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171.
He T Feng X Guo Y Qiu G Li Z Liang L Lu J 《Environmental pollution (Barking, Essex : 1987)》2008,154(1):56-67
The mercury distribution and speciation in the water column were investigated from November 2003 to September 2004. The distribution and concentrations of total mercury (THg) and particulate mercury (PHg) showed that algae had a large capacity to bind mercury in late spring (e.g. in May). It is shown that dissolved gaseous mercury (DGM) concentrations may also be affected by algae activities. The MeHg profile in the water column at a highly eutrophied site in Hongfeng Reservoir demonstrated that most of the MeHg was produced in the hypolimnion, whereas the MeHg profile pattern at another site with less eutrophication indicated that MeHg in water was largely ascribed to release from sediment. In September, the outflow of the reservoir was enriched with MeHg, which was 5.5 times higher than that in the inflows. The discharge of MeHg-concentrated water from the anoxic hypolimnion in the reservoir may pose a risk to downstream fauna. 相似文献
172.
Lihui Gao Yijun Cao Lizhang Wang Shulei Li 《Frontiers of Environmental Science & Engineering》2022,16(6):77
173.
Milko Novi? Irena Grgi? Mateja Poje Vida Hudnik 《Atmospheric environment (Oxford, England : 1994)》1996,30(24):4191-4196
Redox cycling of Fe(II)/Fe(III) during the catalyzed aqueous S(IV) oxidation by dissolved oxygen in the presence of Fe(II) and/or Fe(III) at an initial pHi of 4.4, often observed in atmospheric waters, was studied in detail. It has been found that the reaction rate is not considerably affected by the oxidation state of iron at the start of the reaction. An equilibrium between Fe(II) and Fe(III) was established a few minutes after the start of the reaction, regardless of the oxidation state of iron at the beginning of the experiment. The prevailing oxidation state of iron in a particular phase of the reaction depends on the concentration of S(IV) in the reaction solution. It has been found that the formation of polymerized hydroxo Fe(III) species is also included in the mechanism of the Fe-catalyzed oxidation of S(IV). The formation of these species was confirmed by the on-line measurement of Fe(II) and Fereac. The results also clearly demonstrate that the pHi of the solution is a major factor, controlling the concentration of Fe(III) ions, the form of S(IV) species, and consequently the reaction rate of S(IV) oxidation by oxygen. 相似文献
174.
Everett M. White 《Journal of the American Water Resources Association》1981,17(4):708-712
: The effects of corn, soybean, and oat canopies on plant nutrient contents of throughfall precipitation (TFP) were studied to determine if canopies alter the meteoric precipitation (MP) composition. TFP samples collected at 5 cm from corn or soybean rows contained more NH4, NO3, soluble PO4, total PO4, and soluble K ions than samples collected at 25 and 45 cm distances from the row. Enrichment of MP by the canopies was least at the 45 cm distance. Oat canopies enriched MP more than soybean or corn canopies for most of the ions, probably due to the difference in season of growth. Thus, canopies of these crops alter the nutrient concentration of MP. 相似文献
175.
Phosphorusavailabilityintwosoilsamendedwithpoultrylitter¥HanXingguo(InstituteofBotany,ChineseAcademyofSciences,Beijing100093,... 相似文献
176.
M. H. Hoang Fagerstrm S. I. Nilsson M. van Noordwijk Thai Phien M. Olsson A. Hansson C. Svensson 《Agriculture, ecosystems & environment》2002,90(3):291-304
Agroforestry is considered to be a promising alternative to short-fallow shifting cultivation or other monocropping systems. An on-farm experiment was established in 1996 in northern Viet Nam to examine the contribution of the leguminous bush Tephrosia candida (Roxb.) D.C. as a fallow or hedgerow species and as a mulch producer to improve nutrient cycling and prevent nutrient losses by erosion. The systems tested were upland rice monocropping (Mono), natural fallow (NaFa), fallow of Tephrosia (TepFa), hedgerow intercropping with upland rice (Oryza sativa L.) and internal mulching using pruned Tephrosia biomass (TepAl), and upland rice with external mulching using Tephrosia biomass (TepMu). Over two cropping seasons, from April 1996 to April 1998, nutrients recycled and inputs and exports were recorded, as well as changes in C-, N- and P-pools, and in pH in the 0–5 cm topsoil layer.The Tephrosia systems (TepFa, TepAl, TepMu) prevented nutrient losses by erosion effectively. Compared to the NaFa system, the TepFa system accumulated 34% more N in the above-ground plant parts and increased topsoil N by 20%, probably due to N-fixation. There was a trend that the less labile P-pools (NaOH-P) were reallocated into the more labile P-pools (Bicarb-P) in the soil of the TepFa system. Burning released significant amounts of the inorganic P-pools in both the NaFa and TepFa systems and this effect seemed to be more pronounced in the TepFa than in the NaFa. Organic input to crop export ratios for N and P were >1 in the TepAl and TepMu treatments. This was due to a sufficient quantity and quality of the Tephrosia mulching material. However, moderately labile NaOH-extractable organic P seemed to be depleted in the topsoil due to high P uptake in the TepMu treatment. Thus, nutrient cycling and nutrient balances were improved under the Tephrosia systems. But for long-term P sustainability, there is a belief that a combined use of mulching and mineral P fertiliser is needed. 相似文献
177.
Element cycling in the dominant plant community in the Alpine tundra zone of Changbai Mountains, China 总被引:1,自引:2,他引:1
Element cycling in the dominant plant communities including Rh. aureum, Rh. redowskianum and Vaccinium uliginosum in the Alpine tundra zone of Changbai Mountains in northeast China was studied. The results indicate that the amount of elements from litter decomposition was less than that of the plant uptake from soil, but that from plant uptake was higher than that in soil with mineralization process released. On the other hand, in the open system including precipitation input and soil leaching output, because of great number of elements from precipitation into the open system, the element cycling(except N, P) in the Alpine tundra ecosystem was in a dynamic balance. In this study, it was also found that different organ of plants had significant difference in accumulating elements. Ca, Mg, P and N were accumulated more obviously in leaves, while Fe was in roots. The degree of concentration of elements in different tissues of the same organ of the plants also was different, a higher concentration of Ca, Mg, P and N in mesophyll than in nerve but Fe was in a reversed order. The phenomenon indicates ( 1 ) a variety of biochemical functions of different elements, (2) the elements in mesophyll were with a shorter turnover period than those in nerve or fibre, but higher utilization rate for plant. Therefore, this study implies the significance of keeping element dynamic balance in the alpine tundra ecosystem of Changbai Mountains. 相似文献
178.
Degradation of benomyl, picloram, and dicamba in a conical apparatus by zero-valent iron powder 总被引:6,自引:0,他引:6
Ghauch A 《Chemosphere》2001,43(8):1109-1117
Reduction of some pesticides (benomyl, picloram, and dicamba) was studied in an aerobic batch conical pilot system to investigate the disappearance of these pesticides on contact with iron powder (20 g/l, 325-mesh). Aqueous buffered solutions of the compounds were added to the system followed by zero-valent iron powder (ZVIP), and the decline in the pesticide concentrations was monitored over time. HPLC analyses show a complete disappearance of picloram (1.20 mg/l) after 20 min of reaction. Benomyl (1.00 mg/l) and dicamba (1.25 mg/l) disappear after 25 and 40 min, respectively. The t50 values ranged from 3 to 5.5 min, and were about slightly less than the t1/2 values reported when the log of the relative HPLC peak area was plotted versus time, where the relative peak area was calculated by dividing the measured peak area by the initial peak area. Pathways for the degradation of the studied pesticides by ZVIP are proposed. 相似文献
179.
180.
In this study, iron speciation in five standard clay samples was characterized. Iron mobilization from these clays was then measured in acidic media. For comparison, a commercially available Arizona test dust (ATD) was also observed. The results showed that the free-Fe contents of clays were commonly lower than that of dust aerosols. The components of clays were dominant by the structural Fe held in the aluminosilicate lattice. The iron solubility of the clays were in the order of KGa-2?>?SWy-2?>?CCa-2?>?IMt-2?>?NAu-2. Based upon the Mössbauer spectrum and transmission electron microscopy (TEM) analysis, the Fe(II) fraction and the Fe/Si ratio of clay particles changed after dissolution, suggesting the total Fe solubility depended on the Fe atom states existing within the aluminosilicate lattice. The Fe in KGa-2 and SWy-2 was most likely substituted for alkaline elements as the interlayer ions held by ionic bonds in the aluminosilicate, which are more liable to dissolution. However, the Fe in NAu-2 was more likely to be bound by strong covalent bonds in aluminosilicate mineral, which is less soluble. The much highly soluble Fe in ATD was not only linked to the dissolution of an appreciable fraction of Fe(II), but also could be attributed to the fact that the Fe bonds in the clay fraction of ATD were mainly present as ionic bonds. The TEM images showed that reacted clay particles displayed less aggregate particles, with nanoparticle aggregates and the Fe/S-rich tiny particles attached to the remains. 相似文献