be considered as a new and green approach to prevent nitrate contamination of water resources in the first place without exacerbating energy issues. Although this work is based on the controlled release of nitrate as the water resources contaminant, the NAMCs can also be used for other nutrients and fertilizers.

Investigation of chemical-less UVC/VUV process for advanced oxidation of sulfamethoxazole in aqueous solutions: Evaluation of operational variables and degradation mechanism

Abstract The degradation, mineralization and mechanism of sulfamethoxazole (SMX) oxidation were investigated in the UVC/VUV reactor as a promising chemical-less process. Complete SMX degradation was achieved in pH of 7 and at a fluence of 54.9 mJ/cm2. Continuing the reaction up to 30 min (109.8 mJ/cm2 fluence) brought about 98.5% mineralization. Scavenging tests using salicylic acid indicated that hydroxyl radical was definitely the dominant radical species without which negligible SMX removal was observed. Process efficiency was evaluated in presence of anions and in case of tap water. Anions, except the reduced sulfur species did not significantly affect SMX removal. The possibility of further increase of reaction rate was investigated by adding S2O82−, H2O2 and O3 to the content of VUV/UVC photo-reactor. Transformation products (TPs) were identified and degradation pathway was proposed. The presence of non-cyclic TPs along with high release of nitrate and sulfate endorsed almost complete mineralization of SMX.

579 In situ and in vitro evaluation of a slow release form of nitrate for ruminants: Nitrate release rates, rumen nitrate metabolism and production of methane, hydrogen, and nitrous oxide

579 In situ and in vitro evaluation of a slow release form of nitrate for ruminants: Nitrate release rates, rumen nitrate metabolism and production of methane, hydrogen, and nitrous oxide

Enhancing nitrogen availability from urea using clinoptilolite zeolite

The high costs of nitrogen fertilizers have necessitated best-developed practices to optimize nitrogen fertilizers use whilst minimizing nitrate losses. Ammonium adsorption inhibits loss of nitrogen in the form of nitrate thereby increasing nitrogen availability for crops. Due to the negatively charged properties of nitrate, it moves freely in the soil solution and not adsorbed onto soil particle surfaces. In this study, clinoptilolite zeolite was used in soil leaching and ammonium adsorption and desorption studies to determine: (i) soil total nitrogen availability, exchangeable ammonium, and available nitrate, and (ii) the capacity of clinoptilolite zeolite to adsorb and desorb ammonium from different rates of urea. Different rates of urea amended with clinoptilolite zeolite significantly reduced ammonium and nitrate release from urea compared with urea alone. Clinoptilolite zeolite enhanced retention of soil total nitrogen, exchangeable ammonium, and available nitrate due to the high cation exchange capacity of the mineral to adsorb ammonium, thus, improving nitrogen availability through temporary retention on the exchange sites of the clinoptilolite zeolite. The availability of nitrogen can be enhanced if urea is amended with clinoptilolite zeolite.

Tonoplast-localized nitrate uptake transporters involved in vacuolar nitrate efflux and reallocation in Arabidopsis

A great proportion of nitrate taken up by plants is stored in vacuoles. Vacuolar nitrate accumulation and release is of great importance to nitrate reallocation and efficient utilization. However, how plants mediate nitrate efflux from vacuoles to cytoplasm is largely unknown. The current study identified NPF5.11, NPF5.12 and NPF5.16 as vacuolar nitrate efflux transporters in Arabidopsis. Histochemical analysis showed that NPF5.11, NPF5.12 and NPF5.16 were expressed preferentially in root pericycle cells and xylem parenchyma cells, and further analysis showed that these proteins were tonoplast-localized. Functional characterization using cRNA-injected Xenopus laevis oocytes showed that NPF5.11, NPF5.12 and NPF5.16 were low-affinity, pH-dependent nitrate uptake transporters. In npf5.11 npf5.12 npf5.16 triple mutant lines, more root-fed 15NO3− was translocated to shoots compared to the wild type control. In the NPF5.12 overexpression lines, proportionally less nitrate was maintained in roots. These data together suggested that NPF5.11, NPF5.12 and NPF5.16 might function to uptake nitrate from vacuoles into cytosol, thus serving as important players to modulate nitrate allocation between roots and shoots.

FORMULATION AND EVALUATION OF MICROSPONGE GEL FOR TOPICAL DELIVERY OF ANTIFUNGAL DRUG

Objective: The purpose of present study aims to design novel drug delivery system containing oxiconazole nitrate microsponges and to prepare microsponge gel. Oxiconazole nitrate is an antifungal drug used in the treatment of fungal infection having a poor aqueous solubility, side effects and adverse reactions. The microsponge delivery system is unique technology for controlled release of active agents. Methods: The microsponges were prepared by quasi-emulsion solvent diffusion method by using polymer eudragit S-100 and eudragit L-100. All the formulated microsponges were subjected for various evaluation parameters such as production yield, encapsulation efficiency, particle size analysis and in vitro drug release study. The optimised microsponge formulation F3 and F9 were further formulated as gel formulation for topical delivery. Prepared gel was evaluated for physical parameters like pH, spreadability, viscosity, drug content and in vitro diffusion study and compared with the marketed formulation.Results: The Fourier transform infrared radiation measurement (FTIR) and Differential scanning colorimetry (DSC) of drug and excipient confirm compatibility. Results revealed that quasi-emulsion solvent diffusion method is a suitable technique for the preparation of microsponges as most of the formulations were discrete and spherical in shape with a good production yield of 61.44% to 80.45% and The highest drug release for F3 and F9 formulation was found to be 87.77 % and 83.24 % respectively for the 8 h. The microsponge gel formulation MGI (F3) showed the controlled release of oxiconazole nitrate for 12 h. The drug release data of optimised batch MGI (F3) were fitted into different kinetic models and showed that the drug release from gel formulation follows zero order release.Conclusion: As compared to conventional formulation, the prepared microsponge gel are expected to remain on the skin for a longer time, gradually releasing their contents over the time. Hence, oxiconazole nitrate microsponges and microsponge gel prepared in this study are promising as being more useful than conventional formulation therapy.

In situ and in vitro evaluations of a slow release form of nitrate for ruminants: Nitrate release rate, rumen nitrate metabolism and the production of methane, hydrogen, and nitrous oxide

In situ and in vitro experiments were conducted to determine nitrate (NO3−) release rate from encapsulated NO3− (EN) in the rumen and to examine metabolism of EN-NO3− in conjunction with methane (CH4), hydrogen (H2), and nitrous oxide (N2O) production. Three ruminally-cannulated beef heifers were used to incubate the following substrates in the rumen for 72h: soybean meal, EN, and unencapsulated NO3− (UEN). Because of immediate solubilisation, soluble nitrogen (N) fraction of UEN was assumed to be 100%. A non-linear regression model fitted to N disappearance of EN (R2=0.93, P<0.01) indicated 35.4% of soluble N fraction and 54.7% of slowly degradable N fraction. Two in vitro experiments were conducted where UEN and EN were incubated for 24h in buffer alone without substrate or in buffered-rumen fluid with substrates containing starch and xylan with urea, UEN, or EN as sole N sources. When UEN was incubated with buffer, 99.9% of UEN-NO3−-N was recovered as NO3−-N in the buffer over 24h. However, recovery of EN-NO3− as NO3−-N gradually increased over 24h up to 58%. When urea, EN or UEN were incubated with buffered-rumen fluid, total gas production decreased (P=0.022) for UEN compared with urea and EN. Methane production decreased (10.7 and 13.3 vs. 19.6mL; P<0.01) for UEN and EN, respectively, compared with urea. Hydrogen production considerably increased (P<0.01) for UEN compared with urea and EN without a difference between urea and EN. Nitrous oxide production was greater for UEN followed by EN and urea (20.8, 7.5 and 0.02μL, respectively; P <0.05). During the incubation with buffered-rumen fluid, 100% of UEN-NO3− was recovered as NO3−-N in the medium until 6h and then the recovery gradually decreased to 18% at 24h while recovery as NO2−-N increased up to 22% at 24h. However, recovery of EN-NO3−-N as NO3−-N in the medium increased by 20% at 12h and then gradually decreased to 5% at 24h without accumulation of NO2−-N in the medium. In conclusion, EN released NO3− slowly in the rumen and decreased CH4 production without negatively affecting microbial fermentation. Increases in H2 and N2O production and accumulation of NO3− and NO2− in the medium were not observed for EN compared with UEN, indicating that EN could be a promising NO3− source to lower CH4 production with less risk of NO3−/NO2− toxicity.

Nitrate release from waste rock dumps in the Elk Valley, British Columbia, Canada

The origin, distribution and leaching of nitrate (NO3−) from coal waste rock dumps in the Elk Valley, British Columbia, Canada were defined using chemical and NO3− isotope analyses (δ15N- and δ18O-NO3−) of solids samples of pre- and post-blast waste rock and from thick (up to 180m) unsaturated waste rock dump profiles constructed between 1982 and 2012 as well as water samples collected from a rock drain located at the base of one dump and effluent from humidity cell (HC) and leach pad (LP) tests on waste rock. δ15N- and δ18O-NO3− values and NO3− concentrations of waste rock and rock drain waters confirmed the source of NO3− in the waste rock to be explosives and that limited to no denitrification occurs in the dump. The average mass of N released during blasting was estimated to be about 3–6% of the N in the explosives. NO3− concentrations in the fresh-blast waste rock and recently placed waste rock used for the HC and LP experiments were highly variable, ranging from below detection to 241mg/kg. The mean and median concentrations of these samples ranged from 10–30mg/kg. In this range of concentrations, the initial aqueous concentration of fresh-blasted waste rock could range from approximately 200–600mg NO3−-N/L. Flushing of NO3− from the HCs, LPs and a deep field profile was simulated using a scale dependent leaching efficiency (f) where f ranged from 5–15% for HCs, to 35–80% for the LPs, to 80–90% for the field profile. Our findings show aqueous phase NO3− from blasting residuals is present at highly variable initial concentrations in waste rock and the majority of this NO3− (>75%) should be flushed by recharging water during displacement of the first stored water volume.

Nitrogen dynamic in Eurasian coastal Arctic ecosystem: Insight from nitrogen isotope

AbstractPrimary productivity is limited by the availability of nitrogen (N) in most of the coastal Arctic, as a large portion of N is released by the spring freshet and completely consumed during the following summer. Thus, understanding the fate of riverine nitrogen is critical to identify the link between dissolved nitrogen dynamic and coastal primary productivity to foresee upcoming changes in the Arctic seas, such as increase riverine discharge and permafrost thaw. Here we provide a field‐based study of nitrogen dynamic over the Laptev Sea shelf based on isotope geochemistry. We demonstrate that while most of the nitrate found under the surface freshwater layer is of remineralized origin, some of the nitrate originates from atmospheric input and was probably transported at depth by the mixing of brine‐enriched denser water during sea ice formation. Moreover, our results suggest that riverine dissolved organic nitrogen (DON) represents up to 6 times the total riverine release of nitrate and that about 62 to 76% of the DON is removed within the shelf waters. This is a crucial information regarding the near‐future impact of climate change on primary productivity in the Eurasian coastal Arctic.

Microbial activity and metabolic quotient of microbes in soils amended with biochar and contaminated with atrazine and paraquat

ABSTRACTThe study was conducted to determine how biochar as a soil amendment maintained the microbial community in pesticide contaminated soils. Alfisol (Adenta series – Typic Kandiustalf) and Vertisol (Akuse series – Typic Calciustert) were amended with biochar (0 t/ha biochar, 10 t/ha cocoa husk biochar (CHB), 10 t/ha rice husk biochar (RHB)) and pesticides (atrazine and paraquat at two rates each namely 0 kg/ha pesticide and 10 times the normal recommended rate of pesticide) were applied. The CHB-amended soils stimulated microbial activities such as ammonia and nitrate release more than the RHB-amended soils. Basal respiration was significantly higher in the atrazine polluted soils than in paraquat polluted soil. Significant interaction occurred between soil type and biochar and high microbial biomass carbon was recorded for vertisol amended with CHB. Metabolic quotient was lower in soils amended with biochar and polluted with atrazine than in the un-amended soil. The use of CHB in soil of high clay content (47.5%, i.e. the vertisol) was a more effective management tool in maintaining the microbial community in a pesticide-polluted environment than in soil of lower clay content (22.5%). Soils of high clay content amended with biochar can sustain the soil microbial community even in a disturbed environment.