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991.
部分氮杂环类化合物的遗传毒性及其QSAR研究 总被引:1,自引:0,他引:1
本文利用蚕豆细胞微核试验评价了10种氮杂环类化合物的遗传毒性,一化合物的最低未占据轨道能Elumo、分子的量负的原子净电荷q建立了较好的相关方程:MN=-2.96(1.14)+4.93(0.48)Elumo+13.68(2.72)q^-R^2=0.94 SE=0.71 F=53.92 P〈0.0005推测此类化合物的至于致毒机制可能是它们作为电荷给予体和氢键予体作用于生物受体而引起的突变。 相似文献
992.
研究了结缕草放牧草地根系层土壤氮素的季节性变化特征.结果表明:结缕草放牧草地根系层土壤的全氮量和C/N比值的变化与草地土壤总的肥力水平有关,同时也受到草地放牧的强度和历史的影响;但无机态氮(硝态氮和铵态氮)却较少受到这些因素的影响;铵态氮在根系层土壤的无机态氮总量中占优势.在所研究的放牧草地上,放牧牛在前一年排泄的粪斑对下一个生长季根系层土壤氮素水平的影响很小,因此,由粪斑引起的结缕草放牧草地根系层土壤氮素的空间异质性持续时间一般可能不会超过两个生长季.表1参10 相似文献
993.
Optimum Nitrogen Use and Reduced Nitrogen Loss for Production of Rice and Wheat in the Yangtse Delta Region 总被引:1,自引:0,他引:1
A long-term field and lysimeter experiment under different amount of fertilizer-N application was conducted to explore the optimal N application rates for a high productive rice–wheat system and less N leaching loss in the Yangtse Delta region. In this region excessive applications of N fertilizer for the rice–wheat production has resulted in reduced N recovery rates and environment pollution. Initial results of the field experiments showed that the optimal N application rate increased with the yield. On the two major paddy soils (Hydromorphic paddy soil and Gleyed paddy soil) of the region, the optimal N application rate was 225–270 kg N hm–2 for rice and 180–225 kg N hm–2 for wheat, separately. This has resulted in the highest number of effective ears and Spikelets per unit area, and hence high yield. Nitrogen leaching in the form of NO
3
–
-N occurs mainly in the wheat-growing season and in the ponding and seedling periods of the paddy field. Its concentration in the leachate increased with the N application rate in the lysimeter experiment. When the application rate reached 225 kg N hm–2, the concentration rose to 5.4–21.3 mgN l–1 in the leachate during the wheat-growing season. About 60% of the leachate samples determined contained NO
3
–
-N beyond the criterion (NO
3
–
-N 10 mg l–1) for N pollution. In the field experiment, when the N application rate was in the range of 270–315 kg hm–2, the NO
3
–
-N concentration in the leachate during the wheat-growing season ranged from 1.9 to 11.0 mg l–1. About 20% of the leachate samples reached close to, and 10% exceeded, the criterion for N pollution. Long-term accumulation of NO
3
–
-N from leaching will no doubt constitute a potential risk of N contamination of the groundwater in the Yangtse Delta Region. 相似文献
994.
不同氮浓度下三角褐指藻生长特性和化学组成 总被引:2,自引:0,他引:2
三角褐指藻是一类海洋单细胞硅藻,富含多不饱和脂肪酸,可以作为鱼、虾、贝等理想的饵料。而近年该藻曾多次在我国沿海海域发生暴发性增殖,给当地生态环境带来了一定的影响。为了探讨不同氮浓度对三角褐指藻生长特性和化学组成的影响,设置了低氮(44 μ mol.L-1)、中氮(880 μmol.L-1)和高氮(4 400 μmol.L-1)浓度三种处理,着重测定三角褐指藻的细胞密度、比生长率、生物量、可溶性糖、蛋白质含量和叶绿素含量等指标。结果表明,高氮浓度明显地促进了藻细胞的生长繁殖。高氮浓度下的藻细胞密度、比生长率和生物量分别比低氮浓度下的提高了 5.38 倍、0.81 倍和 2.86 倍。藻生长前期,高氮浓度和中氮浓度下的生长曲线相似,呈现一个"S"型的曲线。另外,高氮浓度下的藻细胞可溶性糖、蛋白质和叶绿素a含量分别是低氮浓度下的 2.5 倍、1.5 倍和 15 倍,说明高氮浓度促进了藻细胞化学组成的转化和积累。结果揭示,氮浓度可能是导致三角褐指藻近年在我国沿海海域发生暴发性增殖的重要因素。 相似文献
995.
996.
五里湖不同疏浚深度沉积物对氮磷释放的影响 总被引:4,自引:0,他引:4
对太湖东五里湖区污染沉积物样模拟了3种不同疏浚深度(0cm、30cm和60cm)下的60d形态氮磷释放实验,并对沉积物间隙水中氮磷的变化进行了分析。研究结果表明:疏浚与未疏浚比较,疏浚初期的0~10d内,沉积物对上覆水NH4 -N、NO2--N和TN释放增大,NO3--N释放减小,与疏浚后沉积物扩散层变薄和好氧环境的抑制有关,而对PO43--P、TP疏浚后次日出现短暂的释放现象外,此后均处于明显的磷释放受抑状态;疏浚约10d后,沉积物各氮磷形态释放出现分异现象,沉积物对水体的TN和TP释放受到显著抑制,其中20d后上覆水中NH4 -N含量的上升和PO43--P的缓慢增加,预示着底泥疏浚后仍有内源负荷回复的可能。 相似文献
997.
中国北方土壤硝态氮的累积及其对环境的影响 总被引:98,自引:0,他引:98
运用统计资料和调查研究资料,揭示中国氮肥用量在地区之间和作物之间分配的不平衡现象,经济发达的东南部地区和城郊地区氮肥施用量远高于西北部地区,经济作物远高于粮食作物,氮肥短缺和过量施用并存。中国北方某些地区土壤剖面硝态氯的大量累积对水体环境构成了某种程度的威胁。由于大田作物获得较高产量的“平均适宜施氮量(N150—180kg/hm^2)”与氮素环境安全指标尚有一定距离,中国完全可以实现水体环境安全和农业高产优质的双重目标。氮肥对水体环境的影响主要是由不合理大量施用氮肥造成的。因此,中国应制定施肥技术标准和法规,鼓励农民降低氮肥用量。 相似文献
998.
This paper reports the fluvial fluxes and estuarine transport of organic carbon and nutrients from a tropical river (Tsengwen River), southwestern Taiwan. Riverine fluxes of organic carbon and nutrients were highly variable temporally, due primarily to temporal variations in river discharge and suspended load. The sediment yield of the drainage basin during the study period (1995–1996, 616 tonne km–2 year–1) was ca. 15 times lower than that of the long-term (1960–1998) average (9379 tonne km2 year–1), resulting mainly from the damming effect and historically low record of river water discharge (5.02 m3 s–1) in 1995. The flushing time of river water in the estuary varied from 5 months in the dry season to >4.5 days in the wet season and about 1 day in the flood period. Consequently, distributions of nutrients, dissolved organic carbon (DOC) and particulate organic carbon (POC) were of highly seasonal variability in the estuary. Nutrients and POC behaved nonconservatively but DOC behaved conservatively in the estuary. DOC fluxes were generally greater than POC fluxes with the exception that POC fluxes considerably exceeded DOC fluxes during the flood period. Degradation of DOC and POC within the span of flushing time was insignificant and may contribute little amount of CO2 to the estuary during the wet season and flood period. Net estuarine fluxes of nutrients were determined by riverine fluxes and estuarine removals (or additions) of nutrients. The magnitude of estuarine removal or addition for a nutrient was also seasonally variable, and these processes must be considered for net flux estimates from the river to the sea. As a result, nonconservative fluxes of dissolved inorganic phosphorus (DIP) from the estuary are –0.002, –0.09 and –0.59 mmol m–2 day–1, respectively, for dry season, wet season and flood period, indicating internal sinks of DIP during all seasons. Due to high turbidity and short flushing time of estuarine water, DIP in the flood period may be derived largely from geochemical processes rather than biological removal, and this DIP should not be included in an annual estimate of carbon budget. The internal sink of phosphorus corresponds to a net organic carbon production (photosynthesis–respiration, p–r) during dry (0.21 mmol m–2 day–1) and wet (9.5 mmol m–2 day–1) seasons. The magnitude of net production (p–r) is 1.5 mol m–2 year–1, indicating that the estuary is autotrophic in 1995. However, there is a net nitrogen loss (nitrogen fixation–denitrification < 0) in 1995, but the magnitude is small (–0.17 mol m–2 year–1). 相似文献
999.
1000.
通过实验室血清瓶培养试验,研究了pH、碱度、FA、FN、HRT等因素对低氨氮、低碱度废水亚硝化过程的影响。研究结果表明:出水的pH值可以通过控制反应器内部的碱度来进行调节。控制进水碱度在113.1~269.7mg/L,HRT为48h,其亚硝酸累积率可达到67.15%。在氨氮亚硝化过程的同时,有部分有机氮也在向亚硝酸盐进行转化。通过污泥亚硝化驯化过程,游离氨对亚硝化单胞菌抑制浓度的临界值可以达到0.96mg/L。 相似文献