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21.
Agriculture as a source of phosphorus causing eutrophication in Central and Eastern Europe 总被引:5,自引:0,他引:5
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Harald Köthe 《Journal of Soils and Sediments》2006,6(2):75-83
Background Under anoxic conditions typically prevailing in disposal sites for dredged sediment, methanogenesis is the terminal step
during microbial degradation of sediment organic matter. Sediment gas production may pose several problems to site management
and post-closure utilisation. Depending on the magnitude of gas/methane formation and the intended utilisation of the site,
countermeasures will have to be effected during and after deposition of the dredged material. For this purpose it may be of
interest to pre-estimate the extent of gas formation from simple sediment variables. Therefore, the aim of the investigations
presented here was to analyse the interrelations between gas formation and sediment physical, chemical and biological qualities.
Methods Freshly sampled riverbed sediment from nine German federal waterways was analysed for standard solid physical and chemical
parameters, pore water composition, cell counts of methanogenic and sulfate-reducing bacteria, and gas formation over a period
of 500 days. Particle size and density fractionation were carried out in order to characterise organic matter quality. Correlations
between methane formation and sediment chemical, physical and microbiological characteristics were tested using linear and
multiple correlation analysis.
Results and Discussion The selected sediments, including two with marine influence, differed strongly regarding texture, chemical parameters, pore
water composition, and methanogen cell counts. The course of methane formation was found to follow distinct phases. The commencement
of methane formation was preceded by a lag phase of variable duration. The lag phase was followed by a strong increase of
the methane formation rate up to a sediment-characteristic maximum of 5–30 nmol CH4 h–1 g dw–1. Eventually, the rate of methane
formation decreased and reached a more stable, long-term level. The extent and amplitude of each phase varied strongly between
sediments and could be correlated well with only a few standard analytical parameters, despite the strong heterogeneity of
sediment with respect to chemical, physical, and biological characteristics. Lag phase duration depended strongly on the content
of inorganic electron acceptors and also on the number of methanogens present at the beginning of the experiment. Maximum
and steady state methanogenesis were mainly determined by sediment total nitrogen. As analysis of sediment density fractions
revealed that total nitrogen reflected the share of readily degradable macroorganic matter.
Conclusion and Outlook The results imply that the observed methane formation is a function of the temporally changing balance of the availability
of electron acceptors and H2, and the share of easily degradable organic matter. For fresh riverbed sediments, the latter
may be deduced from total nitrogen content. Overall, the results showed that methane formation by freshly dredged material
may well be pre-estimated from standard analytical data within the first few years of deposition. However, the differently
degradable organic matter pools will change over time with respect to size, chemical nature and association with the sediment
mineral phase. It can thus be expected that the correlations found in this study will not be readily transferable to older
materials. Further studies on the gas formation and organic matter quality by older sediments, e.g. from older dredged material
disposal sites of known age, should be conducted and results should be combined with existing organic matter degradation models
in order to improve the prediction of sediment gas formation over time. 相似文献
24.
Jiongxin Xu 《CATENA》2002,49(4)
According to the yearly maximum suspended sediment concentrations (SSC) in the Yellow River and its tributaries, the rivers are divided into three types of more than 300, 20–300, and less than 20 kg/m3. The middle Yellow River basin is located in the transitional zone from subhumid to semiarid climates, and covered by a thick loess mantle. Neighboring on the desert areas to the northwest, the surface material of the Loess Plateau exhibits some marked areal differentiation in grain size and forms three zones covered by sandy loess, (typical) loess and clayey loess from northwest to southeast. Controlled by these physico-geographical conditions, the grain size of river-transported sediment shows some particular characteristics; at small water discharge or SSC, the grain size of suspended sediment abruptly decreases to a minimum with increasing water discharge or SSC. At water discharge of more than ca. 40 m3/s or at SSC of more than ca. 40 kg/m3, the grain size increases with water discharge or SSC.During the low-stage season, the relatively clear baseflow may scour the coarse bed materials, so the suspended sediment is relatively coarse. In the rainy season, rainstorm runoff washes out fine loess materials to the river, making suspended sediment fine. During relatively strong rainstorms, there often occur hyperconcentrated flows at SSC of more than 300 kg/m3. The relatively coarse grains could then remain suspended in the mixture of water and fine suspended sediment. 相似文献
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26.
汽车变速器的关键部件齿轮因其加工和装配质量的影响,工作时容易引起振动噪声大及承载能力降低等问题,而齿轮修形是解决这些问题的有效方法,且成本较低。针对某款汽车变速器,利用Romax对齿轮进行修形分析。结果表明,修形后减小了齿轮的传动误差和最大接触应力,齿面载荷分布更加合理。有效改善了齿轮的传动性能,增加了齿轮寿命。 相似文献
27.
[目的]探讨磷石膏改良吹填土的机理。[方法]通过室内模拟脱盐试验,探讨磷石膏对吹填土理化性质的改良效果。[结果]施用磷石膏可提高吹填土的脱盐速率,以混施效果最好,与对照相比差异达0.01显著水平;磷石膏的施入使单位体积水量的淋盐效率下降,增加淋洗用水量;混施磷石膏可以部分抑制吹填土脱盐碱化,淋洗后pH比对照低0.6个单位,总碱度、RSC、SAR都低于对照,而且可使吹填土的离子组成由NaCl型转为CaSO4或Ca(HCO3)2型。[结论]磷石膏对吹填土淋洗脱盐不但有促进作用,而且可以改善吹填土的理化性状。不同施用方式的效果存在一定的差异,以与吹填土混合施用效果最好。 相似文献
28.
为探究互花米草(Spartina alterniflora)入侵对滨海湿地沉积物重金属的富集迁移效应,为滨海湿地生态保护与合理利用提供依据,在山东省日照市黄家塘湾滨海湿地选取不同互花米草入侵年限的斑块,以5 cm为间隔采集0~30 cm沉积物样品和互花米草样品,分析沉积物和互花米草不同部位中重金属元素Cu、Zn、Pb和Cd的含量,并采用地累积指数法、潜在生态风险评价法、生物富集系数及转运系数等方法进行评价。结果表明:湿地沉积物重金属Cu、Zn、Pb和Cd 的含量范围为5.94~31.94 mg(kg-1,18.59~56.87 mg(kg-1,4.76~30.36 mg(kg-1,0.021~0.083 mg(kg-1,整体低于研究区域重金属环境背景值;但Cu、Pb在0~15 cm内存在轻度污染;与光滩湿地相比,互花米草入侵湿地沉积物中重金属含量增加,且随互花米草入侵年限增加,沉积物重金属含量呈增加趋势,在上层(0~15 cm)表现尤为显著;互花米草不同部位对重金属的累积存在一定差异,大致表现根>叶>茎;不同重金属在根部的富集效应表现为Cd > Zn > Cu > Pb,互花米草对重金属转运效应为Pb > Zn > Cu > Cd。相关分析表明,沉积物中重金属的累积与互花米草入侵对湿地沉积物粒度组成、有机质含量及pH的改变密切相关。不同重金属在沉积物-植物体系的迁移转运差异则主要与互花米草各部位对重金属元素的吸收差异有关。 相似文献
29.
Suwanit Chainark 《Journal Of Applied Aquaculture》2013,25(2):171-185
Three channel catfish (Ictalurus punctatus) ponds were treated at two-week intervals with sodium nitrate at 2 mg NO3 ?-N/L per application and three ponds served as controls. Average concentration of nitrite-nitrogen measured midway between application dates never exceeded 1.2 mg/L in treated ponds, but on most sampling dates, nitrate concentrations were greater than those in control ponds (P < 0.1). Disappearance of nitrate-nitrogen from waters of treated ponds resulted primarily from nitrate reduction to free nitrogen gas. Soluble reactive and total phosphorus concentrations tended to be higher (P < 0.1) in treated ponds than in control ponds. There were no differences (P > 0.1) in pH and concentrations of total alkalinity, total ammonia nitrogen, and dissolved oxygen between treated and control ponds. The higher chlorophyll a concentration (P < 0.1) suggested that greater availability of nutrients in treated ponds resulted in more phytoplankton growth than in control ponds. Because of greater phytoplankton biomass, turbidity was higher and Secchi disk visibility less in treated ponds as compared to control ponds (P < 0.1). There were no obvious differences in phytoplankton community composition with respect to treatment—blue-green algae dominated the phytoplankton community in both treated and control ponds. Redox potential in sediment during crops was higher in ponds treated with sodium nitrate than in control ponds, indicating less anaerobic conditions. However, catfish survival, production, and feed conversion ratio did not differ (P > 0.1) between treatment and control. 相似文献
30.
太湖地区农业源对水体氮污染的贡献——以宜溧河流域为例 总被引:3,自引:4,他引:3
宜溧河流域是太湖上游的主要集水流域,该流域的污染物排放是太湖污染负荷的重要来源。重点针对种植业、畜禽养殖业和水产养殖业三种农业污染源,基于统计年鉴、遥感解译、野外监测和调研等多种手段,对种植业、水产养殖业和禽畜养殖业分行业进行了氮污染负荷核算。结果表明,2013年宜溧河流域主要农业源氮污染负荷总量为6861 t,单位排放强度为22.2 kg·hm-2;种植业和禽畜养殖业是宜溧河流域氮污染的主要来源,其中种植业源TN排放量最大,为3832 t,占总负荷的55.9%,种植业中蔬菜地对氮污染的贡献较大,TN排放量占总农业源负荷的18.7%;禽畜养殖业源TN排放量次之,占总负荷的34.4%;水产养殖业源TN排放量最小,占总负荷的9.8%.因此,针对宜溧河流域农业源氮污染的治理,在考虑禽畜养殖和水产养殖的同时,应以种植业污染尤其是菜地作为重点研究对象,制定合理的控制措施。 相似文献