Multiple isotopes reveal the driving mechanism of high NO3- level and key processes of nitrogen cycling in the lower reaches of Yellow River

The continuous increase of nitrate (NO3-) level in rivers is a hot issue in the world. However, the driving mechanism of high NO3- level in large rivers is still lacking, which has limited the use of river water and increased the cost of water treatment. In this study, multiple isotopes and source resolution models are applied to identify the driving mechanism of high NO3- level and key processes of nitrogen cycling in the lower reaches of the Yellow River (LRYR). The major sources of NO3- were sewage and manure (SAM) in the low-flow season and soil nitrogen (SN) and chemical fertilizer (CF) in the high-flow season. Nitrification was the most key process of nitrogen cycling in the LRYR. However, in the biological removal processes, denitrification may not occur significantly. The temporal variation of contributions of NO3- sources were estimated by a source resolution model in the LRYR. The proportional contributions of SAM and CF to NO3- in the low-flow and high-flow season were 32.5%-52.3%, 44.2%-46.2% and 36.0%-40.8%, 54.9%-56.9%, respectively. The driving mechanisms of high NO3- level were unreasonable sewage discharge, intensity rainfall runoff, nitrification and lack of nitrate removal capacity. To control the NO3- concentration, targeted measures should be implemented to improve the capacity of sewage and wastewater treatment, increase the utilization efficiency of nitrogen fertilizer and construct ecological engineering. This study deepens the understanding of the driving mechanism of high nitrate level and provides a vital reference for nitrogen pollution control in rivers to other area of the world.

Spatial patterns in water quality and source apportionment in a typical cascade development river southwestern China using PMF modeling and multivariate statistical techniques

River cascade development is one of the human activities that have the most significant impact on the water environment. However, the mechanism of cascade development affecting river hydrochemical components still needs to be further studied. In this study, water quality index(WQI), positive matrix factorization(PMF) model and multivariate statistical techniques were used to identify the mechanism of cascade development affecting river hydrochemical components in an typical cascade development Rivers, Lancang River, China. The results showed that the water quality of Lancang River is relatively good due to less affected by human activity. The spatial variation of river hydrochemistry is affected by the development of cascade reservoirs, and shows three patterns: irregular variation (pH and DO), fluctuating decreasing (Na+, Cl-, SO42- and HCO3-) and multi-peak variation (TN, TDN, NO3--N and NH4+-N). It's worth noting that the concentration of the most hydrochemical parameters is higher in the upper reaches (less human activities) than that in the middle and lower reaches of river due to the retention effect of the reservoir on the chemical composition. The PMF model outputs revealed that the rock weathering and internal source, sewage and soil nitrogen, and chemical fertilizer were primary material sources of Lancang River. Compared with the natural channel zone (41.0%), the interaction of water-rock has more influence on chemical component in the reservoir area (56.3%), while the contribution of fertilizer (11.2%) to the river hydrochemistry is less. The sites of downstream of the reservoir dam were affected by the retention of the reservoir and the disturbance of the bottom drainage, which leads to the weakening of the influence of the sewage (44.7%) on the river material and the increase of the contribution of fertilizer (25.0%). These results could provide valuable information in controlling the eutrophication of cascade reservoirs and the scientific construction of river cascade reservoirs.

Research Advances in the Analysis of Nitrate Pollution Sources in a Freshwater Environment Using δ15N-NO3- and δ18O-NO3. Int J Environ Res Public Health 2021;18:ijerph182211805. [PMID: 34831560 PMCID: PMC8623930 DOI: 10.3390/ijerph182211805]

Nitrate is usually the main pollution factor in the river water and groundwater environment because it has the characteristics of stable properties, high solubility and easy migration. In order to ensure the safety of water supply and effectively control nitrate pollution, it is very important to accurately identify the pollution sources of nitrate in freshwater environment. At present, as the most accurate source analysis method, isotope technology is widely used to identify the pollution sources of nitrate in water environment. However, the complexity of nitrate pollution sources and nitrogen migration and transformation in the water environment, coupled with the isotopic fractionation, has changed the nitrogen and oxygen isotopic values of nitrate in the initial water body, resulting in certain limitations in the application of this technology. This review systematically summarized the typical δ¹⁵N and δ¹⁸O-NO₃^- ranges of NO₃^- sources, described the progress in the application of isotope technique to identify nitrate pollution sources in water environment, analyzed the application of isotope technique in identifying the migration and transformation of nitrogen in water environment, and introduced the method of quantitative source apportionment. Lastly, we discussed the deficiency of isotope technique in nitrate pollution source identification and described the future development direction of the pollution source apportionment of nitrate in water environment.

Genome-wide identification and characterization of microRNAs responding to ABA and GA in maize embryos during seed germination

MicroRNAs (miRNAs) are an important class of non-coding small RNAs that regulate the expression of target genes through mRNA cleavage or translational inhibition. Previous studies have revealed their roles in regulating seed dormancy and germination in model plants such as Arabidopsis thaliana, rice (Oryza sativa) and maize (Zea mays). However, the miRNA response to exogenous gibberellic acid (GA) and abscisic acid (ABA) during seed germination in maize has yet to be explored. In this study, small RNA libraries were generated and sequenced from maize embryos treated with GA, ABA or double-distilled water as control. A total of 247 miRNAs (104 known and 143 novel) were identified, of which 45 known and 53 novel miRNAs were differentially expressed in embryos in the different treatment groups. In total, 74 (37 up-regulated and 37 down-regulated) and 55 (23 up-regulated and 32 down-regulated) miRNAs were expressed in response to GA and to ABA, respectively, and a total of 18 known and 38 novel miRNAs displayed differential expression between the GA- and ABA-treated groups. Using bioinformatics tools, we predicted the target genes of the differentially expressed miRNAs. Using GO enrichment and KEGG pathway analysis of these targets, we showed that miRNAs differentially expressed in our samples affect genes encoding proteins involved in the peroxisome, ribosome and plant hormonal signalling pathways. Our results indicate that miRNA-mediated gene expression influences the GA and ABA signalling pathways during seed germination.

The MAGI2 gene polymorphism rs2160322 is associated with Graves' disease but not with Hashimoto's thyroiditis

PURPOSE

Autoimmune thyroid diseases (AITDs) are chronic organ-specific autoimmune disorders, predominantly including Graves' disease (GD), and Hashimoto's thyroiditis (HT). This study aimed to investigate whether single-nucleotide polymorphisms (SNPs) in MAGI2 and MAGI3 gene contributed to the etiology of AITDs.

METHODS

We conducted a case-control study including 1001 patients with AITDs (625 GD, 376 HT) and 846 healthy controls. Subgroup analyses in GD and HT were also performed.

RESULTS

The genotypes of rs2160322 in MAGI2 showed a borderline association with AITDs (P = 0.048), and they had a strong correlation with GD (P = 0.012). The frequency of the minor allele G of rs2160322 was significantly higher in the GD patients than in the controls (P = 0.027; OR 1.91; 95% CI 1.020-1.391), especially for GD females (P = 0.008; OR 1.304; 95% CI 1.072-1.587), and those who had positive family history (P = 0.011; OR 1.412; 95% CI 1.083-1.843). For genetic model analysis, the recessive model and homozygous model of rs2160322 showed significant associations with AITDs (P = 0.009; P = 0.019) and GD (P = 0.004; P = 0.005). Nevertheless, our study could not identify any relationship between these SNPs and HT. Due to the low mutation rate of rs1343126 in MAGI3, we were unable to obtain a credible conclusion on its association with AITDs.

CONCLUSIONS

Our study identified that MAGI2 rs2160322 was strongly associated with GD susceptibility. The potential dysfunction of tight junction proteins and aberrant epithelial barrier caused by abnormal MAGI2 expression may be a novel mechanism of GD.

Influence of grain orientations on the initiation of fatigue damage in an Al-Li alloy

The variation in microstructure and texture in a rectangular bar extruded from a billet of spray-cast 8090 Al-Li alloy has been examined. The fine grain size of the as sprayed billet and the moderate extrusion ratio ( approximately 25 : 1) were seen to cause geometric dynamic recrystallization (GDR) in regions of higher strain towards the edge of the bar. The grain morphology varied from the expected elongated grains at the centre of the bar to equiaxed grains where GDR occurred at the bar edges. A <111> + <100> double fibre texture, significantly distorted towards rolling components and varying through the bar thickness, was found using electron backscatter diffraction. Fatigue resulted in a high density of short secondary cracks, many of which had arrested at grain boundaries. The cracks preferentially nucleated in grains from the <100> fibre texture corresponding to high Schmid factors.

Nonlinear-optical studies of molybdenum metal organics

We have measured the third-order susceptibility, X((3)), versus concentration for a number of molybdenum-based metal-organic complexes in solution, using independent degenerate four-wave mixing and Z-scan techniques. Good agreement was obtained between the degenerate four-wave mixing and Z-scan measurements. The variation of X((3)) with concentration yielded the second-order hyperpolarizability gamma. A close correlation was observed between the number of delocalized pi electrons and the magnitude of gamma.