Detection of limited-energy α particles using CR-39 in laser-induced p −11B reaction

Due to the harsh radiation environment produced by strong laser plasma, most of the detectors based on semiconductors cannot perform well. So, it is important to develop new detecting techniques with higher detection thresholds and highly charged particle resolution for investigating nuclear fusion reactions in laser-plasma environments. The Columbia Resin No. 39 (CR-39) detector is mainly sensitive to ions and insensitive to the backgrounds, such as electrons and photons. The detector has been widely used to detect charged particles in laser-plasma environments. In this work, we used a potassium–ethanol–water (PEW) etching solution to reduce the proton sensitivity of CR-39, by raising the detection threshold for the research of laser-induced 11B(p, α)2α reaction. We calibrated the 3–5 MeV α particles in an etching condition of 60°C PEW-25 solution (17% KOH + 25%C2H5OH + 58%H2O) and compared them with the manufacturer’s recommended etching conditions of 6.25 N NaOH aqueous solution at 98°C in our laser-induced nuclear reaction experiment. The results indicate, with the PEW-25 solution, that CR-39 is more suitable to distinguish α tracks from the proton background in our experiment. We also present a method to estimate the minimum detection range of α energy on specific etching conditions in our experiment

Continuous time random walk model better describes the tailing of atrazine transport in soil

Contaminant transport in soils is complicated and involves some physical and chemical nonequilibrium processes. In this research, the soil column displacement experiments of Cl− and atrazine under different flow velocities were carried out. The data sets of Cl− transport in sandy loam fitted to the convection dispersion equation (CDE) and the two-region model (TRM) indicated that the effects of physical nonequilibrium process produced by immobile water on the breakthrough curves (BTCs) of Cl− and atrazine transport through the repacking soil columns were negligible. The two-site model (TSM) and the continuous time random walk (CTRW) were also used to fit atrazine transport behavior at the flow rate of 19.86 cm h−1. The CTRW convincingly captured the full evolution of atrazine BTC in the soil column, especially for the part of long tailing. However, the TSM failed to characterize the tailing of atrazine BTC in the soil column. The calculated fraction of equilibrium sorption sites, F, ranging from 0.78 to 0.80 for all flow rates suggested the contribution of nonequilibrium sorption sites to the asymmetry of atrazine BTCs. Furthermore, the data sets for the flow rates of 6.68 cm h−1 and 32.81 cm h−1 were predicted by the TSM and the CTRW. As to the flow rate of 6.68 cm h−1, the CTRW predicted the entire BTC of atrazine transport better than the TSM did. For the flow rate of 32.81 cm h−1, the CTRW characterized the late part of the tail better, while the TSM failed to predict the tailings of atrazine BTC

Spatio-Temporal Differences in Nitrogen Reduction Rates under Biotic and Abiotic Processes in River Water of the Taihu Basin, China

Understanding spatio-temporal differences in nitrogen (N) transformation, transport and reduction rates in water bodies is critical to achieve effective mitigation of river eutrophication. We performed culture experiments in six rivers in the Taihu Basin using a custom made in-situ experimental apparatus. We investigated spatio-temporal differences in reduce processes and rates of different N forms and assessed the contribution of biological processes to dissolved inorganic N (DIN) reduce. Results showed that biological processes played a major role in N reduction in summer, while non-microbial processes were dominant in winter. We observed significant spatial and temporal differences in the studied mechanisms, with reduction rates of different N compounds being significantly higher in summer and autumn than spring and winter. Reduction rates ranged from 105.4 ± 25.3 to 1458.8 ± 98.4 mg·(m3·d)−1 for total N, 33.1 ± 12.3 to 440.9 ± 33.1 mg·(m3·d)−1 for ammonium, 56.3 ± 22.7 to 332.1 ± 61.9 mg·(m3·d)−1 for nitrate and 0.4 ± 0.3 to 31.8 ± 9.0 mg·(m3·d)−1 for nitrite across four seasons. Mean DIN reduction rates with and without microbial activity were 96.0 ± 46.4 mg·(m3·d)−1 and 288.1 ± 67.8 mg·(m3·d)−1, respectively, with microbial activity rates accounting for 29.7% of the DIN load and 2.2% of the N load. Results of correlation and principal component analysis showed that the main factors influencing N processing were the concentrations of different N forms and multiple environmental factors in spring, N concentrations, DO and pH in summer, N concentrations and water velocity in autumn and N concentrations in winter

Niche analysis of dominant species in alpine desert grassland communities in Qaidam Basin

Community dominant plants and their ecological niche research is the focus of community ecology research. To explore the niche characteristics of desert dominant plants and the relationship between them and soil factors in Qaidam Basin, and to provide a basis for the construction of desert plant communities and the sustainable management of natural resources in Qaidam Basin. Taking 13 desert plant communities in Qaidam Basin, Qinghai Province as the research objects, this paper analyzed the characteristics of desert plant communities and dominant species based on soil physical and chemical properties, and calculated the niche width and niche overlap of dominant plants. The dominant plants are, Haloxylon ammodendron, Tamarix chinensis, Achnatherum splendens, Poacynum hendersonii, Reaumuria songonica, Phragmites australiss, Sympegma regelii, and Ajania Tenuifolia, Artemisia sphaerocephala, Ceratoides latens, Pearl russianthistle, Scirpustriquter. There were different degree of niche overlap among species in the community. In addition, CCA sequencing showed that different species had different requirements on the environment, and the distribution of dominant species was mainly affected by soil total nitrogen and soil organic matter

Variations in the Distribution of Chl-a and Simulation Using a Multiple Regression Model

Chlorophyll a (Chl-a) is an important indicator of algal biomass in aquatic ecosystems. In this study, monthly monitoring data for Chl-a concentration were collected between 2005 and 2015 at four stations in Meiliang Bay, a eutrophic bay in Lake Taihu, China. The spatiotemporal distribution of Chl-a in the bay was investigated, and a statistical model to relate the Chl-a concentration to key driving variables was also developed. The monthly Chl-a concentration in Meiliang Bay changed from 2.6 to 330.0 μg/L, and the monthly mean Chl-a concentration over 11 years was found to be higher at sampling site 1, the northernmost site near Liangxihe River, than at the three other sampling sites. The annual mean Chl-a concentration fluctuated greatly over time and exhibited an upward trend at all sites except sampling site 3 in the middle of Meiliang Bay. The Chl-a concentration was positively correlated with total phosphorus (TP; r = 0.57, p < 0.01), dissolved organic matter (DOM; r = 0.73, p < 0.01), pH (r = 0.44, p < 0.01), and water temperature (WT; r = 0.37, p < 0.01), and negatively correlated with nitrate (NO3−-N; r = −0.28, p < 0.01), dissolved oxygen (DO; r = −0.12, p < 0.01), and Secchi depth (ln(SD); r = −0.11, p < 0.05). A multiple linear regression model integrating the interactive effects of TP, DOM, WT, and pH on Chl-a concentrations was established (R = 0.80, F = 230.7, p < 0.01) and was found to adequately simulate the spatiotemporal dynamics of the Chl-a concentrations in other regions of Lake Taihu. This model provides lake managers with an alternative for the control of eutrophication and the suppression of aggregations of phytoplankton biomass at the water surface

Evaluation of Heavy Metal Level in Soil of Typical Alpine Grassland Communities

Objective: Through the investigation, determination and analysis of heavy metals in the soil of typical alpine grassland community, five kinds of alpine grasslands with different degeneration degree of Maduo County in Alpine area, two kinds of alpine grassland with high Maqu County, high Alpine desert along the coast of Qinghai Lake, alpine thickets in the yellow South region, Alpine wetlands, The condition of soil heavy metals in alpine meadow and other communities is analyzed, which provides scientific guidance for the ecological protection measures of typical alpine grassland communities, and provides a basis for the sustainable utilization of Alpine grassland. Methods: The content of various kinds of heavy metals in soil samples was determined by ICP-MS, and the pollution status of heavy metals was analyzed by means of single factor pollution index method, Nemero comprehensive pollution index method and potential ecological risk index method by using Excel. Results: (1) The content of Cd in Maduo, Maqu, Qinghai Lake and Huangnan was 1.74, 0.97, 1.84 and 1.06 times times the soil environment background respectively, and the content of Hg in Maqu was 1.36 times times that of soil environmental background value. The variation coefficient of Hg and Pb in Maqu and the coefficient of variation of Cd in Qinghai Lake are more than 100%, which is in the degree of high variation, which is greatly influenced by man. (2) The highest total pollution index in the 4 sample places was in the area of MA diversity, at 1.33. The second is the Huangnan sample, with an exponential value of 0.86. The Nemero comprehensive pollution Index of the Maqu sample is 0.77. The index value of Qinghai Lake sample is the lowest, at 0.61. (3) The highest potential ecological hazard index is the most diverse, in 0-10, 10-20, 20-30cm three soil layers are 96.96, 103.58, 102.46, Maqu in 0-10, 10-20cm soil, the potential ecological hazard index is 65.70, 71.01, the potential ecological hazard index of Huangnan in three soil layer is 78.23, 73.42 and 72.84 respectively, which refers to the smallest value of Qinghai Lake sample, three, 51.07 and 51.72 in 51.48 soil layer respectively. Conclusion: The Nemero comprehensive pollution Index of Qinghai Lake sample is less than 0.7, at the level of cleanliness, the exponential value of Huangnan and Maqu two samples is between 0.7~1, at the level of cordon, and the exponential value of ma variety is between 1~2, at the level of mild pollution. The comprehensive potential ecological hazard index of 80~160 has the potential ecological risk of strength, and the exponential value of the other three samples is between 40~80, which has medium potential ecological risk. Generally, the pollution degree of heavy metals is small in the whole alpine grassland area

Triolein Embedded Cellulose Acetate Membrane as a Tool to Evaluate Sequestration of PAHs in Lake Sediment Core at Large Temporal Scale

Although numerous studies have addressed sequestration of hydrophobic organic compounds (HOCs) in laboratory, little attention has been paid to its evaluation method in field at large temporal scale. A biomimetic tool, triolein embedded cellulose acetate membrane (TECAM), was therefore tested to evaluate sequestration of six PAHs with various hydrophobicity in a well-dated sediment core sampled from Nanyi Lake, China. Properties of sediment organic matter (OM) varying with aging time dominated the sequestration of PAHs in the sediment core. TECAM-sediment accumulation factors (MSAFs) of the PAHs declined with aging time, and significantly correlated with the corresponding biota-sediment accumulation factors (BSAFs) for gastropod (<i>Bellamya aeruginosa</i>) simultaneously incubated in the same sediment slices. Sequestration rates of the PAHs in the sediment core evaluated by TECAM were much lower than those obtained from laboratory study. The relationship between relative availability for TECAM (MSAF_t/MSAF₀) and aging time followed the first order exponential decay model. MSAF_t/MSAF₀ was well-related to the minor changes of the properties of OM varying with aging time. Compared with chemical extraction, sequestration reflected by TECAM was much closer to that by <i>B. aeruginosa</i>. In contrast to <i>B. aeruginosa</i>, TECAM could avoid metabolism and the influences from feeding and other behaviors of organisms, and it is much easier to deploy and ready in laboratory. Hence TECAM provides an effective and convenient way to study sequestration of PAHs and probably other HOCs in field at large temporal scale