Nitrate Peak Research Articles

Performance of carbon and nitrogen removal in a system combining an aerobic trickling filter followed by two stages of vertical flow treatment wetland

Treatment wetland has become a reference in wastewater treatment, particularly for the treatment of domestic or agricultural effluent in rural areas. The AZOE process developed by the company SCIRPE is an optimised system of water treatment based on a conventional two-stage treatment wetlands with vertical hydraulic flow. A trickling filter has been added at the head of the system and filtration stages have been partially saturated to promote anoxic conditions. This study presents the monitoring of a complete pilot-scale AZOE system receiving real and continuous effluents. Effluents from two periods of the year are studied: autumn and spring when the organic load is higher. The performance of each treatment unit, as well as the total treatment unit is presented in this study. The main results show that i) the trickling filter consumes about half of the carbon load whatever the season but that nitrification is lower when the incoming organic load is higher ii) the first stage of filtration contributes a lot to denitrification thanks to the anoxic zones iii) the contribution of the second stage is lower but can increase in case of higher incoming load highlighting a safety role of the treatment. The continuous ammonium and nitrate data at the outlet of the first and second stages show a very characteristic dynamic of this system during the feeding period: a well-defined nitrate peak at the outlet of the first stage which is found on the second stage. The lack of carbon is pointed out as the most limiting factor to denitrification on the second stage.

Synthesis of Copper-Substituted Polyoxovanadate and Oxidation of 1-Phenyl Ethanol

Dicopper-substituted polyoxovanadate [Cu2V16O44(NO3)]5− (Cu2V16) was synthesized through the reaction of [Cu2V8O24]4− and [V4O12]4− in the presence of nitrate salt. From single crystal X-ray analysis, Cu2V16 exhibited the same helical structure as that of nitrate-incorporated polyoxovanadate, [V18O46(NO3)]5− (V18). Both complexes had the same framework with the same guest anion and are considered to be substituted isomers for each other by replacing two Cu2+ ions and two [VO]2+ ions. The incorporated nitrate showed short and long N–O bond lengths (1.14, 1.26 and 1.30 Å) as in the case of V18 (1.09, 1.16 and 1.28 Å). Reflecting the inequivalent bond lengths of the nitrate, the IR spectrum of V18 shows split peaks at 1359 and 1342 cm−1. But the Cu2V16 spectrum showed a single peak due to the presence of nitrate at 1353 cm−1. When the temperature was lowered, the nitrate peak in Cu2V16 was split into two positions at 1354 and 1345 cm−1 when the temperature reached −140 °C. These results indicate that the nitrate incorporated in Cu2V16 rotates relatively easily in the Cu2V16 cavity at room temperature compared to V18. In addition, the oxidation of 1-phenyl ethanol to acetophenone with Cu2V16 smoothly proceeded in comparison with V18. By taking advantage of the same framework in both catalysts, we can deduce the position of potential active sites in the oxidation reaction. We have concluded that the most active site is not on the peripheral of the vanadate framework, but it is reasonable to suggest that the active site is on the substituted copper atoms rather than the polyoxovanadate framework.

Developing a Portable Spectrometer to Detect Chemical Contaminants in Irrigation Water

Water pollution is a critical issue since it can severely affect health and the environment. The purpose of the study is to develop a portable spectrometer (ESP32-based spectrometer) to detect chemical contaminants in irrigation water by observing the light absorbance of contaminants. ESP32 and a light sensor (photodiode) were respectively, used as the main controller and detector of the portable spectrometer. It was developed based on optical dispersion and Beer–Lambert law theory. The light absorbance of different types of contaminants was displayed in a Blynk application for real-time monitoring. The samples were also tested using a lab-based spectroscopy method, ultraviolet-visible (UV-Vis) spectrometer. The spectral range of the measurement is from 350 nm to 700 nm and the standard error of the ESP32-based spectrometer is from 0.01 to 0.05. Five water samples were tested, consisting of ammonium nitrate, organic pesticide, zinc oxide and two different reservoirs used for irrigation. The absorption peaks of the ammonium nitrate and organic pesticide are 363 nm and 361 nm, respectively. Zinc oxide shows the absorbance peak at 405 nm, whereas both reservoirs show absorbance peaks lie in the region from 300 nm to 370 nm. Therefore, this study shows that different types of contaminants can absorb light only at specific wavelength regions by considering the concentration of samples. The developed ESP32-based spectrometer can be applied for on-site water quality monitoring as it is portable, light, simple and can be monitored in real time using multiple devices.

Studies on the intercalation of calcium–aluminium layered double hydroxide-MCPA and its controlled release mechanism as a potential green herbicide

Abstract The intercalation of 2-methyl-4-chlorophenoxyacetic acid (MCPA) herbicide into the interlayer matrix of calcium–aluminium layered double hydroxide (CaAl LDH) host has been successfully done via the co-precipitation method to form CaAl-MCPA nanocomposite, proposing an eco-friendly alternative with an adjusted delivery system for herbicide application. The intercalation process is supported by powder X-ray diffraction analysis with an expanded interlayer spacing from 8.6 to 19.6 Å for nanocomposite pH 13, which is due to the inclusion of larger size anion in the interlayer. Next, the absence of a nitrate peak at 1,326 cm−1 and the presence of a newly formed peak at 1,416 cm−1 in the Fourier transformed infrared spectroscopy analysis also confirmed the process of the intercalation. The significant decrease in nitrogen content to 0.50% indicates the intercalation of MCPA using the carbon, hydrogen, nitrogen, sulphur analyser. The release rate of the MCPA anion in the aqueous solutions is initially rapid, followed by the slow release in the order of phosphate > carbonate > chloride and followed the pseudo-second-order kinetic model. Hence, the conducted studies exhibit the successful intercalation of the MCPA herbicide anion and its controlled release mechanism as a potential hybrid green herbicide.

Nitrogen in surface aquifer - Coastal lagoons systems: Analyzing the origin of eutrophication processes

Coastal lagoons can act as sinks and sources of a wide range of substances, including nutrients, and pollutants. In these ecosystems, primary production is limited more by nitrogen than by phosphorus. For this reason, they are significantly vulnerable to nitrate pollution. In this study, a joined analysis of surface and ground water was conducted to determine the origin, occurrence and processes affecting nitrogen fate in a Mediterranean coastal aquifer-lagoon system. This included the analysis of water levels, as well as hydrochemical and isotopes data evolution for a 4-year period, which revealed two important insights of nitrogen cycling within the system. Firstly, we detected different origins for nitrate pollution (a mixture of sewage, manure and chemical fertilizers), as well as their nearly complete attenuation in the alluvial aquifer due to heterotrophic and autotrophic processes, favoured by the presence of organic matter and Fe-minerals in its sediments. Secondly, due to its rapid assimilation, inorganic nitrogen peaks in the lagoons were mainly detected after storm events. While nitrate peaks may be attributed to surface water runoff, ammonium peaks may be related to organic nutrient cycling. In contrast, we did not detect continuous and low N inputs, associated to groundwater flow. These results depict the need of a more integrated management strategy of these aquifer-lagoon systems.

Vertical distribution of picophytoplankton in the NW shelf and deep-water area of the Black Sea in spring

Structure and functions of picophytoplankton and their links to the water column density stratification and nutrient vertical profiles were studied in the Black Sea open waters along a transect from the Western Gyre to the NW shelf during spring homothermy in April of 2017. Abundances of picocyanobacteria of the genus Synechococcus (0.85 ± 0.96 (SD) × 10 3 cells ml −1 ) and eukaryotic picoalgae (5.74 ± 5.99 × 10 3 cells ml −1 ) and their intracellular pigment (chl a , phycoerythrin) contents were quantified using flow cytometry. The distribution of these variables in the upper 100-m layer was non-uniform. Along the whole transect, Synechococcus and picoeukaryote abundance maxima (up to 4 × 10 3 and 3 × 10 4 cells ml −1 , respectively) were observed at the water temperature of 8–8.5°С in the depth range between 30 and 40 m. Picoeukaryotes dominated the total community. The share of Synecococcus averaged about 22% and increased with depth up to 80%. Picophytoplankton abundance dropped abruptly through the oxycline but the cells were found in the suboxic layer at about 10 3 cells ml −1 and in a sample from the anoxic zone at 10 2 cells ml −1 . Intracellular chl a maxima were revealed in the nitrate peak at sigma- t density of 15.5. In the surface and suboxic layers, non-specific green autofluorescence (GAF) was detected in picophytoplankton cells that might provide evidence of their stress state in adverse environment. Multivariate analysis has revealed tight coupling between abiotic and microbiological variables in three statistically distinct pelagic regions of the transect, corresponding to the abyss, the continental slope and the shelf. • Picoeukaryotes dominated picophytoplankton but the proportion of Synecococcus increased with depth. • Picophytoplankton abundance dropped abruptly through oxycline but still survived in suboxic layer. • Non-specific green autofluorescence (GAF) was detected in picophytoplankton by flow cytometry. • Picophytoplankton GAF maxima were revealed in surface and suboxic layers, indicating stress conditions.

Characterization of nanoparticles in gunpowder 3x, 6x, 12x and 24x potencies using Raman spectroscopy

Background: According to the literature of homoeopathy the remedy gun powder has the property to cure Abscesses, Acne, Bites, Blood-poisoning, Boils, Carbuncles, Cuts - poisoned, Ivy (Hedera) poisoning, Osteo-myelitis, Tonsillitis – septic, Vaccinosis, Worms. Homoeopathic system of medicine uses ultra-high dilutions as their medication. Avogadro’s Limit is a threshold limit where there is no possibility of presence of original molecules over the dilution of Avogadro’s constant which is 6.02254 x 1023. When the potency goes above 23x in Decimal scale of potentization, it crosses the Avogadro’s limit. So, this study is done to find the presence of nano particles of the source materials in the homoeopathic medicine gun powder in 3x, 6x, 12x and 24x potencies using Raman spectroscopy.Method: Gun powder 6x, 12x, and 24x were prepared from 3x potency. Then the source materials such as, sulfur, charcoal, potassium nitrate and lactose were tested separately under Raman spectroscopy along with gun powder 3x, 6x, 12x, and 24 potencies. The values of lactose were subtracted from the 3x, 6x, 12x, and 24x potencies. A line graph of all the values obtained were plotted and then comparedResult: The peaks of potassium nitrate and Sulphur coincides with all the triturations of gun powder tested.Conclusion: The presence of nano-particles of the source materials of gunpowder in the homoeopathic triturations of the same till 24x potency is found. This may indicate that even other homoeopathic trituration up to 24x potency have the nano particles of its source materials.

Synthesis and Characterization of 2,4-Dichlorophenoxypropanoic Acid (2,4-DP) Herbicide Interleaved into Calcium-Aluminium Layered Double Hydroxide and the Study of Controlled Release Formulation

The commonly used herbicide in agriculture, namely 2,4-dichlorophenoxypropanoic acid (2,4-DP), is an anionic herbicide used to interleave into the interlayer of calcium-aluminum layered double hydroxide (Ca-Al LDH) employing co-precipitation method to form a new nanohybrid labeled as CAL-2,4DP. The LDH compound serves as a host in supporting the herbicide’s controlled release formulation. The effective interleave was investigated by employing a powder X-Ray Diffraction (XRD) pattern at 0.025 M nanocomposite, which revealed that the basal spacing has increased from 8.0 Å to 23.8 Å. The ATR-FTIR spectra further supported the interleaving, where the nitrate peak (NO−) diminished, and the carboxylate ion (COO−) band appeared at 1653 cm−1. The percentage loading of CAL-2,4DP was 71.26%, calculated from the carbon content in the sample. The BET analysis shows that CAL-2,4DP was a mesoporous material relying on nitrogen-desorption isotherms. The release of 2,4-DP ions into the aqueous solutions followed the order of PO43− > CO32− > Cl− with a percentage of 83, 65, and 30%, respectively. This work indicates the successful interleaving process of the 2,4-DP anion and the potential of CAL-2,4DP as an eco-friendly agrochemical that can be beneficial for farmers in minimizing herbicide usage to the environment.

Double-blind controlled dietary cross-over intervention with differentially fertilised intact lettuce leaves shows acute reduction in blood pressure in young adults, associated with faster uptake of nitrate than of phenolics

PurposeTo compare acute effects on blood pressure (BP) of ingestion of visually similar lettuce with controlled high and low content of either nitrate or phenolic compounds.MethodsIn a randomised cross-over design, 19 healthy participants (22–31 years) received 50 g of lettuce containing either 530 mg (8.4 mmol) nitrate + 11 mg (0.03 mmol) phenolic compounds (HNLP); or 3 mg nitrate (0.05 mmol) + 77 mg (0.2 mmol) phenolic compounds (LNHP), obtained by differential fertilisation. Ambulatory BP was recorded along with plasma, salivary and urinary nitrate and nitrite and plasma concentrations of cyclic guanosine monophosphate (cGMP), phenolic metabolites, Trolox equivalent antioxidant capacity (TEAC) and ferric reducing antioxidant power (FRAP).ResultsCompared with LNHP, 3 h post ingestion of HNLP, plasma nitrate increased 0.31 ± (95%CI) 0.12 mM (+ 240%), and salivary nitrate 5.5 ± 1.4 mM (+ 910%); accumulated urinary nitrate excretion increased 188 ± 72 mg (+ 296%) (all P < 0.001). Systolic BP was reduced 4.9 ± 4.2 mmHg (P = 0.031) between 3 and 6 h after ingestion of HNLP compared with LNHP; systolic BP differences were negatively correlated (P = 0.004) with differences in saliva nitrate concentrations. LNHP increased plasma phenolics at 6 h, predominantly 3ʹ-methoxycinnamic acid-4ʹ-glucuronide (ferulic acid-4ʹ-glucuronide), 116%, 204 ± 138 nM more than HNLP (P = 0.001); increased cGMP 14% (P = 0.019); and reduced FRAP 3.1% (P = 0.009).ConclusionThe acute BP difference within 6 h of consumption matched the plasma/saliva nitrate peak, not the slower changes of plasma phenolics. This is the first double-blind controlled dietary intervention demonstrating differential effects on human physiology by consumption of an intact plant food, where compositional differences were obtained by controlling growing conditions, indicating potential opportunities for health claims relating to precision/vertical farming.Clinical trial registrationThe trial was retrospectively registered on ClinicalTrials.gov, with identifier NCT02701959, on March 8, 2016.

Physicochemical and structural characterisation of oil palm trunks (OPT) hydrochar made via wet torrefaction

This study evaluates the effect of wet torrefaction of OPT under autogenous pressures at 3 different relatively low temperatures (i.e. 180, 200, and 220 oC) and extended residence times (i.e. 3, 6, 9, 12, 18, 24, 48, and 72 h) on the hydrochar's physical, chemical, and structural properties. Logarithmic-like increase of HHV profile was observed at the highest temperature of 220 oC, in which a plateau was reached at 24 h. Between temperature and residence time, temperature gave a more significant influence on the characteristics of the produced biochar. The HHV of the biomass sample increases from 16.4 MJ kg−1 in raw OPT to the highest HHV of 26.9 MJ kg−1 when torrefied at 220 oC for 72 h. Van Krevelen analysis shows dehydration was the primary reaction pathway that occurred during wet torrefaction of OPT at 180 oC for 24 h, 200 oC for 24 h, 220 oC for 6 h, and 220 oC for 12 h. Decarboxylation dominates the reaction when temperature and residence time was increased to 220 oC for 24 h, respectively. Further increasing the residence time to 48 and 72 h at 220 oC promotes demethylation as the dominant reaction. FTIR analysis reveals that most hemicellulose and parts of cellulose decomposed when OPT was subjected to lower temperature and/or residence time (i.e. 180 oC for 24 h, 200 oC for 24 h, 220 oC for 6 h, and 220 oC for 12 h). However, increasing temperature to 220 oC and beyond 24 h resulted in carbon-rich and lignin-dense hydrochar, which was observed in powder XRD results where graphite nitrate peak at 2θ of 7.4o appears. Morphology analysis reveals that most of the hemicellulose and cellulose-rich parenchyma was removed when subjected to wet torrefaction at 220 oC for 24 h. The formation of microspheres from the repolymerisation of 5-HMF was observed in large quantities in OPT hydrochar treated at 220 oC for 72 h. Inorganic elemental analysis shows that wet torrefaction of OPT effectively removes K and Cl from the biomass. The removal of K increased with increased temperature, which may partially resolve the corrosion problems in combustion reactions related to silicate deposition. OPT hydrochar from WT under autogenous condition and relatively low temperature exhibits much more improved fuel properties compared to raw OPT.

Explanation of the Non-Linear Electrical Behavior of a Resistive NOx Dosimeter By Operando DRIFT Spectroscopy

Introduction To detect low NOx concentrations is still a focus for air-quality monitoring. The direct detection of the total dose of NOx is beneficial since the air pollution limits are given as hourly and annual mean values. A gas dosimeter for direct detection of the dose of NOx was presented in [1,2,3]. In the sorption phase, NOx molecules are adsorbed on the functional film and the electrical resistance changes. During this phase, the correlation between NOx dose and resistance change is linear until a certain loading state is reached. As soon as the characteristic curve gets non-linear, described often as saturation of the NOx adsorption [1], sensor regeneration is necessary. During thermal regeneration, the sorbed NOx species is desorbed from the surface, and a new sorption cycle can begin.To further understand the sensing mechanism and the effects of non-linearity, NOx dosimeters are investigated by operando DRIFT spectroscopy [4]. The electrical sensor signal and the formation of adsorbed species are investigated operando on the dosimeter. The non-linear behavior of the electrical properties occurring at a certain sensor signal are investigated at various film thicknesses [5] and are combined with the sorption properties. Materials and Methods Potassium-permanganate impregnated on lanthanum-stabilized alumina powder (K/Mn-La-Al2O3) [1] serves as the functional material. It is applied by screen-printing on an alumina substrate equipped with interdigitated Au electrodes and fired at 650 °C. Different layer thicknesses of the functional films are achieved by several screen-printing steps. The sensors are mounted in a gas purgeable operando DRIFTS cell (Fig. 1) [4] and heated by an integrated platinum heating structure to 350 °C. They are exposed to synthetic air (20 % O2 and 2 % humidity in N2 balance). NOx concentrations (ppb-range) are added and validated by a chemiluminescence detector (CLD). The sensor resistance is derived by impedance spectroscopy (f = 200 Hz, U eff = 200 mV) from an R||C equivalent circuit. The sensor signal is defined as the relative resistance change (R-R 0/R 0), with R 0 being the resistance in base gas and R the resistance during NOx exposure. Simultaneous DRIFT spectra are obtained and the absorbance -log(I/I 0), with the intensity I 0 in base gas and the intensity I during NOx adsorption, is calculated. The sensors are regenerated by heating up to 650 °C. Results and Discussion An operando DRIFTS result during exposure to three peaks of 50 ppb NOx with NOx pauses in-between is shown in Fig. 2. The NOx dose in ppm∙s is derived from the integration of the CLD NOx signal. The dose increases linearly during NOx exposure and remains constant during dosing pauses. The sensor signal shows the same behavior: ΔR/R 0 increases linearly when 50 ppb NOx are present and stays constant during NOx absence. The calculated absorbance shows a clear peak at a wave number of 1370 cm-1 occurring during NOx exposure. It can be attributed to the nitrate formation on potassium sites of K/Mn-La-Al2O3 and is characteristic for the sorption phase [4]. The calculated peak area A E of this nitrate peak is shown in Fig. 2, too. A E and therefore the amount of formed nitrates increases linearly during NOx addition and remains constant during NOx pauses. The electrical properties of the dosimeter can be related directly to the NOx dose and to the formed nitrates. One important point is that all curves increase linearly during NOx exposure and no saturation effects can be observed for the sensor signal and the nitrate formation. In Fig. 3, the sensor is exposed to three peaks of 390 ppb NOx. ΔR/R 0 gets non-linear after reaching 40 %. The sensor seems to saturate. The slope during NOx exposure is non-linear and the signal in NOx pauses decreases. In contrast, A E behaves almost linear. It is assumed that the electrically observed non-linearity cannot be explained by a saturation of the adsorption capability of K/Mn-La-Al2O3. It seems that the NOx adsorption capability is not exhausted, but the resistance shows a saturation effect. Conclusions The results show that the sensor behaves like a dosimeter with linear characteristics between NOx dose, sensor signal and formed nitrate species until a certain sensor signal of around 40 % is reached. At higher relative resistance changes, the electrical signal becomes non-linear, whereas the adsorption capability itself, i.e. the nitrate formation, remains linear and the NOx adsorption on K/Mn-La-Al2O3 is not saturated. This behavior will be investigated by operando DRIFTS in dependence on the film thickness.

Au-modified organic/inorganic MWCNT/Cu/PANI hybrid nanocomposite electrode for electrochemical determination of nitrate ions.

Anew electrochemical sensor is reported for thebased on the application of noble bimetal nanoparticles (gold and copper) to polymeric-carbon-modifiers for thereduction of nitrate. This sensor was designed fornitrate ion measurement at the surface of pencil graphite electrodemodified by a nanocomposite. The modification was the electrosynthesis of gold nanoparticles on the MWCNT/copper-polyaniline (Cu-PANI) nanocomposite. Physicochemical properties of thesynthesized hybrid nanocomposites and their surface performance efficiency are characterized using microscopic, spectroscopic, and electrochemical techniques. At optimized pH, the nitrate peak current (at working potential of 1084mV versus Ag/AgCl reference electrode) was linear in the concentrationrange 0.8-30.0μM with a detection limit of 0.09μM usingdifferential pulse voltammetry. Modified sensor was successfully implemented to quantify nitrate ions in wastewater resulting from the production line for industrial barium chromate and an example of aqueduct water with appropriate recovery levels. • Aniline was polymerized in phosphoric acid solution using peroxydisulfate as an initiator. • MWCNT@CuNPs@PANNSs@AuNPs nanocomposite on PGE electrode was revealed specific recognition for NO3-. • The electrochemical sensor displayed high selectivity and sensitivity for the detection of NO3-.

Biofloc Technology(BFT) 적용을 위한 수질특성에 대한 연구

The growth of aquaculture industry is on the rise as the world"s population grows and food sources become scarce. However, the increase in aquaculture faces environmental problems due to polluted effluent. Therefore, the aquaculture industry is actively developing biofloc technology (BFT), an eco-friendly aquaculture method. This study analyzed the water quality characteristics during biofloc formation for 30 days (1, 3, 6, 12, 18, 24, 30 days). As a result, changes in color (light brown → dark brown) and foam on the water surface were observed over time. Peaks of ammonia (5.7 mg/L, 1 day), nitrite (3.4 mg/L, 6 days) and nitrate appeared as a sequence (60.1 mg/L, 12 days), and it was confirmed that water quality stabilization occurred 24 days after cultivation. In addition, changes in the amount of floc in the water quality (34 mL/L, 1 day → 2 mL/L, 12 days → 6 mL/L, 18 days) and TSS change occurred using the Imhoff cone, and the floc size changed (73,481 μm², day 1 → 1,838 μm², day 12 → 9,940 μm², day 24). These results will provide data on dynamics of water quality during the biofloc formation process in freshwater, and may help understand biofloc formation in using BFT.

Biofloc Technology(BFT) 적용을 위한 수질특성에 대한 연구

The growth of aquaculture industry is on the rise as the world"s population grows and food sources become scarce. However, the increase in aquaculture faces environmental problems due to polluted effluent. Therefore, the aquaculture industry is actively developing biofloc technology (BFT), an eco-friendly aquaculture method. This study analyzed the water quality characteristics during biofloc formation for 30 days (1, 3, 6, 12, 18, 24, 30 days). As a result, changes in color (light brown → dark brown) and foam on the water surface were observed over time. Peaks of ammonia (5.7 mg/L, 1 day), nitrite (3.4 mg/L, 6 days) and nitrate appeared as a sequence (60.1 mg/L, 12 days), and it was confirmed that water quality stabilization occurred 24 days after cultivation. In addition, changes in the amount of floc in the water quality (34 mL/L, 1 day → 2 mL/L, 12 days → 6 mL/L, 18 days) and TSS change occurred using the Imhoff cone, and the floc size changed (73,481 μm², day 1 → 1,838 μm², day 12 → 9,940 μm², day 24). These results will provide data on dynamics of water quality during the biofloc formation process in freshwater, and may help understand biofloc formation in using BFT.

Rotational correlation times, diffusion coefficients and quadrupolar peaks of the protic ionic liquid ethylammonium nitrate by means of 1H fast field cycling NMR relaxometry

The protic ionic liquid (PIL) ethylammonium nitrate (EAN) is characterized by hydrogen bonding between the NH bonds of the cations and the oxygen atoms of the anions. The three-dimensional H-bond network of EAN very much resembles that of water. Although this first ionic liquid is known for more than 100 years, there is still lack of information about the rotational and translational dynamics, and how both are related to each other. For that purpose, we measured the 1H nuclear magnetic relaxation dispersion curves (NMRD) of EAN by means of Fast Field Cycling (FFC) NMR relaxometry. We were able to analyze the measured 1H spin-lattice relaxation rates R1 covering a large temperature range between 248 and 333 K simultaneously. Applying the well-known Bloembergen-Purcell-Pound (BPP) approach, we decomposed the total relaxation rates into intramolecular and intermolecular contributions, describing the rotational and translational dynamics of the ethylammonium cation. Here, we report rotational correlation times, τR, and translational diffusion coefficients, DT, both derived from the total 1H spin-lattice relaxation rates as a function of temperature and frequency. Self-diffusion coefficients, DT, were also determined from the total relaxation rates in the low frequency range, wherein only the intermolecular relaxation contribution is frequency dependent. Then, DT results from the slope of a linear fit of the spin-lattice relaxation rate R1 as a function of the square root of frequency, ν. The diffusion coefficients obtained from both methods are in good agreement with self-diffusion coefficients measured by pulsed-field-gradient (PFG) NMR. The rotational correlation times, τR, derived from the intramolecular 1H relaxation contribution were compared to correlation times obtained from high-field NMR deuteron relaxation experiments, dielectric spectroscopy (DS) and femto-second-infrared (fs-IR) spectroscopy. For EAN, we also observed a local enhancement of the 1H spin-lattice relaxation rates R1 at high frequencies. This so-called quadrupole relaxation enhancement (QRE) results from the interference of the Zeeman transition energy of the 1H spins and the energy difference of two levels of the quadrupole 14N nuclei. QRE is usually known for solids, but rarely for the liquid state as observed here for EAN. Overall, we show that FFC relaxometry provides access to rotational correlation times, translational diffusion coefficients and quadrupole relaxation enhancement at the same time.

Interplay of regional oceanography and biogeochemistry on phytoplankton bloom development in an Arctic fjord

Ongoing sea-ice melting and associated environmental changes influence the bloom phenology and biogeochemistry of the Arctic Ocean. Kongsfjorden, a fjord in Svalbard, has already undergone the transition of being sea-ice covered in winter to sea-ice free, and now stands vulnerable to Atlantic water intrusion and glacier melting. We monitored physical and biogeochemical variables in the fjord between July 2015 and July 2016 using Indian Arctic subsurface mooring in Kongsfjorden. The year-round records of nitrate represent the first reported sensor-based observation in the region. Here, we used the high-resolution time-series of chlorophyll a, nitrate, dissolved oxygen, photosynthetically active radiation, turbidity, temperature, and salinity to study their interactions and assess how do they relate to the development of phytoplankton bloom. Results indicated a high nitrate concentration (up to 13.3 μM) and near-zero chlorophyll a in winter. The spring bloom was spotted from mid-April to the first week of June (up to 7.2 μg/L chlorophyll a at 25 m), however, with discontinuities due to high winds events. The chlorophyll a was negatively correlated with nitrate (r = −0.7, p < 0.001). Further, we observed temperature, salinity, and density characteristic of Atlantic water at 25 m and 35 m in autumn and early-winter, which coincided with nitrate peaks. This indicated nitrate supply by Atlantic inflow during the non-bloom period. We say that the features of the bloom start evolving from rather quiescent autumn and winter before it reaches an active state in spring-summer. Year-round high-resolution observations are crucial to study phytoplankton bloom phenology as any shift or change in the phenology will affect higher trophic levels and biogeochemical cycles.

The reductions of oxalate and its precursors in cloud droplets relative to wet particles

Abstract The formation mechanism of oxalate in the aqueous phase remains uncertain. Approximately 600 000 oxalate-containing particles and 450 000 its precursors-containing particles (e.g., acetate, glyoxylate, pyruvate and malonate) were obtained using a single particle aerosol mass spectrometer at a mountain site in southern China from 9 May to 4 June, 2018. The number fraction of oxalate or its precursors was compared within three representative aerosols with different liquid water contents including cloud droplet residues (RES), cloud interstitial particles (INTER) and cloud-free ambient particles (AMB). Lower number fraction of oxalate was found in the RES relative to INTER and AMB, mostly attributed to the decrease in precursors. This was conflicted with the enhancement of in-cloud oxalate formation previously reported. Further analysis indicated that the aerosol acidity had a major influence on the formation of precursors and their conversion to oxalate. With the increase of relative aerosol acidity (defined as the sum of sulfate and nitrate peak areas divided by ammonium peak area), the formation of precursors was increased while the conversion of precursors to oxalate was suppressed. Meanwhile, this influence was more pronounced in the INTER and AMB relative to RES. This work highlighted the roles of aerosol acidity and liquid water content in the aqueous phase formations of oxalate and its precursors.

Nitrate-leaching and groundwater vulnerability mapping in North Bihar, India

Aquifer vulnerability assessment is crucial for studying the impact of increasing pollution load scenarios on the quantification of contaminant concentration with movement of plume for protecting groundwater resources. Only a few recent studies have focused on the performance evaluation of vulnerability assessment methods using process-based modeling approach. However, the moisture flow and pollutant transport through partially saturated zone plays a crucial role under varying hydrogeological conditions, which are generally ignored in index-based methods. Thus, the objective of this research is to evaluate the vulnerability of groundwater resources to nitrate in Samastipur, Darbhanga and Madhubani districts of Bihar State, India, using soil moisture flow and solute transport modeling. Richard’s equation integrated with the classical advection dispersion equation is simulated using HYDRUS 1D by incorporating a constant head and atmospheric boundary conditions. The time taken to reach the nitrate peak concentration at groundwater table is considered to estimate vulnerability index (VI). Results have shown that high risk in terms of nitrate-leaching vulnerability in southern part of study area is dominated by Gangetic kankar in subsurface. Further, high pollution risk was reported in eastern north part of study area having alluvial deposition in subsurface. The main causes of high risk were due to the short depth of water table, little discharge and more hydraulic conductivity presence in the subsurface media. Moreover, comparatively low vulnerability was observed in area having clay capping of 2–4 m from surface. This research may help in better implementation of agricultural, soil–water conservation practices and urban/industrial infrastructure development in and around the study area.

Behavior simulation of nitrogen compounds in rivers with uncertainty analysis

This study simulated nitrogen-compound concentration changes in rivers, taking into account uncertainty analysis carried out by the Monte Carlo Method. The study area is the final stretch of the Piracicaba River, located in Minas Gerais, Brazil, which is an important Doce River tributary. The uncertainty analysis took into account random generation of hydrodynamic variables, initial water quality conditions and kinetic constants. Different variation percentages for the organic nitrogen decay kinetic constants random generation did not influence considerably the ammonia or organic nitrogen maximum concentration extreme values. In the simulations, maximum organic nitrogen concentrations were most frequently between 0.20 mg.L-1 and 0.22 mg.L-1 (42%), maximum ammonia nitrogen between 0.28 mg.L-1 and 0.30 mg.L-1 (30%), maximum nitrite between 0.05 mg.L-1 and 0.07 mg.L-1 (49%) and maximum nitrate between 0.46 mg.L-1 and 0.50 mg.L-1 (37%). Estimated maximum concentrations for ammonia nitrogen, nitrite and nitrate did not exceed the environmental quality standards established by Brazilian CONAMA Resolution 357/2005 for Class 2 watercourses. Random generation of kinetic constants that regulate ammonia and nitrite decay produced significant ammonia nitrogen, nitrite, and nitrate peak concentrations value frequencies, histograms and forms changes, when considering variation percentages equal to or greater than 50%. Some simulation results showed more inhibition of oxidized nitrogen forms production.

Monsoonal variation of the marine phytoplankton community in Kota Kinabalu, Sabah

Monsoon-driven changes of environmental factors have been reported to be significantly variable and affects the phytoplankton community in tropical waters. This study examined the monsoonal changes of environmental parameters and the coastal phytoplankton community, including potential harmful algal bloom species, in the waters of Kota Kinabalu, Sabah, Malaysia. Bi-weekly observations were conducted from August 2017 to January 2019, covering the Southwest Monsoon (SWM), Northeast Monsoon (NEM), and inter-monsoon periods (IMPs). Sea surface temperature, salinity, and daily average photosynthetic active radiation (PAR) were significantly different between the SWM and the NEM. Total phytoplankton densities were significantly higher in the SWM with median cell densities of 1.12 × 104 cells L−1 compared to the NEM with 3.98 × 103 cells L−1. Nutrient measurements indicated that the waters were mesotrophic, with low phosphate (P) levels (<0.3 μM-P on average). N:P ratios were often above the Redfield ratio (16N:1P), while high Si:N (>1) and Si:P ratios (>16Si:1P) indicated that silicate was not limiting, a condition favourable for diatom growth. Phytoplankton dynamics shifted from a dinoflagellate-dominant community (Protoperidinium spp. and Prorocentrum spp.) to a diatom-dominant community (Leptocylindrus spp. and Dactyliosolen spp.) during the NEM, which was preceded by a peak in silicate and nitrate. Later, Chaetoceros spp. became dominant during the second SWM. The presence of intermittent increases in Margalefidinium polykrikoides and Pyrodinium bahamense var. compressum cell densities may trigger future blooms in these waters. Canonical Correspondence Analysis suggests that the dinoflagellate-dominant community was driven by changes in PAR and Si:N while changes in N:P and salinity shaped the diatom-dominant community. The shifts of the phytoplankton community composition in relation to the different monsoonal periods suggests that the monsoons function as environmental drivers which structure the phytoplankton community of this coastal ecosystem.