As natural selenium (Se)-rich soil in China is generally characterized by a high geological background of cadmium (Cd), the safe utilization of such seleniferous soil remains a challenge. The accumulating evidence shows that the threshold value of the Se:Cd ratio is a determinant of regulating Cd accumulation in plants. However, the factors modulating the soil’s Se:Cd ratio in selenium-enriched regions are not well understood. Here, a comprehensive study aimed at quantitatively analyzing the effects of land-use types, parent-material types, and soil properties on the distribution and influencing factors of Se, Cd, and the Se:Cd ratios. According to land use and parent-material types, 77 soil samples were collected in Yuanzhou District, a typical naturally seleniferous area in the subtropical hilly area. The results suggested that, compared with quaternary red clays (qrc), the Se content of soils derived from river and lake sediments (rls) and weathered acidic crystalline rocks (wacr) decreased by 5.81%–19.75%, while the weathered quartzite (wq)-derived soils was increased significantly. The soil Cd content in an orchard was significantly reduced compared with that in a paddy field. A redundancy analysis (RDA) revealed that SOM, Total K, and Total P significantly affected the changes in Se and Cd contents. In addition, the land-use type had the most significant effect on the Se:Cd ratio, with a regression coefficient of −0.6999 analyzed by the binary logistic regression model (p < 0.05). Furthermore, pH and Total K were the critical soil properties in controlling the Se:Cd ratio. The study indicated that the Se:Cd ratio in natural selenium-rich soil was mainly regulated by land-use types. Therefore, it is a feasible measure to regulate the Se:Cd ratio by using agronomic practices, mainly regulating soil pH, for the safe utilization of selenium-rich soil with a high Cd background.
The lotus (Nelumbo nucifera Gaertn.) is an aquatic plant that grows in shallow water and has long been cultivated in South China. It can improve the incomes of farmers and plays an important role in alleviating poverty in rural China. However, a modern method is required to accurately estimate the area of lotus fields. Lotus has spectral characteristics similar to those of rice, grassland, and shrubs. The features surrounding areas where it is grown are complex, small, and fragmented. Few studies have examined the remote sensing extraction of lotus fields, and automatic extraction and mapping are still challenging methods. Here, we compared the spectral characteristics of lotus fields and other ground objects and devised a remote sensing method for the rapid extraction of lotus fields. Using this method, the extraction accuracy of lotus was 96.3%. The Kappa coefficient was 0.926, which is higher than those of the unsupervised K-means classification, Mahalanobis distance, and support vector machine supervised classification, and demonstrates the potential of this method for extracting and mapping lotus fields by remote sensing.
This paper discussed the preparation of modified activated carbon (PAC-1) and its adsorption performance for nitrosodiethylamine (NDEA). The PAC-1 was characterized by SMS and X-ray diffractometer, and its NDEA removal mechanism was investigated. The results showed that, compared with unmodified activated carbon, PAC-1 had a better adsorption effect for NDEA after pre-soaking with 0.8 mol/L permanganate (PM) for 24 hours and calcination at 400 °C for 7 hours. Under the conditions of 8 g/L PAC-1 dosage, pH = 6, and adsorption time of 6 h, the adsorption rate of NDEA with an initial concentration of 50 mg/L reached 78.66%, the maximum equilibrium adsorption capacity was 4.916 mg·g−1, and the adsorption rate of unmodified activated carbon to NDEA was increased by 42.5%. The number of oxygen-containing surface functional groups of activated carbon was increased after permanganate prepreg, which can enhance the NDEA adsorption rate. The adsorption process of NDEA on modified activated carbon conforms to pseudo-second-order kinetics, and the adsorption isotherm corresponds to the Freundlich model.
This paper simulates sediment motion under different hydrodynamic conditions, aiming to investigate the release flux of heavy metals in river sediments. During the lab experiments, carried out in a circular rectangular flume device, water velocity in the flume was altered by controlling the gate switch, and the flow rate was controlled from 0 to 1 m/s. Sediment from the Le'an River and chlorine-removed tap water were used as experimental sediment and water, respectively. Through analyses of Cu, Zn, Cd, and Pb concentration in water at different flow rates, the relationship between the release flux (y) of Cu, Zn, Cd, and Pb and the flow rate (x) was established with a fitting error of less than 15%. In order to judge the reliability of the conclusions, experimental results were verified outdoors. The results showed when the sediment particle size is between 0 and 250 μm, within 1 hour, a quadratic polynomial correlation between the release flux of Cu, Cd, and Pb from river sediments and water velocity when the water pH is 5–9 and the flow rate is 0–65 cm/s; when the water pH is 5–9, the flow rate is 0–35 cm/s, the release flux of Zn from river sediments was shown to have a quadratic polynomial relationship with water velocity. The error between the calculated and measured values of heavy metals released from sediment in the Le'an River were within 5–30%. Our results can provide a theoretical reference for the control and treatment of heavy metal pollution in rivers and further improve corresponding water quality models.
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