Increase In Nitrate Concentration Research Articles

Assessing seasonal nitrogen transformations in the Godavari estuary, India

Indian estuaries are hypothesized to export a significant amount of nitrogen nutrients to the coastal waters due to the high use of fertilizers. To examine the possible sources of nitrogen nutrients and their modifications within the estuary, a study was conducted by collecting samples at monthly intervals for a period of a year. The river Godavari is the largest monsoonal estuary in India and is fed by monsoon rainfall. Hence the entire estuary is filled with fresh water from July to September (the wet period) whereas saline water is dominant during the dry period. An order of magnitude increase in nitrate concentrations was observed during the wet due to a peak in discharge compared to the dry period. The isotopic composition of nitrogen in nitrate (δ15NNO3) was lower during the wet than the dry period and displayed a significant linear relationship with Chlorophyll-a (Chl-a), particulate organic nitrogen (PON) and carbon (POC) indicating that biological process modified their composition. The lower δ15NNO3 and higher δ18ONO3 values were noticed during the wet than during the dry period. The δ15NNO3 versus δ18ONO3 plot suggests a possible source of nitrate through the nitrification of soil/sewage-borne nitrogen. The higher δ18ONO3/δ15NNO3 ratios (>1) were observed during August and September than in other months indicating the occurrence of denitrification during the former months. In contrast, an insignificant change in δ15NNO3 and δ18ONO3 within the estuary suggested that denitrification occurred upstream and not within the estuarine zone. River discharge brought residual nitrate to the estuary leading to less input of nitrate to the coastal Bay of Bengal than hitherto hypothesized.

Simultaneous phosphorus recovery from wastewater and sludge by a novel denitrifying phosphorus removal system

A novel process was proposed for simultaneous denitrification and phosphorus (P) recovery. The increased nitrate concentration facilitated the activity of denitrifying P removal (DPR) in P enrichment, which stimulated P uptake and storage, making P more readily accessible for release into the recirculated stream. The total P content in the biofilm (TPbiofilm) rose to 54.6 ± 3.5 mg/g SS as the nitrate concentration increased from 15.0 to 25.0 mg/L, while the P concentration of the enriched stream reached 172.5 ± 3.5 mg/L. Moreover, the abundance of denitrifying polyphosphate accumulating organisms (DPAOs) increased from 5.6% to 28.0%, and the increased nitrate concentration facilitated the process of carbon, nitrogen, and P metabolism due to the rise in the genes involved in critical functions of metabolism. Acid/alkaline fermentation analysis indicated that the EPS release was the primary P-release pathway. Additionally, pure struvite crystals were obtained from the enriched stream and fermentation supernatant.

Effect of Nitrogen Addition to the Soil on Atlantic Forest Tree Seedlings

The input of large amounts of fertilizers in agricultural areas may result in nitrogen (N) leakage to nearby forest fragments, which can impact the physiology and growth of trees. The current study aimed to assess the effects of soil N addition on seedlings of four tree species in the Brazilian Atlantic Forest: Croton floribundus and Astronium graveolens (pioneer), Guarea kunthiana and Aspidosperma polyneuron (non-pioneer). The experiment was carried out in a greenhouse condition with three treatments: reference (soil without addition of nutrients), N addition (N: soil with addition of ammoniacal-N), and complete (C: soil with addition of ammoniacal-N and other macro and micronutrients). Croton floribundus seedlings presented higher shoot growth with N addition, mainly in treatment C, and only this treatment increased net photosynthesis. There was great variation in the metabolic responses induced by treatments N and C, with accumulation of nitrate in the leaves and xylem sap only in seedlings in treatment N. In A. graveolens, there was a decrease in transpiration in response to treatments N and C. However, water use efficiency, leaf area, and dry mass increased only in seedlings subjected to treatment C. Regarding metabolic parameters, A. graveolens was little responsive to the treatments. In G. kunthiana seedlings, the treatments decreased net photosynthesis and increased leaf total N. Only treatment N led to decreased stem dry mass and increased nitrate contents in leaves and xylem sap. Aspidosperma polyneuron exhibited no change in growth, but there was an accumulation of N compounds in the leaves for both treatments N and C, which suggests that this species could be a good bioindicator of N addition to the soil. Although influencing different parameters, the results indicate that soil N addition affects the performance of both pioneer and non-pioneer species. Finally, the implications of these results for biomonitoring of N availability in the soil of forest fragments are discussed.

Extended pilot test of a cross-injection in situ denitrification system for pre-emptive treatment of municipal well water

Elevated groundwater nitrate concentrations have been linked to deleterious health and environmental effects. A significant source of the nitrate is nitrogen fertilizers applied to agricultural landscapes. Beneficial Management Practices (BMPs), including the optimization of fertilizer use and selective crop rotations, have proven to be effective in some cases. The city of Woodstock in southern Ontario relies on public wells for all of its municipal supply. Several of the wells have experienced chronic increases in nitrate concentrations exceeding the maximum allowable limit of 10 mg/L N-NO3−. While BMPs are established, an interim reduction plan based on enhanced in situ denitrification (Cross Injection System, CIS) in a 15 m thick zone of high nitrate mass flux within the aquifer zone was evaluated. Based in the results of preliminary acetate injection experiments, a C:N ratio of 2.35, (approximately 260 mg acetate/L), was selected to optimize the denitrification reaction. Injections were performed for six hours a day every day for a period of approximately two months. Dissolved oxygen (DO) and nitrate concentrations recorded over time indicated that reduction of both commenced within a few days of the beginning of the acetate injections and reduced levels were maintained for the remainder of the two-month injection period. Denitrification occurred throughout the profile although nitrate reduction was the highest in the lower groundwater velocity zones. An overall reduction of nitrate of 50% was achieved through the treated section of the aquifer. It is estimated that an upscaled treatment system utilizing a treatment width of only 70 m would be sufficient to reduce the nitrate concentrations to below the drinking water limit demonstrating the potential for the CIS method to functions as an interim groundwater nitrate reduction strategy.

A GIS-based analysis of groundwater manganese and nitrate concentration for sustainable water supply

Groundwater is the main source of water supply in Sleman Regency. Although the water quantity is not an issue, the quality of groundwater should be understood to ensure the sustainability of the water supply. A previous study shows an increase in manganese (Mn) and nitrate (NO3) concentration in groundwater, yet the concentration distribution is unknown. Therefore, this study aims to develop a map of the spatial distribution pattern and to analyze the potential source of manganese and nitrate in groundwater in Sleman Regency in Yogyakarta Province. The method used is mapping groundwater quality using the ArcGIS application, analyzing groundwater pollution with water quality standards in the Indonesian Ministry of Health regulation number 492/Menkes/per/IV/2010 regarding drinking water quality requirements, and identifying the potential source of high pollution. Data processing uses the ArcGIS 10.8 application by performing the IDW (Inverse Distance Weighting) Interpolation technique. The result of this study has obtained a map of the distribution of groundwater quality for manganese and nitrate from 2017-2019. Manganese contamination may come from industrial and/or agricultural waste, while higher nitrate concentration might be a result of a septic tank leak and/or pesticide/fertilizer residue in paddy fields.

Arthur Marble Aquifer and Te Waikoropupu Springs, New Zealand: flow contributions and nitrate sources

This paper investigates sources of early signs of nitrate pollution in a karst aquifer and major karst spring. Te Waikoropupu Springs are the largest springs in New Zealand and amongst the largest in the Southern Hemisphere with a mean outflow of 13.4 m3/s. They discharge the clearest water ever recorded from a karst spring, but early warning of water quality deterioration is signalled by increasing nitrate concentrations. The springs discharge water from a partly artesian aquifer of 2.85 km3 volume in karstified Ordovician marble with a transmission time averaging 7.9 years. Reservoir porosity is unusually high for a crystalline carbonate rock, estimated as 6%. Water emerging at Main Spring (9.89 m3/s) and adjacent Fish Creek Springs (3.48 m3/s) is a mix of recharge from four main sources. The paper investigates by means of mass balance modelling the proportions of water coming from each source, the origins of nitrate contamination and the contribution of nitrification. Water losses into the bed of the upper Takaka River, about 17 km from the Springs, provide 13% of the mean flow at Main Spring, 34% of the flow at Fish Creek Springs, and 83% of the volume discharged at submarine springs. Infiltration from rain falling over farmed land in the middle valley is estimated to supply 10% of total outflow at Main Spring and Fish Creek Springs but to contribute 82% of the NO3-N output discharged at the springs. Nitrification accounts for 16% of the nitrate discharged. A 34% reduction of leachate concentration in the middle valley would be required to bring NO3-N values at Main Spring back to levels recorded in the 1970s.

Nitrifying Microorganisms Linked to Biotransformation of Perfluoroalkyl Sulfonamido Precursors from Legacy Aqueous Film-Forming Foams.

Drinking water supplies across the United States have been contaminated by firefighting and fire-training activities that use aqueous film-forming foams (AFFF) containing per- and polyfluoroalkyl substances (PFAS). Much of the AFFF is manufactured using electrochemical fluorination by 3M. Precursors with six perfluorinated carbons (C6) and non-fluorinated amine substituents make up approximately one-third of the PFAS in 3M AFFF. C6 precursors can be transformed through nitrification (microbial oxidation) of amine moieties into perfluorohexane sulfonate (PFHxS), a compound of regulatory concern. Here, we report biotransformation of the most abundant C6 sulfonamido precursors in 3M AFFF with available commercial standards (FHxSA, PFHxSAm, and PFHxSAmS) in microcosms representative of the groundwater/surface water boundary. Results show rapid (<1 day) biosorption to living cells by precursors but slow biotransformation into PFHxS (1-100 pM day-1). The transformation pathway includes one or two nitrification steps and is supported by the detection of key intermediates using high-resolution mass spectrometry. Increasing nitrate concentrations and total abundance of nitrifying taxa occur in parallel with precursor biotransformation. Together, these data provide multiple lines of evidence supporting microbially limited biotransformation of C6 sulfonamido precursors involving ammonia-oxidizing archaea (Nitrososphaeria) and nitrite-oxidizing bacteria (Nitrospina). Further elucidation of interrelationships between precursor biotransformation and nitrogen cycling in ecosystems would help inform site remediation efforts.

OBTAINING AND PROPERTIES OF THE IMPLANT FILM MADE WITH CARBOXYMETHYLCELLULOSE CONTAINING SILVER NANOPARTICLES USED FOR TREATMENT OF BURN WOUNDS

This article studies feasibilities of making an implant-film for treatment of burn wound, based on silver nanoparticles (AgNPs) stabilized by sodiumcarboxymethylcellulose (Na-CMC) with degrees of substitution (DS) 0.65-0.90 and polymerization (DP) 200-600 synthesized using a photochemical method. The structural, physical and chemical, and physicalmechanical, burn wound healing properties as well as antimicrobial effects of implant-films containing the Na-CMC and AgNPs have been investigated. The shape, quantity, and size of the AgNPs embedded into the Na-CMC films were determined by UV-Vis spectroscopy, dynamic light scattering (DLS), atomic force microscopy (AFM) and transmission electron microscopy (TEM). It was found that the increase of silver nitrate concentration in solution of Na-CMC followed by photoirradiation leads to changes of AgNPs size and shape. It was found out that Na-CMC films containing AgNPs in the size ranging from 5 to 35 nm had enhanced the microbicide effects and burn wound healing properties within 14 days.

Instream sensor results suggest soil–plant processes produce three distinct seasonal patterns of nitrate concentrations in the Ohio River Basin

AbstractThe Ohio River Basin (ORB) is responsible for 35% of total nitrate loading to the Gulf of Mexico yet controls on nitrate timing require investigation. We used a set of submersible ultraviolet nitrate analyzers located at 13 stations across the ORB to examine nitrate loading and seasonality. Observed nitrate concentrations ranged from 0.3 to 2.8 mg L−1 N in the Ohio River's mainstem. The Ohio River experiences a greater than fivefold increase in annual nitrate load from the upper basin to the river's junction with the Mississippi River (74–415 Gg year−1). The nitrate load increase corresponds with the greater drainage area, a 50% increase in average annual nitrate concentration, and a shift in land cover across the drainage area from 5% cropland in the upper basin to 19% cropland at the Ohio River's junction with the Mississippi River. Time‐series decomposition of nitrate concentration and nitrate load showed peaks centered in January and June for 85% of subbasin‐year combinations and nitrate lows in summer and fall. Seasonal patterns of the terrestrial system, including winter dormancy, spring planting, and summer and fall growing‐harvest seasons, are suggested to control nitrate timing in the Ohio River as opposed to controls by river discharge and internal cycling. The dormant season from December to March carries 51% of the ORB's nitrate load, and nitrate delivery is high across all subbasins analyzed, regardless of land cover. This season is characterized by soil nitrate leaching likely from mineralization of soil organic matter and release of legacy nitrogen. Nitrate experiences fast transit to the river owing to the ORB's mature karst geology in the south and tile drainage in the northwest. The planting season from April to June carries 26% of the ORB's nitrate and is a period of fertilizer delivery from upland corn and soybean agriculture to streams. The harvest season from July to November carries 22% of the ORB's nitrate and is a time of nitrate retention on the landscape. We discuss nutrient management in the ORB including fertilizer efficiency, cover crops, and nitrate retention using constructed measures.

Agricultural Pressures on the Quality of Ground and Surface Waters in Catchments of Artificial Reservoirs

Changes in nutrient concentrations in groundwater were investigated to determine the impact of agriculture on water quality in artificial lakes. The study covered three reservoirs in an agricultural area of Wielkopolska (central-western part of Poland). Assessing the agricultural impact required a network of piezometers around the reservoirs, used to determine the degree of groundwater pollution from nutrients supplied to the reservoirs. Moreover, the analysis covered the quality of water in streams flowing into the reservoirs, and in the reservoirs themselves. Field research was conducted every month of the growing season from March to November. The analysis covered land inclination, ground permeability, and soil type. Detailed objectives included: (1) assessment of the agricultural impact on the chemical parameters of ground and surface water quality, and (2) evaluation of the impact of different sources of agricultural pollution on water quality in artificial reservoirs in regards to their management. This study revealed high dynamics of nutrient concentrations, particularly for nitrates and phosphates, in groundwater and surface water. A significant effect of maize cultivation on an increase in nitrate concentrations in the groundwater of the catchment of the Przebędowo Reservoir was evidenced, as well as a substantial effect of the functioning of an animal farm on the quality of groundwaters in the catchment of the Lachotka Reservoir. The nutrient load of agricultural origin in the catchment of the Miedzichowo Reservoir was relatively low. Our study revealed elevated amounts of nutrients such as nitrogen and phosphorus, detected more frequently in groundwater than in running waters, which confirms our hypothesis of the importance of groundwater analysis in detecting the source of pollution of the studied lakes. High nutrient concentrations recorded in groundwater leached from arable fields were also observed in the summer period, failing to confirm the hypothesis that the greatest effect of factors would be related to the spring effect of arable fields on water quality (lack of compact vegetation cover, high water level, etc.). Our study also indicated a greater importance of the type of land use than lithology or permeability of deposits.

Increased Nitrogen Loading Facilitates Nitrous Oxide Production through Fungal and Chemodenitrification in Estuarine and Coastal Sediments.

Estuarine and coastal environments are assumed to contribute to nitrous oxide (N2O) emissions under increasing nitrogen loading. However, isotopic and molecular mechanisms underlying N2O production pathways under elevated nitrogen concentration remain poorly understood. Here we used microbial inhibition, isotope mass balance, and molecular approaches to investigate N2O production mechanisms in estuarine and coastal sediments through a series of anoxic incubations. Site preference of the N2O molecule increased due to increasing nitrate concentration, suggesting the changes in N2O production pathways. Enhanced N2O production under high nitrate concentration was not mediated by bacterial denitrification, but instead was mainly regulated by fungal denitrification. Elevated nitrate concentration increased the contribution of fungal denitrification to N2O production by 11-25%, whereas it decreased bacterial N2O production by 16-33%. Chemodenitrification was also enhanced by high nitrate concentration, contributing to 13-28% of N2O production. Elevated nitrate concentration significantly mediated nirK-type denitrifiers structure and abundance, which are the keystone taxa driving N2O production. Collectively, these results suggest that increasing nitrate concentration can shift N2O production pathways from bacterial to fungal and chemodenitrification, which are mainly responsible for the enhanced N2O production and have widespread implications for N2O projections under ongoing nitrogen pollution in estuarine and coastal ecosystems.

Groundwater management: Effectiveness of mitigation measures in nitrate vulnerable zones – a Portuguese case study

Groundwater vulnerability depends on hydrogeological characteristics, land use dynamics and pollutant sources. In Europe, agriculture is the main source of diffuse groundwater pollution. The over-application of nitrogen (N) soil inputs promotes nitrate leaching to surface and groundwater and associated impacts on human health and biodiversity. Mitigation programs have been implemented across the Europe Union (EU) to reduce N loads to water bodies. The EU Nitrates Directive (1991/676/EEC) aims to reduce water nitrate pollution associated to agriculture. The reduction implies the implementation of Good Agricultural Practices and National Action Programs with mandatory measures for the Nitrate Vulnerable Zones (NVZ).The Esposende-Vila do Conde is one of the nine Portuguese nitrate vulnerable zones. The application of organic and chemical fertilizers, especially on intensive agricultural farms, without the implementation of good agricultural practices and effluent management, will promote an increase in groundwater nitrate concentration. A total of 1728 groundwater sampling points were collected to determine nitrate contents, from 2007 to 2020. A space-time database including farmer questionnaires, field data and groundwater nitrate contents were prepared.The groundwater points located in artificialized territories and agricultural areas show the highest nitrate concentration. This situation is mainly due to a decrease of surface water recharge, associated to the increase of pollutant sources, as well as inadequate agricultural practices. The areas with considerable agricultural productivity and located away from surface water show an increase in nitrate concentration. The occurrence of total organic N on the soil is not an influence of groundwater nitrate contents and there is a casual relation between groundwater nitrate contents and mineral N. The methodology allows the identification of higher groundwater nitrate content, as well as pressure, state, and response indicators. However, despite the global decrease in nitrate contents, the measures remain insufficient and appropriate mitigation will be required to reduce groundwater contamination.

Assessment of River-Aquifer Interaction and Nitrogen Contamination in an Agricultural Zone Located in the Guarani Aquifer System Outcrop Area.

The excessive use of nitrogen fertilizers is responsible for an increase in nitrate concentrations in water bodies, which in the future could led to an irreversible contamination compromising the water resource quality. In this way, understand the water movement within a watershed and evaluate the impacts related to agricultural practices is relevant for water management, especially in an environmental fragile region, such as the outcrop area of the Guarani Aquifer. Water samples from a small watershed located at the Guarani Aquifer region in São Paulo state, representing surface water and groundwater discharge in riverbeds from two creeks, as well as groundwater (springs and wells) were collected for isotopic ratios (δ18O e δ2H) and nitrate determination. The results indicated that the river flow is mostly supplied by groundwater discharge, and despite the observed concentrations of nitrate in groundwater reaching the creeks, the current scenario indicate contamination in the surface water, above the regulatory levels. Therefore, the expansion in sugarcane production increases the possibility that the released nitrate reaches high levels in the future in this watershed.

Evaluation of the Impact of Changing from Rainfed to Irrigated Agriculture in a Mediterranean Watershed in Spain

The conversion of cultivated areas from rainfed to irrigated agriculture alters the watershed’s hydrology and could affect the water quality and quantity. This study examined how streamflow, nitrate load, and nitrate concentration changed after irrigation implementation in a Mediterranean watershed in Navarre, Spain. The Soil Water Assessment Tool (SWAT) model was applied in the Cidacos River watershed to simulate streamflow and nitrate load under rainfed conditions. The simulated outputs were then compared with the post-irrigation observed values from mid-2017 to 2020 at the watershed outlet in Traibuenas to determine the irrigation impact. The model calibration (2000–2010) and validation (2011–2020) results for streamflow (NSE = 0.82/0.83) and nitrate load (NSE = 0.71/0.68) were satisfactory, indicating the model’s suitability for use in the watershed. A comparison of the rainfed and post-irrigation periods showed an average annual increase in streamflow (952.33 m3 ha−1, +18.8%), nitrate load (68.17 kg ha−1, +62.3%), and nitrate concentration (0.89 mg L−1 ha−1, +79%) at the watershed outlet. Irrigation also caused seasonal changes by altering the cropping cycle and increasing the streamflow and nitrate export during the summer and autumn when irrigation was at its peak. The increases in the post-irrigation period were attributed to the added irrigation water for streamflow and increased nitrogen fertilizer application due to changes in cropping for nitrate concentration and export. These findings are useful to farmers and managers in deciding the best nitrate pollution control and management measures to implement. Furthermore, these results could guide future development and expansion of irrigated lands to improve agricultural sustainability.

Nitrate adsorption by fired clay in fixed bed column

Excessive use of nitrogen fertilizers has increased nitrate concentrations in groundwater, which poses a health hazard from nitrate-contaminated drinking water and contributes to eutrophication. Nitrate removal from water systems has been carefully studied; However, new, low-cost solutions are urgently needed. Clay and terracotta minerals are commonly used in environmental applications due to their non-toxicity, global availability, low cost, and physical and chemical properties (ion-exchange capacity, high surface area, high adsorption, and catalytic properties). Although most are used to reduce cationic pollutants, depending on the method of modification or the materials with which they are mixed, they can be equally effective in removing anionic contamination. The goal of the study is to treat water containing excessive concentrations of nitrates to produce water of acceptable environmental specifications and to evaluate the performance of fired clay as a low-cost and environmentally friendly water treatment material.

Seasonal variation in the community distribution of protists off Wakasa Bay, Southern Sea of Japan

There is a dearth of knowledge regarding the spatiotemporal distribution of protistan community composition and seasonal environmental changes. High-throughput sequencing of the 18S rRNA gene was performed to assess changes in the community composition of protists over four seasons at four sites in Wakasa Bay, located in the center of Japan's northern coast. The community composition varied seasonally rather than geographically, even among few local communities confined to the bay head. Throughout the year, Alveolata and Chlorophyta were widely distributed and represented the predominant groups. Groups I and II of Syndiniales and Dinoflagellata were significant taxa in terms of operational taxonomic unit richness and sequence read abundance. Although three lineages of prasinophyte Clade VII, Pycnococcus-related prasinophyte, and Ostreococcus-related Mamiellophyceae were common, prasinophyte Clade VII was dominant during summer–autumn, whereas others were dominant during winter and spring. These results indicate the differential dominance of Chlorophyta at the intrataxon level. In the protistan community, increased temperature exerted an effect on the summer–autumn composition, whereas increased nitrate concentration showed an effect on the winter composition, suggesting that seasonal environmental changes affect the protistan community composition with different fluctuation patterns being observed among taxa.

In-situ utilization of nitrogen-rich wastewater discharged from a biotrickling filter as a moisture conditioning agent for composting: Insights into nitrogen transformation behavior and microbial mechanism

An NH4+–NO2–-rich wastewater discharged from a composting-biotrickling filter coupled system can be reused as a composting moisture adjustment agent. To investigate the impact mechanism of reuse, NH4+–NO2–-rich wastewater, NH4+-rich wastewater, NO2–-rich wastewater, and distilled water were added into the composting (i.e., AMN, AAN, ANO2, and ADW groups). Results show that compost of all groups met the corresponding criteria for stabilization, humification, and non-phytotoxicity of mature compost. AMN increased organic-N and NO3–-N content and reduced NH3 emissions, like AAN or ANO2, and avoid stimulating N2O emission in AAN and ANO2. Furthermore, LEfSe analysis of microorganisms revealed that AMN reduced NH3 emissions and increase organic-N content probably due to the inhibition of Alphaproteobacteria by ammonium, and increased nitrate content probably due to the stimulation of Aquamicrobium by nitrite. The avoided N2O emission is probably due to a negative synergistic effect on the stimulation from ammonia and nitrite to denitrifying bacteria (eg., Sphingobacteriaceae).

Влияние Cr2(SO4)3 на состояние клеток культуры Chlorella vulgaris при различном содержании в питательной среде источника азота – KNO3

The Cr2(SO4)3 effect at 10–2–10–8 M concentration on the biomass yield, the concentration of intracellular protein, chlorophylls a and b, and carotenoids on the culture of Chlorella vulgaris strain C 111 IBCE C-19 was studied. In separate experiment series, the nitrogen source, KNO3 concentration was increased by 10 and 20%. Chromium (III) had an ambiguous effect on the functional and metabolic state of the chlorella culture, depending on its concentration and the nitrogen source – KNO3 concentration. In general, at 5.0 g/l KNO3 concentration, chromium sulfate in the 10–2–10–6 M concentration inhibited the algae culture development, and at the maximum concentration caused rapid death. In the initial period of cultivation, the level of chlorophylls a and b sharply increased, which, apparently, was of a compensatory-adaptive nature. From the side of biomass, the level of intracellular protein, chlorophylls, no dynamics of an oscillatory nature, inherent in the control variant of the nutrient medium, was revealed. An increase in the concentration of KNO3 to 5.5 g/l at Cr2(SO4)310–4–10–8 M concentration was not only accompanied by an increase in biomass, but also by a noticeable (17–74%) increase in the intracellular protein level, a decrease in the “tension” of the photosynthetic apparatus (judgment by the level of pigments) and restoration of the oscillatory dynamics of photosynthetic pigments. A further increase in the potassium nitrate concentration did not give a positive result and led to the aggravation of the chlorella culture functional and metabolic state.

In Situ Synthesis of Zeolites in Solidified Fly Ash/Cement Matrices with High Na Content: Products, Pore Structure, and Leaching Behavior

Due to its high retention capacity and well durability, fly ash-based geopolymers rich of zeolites are considered to be potential solidified materials for low- and intermediate-level radioactive waste stream. This study mainly focused on the phase transformation, pore structure, and leaching characteristic of Sr2+ and Cs+ in solidified fly ash/cement matrices under different sodium hydroxide contents or sodium nitrate concentrations after thermal curing of 28 d. The results obtained from the experiments indicated that the geopolymers prepared from pure fly ash had the potential to transform into ordered structures at high temperatures of 90°C instead of room temperature, such as Na-P1 zeolite and chabazite. With the increase in sodium hydroxide contents, more sodium nitrate participated in the reaction to form a zeolite phase in solidified fly ash/cement matrices, while the coexistence phenomenon of chabazite and Na-P1 zeolite appeared under the condition of high sodium hydroxide contents of more than 5%. Just a proper number of zeolites can effectively inhibit the leaching of radionuclides Sr2+, as too many zeolites would lead to the increase in porosity, which was harmful to the retention of radionuclides. Solidified fly ash/cement matrices at a sodium hydroxide content of 5% or at a sodium nitrate concentration of 300 g/L obtained the lowest cumulative leaching fraction of Sr2+. Moreover, sodium hydroxide increased the cumulative leaching fraction of Cs+ which reversely decreased significantly with the increase in sodium nitrate concentrations.

Comparative analysis of nitrate evolution patterns during pollution episodes: Method development and results from Tianjin, China

Particulate nitrate plays an increasingly important role in the formation of air pollution process, while the main mechanisms of nitrate concentration change are different in each stage, same as the driving factors. In this study, we proposed an episode-based analysis to illustrate the typical nitrate evolution patterns and identify the possible impacting factors in different evolution stages. Applying into twelve air pollution episodes, three typical patterns of nitrate evolution were abstracted, and the corresponding conceptual models were constructed. All the pollution episodes were grouped by their evolving shapes, which were driven by physical and chemical processes. Episodes started slowly typically arose from gradual pollutant accumulation, both locally and regionally, and chemical formation under high humidity. Type 1 (“hump-shaped type”), accounting for 66.3 % of the total episode durations, including two “peak” concentrations, displays a rapid growth rate which could up to 4.6 μg m−3 h−1 in average, mainly relying on the sharp drop in the planetary boundary layer height. Short scavenging processes and thoroughly dissipated stages of the pollution episodes always accompanied by strong north wind affected by Siberia-Mongolia cold current. Type 2 (“triangle-shaped type”, 24.3 %) shows a gentle growth rate and short duration. Compared with Type 1, chemical process may be more important “source” for the increase of nitrate concentration during Type 2. Type 3 (“trapezoid-shaped type”, 9.4 %) presents a long platform stage, during which high humidity (RH > 90 %) provides favorable conditions for wet removal and secondary production, and the updraft can carry pollutants to high altitude. The source and sink are roughly balanced for Type 3. Our study highlights the importance of pattern identification for understanding the nitrate evolution behavior, it may also provide insights for pollution prediction and scientific mitigation strategies.