Total Mn Research Articles

Anthropic and Meteorological Controls on the Origin and Quality of Water at a Bank Filtration Site in Canada

At many bank filtration (BF) sites, mixing ratios between the contributing sources of water are typically regarded as values with no temporal variation, even though hydraulic conditions and pumping regimes can be transient. This study illustrates how anthropic and meteorological forcings influence the origin of the water of a BF system that interacts with two lakes (named A and B). The development of a time-varying binary mixing model based on electrical conductivity (EC) allowed the estimation of mixing ratios over a year. A sensitivity analysis quantified the importance of considering the temporal variability of the end-members for reliable results. The model revealed that the contribution from Lake A may vary from 0% to 100%. At the wells that were operated continuously at >1000 m3/day, the contribution from Lake A stabilized between 54% and 78%. On the other hand, intermittent and occasional pumping regimes caused the mixing ratios to be controlled by indirect anthropic and/or meteorological forcing. The flow conditions have implications for the quality of the bank filtrate, as highlighted via the spatiotemporal variability of total Fe and Mn concentrations. We therefore propose guidelines for rapid decision-making regarding the origin and quality of the pumped drinking water.

Phenazine-1-Carboxylic Acid-Producing Bacteria Enhance the Reactivity of Iron Minerals in Dryland and Irrigated Wheat Rhizospheres.

Phenazine-1-carboxylic acid (PCA) is a broad-spectrum antibiotic produced by rhizobacteria in the dryland wheat fields of the Columbia Plateau. PCA and other phenazines reductively dissolve Fe and Mn oxyhydroxides in bacterial culture systems, but the impact of PCA upon Fe and Mn cycling in the rhizosphere is unknown. Here, concentrations of dithionite-extractable and poorly crystalline Fe were approximately 10% and 30-40% higher, respectively, in dryland and irrigated rhizospheres inoculated with the PCA-producing (PCA+) strain Pseudomonas synxantha 2-79 than in rhizospheres inoculated with a PCA-deficient mutant. However, rhizosphere concentrations of Fe(II) and Mn did not differ significantly, indicating that PCA-mediated redox transformations of Fe and Mn were transient or were masked by competing processes. Total Fe and Mn uptake into wheat biomass also did not differ significantly, but the PCA+ strain significantly altered Fe translocation into shoots. X-ray absorption near edge spectroscopy revealed an abundance of Fe-bearing oxyhydroxides and phyllosilicates in all rhizospheres. These results indicate that the PCA+ strain enhanced the reactivity and mobility of Fe derived from soil minerals without producing parallel changes in plant Fe uptake. This is the first report that directly links significant alterations of Fe-bearing minerals in the rhizosphere to a single bacterial trait.

Impact of Peroxymonocarbonate on the Transformation of Organic Contaminants during Hydrogen Peroxide in Situ Chemical Oxidation

Under the conditions employed when in situ chemical oxidation is used for contaminant remediation, high concentrations of H2O2 (e.g., up to ~10 M) are typically present. Using 13C NMR, we show that in carbonate-rich systems, these high concentrations of H2O2 result in a reaction with HCO3- to produce peroxymonocarbonate (HCO4-). After formation, HCO4- reacts with phenol to produce di- and tri-hydroxyl phenols. HCO4- reacts with substituted phenols in a manner consistent with its electrophilic character. Exchanging an electron-donating substituent in the para position of a phenolic compound with an electron-withdrawing group decreased the reaction rate. Results of this study indicate that HCO4- is a potentially important but previously unrecognized oxidative species generated during H2O2in situ Chemical Oxidation (ISCO) that selectively reacts with electron-rich organic compounds. Under conditions in which HO· formation is inefficient (e.g., relatively high concentration of HCO3-, low total Fe and Mn concentrations), the fraction of the phenolic compounds that are transformed by HCO4- could be similar to or greater than the fraction transformed by HO·. It may be possible to adjust treatment conditions to enhance the formation of HCO4- as a means of accelerating rates of contaminant removal.

Dietary Intake and Urinary Excretion of Manganese in Korean Healthy Adults.

Manganese (Mn) is an essential element for the body's composition and is required for various functions, including nutrient metabolism, immune system function, and antioxidant ability. However, there are insufficient data on the nutritional status of Mn. In this study, we aimed to analyze the relationship between Mn intake and urinary excretion in Korean adults. A twice dietary intake survey using a 24-h recall method was conducted on 640 adults (320 men and 320 women), aged 20 to 69 years. Eighty 24-h urine samples were also twice collected and urinary Mn excretions were analyzed. Results indicated that total Mn intake per day was 4.1 mg for men and 3.9 mg for women (p < 0.05). Mn intake per 1000 kcal of energy consumption was significantly higher in women than in men (2.0 mg/1,000 kcal vs. 2.2 mg/1000 kcal, p < 0.01). Additionally, Mn intake as a percentage of Adequate Intake was 103.0% for men and 110.3% for women (p < 0.05). Mn was mostly consumed from cereals (1.78 mg/day for men and 1.53 mg/day for women), followed by vegetables, seasonings, fruits, and pulses. The main food sources of Mn were rice (27.8% for men, 22.0% for women), kimchi (3.5% for men, 1.4% for women), and tofu (2.8% for men, 2.3% for women); the percentage of Mn consumed from 20 types of foods was 55.6% (women) to 60.4% (men). Urinary Mn excretion was negatively correlated with Mn intake from cereals and positively with mushrooms only for women after adjusting for confounding factors (p < 0.05). In conclusion, dietary Mn intake by Korean adults was adequate to meet the Dietary Reference Intake, but the relationship between Mn intake and urinary excretion was not clear.

Biogeochemical specialization of macrophytes and their role as a biofilter in the Selenga delta

This study aims to evaluate the biofiltration ability of higher aquatic vegetation of the Selenga delta as a barrier for heavy metals and metalloids (HMM) flows into the Lake Baikal. Main aquatic vegetation species have been collected from deltaic channels and inner lakes: Nuphar pumila, Potamogeton perfoliatus, P. pectinatus, P. natans, P. friesii, Butomus umbellatus, Myriophyllum spicatum, Ceratophyllum demersum, Phragmites australis. Analysis of the obtained data showed that regardless of the place of growth hydatophytes spiked water-milfoil (M. spicatum) and the fennel-leaved pondweed (P. pectinatus) most actively accumulate metals. Opposite tendencies were found for helophytes reed (Ph. australis) and flowering rush (B. umbellatus), which concentrate the least amount of elements. This supports previous findings that the ability to concentrate HMM increases in the series of surface – floating – submerged plants. Regarding river water, the studied macrophyte species are enriched with Mn and Co, regarding suspended matter – Mo, Mn and B, regarding bottom sediments – Mn, Mo and As. We identified two associations of chemical elements: S-association with the predominant suspended form of migration (Be, V, Co, Ni, W, Pb, Bi, Mn, Fe and Al) and D-association with the predominant dissolved form of migration (B, U, Mo, Cr, Cu, Zn, As, Cd, Sn and Sb). Due to these associations three groups of macrophytes were distinguished – flowering rush and reed with a low HMM content; small yellow pond-lily and common floating pondweed with a moderate accumulation of S-association and weak accumulation of D-association elements; and clasping-leaved pondweed, fennel-leaved pondweed, and pondweed Friesii accumulating elements of both S and D groups. The results suggest that macrophytes retain more than 60% of the total Mn flux that came into the delta, more than 10% – W, As, and from 3 to 10% B, Fe, Co, Mo, Cd, V, Ni, Bi, Be, Cu, Zn, Cr, U, Al. The largest contribution is made by the group of hydatophytes (spiked water-milfoil and pondweed), which account for 74 to 96% of the total mass of substances accumulated by aquatic plants.

Systematic study on separation of Mn and Fe from ferruginous manganese ores by carbothermic reduction roasting process: Phase transformation and morphologies

Carbothermic roasting reduction followed by magnetic separation process is reported as an effective technological process to separation and recovery of Fe and Mn from low-grade ferruginous manganese ores (Fe–Mn ores) as an acceptable feed to meet the demands of the developing manganese industry. In this study, the effects of operating variables on the recovery and grade of Fe and Mn are initially investigated during the carbothermic roasting reduction process followed by magnetic separation. Then, the phase transformation and morphologies of spinel (FeyMn1−y)Al2O4, fayalite FeyMn2−ySiO4 and (FeO)x(MnO)1−x are investigated by SEM-EDS, XRD, TG/DTG and thermodynamic analyses. Finally, the stepwise reduction and interfacial reaction of three types of phases are investigated at 700–1100 °C for 10–120 min to clarify the reason for the poor separation of Mn and Fe from Fe–Mn ores. The effect of MnO on the stepwise reduction behavior of Fe2SiO4 and FeAl2O4 is analyzed in detail. Finally, the tight integration of the MnO phase with a metallic Fe–Mn alloy derived from the stepwise reduction of (FeO)x(MnO)1−x are closely associated with the stepwise reduction of the FeyMn2−ySiO4, (FeyMn1−y)Al2O4 and (Fe,Mn)2O3 phases. In addition, the formation mechanism and the interfacial reduction reaction of (FeO)x(MnO)1−x, (FeyMn1−y)Al2O4 and FeyMn2−ySiO4 are systematically analyzed to show the effect of the MnO phase on the stepwise reduction of the Fe2SiO4 and FeAl2O4 phases. Finally, some suggestions were recommended for the carbothermic reduction followed by magnetic separation for utilizing the Fe–Mn ores effectively. The manganese-rich product an acceptable feed containing 53.60 wt.% total Mn with the Mn recovery of 89.38% and mass fraction of Mn/Fe of 5.43 are obtained.

Chemical Properties of Soil Influence by Sewage Water Irrigation of Different District of Haryana

The present study deals with the difference of chemical properties between sewage and tube well water irrigated soils. Samples were collected from sewage and tube well water irrigated soil of various site like Kaithal, Narwana and Jind district of Haryana state where these waters are directly used for irrigating the crops. Soil samples (0-15 and 15-30 cm) were also collected from fields irrigated with these waters and from nearby fields irrigated with non-sewage waters to determine the changes in soil chemical properties due to sewage irrigation. Total Zn, Cu, Mn, Fe, Cd, Pb, Co, and Cr along with nitrogen, phosphorus and potassium were estimated form the samples. The mean value of N (200.50 kg ha-1) was found highest in the soils irrigated with sewage water of Kaithal. The mean value of P (35.85 kg ha-1) and K (236.40 kg ha-1) was found highest in the soils irrigated with sewage water of Jind. The mean value of K (236.40 kg ha-1) was found highest in the soils irrigated with sewage water of Jind. The mean value of Zn (4.43 mg kg-1), Cu (3.33 mg kg-1) and Fe (19.43 mg kg-1) was found highest in the soils irrigated with sewage water of Jind. The mean value of Mn (15.13 mg kg-1) was found highest in the soils irrigated with sewage water of Kaithal. The DTPA extractable heavy metals like Cd, Pb and Co were found higher in the soils irrigated with sewage water as compared to soils irrigated with non-sewage water. The value of Cr content was found nil all the soils samples collected from different cities from sewage and non-sewage water irrigated sites.

Long-Term Influence of Nutrient Management on Carbon and Nutrients In Typic-Ustochrept Soils

ABSTRACTContinuous incorporation of green manure (GM) and rice straw residue (RSR) over a long period of time generally improved soil physico-chemical properties. To generate this information, laboratory studies were conducted during 2014 on the soil samples collected from an on-going long-term experiment on rice–wheat sequence in progress since 2001. The results of the study reported improvement in bulk density, water holding capacity, and total porosity with green manuring. The maximum organic carbon build up was recorded in manure @ 15 t ha−1 which was applied through GM. The application of fertilizers, GM and RSR incorporation improved the buildup of the available and total N, P, and K contents of surface soil. The data further indicated that the DTPA-extractable and total Zn, Cu, Fe, and Mn in soil increased significantly in all the fertilizer and manurial treatments over recommended practice. The integrated use of GM and RSR in combination with chemical fertilizers improved the soil fertility status, as well as its physical environment. To sustain the soil health of rice–wheat system in loamy sand soil, it is imperative to apply GM and RSR in combination with chemical fertilizers. Also the increase in DTPA-extractable and total Zn, Cu, Fe, and Mn may be attributed to chelating action of organic compounds released from manures applied in the form of GM and RSR under rice–wheat system.

Spacecraft Maximum Allowable Concentrations for Manganese Compounds in Mars Dust.

INTRODUCTION: Exposure to excess manganese (Mn) can cause multiple toxicological outcomes in humans, most notably neurotoxicity. Ample epidemiological evidence suggests that chronic, low-level exposure causes subclinical cognitive effects. Because NASA astronauts will be exposed to Mars regolith, Spacecraft Maximum Allowable Concentrations (SMACs) were developed following an extensive literature review.METHODS: Multiple databases were searched for information relevant to derivation of Mn SMAC values. An additional search for Mars dust data was performed. Risk assessment approaches were applied, including adjustments for space-relevant susceptibility to Mn effects, to develop limits for 1-h to 1000-d exposures. Rover data informed the assessment and enabled calculation of allowable total dust exposure based on Mn content.RESULTS: Over 400 relevant sources were identified. Applicability of exposure characteristics and data collection methods influenced key study choice. SMACs ranging from 3 mg · m-3 (1 h) - 0.0079 mg · m-3 (1000 d) were set to protect primarily against neurocognitive and respiratory effects. Considering 0.38 wt% total Mn presence in the dust, maximum recommended total dust exposure should not exceed 790 mg · m-3 (1 h) - 2 mg · m-3 (1000 d).DISCUSSION: This literature review allowed for identification of relevant studies to inform SMAC development. Manganese is one of several components to consider when developing an appropriate total dust limit for Martian dust; other dust elements may alter Mn bioavailability. Mission-specific activities may require alteration of assumptions regarding Mn dust concentration and exposure duration. However, based on expected toxicity of particulate matter itself, the acute SMACs are protective, even with transient exposure during activities that could produce higher concentrations.Romoser AA, Ryder VE, McCoy JT. Spacecraft maximum allowable concentrations for manganese compounds in Mars dust. Aerosp Med Hum Perform. 2019; 90(8):709-719.

Accumulation and dynamics of manganese in raspberry

The aim of this study was to evaluate the dynamics of Mn in ‘soil - raspberry’ system on the area around the manganese ore deposits Radostovo in Bužim municipality. Atomic absorption spectroscopy was used to determine the concentration of Mn in soil and plant samples. Fe, Zn and Cu concentration in soil and raspberry plants was also subject of analysis, since these elements have antagonistic relationship with Mn in soils. The concentration of available Mn in soils was low, although the total Mn in the same soils exceeded the Mn toxic values noted in the scientific literature. The chemical and physical properties of the examined soils characterized by a relatively high pH value and good ability to store root-zone air certainly contributed to the decreasing release of available Mn2+ from manganese oxides in soils as well as Mn2+ oxidation to insoluble Mn3+ or Mn4+ ions, resulting in low uptake of Mn by plant roots. The results of study also showed that the absorbed Mn mostly accumulates in leaves and roots of raspberry, and much less in the stem and fruits. That rule in Mn distribution within raspberry plant is in fact identical to all food crops.

Field studies of manganese deposition and release in drinking water distribution systems: Insight into deposit control

Drinking water discoloration is one of the most common customer complaints. The accumulation of residual manganese (Mn) in drinking water distribution systems (DWDS) accounts for part of the discolored water that reaches household taps. Field studies were conducted at seven full-scale DWDS to investigate the deposition and release behaviors of Mn in different forms and at different concentrations in finished water. The results show that particulate Mn tended to accumulate in DWDS even at concentrations as low as 10 μg/L. The oxidation of soluble Mn(II) ions in DWDS was highly affected by water chemistries as well as water age; 10 μg/L of soluble Mn could still transform into particulate Mn under suitable conditions. When total Mn concentration in finished water was below 5 μg/L, erosion of Mn deposits occurred in DWDS with a Mn deposit inventory. Soluble Mn release was observed when chlorine or chlorine dioxide concentration was lower than 0.1 mg/L, and the release was speculated to be a result of microbial reductive dissolution of Mn oxides. Ensuring the total Mn concentration is below 10 μg/L and decreasing the particulate Mn concentration to 5 μg/L in finished water are both recommended to minimize Mn accumulation risk in DWDS. Enhanced oxidation and filtration for Mn removal during water treatment processes are proposed.

Indicators of Groundwater Evolution Processes Based on Hydrochemistry and Environmental Isotopes: A Case Study of the Dongyuan Drinking Water Source Area in Ji'nan City

The Dongyuan groundwater source area, which is the main drinking water source of Ji'nan City, is karst fissure water. To identify groundwater recharge sources, the influence of surface water, hydrochemical evolution, hydrochemical and isotopic components (2H and 18O) of groundwater and surface water samples collected from the Dongyuan groundwater source were investigated.The results showed that the hydrochemical characteristics of groundwater were similar, and the main ions were Ca2+, HCO3-, and SO42-. The groundwater, which suffered evaporation to varying degrees, was recharged mainly by precipitation. The hydrochemical composition of regional groundwater is mainly controlled by water-rock interactions, including dissolution/precipitation of carbonate minerals in the limestone aquifers and hydrolysis of silicates minerals in the quaternary aquifers, above the limestone aquifers. In some areas, groundwater was polluted by infiltration of river water. The main indicators of groundwater pollution that exceeded groundwater quality standards were total hardness, NO3-, NH4+, SO42-, Fe, and Mn.

Exploring the role of soil geochemistry on Mn and Ca uptake on 75-year-old mine spoils in western Massachusetts, USA.

Manganese pollution to plants, soils, and streams from Mn-rich mine spoils is a global and persistent issue. Some former mining sites can be revegetated readily while others struggle to support plants. We explored Mn in plants and soils following 75years of soil development and reforestation of a pine-northern hardwood forest at the former Betts Mine in western Massachusetts, USA. We studied soils on four Mn-rich mine spoils and at two control sites: an undisturbed location adjacent to the mine and on a non-Mn mineral bearing rock formation to determine if soil conditions have influenced the uptake of Mn and Ca by vegetation. We collected mid-season foliage from five dominant canopy trees and four common understory plants and excavated three soil pits at each site during July 2018. We found that control sites had lower total Mn (980 ± 140µgg-1) in their soils than on the mine spoil sites (5580 ± 2050µgg-1). Our soil data indicated that < 1% of total Mn was strong acid extractable at mine spoil soils and control sites. Surprisingly, the canopy trees established on mine spoils at the Betts Mine had equal to or lower foliar Mn concentrations (840 ± 149µgg-1) and lower Mn/Ca ratios (0.3 ± 0.1molmol-1) than at control sites (1667 ± 270µgg-1; 1.1 ± 0.2molmol-1), refuting our hypothesis of mine spoils driving highest Mn uptake. Soil pH and physicochemical properties suggest Mn primarily exists within primary minerals or form insoluble oxides at the mine spoil sites. Our results suggest higher Ca availability and pH in soils likely reduced Mn uptake and promoted reforestation of the mine spoils.

A simultaneous assessment of organic matter and trace elements bio-accessibility in substrate and digestate from an anaerobic digestion plant

This study evaluates a simultaneous assessment of organic matter (OM) and trace elements (TE) bio-accessibility in substrate and digestate from a full-scale anaerobic digester by a sequential OM extraction method. Simultaneous release of TE was determined along with the extraction of different OM fractions and the effects of extracting reagents on characteristics of OM were evaluated by nuclear magnetic resonance (NMR) spectroscopy. The reagents used for sequential extraction of OM were not enough selective. However, proteins were particularly removed by 0.1 M NaOH, while 72% H2SO4 mainly extracted hemicellulose and cellulose. The OM fractionation allowed for simultaneous extraction of >60% of total As, Cd, Co, Fe, Mn, Ni and Zn, while the extraction was limited for Al, Cr, Cu, Mo, and Pb. In substrate, >50% of total As, Co, Mn and Ni and <40% of total Fe, Zn and Mo were identified in bio-accessible fractions. In digestate, all elements demonstrated poor bio-accessibility except for As.

Nitrogen fertilizers promote plant growth and assist in manganese (Mn) accumulation by Polygonum pubescens Blume cultured in Mn tailings soil

This study examined how different nitrogen (N) forms and application levels promote plant growth and assist in manganese (Mn) remediation of Polygonum pubescens Blume (P. pubescens) cultured in soil with a high Mn level. The effects of ammonium chloride (a) and urea (u), at three application levels (10, 20, and 30 mg L−1 N) and control (no N addition, CK) on the growth, Mn accumulation, and enzymatic anti-oxidative defenses of P. pubescens were examined. In general, both ammonium-N and urea-N promoted the plant mass and height of P. pubescens. The total Mn amount of roots, stems, and leaves in N treatments were higher (p < 0.05) than that of CK. The ammonium-N treatments showed greater plant biomass and Mn accumulation compared to the urea-N ones. In general, the accumulations of Mn, Cr, Zn, and Cu were significantly lower (p < 0.05) in the N fertilizer treatment than those in the control; while the accumulations of Pb were higher (p < 0.05) in P. pubescens across all N fertilizer treatments than those in the control. The N addition decreased the contents of O2− and H2O2 in the leaves of P. pubescens, while increasing the activities of enzymatic anti-oxidative defenses.

Biological crusts enhance fertility and texture of gold mine tailings

Biological crusts (BCs) are reported to be soil ecological engineers critical in restoration of degraded ecosystems and rehabilitation of anthropogenic substrates, yet their occurrence and influence on such substrates is not well understood. We studied physical and chemical properties of biological crusts and layers immediately beneath them, compared with non-BC covered patches on two gold mine tailings dumps in tropical Zimbabwe. The aim was to determine the influence of biological crusts on fertility and texture of the substrate. We hypothesized that BCs alter tailings’ chemical and physical properties, yielding improved fertility and finer texture and that the fertility and finer particle content would decrease with depth. Physicochemical properties of tailings were studied within 36 quadrats, each 30 cm × 30 cm, across two gold tailings dumps from three patches, namely; (1) patches consisting of BCs only, (2) patches with both BCs and vegetation, and (3) non-BCs patches without vegetation. In each patch, we sampled the crust along with two layers immediately below (0–1 cm and 1–5 cm). Patch type had a significant effect on mineral and total N, exchangeable K, Ca and Mg, organic carbon (OC), available and total Zn and Mn, and available Ni. The interactive effect of patch type and layer was significant for all parameters except OC and electrical conductivity (EC). Total N, OC, exchangeable Ca, K and Mg and silt content were signficantly higher on the BC patches than the bare patches. Overall, a PCA based on soil properties showed that sites in the three patches were distinct. Our results concurred with our hypothesis and point to the existence of significant effect of BCs on underlying substrate fertility. Results revealed a potential role for BCs in the early development of tailings, notably in enriching the soil N, OC, and basic cations. We recommend close monitoring of the evolution of BC on gold tailings to develop approaches to effectively remediate such environments using BCs.

Manganese tolerance and accumulation characteristics of a woody accumulator Camellia oleifera

This study intended to help illustrate the Mn accumulation ability of Camellia oleifera and provide it as a novel species for possible use in Mn-contaminated sites. Field surveys have been carried out on Mn accumulation in C. oleifera growing near Mn mining area in Hezhou. Pot growth experiments in soil and sand culture were conducted to investigate Mn tolerance, accumulation, and translocation patterns in C. oleifera. C. oleifera grew well and showed no symptoms of Mn toxicity at a Mn treatment level below 1026mgkg-1 in soil culture and 15.0mmolL-1 in sand culture. Mn concentrations in leaves and stems reached a maximum of 9612.8 ± 83.5 and 6134.8 ± 94.0mgkg-1, respectively, in soil culture and 28,465.8 ± 1276.7 and 15,398.4 ± 1148.6mgkg-1, respectively, in sand culture. Meanwhile, most of the Mn taken from the substrates was transported to the aboveground tissues in soil and sand culture, e.g., over 92.07% of the total Mn taken up by C. oleifera was translocated to shoots in the 10.0mmolL-1 treatment. Our findings confirmed that C. oleifera exhibited extraordinary Mn accumulation and toleration abilities, and C. oleifera was a suitable species for phytoremediation of Mn-contaminated sites in Guangxi Province.

Long-term effects of intensive rice–wheat and agroforestry based cropping systems on build-up of nutrients and budgets in alluvial soils of Punjab, India

ABSTRACTA detailed study was conducted to investigate the long-term effects of rice–wheat and poplar-based agro-forestry systems existing on a large area for last 25 years on the distribution of macro as well as micronutrients in surface soils, as well as their profiles. To achieve these objectives, profile soil samples (0–150 cm) were collected from 10 randomly scattered locations each from rice–wheat and poplar-based agro-forestry systems and analyzed for various physico-chemical properties. The results of our investigation revealed that pH, EC, OC available N, P and K reported significantly higher levels in agro-forestry as compared to rice–wheat system. On the other hand, DTPA-extractable and total Zn, Cu, Fe and Mn were significantly higher in D1 (0–15 cm), D2 (15–30 cm) and D3 (30–45 cm) depths of rice–wheat system which may be attributed to the reduced conditions prevailing during rice crop. Nutrient budgeting also assessed the impact of crop removal and fertilizer inputs along with recycling of crop residue and leaf litter. Also, the build-up of available nutrient status in surface layer (0–15 cm) and soil profiles (0–150 cm) continuously under these two systems helped in maintaining agricultural sustainability and soil fertility over a long period of time.

Vertical distribution of microbial communities in chromium-contaminated soil and isolation of Cr(Ⅵ)-Reducing strains

Soil ecosystems surrounding chromium slag undergo continuous harsh physicochemical conditions due to multiple heavy metals contamination. Previous studies of soil microbial communities mainly focused on surface soil layer, while little was known about the depth-related distributions of the microbial communities in chromium (Cr)-contaminated soil. In this study, a comprehensive analysis of depth-related distributions of microbial communities in Cr-contaminated soil was carried out by Illumina sequencing of 16s rRNA genes. The results revealed that bacterial diversities at 0 cm depth layer were significantly higher than those below 20 cm depths. And there was a remarkable difference in bacterial compositions along with the sampling depths especially for the dominant phyla of Proteobacteria, Actinobacteria, Chloroflexi and Fimicutes (p < 0.05). While the archaea accounted for a relatively low proportion of the microbes and showed stability in the compositions with the predominant phyla of Thaumarchaeota and Euryarchaeota. The linear discriminate analysis (LDA) and effect size (LEfSe) analysis showed that there were thirty-seven kinds of biomarker microbes existing in the five soil layers with LDA threshold of 4.0, and each layer showed distinct microbial divisions, indicating that microbes with different biological functions might survive along with the sampling depths. The environmental variables including total chromium (Cr), Cr(Ⅵ), Mn, Ni, and Zn had considerable influences on microbial community composition in the contaminated soil. A total of 25 Cr(Ⅵ)-reducing strains were further isolated and identified, which were phylogenetically affiliated to Proteobacteria, Actinobacteria and Firmicutes. Among the isolated Cr(Ⅵ)-reducing strains, Bacillus stratosphericus was the first time to be reported with Cr(Ⅵ) reducing capacity.

Hypolimnetic oxygenation and aeration in two Midwestern USA reservoirs

Austin D, Scharf R, Chen C-F, Bode J. Hypolimnetic oxygenation and aeration in two Midwestern USA reservoirs. Lake Reserve Manage. 35:266–276.This study compares performance of hypolimnetic aeration (HA) with hypolimnetic oxygenation (HO) from 1988 to 2018, over multiple project phases and a baseline period 1984 to 1986. Saint Paul Regional Water Services, Minnesota, pumps 170 MLD (45 MGD) from the Mississippi River through a chain of 4 lakes before treatment. Two, Pleasant Lake and Vadnais Lake, were equipped with partial-lift HA later replaced by linear diffuser HO. Ferric chloride was injected into inflows and into Vadnais at the HA or HO system. HA failed to relieve hypolimnetic hypoxia in Pleasant (median DO 1.7 mg/L) or Vadnais (median DO 2.7 mg/L). Median HO values were aerobic (Pleasant 4.2 mg/L, Vadnais 8.5 mg/L). Both HA and HO raised hypolimnetic oxidation reduction potential to high positive values from negative values associated with Mn and Fe solubilization. Compared to HA, HO reduced median hypolimnetic total Mn concentrations by 75% in Pleasant and in 93% in Vadnais, and hypolimnetic total Fe by 84% in Pleasant and 81% in Vadnais. HA significantly lowered median hypolimnetic TP from baseline, 0.552 mg/L to 0.146 mg/L in Pleasant, and 0.533 mg/L to 0.045 mg/L in Vadnais. HO median hypolimnetic TP was significantly lower at 0.053 mg/L in Pleasant, 0.030 mg/L in Vadnais. Superior performance of HO occurred at similar oxygen delivery rates: 1775 kg/d in Pleasant and 970 kg/d in Vadnais, versus HA of 1200 kg/d in each lake. Performance differences are likely due to lower induced currents at the sediment surface by HO compared to HA.