铁基硅盐对土壤环境镉砷赋存形态及转化影响

为探明铁基硅盐对土壤镉砷赋存形态影响及各形态间转化规律,采用室内长期淹水培养吸附实验,研究不同比例铁硅材料对土壤离子态镉砷活性影响;筛选适宜铁基硅盐(FS)配比同时添加腐殖酸(FSC)和金属氧化物(FSCa),明确复配处理土壤中镉砷分级形态转化程度.结果显示,铁:硅比值增加10%,土壤pH值平均降低0.35;F₂-S₈处理土壤离子态镉降幅71%;F₁₀-S₀处理土壤离子态砷降低59.9%,离子态镉砷含量与硅酸盐-铁盐施用量互呈反比;处理F₄-S₆和F₆-S₄之间镉、砷钝化率产生交点,约为25%~30%.土壤中镉主要以可溶态为主,占比58%;砷主要以铁铝氧化态和钙结合态为主,占比40%和23%.铁硅比例为5:5或5.5:4.5左右复配能有效将铝结合态砷和铁铝氧化态砷转变为钙结合态砷和残渣态砷,可溶态镉转化为碳酸盐结合态镉以及铁锰氧化态镉,同步降低土壤中镉砷的活性.     

Cultivar-dependent rhizobacteria community and cadmium accumulation in rice: Effects on cadmium availability in soils and iron-plaque formation

The association between the rhizospheric microbial community and Cd accumulation in rice is poorly understood. A field trial was conducted to investigate the different rhizobacterial communities of two rice cultivars with high Cd accumulation (HA) and low Cd accumulation (LA) at four growth stages. Results showed that the Cd content in the roots of the HA cultivar was 1.23 - 27.53 higher than that of the LA cultivar (0.08 - 10.5 µg/plant) at four stages. The LA cultivar had a significantly lower Cd availability in rhizosphere and a higher quantity of iron plaque (IP) on the root surface than the HA cultivar at four stages. This resulted in the reduction of Cd concentration in IPs and Cd translocation from IP-to-root. Microbial analysis indicated that the LA cultivar formed a distinct rhizobacterial community from the HA cultivar and had less α-diversity. The rhizosphere of the LA cultivar was enriched in specific bacterial taxa (e.g., Massilia and Bacillus) involved in Cd immobilization by phosphate precipitation and IP formation by iron oxidization. However, the rhizosphere in the HA cultivar assembled abundant sulfur-oxidizing bacteria (e.g., Sulfuricurvum) and iron reduction bacteria (Geobacter). They promoted Cd mobilization and reduced IP formation via the metal redox process. This study reveals a potential approach in which specific rhizobacteria decrease or increase Cd accumulation in rice on contaminated soil and provides a new perspective for secure rice production.     

SiO2气凝胶隔热性能的影响因素研究

目的 在不同热流条件下,通过调整SiO2气凝胶的孔隙率、涂层厚度等,以满足合适的隔热要求。方法 针对中短程飞行器飞行时外壁面承受短时高热流的特点,在分析孔隙率对SiO2气凝胶热导率影响规律的基础上,通过数值仿真研究不同气凝胶孔隙率、气凝胶厚度及热流作用下的温度响应。结果 得到了不同条件下满足隔热要求的气凝胶最小厚度,以及气凝胶表面的最高温度。高温情况下,气凝胶孔隙率为96%时,有效热导率最低,孔隙率超过96%时,隔热性能变差。结论 当飞行器内壁面温度满足要求时,增大气凝胶的孔隙率,则需要减小气凝胶的厚度,相应的气凝胶表面温度会升高,但升幅很小。当飞行器外壁面承受长时间大热流时,仅调整气凝胶的厚度和孔隙率不能达到结构的隔热要求。     

The legacy of large dams in the United States

The sustainability of large dams has been questioned on several grounds. One aspect that has been less explored is that the development of dams and reservoirs often enables agricultural expansion and urban growth, which in turn increase water consumption. As such, dam development influences, while being influenced by, the spatial and temporal distribution of both supply and demand of water resources. In this paper, we explore the interplay between large dams, patterns of population growth and agricultural expansion in the United States over the past two centuries. Based on a large-scale analysis of spatial and temporal trends, we identify three distinct phases, in which different processes dominated the interplay. Then, we focus on agricultural water use in the Southwest region (Arizona, California and Nevada) and explore chicken-and-egg dynamics where water supply partly meets and partly fuels water demand. Lastly, we show that the legacy of dams in the United States consists of a lock-in condition characterized by high levels of water consumption, especially in the Southwest, which leads to severe water crises and groundwater overexploitation when droughts occur.     

A Call for Urgent Monitoring of Food and Water Security Based on Relevant Indicators for the Arctic

This perspective paper argues for an urgent need to monitor a set of 12 concrete, measurable indicators of food and water security in the Arctic over time. Such a quantitative indicator approach may be viewed as representing a reductionist rather than a holistic perspective, but is nevertheless necessary for actually knowing what reality aspects to monitor in order to accurately understand, quantify, and be able to project critical changes to food and water security of both indigenous and non-indigenous people in the Arctic. More relevant indicators may be developed in the future, taking us further toward reconciliation between reductionist and holistic approaches to change assessment and understanding. However, the potential of such further development to improved holistic change assessment is not an argument not to urgently start to monitor and quantify the changes in food and water security indicators that are immediately available and adequate for the Arctic context.     

Precious metals and rare earth elements in municipal solid waste – Sources and fate in a Swiss incineration plant

In Switzerland many kinds of waste, e.g. paper, metals, electrical and electronic equipment are separately collected and recycled to a large extent. The residual amount of municipal solid waste (MSW) has to be thermally treated before final disposal. Efforts to recover valuable metals from incineration residues have recently increased. However, the resource potential of critical elements in the waste input (sources) and their partitioning into recyclable fractions and residues (fate) is unknown. Therefore, a substance flow analysis (SFA) for 31 elements including precious metals (Au, Ag), platinum metal group elements (Pt, Rh) and rare earth elements (La, Ce, etc.) has been conducted in a solid waste incinerator (SWI) with a state-of-the-art bottom ash treatment according to the Thermo-Re® concept. The SFA allowed the determination of the element partitioning in the SWI, as well as the elemental composition of the MSW by indirect analysis. The results show that the waste-input contains substantial quantities of precious metals, such as 0.4 ± 0.2 mg/kg Au and 5.3 ± 0.7 mg/kg Ag. Many of the valuable substances, such as Au and Ag are enriched in specific outputs (e.g. non-ferrous metal fractions) and are therefore recoverable. As the precious metal content in MSW is expected to rise due to its increasing application in complex consumer products, the results of this study are essential for the improvement of resource recovery in the Thermo-Re® process.     

Effect of environmental forcing on the fate of nutrients, dissolved organic matter and heavy metals released by a coastal wastewater pipeline

Discharges of nutrients, urea, dissolved organic matter and heavy metals by a sewage underwater pipeline are analysed in comparison to environmental conditions in a shallow coastal zone. Variable thermo-haline stratifications of the water column and currents in upper (2.62-34.97 cm s^-1) and deeper (0.83-10.91 cm s^-1) layers drive vertical diffusion and lateral transport of wastewaters. Loads of reactive phosphorus (0.13 tons d^-1) and ammonium (1.62 tons d^-1) by the pipeline are not negligible compared to the major river loads in the gulf. High concentrations of urea (≤11.51 μmol N dm^-3) were found in the area of wastewater release. Ammonium uptake (6.14-534 nmol N dm^-3 h^-1) strongly exceeded nitrate uptake (0.19-138 nmol N dm^-3 h^-1), indicating that discharges of ammonium by the pipeline are actively assimilated by plankton community even at low levels of light. Distribution of Zn (≤27.7 ppb), Cu (≤25.6 ppb), Cd (≤0.80 ppb) and Pb (≤13.5 ppb) in the water column and the measurement of their complex-forming capacity in seawater did not indicate a persistent perturbation of the pelagic environment due to heavy metals.