Impact of nitrogen fertilizer source on nitrous oxide (N2O) emissions from three different agricultural soils during freezing conditions

ABSTRACT

Nitrogen (N) application is the main agricultural management that increases nitrous oxide (N₂O) concentration in the atmosphere. Freezing conditions are common phenomenon in the northern China that significantly affect soil N₂O emissions through alterations in nutrients availability and microbial population. To develop a comprehensive understanding of how N fertilizer managements affect soil N₂O emissions during the freezing process, a lab incubation was conducted in three typical cultivated soils (black soil, fluvo-aquic soil, or loess soil) by adding different N fertilizer sources, including ammonium chloride, sodium nitrate, or urea at different N levels (0, 80, 200, or 500 mg N/kg) at the start of freezing. The N₂O emissions in the fluvo-aquic soil were significantly higher than in other soils. The application of nitrate in the fluvo-aquic soil promoted N₂O emissions by five- and seven-fold higher compared to ammonium chloride and urea, whereas N₂O emissions in black soil were enhanced by application of ammonium chloride. Data indicate that denitrification is the major pathway for N₂O production in the fluvo-aquic soil during the freezing process, while ammonia oxidation responses accounts for elevated N₂O production in black soil. No significant influence of N fertilizer levels on N₂O emissions were found during soil freezing. These results suggest that agricultural practices that focus on mitigation of N₂O emissions need to avoid selection of nitrate as N fertilizer source in fluvo-aquic soil prior to the freezing season. Future studies need to focus on how the expression of enzymes and/or shifts in microbial communities respond to different N fertilizers during freezing conditions.     

Use of a seagrass residency index to apportion commercial fishery landing values and recreation fisheries expenditure to seagrass habitat service

Where they dominate coastlines, seagrass beds are thought to have a fundamental role in maintaining populations of exploited species. Thus, Mediterranean seagrass beds are afforded protection, yet no attempt to determine the contribution of these areas to both commercial fisheries landings and recreational fisheries expenditure has been made. There is evidence that seagrass extent continues to decline, but there is little understanding of the potential impacts of this decline. We used a seagrass residency index, that was trait and evidence based, to estimate the proportion of Mediterranean commercial fishery landings values and recreation fisheries total expenditure that can be attributed to seagrass during different life stages. The index was calculated as a weighted sum of the averages of the estimated residence time in seagrass (compared with other habitats) at each life stage of the fishery species found in seagrass. Seagrass‐associated species were estimated to contribute 30%–40% to the value of commercial fisheries landings and approximately 29% to recreational fisheries expenditure. These species predominantly rely on seagrass to survive juvenile stages. Seagrass beds had an estimated direct annual contribution during residency of €58–91 million (4% of commercial landing values) and €112 million (6% of recreation expenditure) to commercial and recreational fisheries, respectively, despite covering <2% of the area. These results suggest there is a clear cost of seagrass degradation associated with ineffective management of seagrass beds and that policy to manage both fisheries and seagrass beds should take into account the socioeconomic implications of seagrass loss to recreational and commercial fisheries.     

Characterization of odorants in contrasting ecotypes of Lake Taihu: algae-dominated versus macrophyte-dominated zones

Environmental Science and Pollution Research - Globally, odorant incidents are occurring at an increasing frequency, magnitude, and duration under the dual influences of eutrophication and climate...     

导识标识设置对教学楼通道疏散能力影响研究

本文以某学院6号楼为例,研究标识设置对教学楼通道疏散能力影响,测定了不同标识设置情况楼道人流时程,结果表明：自然状态人流速峰值66．8人／min,持时2．823min,拥堵明显;立体标识使人流速峰值提升3％,使峰值持时缩短51．65％,墙面平铺张贴标识使人流速峰值提升1％,使持时缩短44．07％,立体标识优于墙面平铺张贴标识;早期疏导标识使人流速峰值提升6％,使持时缩短60．93％,使峰值出现时刻比自然状态提前约31％,疏散效果明显。同时本文分析了现有标识设置的问题和弊端。     

笔谈:食物浪费

食物浪费是我们长期高度关注和社会发展迫切需要解决的问题,如何正确认识食物浪费并尽量减少食物浪费是研究的重点。文章认为食物浪费是一面折射社会文明的多棱镜,需要从多角度认识食物浪费产生的原因及后果,谨防减少食物浪费的努力变成更大的浪费,减少食物浪费要多管齐下,既要节约,又要推进健康饮食文化,借鉴国外研究方法和经验,填补中国食物浪费数据空白,构建资源智慧型食物系统。     

精冲盲孔工艺研究与应用

通过生产中的四个实例,论述了利用精冲工艺加工盲孔的生产工艺。精冲盲孔的凸凹模间的间隙值只能是被冲裁材料厚度的1％。模具的行程大小是决定精冲盲孔的关键。     

UASB技术处理中小城镇生活垃圾渗滤液的试验研究

本文针对目前中小城镇生活垃圾渗滤液处理的现状 ,运用上流式厌氧污泥床 (UASB)处理垃圾渗滤液 ,反应器容积 131.6 2 L ,发酵温度 17～ 31℃ ,进水 CODCr5 0 0 0～ 12 0 0 0 mg/L ,有机负荷 7～ 12 Kg CODCr(m3· d) ,HRT为 19～2 7h,CODCr去除率达到 90 % ,取得较好的效果。并研究了系统的启动控制条件及有机污染物去除效果影响因素 ,获得了重要的控制参数 ,如运行温度、容积负荷率、水力停留时间、污泥负荷率等 ,为 UASB处理垃圾渗滤液找到了可行的途径。     

城市园林植物生态功能及其评价与优化研究进展

城市当前面临着越来越严重的环境问题.园林植物因其碳氧平衡、蒸腾吸热、吸污滞尘、减菌减噪、涵养水源、土壤活化和养分循环、维持生物多样性、景观功能、防灾减灾等生态功能在缓解城市环境压力方面起着至关重要的作用.为了使城市园林植物生态功能最大限度地发挥和城市生态环境得到较大改观,综述了国内外在城市园林植物生态功能及其评价与优化等方面的最新研究成果,分析研究中存在的不足之处.     

核-壳型纳米双金属微粒的研究进展

纳米材料以其独特的性质，在光学、化工、环保、陶瓷、生物和医药等诸多方面具有广泛的应用价值。而纳米金属材料的表面包覆和修饰是21世纪纳米材料科学的一个新的研究方向。文中比较系统地综述了核-壳型纳米双金属微粒制备方法的研究进展，包括还原化学镀法、共沉淀法等，简要分析了各类制备方法的基本原理、特点及适用的范围，并在此基础上讨论了核-壳型纳米双金属粉末的未来研究发展方向。     

联合多种荧光光谱和GC-MS研究高铁酸钾对菲的降解机理

研究了高铁酸钾对PAHs中的菲的降解反应过程,对该反应过程联合了时间扫描、偏振、偏振三维(PEEM)、三维(EEM)等多种荧光光谱模式进行了表征和分析,并结合GC-MS进一步检测分析了该反应过程的中间产物,最后系统探讨了高铁酸钾对菲降解的动力学反应规律及降解机理.实验结果表明,在设定的高铁酸钾-菲降解体系的物质的量之比为1∶1、1∶2、1∶3、2∶1、3∶1的各个降解反应过程均符合一级反应动力学特征,其拟合系数在0.905—0.995之间.通过不同摩尔比的高铁酸钾-菲降解过程的时间扫描荧光参数直接求得了各反应的动力学方程及曲线;菲降解过程的荧光偏振度值与PEEM共同揭示出高铁酸钾对菲的有效降解,且产物均为无偏振效应、无产生新的特征荧光的小分子结构,各特征光谱峰强与时间变化关系也与时间扫描荧光曲线相符合;最后结合GC-MS深入分析了菲的降解产物,并由此推测了高铁酸钾对菲的降解机理.降解产物中9,10-菲醌的大量存在表明菲结构中9,10位发生氧化而开始降解.