Medium Alkaline Research Articles

Efficient epoxidation of styrene over single-atomic copper-doped ordered mesoporous alumina (Cu-OMA) composited with carbon nitride

The present study assessed the catalytic performance in epoxidation of styrene using tert‑butyl hydroperoxide (TBHP) as an oxidant over single-atomic copper-doped Ordered mesoporous alumina (Cu-OMA) composited with g-C3N4 (CN). The thermal treatment at three temperatures (300, 500, 700 °C) provided a facile mean to modify the texture and electronic structure of the Cu-OMA@CN composite. The X-Ray absorption spectroscopy proved the single-atomic Cu-O-Al and Cu-O-C in Cu-OMA@CN-500 catalyst. Catalytic reaction parameters, namely temperature (60–80 °C), catalyst amount (10–70 mg), substrate/oxidant ratio (1:1–1:3), and solvents (acetone, ethanol, acetonitrile, N, N-dimethylacetamide) were optimized to obtain high conversion of styrene and selectivity to styrene epoxide. Under the optimized reaction conditions (75 °C, 30 mg of catalyst, 1:2 of styrene/TBHP and acetonitrile as solvent), the conversion decreased in the order of Cu-OMA@CN-500 > Cu-OMA@CN-300 > Cu-OMA@CN-700. This sequence was related to the formation of electron-rich single-atom copper sites, high surface area, medium alkaline environment and high content of graphic nitrogen species in Cu-OMA@CN-500. This structure differed from the blocky structure of C3N4 in Cu-OMA@CN-300 and the destroyed tri-s-triazine ring in Cu-OMA@CN-700. The most active Cu-OMA@CN-500 catalyst displayed a high styrene conversion (87.2 %) and striking selectivity to styrene oxide (90.0 %). Its catalytic activity was retained after five recyclability tests. The possible catalytic mechanism for epoxidation of styrene over this catalyst was tentatively proposed.

Using the kinetic approach for the adsorption of base ions (Ca, Mg, Na, K) by the calm flow method in some soils in the northern of Iraq

Abstract. Four soils were selected from northern Iraq, within the ranks (Mollisols, Inceptisols) from the provinces of Dohuk, Erbil and Sulaymaniyah from different agricultural fields from the root zone (0-0.30 m). Their physicochemical and mineral properties were estimated to study thermally isotropic adsorption by the calm flow method of soil columns using an electrolytic solution. At concentrations of (3) mmol charge.L-1, containing Ca, Mg, K, and Na ions in two repetitions at a constant temperature of approximately 298 ± 2 K. Stabilization filters were collected in which the ions were estimated according to the coefficients. The results indicated that the reactions ranged from medium alkaline to medium acidic. (6.7- (7.8), unaffected by salinity (1.44 - 0.29) dS.m-1 with an ion exchange capacity between (22.43 - (33.9 Cmolc.Kg-1) and is calcareous soil due to its high content of total carbonate minerals (-112) g.kg-1 .In addition to the calcareous origin material, and it has a high clay content (304-534) g.kg-1 with the predominance of smectite, chlorite, Ilite, kaolinite and Ilite clay minerals, the nature of ion exchange using the kinetic entrance of adsorption showed a clear effect of the porous fats and the contact time of the electrolyte solution on the adsorbed quantities depending on the type of soil. Show the mathematical description of the process of arranging the kinetic equations according to their validity as follows: Power > First order > Parabolic > Elovage > Zero order

Nickel molybdenum selenide on carbon cloth as an efficient bifunctional electrocatalyst for alkaline seawater splitting

Exploring cost-effective and highly efficient electrocatalysts is desirable for the overall water-splitting challenge. In this work, a promising bifunctional electrocatalyst for oxygen evolution and hydrogen evolution reactions (OER/HER) in an alkaline medium (1 M KOH) and simulated alkaline seawater (1 M KOH + 0.5 M NaCl) was rationally developed by a simple, one-step, inexpensive, and eco-friendly method. Mo-doped nickel selenide supported on activated carbon cloth (NiMoSe@CC) was successfully synthesized via a hydrothermal method. NiMoSe nanoparticles were observed to be densely grown with better uniformity on the carbon fibers, as confirmed by different characterization techniques. The NiMoSe@CC showed an enhanced OER activity with a low overpotential of 320 mV (alkaline medium) and 360 mV (alkaline seawater) at 10 mA cm−2. The HER performance of the NiMoSe@CC was also the highest amongst NiMoSe, NiSe@CC, and MoSe@CC in both the alkaline and seawater environments. In addition, NiMoSe@CC bears a high electrochemically active surface area, low charge transfer resistance of 1.77 Ω, and high stability for both OER and HER. The NiMoSe@CC//NiMoSe@CC system was stable for 5000 LSV cycles with η10 values of 1.63 V (1st LSV cycle) and 1.71 V (5000th LSV cycle).

Addressing salinity challenges: A comprehensive analysis of saline water and salt-tolerant soil for sustainable crop production in UC Tando Qaiser, Sindh, Pakistan

This study focuses on the physico-chemical characteristics of soils in UC Tando Qaiser, District Hyderabad, Sindh, Pakistan, irrigated by tube well water. The soil samples were collected at depths of 0-20, 20-40, and 40-60 cm, and their particle size distribution, organic matter content, pH, and salinity were analyzed. Results indicate that the soils are heavy in texture, likely influenced by the parent material deposited by the Indus River. Organic matter content was found to be low, possibly due to the absence of farmyard manure and limited cultivation of green manure crops. The majority of soils exhibit a slightly to medium alkaline reaction, characteristic of calcareous soils with high Ca2+, Mg2+, and K+ content. Slightly-saline soils were observed, emphasizing the need for soil salinity management. Tube well water analysis revealed variations in electrical conductivity, with some samples exceeding permissible limits. Recommendations include strategies to enhance organic matter, mitigate soil salinity, and implement regular monitoring of tube well water quality for sustainable agriculture in the region.

Deteksi Bakteri Salmonella sp. dengan Kultur Darah Pada Pasien Widal Positif di Laboratorium Klinik X

Until now, the gold standard test for diagnosing typhoid fever is a bacterial culture or also known as a gall culture examination. Blood cultures have the best sensitivity (40–60%) when performed in the first-early second week. Purpose: this study aims to identify the presence of Salmonella sp. in the blood of Widal positive patients. Method: this research is a descriptive study with a cross-sectional approach. This study used the blood culture method. The media used in this study were oxgall, SSA, KIA and IMViC media. The results showed that 20% of Salmonella typhi bacteria were found, 7% of other bacteria and 73% of bacteria did not grow on the media. The macroscopic characteristics of salmonella bacteria found were round colonies, clear in color, convex surface, flat colony edges, semi mucoid consistency, no reduction of tellurit. The microscopic characteristics are rod-shaped, spread arrangement, red in color and are Gram negative. Cultivation on IMViC media showed Indole -, MR +, VP -, Citrate -, KIA medium alkaline slope, acid base, H2S +, gas -. Conclusion: Salmonella thypi was found in the blood cultures of positive widal patients.

Investigation of Cu-ZnO/SiO2 catalysts for CO2 hydrogenation: Effect of SiO2 support with different porous structure

CO2 hydrogenation is one of the reactions to realize effective utilization of CO2, while Cu-Zn based catalyst is widely adopted for CO2 hydrogenation to value-added chemicals like methanol. However, this process is less efficient since the poor performance of catalyst due to its poor dispersion or sintering issue. In this study, three kinds of SiO2 supports (SBA-15, MCM-41 and Nano-SiO2) with different porous structure were conducted to load same amount of 5.0 wt% Cu-ZnO active component (the molar ratio of Cu/Zn is 2.0), which were further applied for CO2 hydrogenation. All catalysts were characterized chemically, morphologically and structurally by different techniques such as XRD, BET, TEM, H2-TPR and CO2-TPD. The results showed that the structure of three catalysts was basically preserved and the surface aera kept stable after loading active component, while the active component had the best dispersion when SBA-15 was used as the support and space-time yield of methanol is about 705.6 gMeOH•kgCu−1•h−1,which is higher than that of Nano-SiO2-5% (532.9 gMeOH•kgCu−1•h−1) and MCM-41–5% (213.2 gMeOH•kgCu−1•h−1). Due to the confined effect of mesoporous channel structure provided by SBA-15 support, the Cu-Zn interaction could be significantly enhanced with increasement of medium and strong alkaline sites, further improving CO2 activation ability. This work provides a useful strategy to improve the catalytic efficiency of classical Cu-Zn catalyst for the CO2 hydrogenation process.

Spatial Variability Mapping of Selected Soil Properties of District Tando Allahyar, Sindh, Pakistan

Spatial variability mapping of soil properties is essential to understand the differences among soils found in a geographical region for their better management. This study aimed at spatial variability mapping of selected soil properties of district Tando Allahyar, Sindh which is one of the most important districts of Sindh province. The results revealed that majority of soils (35.6%) had loamy slightly medium-textured type, including 30.8% silt loam, 3.8% loam and 1.0% silt, followed by clayey, fine-textured heavy type (27.9%), including 18.3% clay, 6.7% silty clay and 2.9% sandy clay. Soils with sandy, coarse-textured light type were 20.2%, including 16.3% sandy loam and 1.9% loamy sand and sand each. Soils with loamy, moderately medium-textured type were 16.3%, including 9.6% clay loam and 6.7% sandy clay loam, while silty clay loam soil texture was total missing. The EC ranged from 0.14 to 4.44 dS m-1 (mean: 0.69 dS m-1, mode: 0.42 dS m-1). Majority (91%) of soils had low (46%) to medium (45) level of salinity. Soil pH ranged from 6.2 to 8.6 (mean: 7.7, mode: 8.3). Majority of soils (84%) had either slightly (24%), medium (22%) or strongly alkaline (38%) soil pH. Interestingly, some soils (13%) had slightly acidic pH. Organic matter ranged from 0.10 to 1.6% (mean: 0.64%, mode: 0.17%). Majority (84%) of soils were deficient in organic matter. Soil ABDTPA-P ranged from 1.2 to 18.8 mg kg-1 (mean: 5.38 mg kg-1, mode: 2.4 mg kg-1). More than half (55%) of the soils had low P, while soils with marginal (14%) or adequate (31%) P were also present. Soil ABDTPA-K ranged from 31 to 376 mg kg-1 (mean: 154 mg kg-1, mode: 230 mg kg-1). Majority of soils (62%) had adequate K, while soils with marginal (28%) or low (11%) K were also found. Spatial variability mapping revealed the dominance of loam, sandy clay loam, sandy loam, silty clay and clay loam textures, medium > low and high > salinity, slightly to medium alkaline soils > strongly alkaline soils, low organic matter content, medium to adequate > low soil P, and adequate soil K. The spatial variation found in various soil properties of district Tando Allahyar, Sindh must be taken in mind while deciding about their site-specific management, using the recently developed maps.

A Comparative Study of ION Diffusion from Calcium Hydroxide with Various Herbal Pastes through Dentin: An In Vitro Study

Background: Intracanal medicaments used during root canal treatment comes in direct contact with cells of pulp and periapical tissues. The antimicrobial property of calcium hydroxide [Ca(OH)2] is broadly utilized. It has the capability to dissolve organic tissues as well as to inactivate bacterial endotoxins. The aim of this in vitro study is ion diffusion from calcium hydroxide with various herbal pastes through dentin. Materials and Methods: Twenty one extracted single-rooted premolar were selected. The crown was transversely sectioned at the CEJ level. Paste was prepared by using 1gm of calcium hydroxide powder and 2mL of solution. Group1-(n=7): Calcium hydroxide-saline paste, Group2 (n=7): Calcium hydroxide-coconut water paste. Group3-(n=7): Calcium hydroxide-Ashwagandha paste; the apical foramen were sealed with epoxy resin. The teeth were placed in containers with 50mL of deionized water for 24, 72, and 168 hours, the pH values of the solution were measured using a pH meter. Results: Coconut water was alkaline in nature initially and after 168 hours, the medium was still alkaline. Ashwagandha was the only herbal preparation that increased the pH up to 168 hours and made the medium alkaline. Saline water preparations were acidic at the start of experiment, increased the pH up to 72 hours, but could not make the medium alkaline. Conclusion: The present study was done with the aim of vehicle used for calcium paste to improve the diffusion capability. Coconut water has a much better composition of minerals like calcium and zinc. The better dif¬fusion ability and marked antimicrobial activity make them the best materials, which can be used as vehicles. Ashwagandha prepara¬tions provided additional benefits of diffusion of ions through the dentinal tubules in a sustained manner (up to 168 hours) in comparison with normal saline.

Valorisation des eaux de retour des serres agricoles chauffée par l’eau géothermique dans le sud tunisien

Le secteur des cultures protégées sous serres chauffées dans le sud tunisien n’a cessé de se développer avec la disponibilité des ressources géothermiques. La mauvaise gestion de ces ressources entraîne leur dégradation en termes de quantité et qualité. Cette situation s’aggrave avec la demande en eau dans le secteur agricole. De ce fait, la valorisation de ces potentiels géothermiquess’avère nécessaire pour assurer leur durabilité. Le présent travail vise la caractérisation des eaux de retour et l’évaluation de leur impact sur les cultures sous serres et les systèmes oasiens. L’étude s’est basée sur des analyses physico-chimiques des eaux de retour prélevées auprès de neuf pôles géothermiques répartis sur les trois gouvernorats (Gabès, Kébili et Tozeur), des visites de terrain et des enquêtes menées auprès des agriculteurs exploitants. Ces analyses physico-chimiques indiquent une qualité d’eau médiocre à moyenne qui présente un risque salin très élevé et un risque alcalin moyen. En effet, la salinité des eaux varie de 2,6 à 11,9 g/l et le SAR de 5,1 à 8,8. Ajoutons que les techniques de gestion de la salinité adoptées par les agriculteurs restentencore limitées à cause de leur faible capacité financière.

Cartographic modeling of soil acidity level of the Zdolbuniv district of the Rivne region

The economic use of agricultural land requires systematic agrochemical surveys, a balanced analysis of the results obtained and the adoption of the right decisions to improve soil fertility, increase agricultural efficiency, and preserve the environment. One of the most important tools in this type of research is mapping modelling. The purpose of this article is to study and analyse the level of soil acidity in one of the most agriculturally developed regions of Rivne Oblast - Zdolbuniv district. Based on the results of the last three rounds of scheduled agrochemical certification of agricultural land (rounds 9-11, 2007-2017) conducted by the Rivne branch of the State Institution "Derzhgruntoochorona", the weighted average indicators of soil pH were calculated in the context of former village councils, a corresponding database was created, and the author's own thematic maps and diagrams were created. The thematic maps were developed using ArcMap software, the coordinate system was Pulkovo 1942 GK Zone 5, the scale was 1:250,000, and the main method of depiction was cartograms. The dynamics of soil acidity in the region during the last three rounds of surveys was summarised and analysed, making it possible to identify areas with optimal, high or low values of indicators, and to identify possible problematic or potentially fertile lands. Specific recommendations for improving soil acidity were provided, primarily for medium acidic soils in the former Staromoshchanytsia and Stupnivka village councils and medium alkaline soils in the former Myrotyn and Uizdets village councils. Thematic maps and diagrams created in this way, with other additional and detailed data, can become an important basis for making informed management decisions to optimise soil acidity both on the territory of former village councils and agricultural formations, individual fields and plots.

Средне-щелочные алкилфенолятные присадки

The article presents the results of research on the sintesis of medium alkaline alkylphenolate additives. Additives are calcium salts of the condensation products of alkylphenols with formaldehyde and ammonia or various amines (monoethanolamine, benzylamine and allylamine) have been synthesized and studied. The physicochemical and functional properties of the synthesized products were studied by standard methods.It has been shown that all aminomethyl derivatives of alkylphenols have multifunctional properties and are superior to their analogs ИХП-101, ИХП-109 and ВНИИНП-370 in terms of their functional properties. In addition, the additives obtained on the basis of nonylphenol in terms of anticorrosion and antioxidant properties are somewhat superior to those obtained on the basis of alkylphenol (C8–C12) due to their homogeneous composition. Thus, all synthesized compounds are multifunctional, and additives containing a secondary nitrogen atom (calcium salt of dialkyldioxybenzylamine) and a benzyl radical at the nitrogen atom (calcium salt of N-benzyldialkyldioxybenzylamine) have the highest antioxidant efficiency.

Nutrient Status of Soils from the Kaleshwaram Project Command Area of Erstwhile Nizamabad District in Telangana State

A research was conducted to study the fertility status of soils from kaleshwaram project command area of erstwhile Nizamabad district in Telangana. A total of 72 geo-referenced soil samples collected from surface (0-15cm) by using GPS coordinate. Samples were analysed for important soil parameters viz., pH, EC, available macronutrients (N, P, K) and micronutrients (Fe, Zn, Mn, Cu). Correlation study was done to study the relation between the various soil properties. The soil pH and EC showed wide variation that soils are low acidic to medium alkaline in reaction and low salinity. Whereas available N content is low (75 to 298 kg ha-1), available P2O5 content medium to high (18-358 kg ha-1) and available K2O content low to high (90 to 630 kg ha-1). The soil available Zn, Cu, Fe and Mn contents of surface soils are very low to adequate. Correlation study depicts that soil reaction was negatively related with soil available N, P2O5, Fe and Mn. the results of the study area showed that these soils are need proper management, supplement with organic manures and inorganic fertilisers.

Spatial Analysis of Some Soil Characteristics in Baqbah City-Diyala-Iraq Using Remote Sensing and GIS

This study was conducted in the district of Baquba within the province of Diyala in central Iraq between latitudes 44º 35 ' 50. 239" - 44º 36 ' 31 .123" and 33º 40ʹ 48.494- 33º 41ʹ 13.404 an area of 145.123 km2, for the purpose of studying the attributes of soil (Texture, Organic Material, pH and Electrical Conductivity (EC), we have depended on the field survey and choose 30 random samples deeply 0- 30 cm per sample, GPS users to determine the samples. We used a satellite image for LANDSAT8 pick up on 24/12/2021, the results of laboratory analysis of soil samples indicated that soil tissue was soft to medium in most samples and the values of pH ranged from 7.0 - 8.3, which are neutral Nutral Soils to medium alkaline soils and ranged EC values for the region Study between 5.75-58 ds.m-1 and Organic Material values ranged from 0.3-18%.

Effect of molarity of NaOH and alkalinity ratio on compressive strength of geo-polymer concrete

Concrete is the most copious man-made material in the planet. One of the main ingredients in a normal concrete mixture is Portland cement. However, the production of cement emits approximately 5% of the world’s carbon dioxide (Greenhouse gas). On the other hand, the climate change due to global warming and environmental protection has become major concerns. The production of Portland cement involves the emission of carbon dioxide, thus replacing of the Portland cement with industrial waste can be one of the solutions for reduction of the carbon dioxide emission. At the same time, thermal power plants produce fly ash in a very large amount and it creates a huge problem for its disposal. Disposal of this fly ash requires approximately 40,000 ha of land every year. In order to avoid the above environmental issues as well as the disposal problem, researchers have employed fly ash an alternative of cement in making of concrete exploiting the binding property of fly ash thereby it led to make attempt to carry out more research on the replacement of cement by fly ash in the concrete. Therefore, the focus to work in this direction acquainting with the idea that the replacement of cement is possible with 100% fly ash and this alternative to regular concrete is known as Geo Polymer Concrete (GPC). The theme of the present work is fully replacement of cement with fly ash to produce the GPC. To produce the GPC, the main constituent materials used are Fly Ash (which is a by-product obtained from thermal power plants) and the alkaline activators in addition to aggregates and water. The alkaline activators used in this study for the polymerization are sodium hydroxide (NaOH) in flakes form and sodium meta -silicate (Na2SiO3) in gel form. The objective of the present work is to study the effect of NaOH molarity and alkaline activator ratios on the compressive strength (3, 7 and 28 days) of GPC at a constant curing period and curing temperature and compare with controlled concrete prepared using ordinary Portland cement (OPC). In the present work 5 and 10 M of NaOH and 1:1, 1:1.5 and 1:2 alkaline ratios were considered with constant curing temperature of 90° C and 24 h curing time. M20 grade of concrete mix design was carried out as per BIS (IS: 10262–2009) for control concrete and the same mix proportion was adopted for GPC also. From the experimental results, it was found that the both NaOH molarity and alkaline solution ratio effecting the compressive strength at 3, 7 and 28 days and maximum compressive strength was obtained at higher NaOH molarity (10 M) and medium alkaline solution ratio (1:1.5). Further, it was found that the compressive strength of GPC was higher than the controlled concrete prepared using OPC.

The influence of blast furnace slag content on the mechanical and durability properties of raw perlite-based geopolymer mortars

In this work, 21 different raw perlite (RP) -based geopolymer mortars (RPGMs) were manufactured. Blast furnace slag (BFS) was replaced by RP in 7 different proportions with respect to the CaO/SiO2 oxide ratio of RP and BFS mixture in the RPGMs. Sodium hydroxide (NaOH= 5, 10, and 15 M) was used as alkaline medium for geopolymer synthesis in the RPGMs. The ultrasound pulse velocity (Upv), flexural strength (ffs) and compressive strength (fcs), water absorption, acid and sulfate durability of the RPGMs are investigated. The test results revealed that the BFS improved the mechanical properties of RPGMs for the low and medium alkaline medium of 5M and 10M, respectively. On the other hand, BFS had negative effect on the mechanical properties of RPGMs produced at a high alkaline medium of 15M. Moreover, the BFS improved the acid and sulfate durability of the RPGMs.

A preliminary investigation of caramelisation and isomerisation of allulose at medium temperatures and alkaline pHs: a comparison study with other monosaccharides

SummaryAllulose, also known as rare sugar, is a very reactive monosaccharide in browning reactions. In this study, the caramelisation of allulose was investigated for the first time. To study caramelisation, sugar solutions (glucose, fructose and allulose) were prepared with distilled water and buffer solutions at pH 7, 10, 12 and were freeze‐dried afterwards. To let caramelisation occur, samples were incubated at 55% relative humidity (RH) and 50 °C. Results showed that samples prepared with pH 10 and pH 12 buffer solutions resulted in a higher browning rate than samples prepared with distilled water (DW) and pH 7 buffer solution. Moreover, according to HPLC and total reducing sugar content results, allulose (Allu) samples had the lowest remaining reducing sugar (RRS) amount, indicating that Allu samples depleted more in the reaction. Overall, the approach followed in this study can be considered as a novel strategy to obtain allulose‐containing caramel‐like products more efficiently than conventional methods.

Performance Evaluation of Enzyme Breaker for Fracturing Applications under Simulated Reservoir Conditions.

Fracturing fluids are being increasingly used for viscosity development and proppant transport during hydraulic fracturing operations. Furthermore, the breaker is an important additive in fracturing fluid to extensively degrade the polymer mass after fracturing operations, thereby maximizing fracture conductivity and minimizing residual damaging materials. In this study, the efficacy of different enzyme breakers was examined in alkaline and medium-temperature reservoirs. The parameters considered were the effect of the breaker on shear resistance performance and sand-suspending performance of the fracturing fluid, its damage to the reservoir after gel breaking, and its gel-breaking efficiency. The experimental results verified that mannanase II is an enzyme breaker with excellent gel-breaking performance at medium temperatures and alkaline conditions. In addition, mannanase II did not adversely affect the shear resistance performance and sand-suspending performance of the fracturing fluid during hydraulic fracturing. For the same gel-breaking result, the concentration of mannanase II used was only one fifth of other enzyme breakers (e.g., mannanase I, galactosidase, and amylase). Moreover, the amount of residue and the particle size of the residues generated were also significantly lower than those of the ammonium persulfate breaker. Finally, we also examined the viscosity-reducing capability of mannanase II under a wide range of temperatures (104–158 °F) and pH values (7–8.5) to recommend its best-use concentrations under different fracturing conditions. The mannanase has potential for applications in low-permeability oilfield development and to maximize long-term productivity from unconventional oilwells.

Impact of Oxides and Physiochemical Properties of Agricultural Soil on Bioaccumulation of Toxic Heavy Elements in Wheat Grains in Yaychi, Northeast of Iraq

To investigate the potential link between toxic heavy elements in soil with soil physiochemical properties and oxides, as well as their impact on the bioaccumulation of these elements in wheat grains. Agriculture soil and wheat grains were sampled from Yaychi area, Kirkuk northeast of Iraq. Soil physiochemical properties, oxides and toxic heavy elements contents were determined. The average concentration of toxic heavy elements in soil was in this order Ni> Cr> Pb> As> Cd> Hg, and some of these elements had exceeded their average in earth's crust and Canadian Agricultural Soil Quality Guidelines. While in wheat grains the toxic heavy elements, contents were in the following order Cr> Ni> Pb> As> Cd> Hg. The soil physiochemical properties in the study area are shown to be medium alkaline, non-saline, calcareous, non-gypsiferous, inorganic and loam texture. It became clear from the correlation matrix that the toxic heavy elements except for arsenic have significant relationships with different soil physiochemical properties and major oxides. In turn, oxides and the physiochemical properties of the soil and its type reduced the bioaccumulation of these elements in wheat grains except for arsenic, as appeared in the present study, that toxic heavy elements do not accumulate in wheat grains. And among the studied elements, arsenic had the highest bioaccumulation rate in wheat grains, because its concentration in soil has been affected by only human activities.

<p><strong>Three new needle-shaped <em>Fragilaria</em> species from Central America and the Tibetan Plateau</strong></p>

Three new needle-shaped Fragilaria species from freshwater lake Apastepeque in El Salvador (Fragilaria salvadoriana sp. nov., F. maarensis sp. nov.) and subsaline lake Nam Co on the Tibetan Plateau (F. huebeneri sp. nov.) are described and compared based on light and scanning electron microscopy observations and morphometric analyses. Fragilaria salvadoriana sp. nov. is characterized by narrowly linear-lanceolate, sometimes centrally constricted valves, subcapitate to rarely capitate apices, and a distinct, dented appearing central area. Striae are composed of 2−5 occluded areolae. It can be differentiated from similar needle-shaped species by the valve outline, relatively low striae density, and shark fin-shaped spines. Characteristic of F. maarensis sp. nov. are a very narrowly lanceolate valve outline and subcapitate apices. The apical pore field is composed of 2–3 rows of poroids and acute, irregularly oriented spines are present at the junction between valve face and mantle. This taxon is clearly different from other Fragilaria species, displaying a high length-to-width ratio and a low number of areolae per stria. The Tibetan species, F. huebeneri sp. nov., forms long ribbon-like colonies linked together by spatula-shaped spines. Valves have subcapitate apices, a spindle- to needle-shaped outline and an indistinct central area. Striae are alternate and composed of 3–5 areolae per stria. Teratological forms of F. huebeneri sp. nov. were commonly observed in the sediment trap samples. Fragilaria salvadoriana sp. nov. and F. maarensis sp. nov. were found in a warm, tropical crater lake characterized by low conductivity and dissolved oxygen content, medium alkaline pH, and magnesium-calcium-bicarbonate-rich waters. Fragilaria huebeneri sp. nov. was frequent in a large, high elevation lake with increased specific conductivity, alkaline pH and sodium-bicarbonate-rich waters. The new species are compared to morphologically similar species from the genus Fragilaria Lyngbye and ecological preferences are discussed.

УРОВНИ УВЛАЖНЕНИЯ ЧЕРНОЗЕМОВ, СПОСОБСТВУЮЩИЕ СОХРАНЕНИЮ ПОЧВЕННОГО ПЛОДОРОДИЯ

Purpose: to study the effect of different levels of moisture on chernozems properties and the crop yield. Materials and methods. Research objects are ordinary chernozem irrigated with fresh water; ordinary chernozem, irrigated with low-mineralized water; southern chernozem irrigated with fresh water (Rostov region). Analysis and evaluation of these soil samples were carried out according to generally accepted methods. Mathematical processing of the data was carried out according to B. A. Dospekhov. Results. It was found that the average yield of agricultural crops in the 0.8 m variant compared to 1 t decreased by 2–3 % (within the limits of reliability of the experiment), and the water saving was 13–18 %. An increase in the water load (1.3 m) during 4-year irrigation with low-mineralized water of sulphate-sodium composition increased the amount of sodium to 9 % of the total soil absorbing complex (AUC) with a simultaneous decrease in the calcium proportion to 69 % of the total AUC and the transformation of soils from weakly to medium alkaline (1.15 mmol/100 g). It was revealed that for 4 years of research, when irrigating chernozems with fresh water in options 1 m and 0.8 m, a positive humus balance is observed, and on ordinary chernozems irrigated with low-mineralized water, and southern chernozems with natural solonetzicity, a negative humus balance is traced in all variants. Conclusions. Comparing the results on soil properties, the yield of cultivated crops and the efficiency of the use of irrigation water at various levels of moisture, one should give preference to soil moisture at a rate calculated for the biological need of plants. It is allowed to reduce the irrigation rate from the calculated one by 20 %, since at this level the chernozem fertility is preserved, the irrigation water consumption is reduced with a slight shortage of cultivated crops yield.