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141.
142.
Ning Zong Peili Shi Minghua Song Xianzhou Zhang Jing Jiang Xi Chai 《Environmental management》2016,57(3):531-542
143.
Applying Statistical Causal Analyses to Agricultural Conservation: A Case Study Examining P Loss Impacts 下载免费PDF全文
Song S. Qian R. Daren Harmel 《Journal of the American Water Resources Association》2016,52(1):198-208
Estimating the effect of agricultural conservation practices on reducing nutrient loss using observational data can be confounded by factors such as differing crop types and management practices. As we may not have the full knowledge of these confounding factors, conventional statistical meta‐analysis methods can be misleading. We discuss the use of two statistical causal analysis methods for quantifying the effects of water and soil conservation practices in reducing P loss from agricultural fields. With the propensity score method, a subset of data was used to form a treatment group and a control group with similar distributions of confounding factors. With the multilevel modeling method, data were stratified based on important confounding factors, and the conservation practice effect was evaluated for each stratum. Both methods resulted in similar estimates of the conservation practice effect (total P load reduction avg. ~70%). In addition, both methods show evidence of conservation practices reducing the incremental increase in total P export per unit increase in fertilizer application. These results are presented as examples of the types of outcomes provided by statistical causal analyses, not to provide definitive estimates of P loss reduction. The enhanced meta‐analysis methods presented within are applicable for improved assessment of agricultural practices and their effects and can be used for providing realistic parameter values for watershed‐scale modeling. 相似文献
144.
Yongxiang Han Xiaomin Fang Tianliang Zhao Huzhi Bai Shichang Kang Lianchun Song 《Atmospheric environment (Oxford, England : 1994)》2009,43(3):568-574
Dust aerosols play an important role in modulating the hydrologic cycle. The Tibetan Plateau (TP) is little polluted by human activities as an ideal site to study the effect of dust aerosol on precipitation. In this study, observational data of dust storms and precipitation in the TP and its vicinities as well as CALIPSO satellite data were used to analyze the distributions and vertical structure of dust storms on the plateau. The results showed that dust storms occur with high frequency and raise dust particles into the troposphere from ground level to a height of 5–9 km to modulate the hydrologic cycle in the TP. There are significant negative correlations between dust aerosol and precipitation in the dust source regions during the period of both 40 and 200 years. It is found that the role of precipitation in suppressing dust storms could be unimportant, while dust aerosol may play an important role in suppressing precipitation in the hinterland of the TP. Our study provides a potential approach to better understand the climate changes in the TP. 相似文献
145.
Zhi-Ping Wang Yang Song Jay Gulledge Qiang Yu Hong-Sheng Liu Xing-Guo Han 《Atmospheric environment (Oxford, England : 1994)》2009,43(13):2148-2153
A budget for the methane (CH4) cycle in the Xilin River basin of Inner Mongolia is presented. The annual CH4 budget in this region depends primarily on the sum of atmospheric CH4 uptake by upland soils, emission from small wetlands, and emission from grazing ruminants (sheep, goats, and cattle). Flux rates for these processes were averaged over multiple years with differing summer rainfall. Although uplands constitute the vast majority of land area, they consume much less CH4 per unit area than is emitted by wetlands and ruminants. Atmospheric CH4 uptake by upland soils was ?3.3 and ?4.8 kg CH4 ha?1 y?1 in grazed and ungrazed areas, respectively. Average CH4 emission was 791.0 kg CH4 ha?1 y?1 from wetlands and 8.6 kg CH4 ha?1 y?1 from ruminants. The basin area-weighted average of all three processes was 6.8 kg CH4 ha?1 y?1, indicating that ruminant production has converted this basin to a net source of atmospheric CH4. The total CH4 emission from the Xilin River basin was 7.29 Gg CH4 y?1. The current grazing intensity is about eightfold higher than that which would result in a net zero CH4 flux. Since grazing intensity has increased throughout western China, it is likely that ruminant production has converted China's grazed temperate grasslands to a net source of atmospheric CH4 overall. 相似文献
146.
对生物膜填料塔对模拟烟气和电厂烟气的净化效果进行了实验研究。实验对比分析了在相同的实验条件下生物膜填料塔对不同烟气中SO2和NOx的净化效率。实验结果表明,在循环液温度在24~35℃、空床停留时间(EBRT)为60s、喷淋量为8~10L/h、脱硫塔的pH为0.8~1.5、脱氮塔的pH为7.5~8.0的条件下,生物膜填料塔对模拟烟气和电厂烟气中SO2的净化效率都很高,但模拟烟气条件下的总脱氮率的平均值为80%,而在电厂烟气条件下只有35%。经分析认为,脱氮率产生差异的主要原因是电厂烟气中杂质的影响,以及烟气中氧气含量的不同,同时因为生长条件不同从而驯化出的微生物群体组成也不同。 相似文献
147.
光催化过程中羟基自由基的产生与效能 总被引:1,自引:0,他引:1
采用异丙醇淬灭的方法考察了羟基自由基在光催化氧化酸性橙II过程中的产生和效能,研究了TiO2(P-25)的浓度、异丙醇的用量、酸性橙II的初始浓度、初始pH条件和天然共存离子对羟基自由基贡献率的影响。结果表明,在TiO2(P-25)浓度提高时羟基自由基的贡献率逐步提高并稳定在77.6%,异丙醇的投加量对羟基自由基的贡献率影响不大,酸性橙II初始浓度的提高则使羟基自由基的贡献率降低。在中性pH条件下羟基自由基的贡献率最高,酸性或碱性条件下较低。天然共存离子中HCO3-对羟基自由基的淬灭效应最强,F-的淬灭效应最弱。 相似文献
148.
149.
150.
Da Chen Bixian Mai Jie Song Eddy Y. Zeng 《Environmental pollution (Barking, Essex : 1987)》2009,157(7):2023-2029
Little data are available on organochlorine contamination in Chinese terrestrial birds of prey. This study examined the presence of PCBs, DDTs and other organochlorine pesticides in various raptors from northern China. DDE exhibited the highest concentrations among targeted compounds. Greatest levels (23.5-1020 mg/kg lipid weight) were observed in Eurasian sparrowhawks. This may be due to their stopover in southeastern China, where high DDT and dicofol applications have been documented. Residential kestrels exhibited much lower DDE, but similar PCB and HCH concentrations. ΣTEQs and PCB-126/-77 concentration ratios exhibited significant positive correlations with ΣPCB concentrations, respectively. Similar results were also demonstrated by a meta-analysis of previously published data across avian species. Possible hepatic sequestration of coplanar PCB-77, -126, -169 and -118 was observed as liver TEQs increased in Eurasian sparrowhawks. These observations may indicate an induction of CYP1A enzymes, as a result of elevated contamination in some species. 相似文献