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481.
L. J. Sheppard A. Crossley I. D. Leith K. J. Hargreaves J. A. Carfrae N. van Dijk J. N. Cape D. Sleep D. Fowler J. A. Raven 《Water, Air, & Soil Pollution: Focus》2004,4(6):197-205
Critical N loads for ombrotrophic bogs, which often contain rare and N-sensitive plants (especially those in lower plant groups: lichens, mosses and liverworts), are based on very few experimental data from measured, low background N deposition areas. Additionally the relative effects of reduced versus oxidised N are largely unknown. This paper describes an automated field exposure system (30 km S. of Edinburgh, Scotland) for treating ombrotrophic bog vegetation with fine droplets of oxidised N (NaNO3) and reduced N (NH4Cl). Whim Moss exists in an area of low ambient N deposition (ca. 8 kg N ha–1 y–1), the sources and quantification of which are described. The wet N treatment system is run continuously, and is controlled/activated by wind speed and rainfall to provide a unique simulation of real world treatment patterns (no rain=no treatment). Simulated precipitation is supplied at ionic concentrations below4mMin rainwater collected on site. Treatments provide a replicated dose response to 16, 32 and 64 kg N ha–1 y–1 adjusted for ambient deposition (8 kg N ha–1 y–1). The 16 and 64 kg N ha–1 y–1 are duplicated with a P+K supplement. Baseline soil chemistry and foliar nutrient status was established for all 44 plots for Calluna vulgaris, Sphagnum capillifolium, Hypnum jutlandicum and Cladonia portentosa. 相似文献
482.
The dry deposition of ozone to aconiferous forest in northeastern Bavaria(southern Germany) was quantified during 1999with both the eddy correlation method and a bigleaf model. The model included parameterizationsof the atmospheric transfer resistances fromdirect measurements, stomatal resistance from aplant ecological model, and an estimation of thecuticle resistance as function of leaf wetness.Early in the season, the measured and themodelled deposition fluxes were in goodagreement, although the modelled fluxes tended tounderestimate the measured ones. Thisunderestimation was more pronounced in the latesummer, when high nocturnal fluxes werefrequently measured. The model parameterizationof the cuticle and the stomatal resistances didnot allow for such high fluxes. In these cases,the 24 hour average of the measured fluxes wereup to 4.5 times higher than the modelled ones.The reasons for these large discrepancies remainunknown. However, assigning the unaccounted partof the deposition to a nonstomatal surfacedeposition pathway, a new parameterization of therespective resistance yielded an average value of300 s m-1. It exhibited a decreasing trendthrough the vegetation period. 相似文献
483.
Radioactive contamination of agricultural land may necessitate long-term changes in food production systems, through application
of selected countermeasures, in order to reduce the accumulation of radionuclides in food. We quantified the impact of selected
countermeasures on habitat diversity, using the hypothetical case of two agricultural areas in Finland. The management scenarios
studied were conversions from grassland to cereal production and from grassland and crop production to afforestation. The
two study sites differed with respect to present agricultural production: one being predominantly cereal production and seminatural
grasslands, while the other was dominated by intensive grass and dairy production. Some of the management scenarios are expected
to affect landscape structures and habitat diversity. These potential changes were assessed using a spatial pattern analysis
program in connection with geographic information systems. The studied landscape changes resulted in a more monotonous landscape
structure compared to the present management, by increasing the mean habitat patch size, reducing the total habitat edge length
and reducing the overall habitat diversity calculated by the Shannon diversity index. The degree of change was dependent on
the present agricultural management practice in the case study sites. Where dairy production was predominant, the landscape
structure changes were mostly due to conversion of intensive pastures and grasslands to cereal production. In the area dominated
by cereal production and seminatural grasslands, the greatest predicted impacts resulted from afforestation of meadows and
pastures. The studied management changes are predicted to reduce biodiversity at the species level as well as diminishing
species-rich habitats. This study has predicted prominent side effects in habitat diversity resulting from application of
management scenarios. These potential long-term impacts should be considered by decision-makers when planning future strategies
in the event of radionuclide deposition. 相似文献
484.
钛合金ZrN耐磨抗冲蚀防护涂层 总被引:3,自引:0,他引:3
采用真空多弧镀设备在TC11钛舍金表面沉积超硬耐磨ZrN防护涂层,通过增压气流固体颗粒冲蚀实验评价ZrN涂层的耐磨抗冲蚀性能,划痕仪测试涂层与基体的结合力,SEM、X射线分析涂层组成及观察涂层冲蚀前后表面形貌,盐雾及电化学实验测试涂层耐腐蚀性能。结果表明,ZrN涂层成分主要为(111)择优取向的ZrN相;ZrN涂层不影响钛合金的耐腐蚀性能及疲劳性能;ZrN涂层与基体结合牢固.涂层大大提高了基体的耐磨抗冲蚀性能。 相似文献
485.
486.
以韶山蔡家塘森林小流域2001年实地监测的大气降水、穿透水和地表水数据为基础,对酸沉降作用下韶山森林N的输入、输出的月均通量及变化特征进行了研究.结果表明:2001年N输入通量为53.81 kg/hm2,主要以NH4+ 形式(占总输入的64%)输入该森林生态系统;2001年N输出通量为3.57 kg/hm2,主要以NO3-形式(占总输出的64%)输出该森林生态系统.韶山森林2001年N净滞留量达到50.24 kg/hm2.月均输出通量极大值出现在降雨量较多的5-7月,其N输出通量占全年N总输出通量的59%.从N的总输入通量、总输出通量的变化来看,N输出并不随输入的增加而增加,N的输出主要受到降水量的影响. 相似文献
487.
488.
Zhang Leiming Brook Jeffrey R. Vet Robert Shaw Mike Finkelstein Peter L. 《Water, Air, & Soil Pollution: Focus》2001,1(5-6):67-78
A dry deposition model (RDM) for operational application has beenevaluated and modified in the present study. Field measurements of friction velocity and dry deposition velocity of SO2 andO3 over a mixed forest have been used to evaluate RDM. It was found that RDM predicts friction velocities very close to measurements and thus it can predict reasonable aerodynamic resistance. RDM overestimated O3 deposition during dry nighttime conditions and underestimated both O3 andSO2deposition for early morning hours. It could not predict the mean diurnal variation in deposition velocity for either O3 or SO2 deposition under wet surface conditions. Modifications have been made for O3 and SO2 dry deposition based on the comparison of results and based upon additional published data. Compared to an earlier version of RDM, the modified versionpredicts better results for O3 and SO2 dry deposition,especially under rain and dew conditions. 相似文献
489.
Long range atmospheric transport is the most important sourceof contamination to the natural environment in Norway with manyheavy metals. Investigations based on aerosol studies, bulkdeposition measurements and moss analysis show that airborne transport from other parts of Europe is the major mode for supplyof vanadium, zinc, arsenic, selenium, molybdenum, cadmium, tin,antimony, tellurium, thallium, lead, and bismuth, whereas metalssuch as chromium, nickel, and copper are mainly derived from point sources within Norway and in northwestern Russia close tothe Norwegian border. Elements associated with long range transport show substantial enrichment in the humus horizon of natural soils in southern Norway, sometimes to levels suspected to cause effects on soil microbial processes. E.g. lead concentration values of 150–200 ppm are observed in the mostcontaminated areas in the south as compared to about 5 ppm inthe far north. Elements such as lead and cadmium also show enrichment in some terrestrial food chains. These elements alsoshow considerably elevated levels over background concentrationsin the water and sediment of small lakes in the southern part ofthe country. Retrospective studies based on ombrogenous peatcores indicate that long range transport has been a significantsource of heavy metal contamination in southern Norway for thelast couple of centuries. The deposition of most heavy metals inNorway has been considerably reduced over the last 20 yr, withthe exception of contributions in the north from Russian smelters. 相似文献
490.
D. Golomb E. Barry G. Fisher P. Varanusupakul M. Koleda T. Rooney 《Atmospheric environment (Oxford, England : 1994)》2001,35(36)
Wet and dry deposition of polycyclic aromatic hydrocarbons (PAHs) was measured at Nahant, Massachusetts, a peninsula jutting into Massachusetts Bay and Wolf Neck, a peninsula jutting into Casco Bay, Maine. Wet deposition (rain and snow) was collected in a funnel which drains into a shielded, temperature controlled receiving bottle. Dry deposition of gaseous and particulate PAHs was collected onto an exposed water surface. PAHs were analyzed by solid phase extraction and gas chromatography-mass spectrometry. Sixteen PAH species were analyzed, ranging from acenaphthylene to coronene. The mean wet deposition rate of the sum of the 16 species is 720 ng m−2 cm−1 precipitation at Nahant, and 831 ng m−2 cm−1 precipitation at Wolf Neck. Wet deposition is attributed to regional PAH emitting sources. Storm patterns appear to bring somewhat higher wet deposition of PAHs to Wolf Neck than to Nahant. The mean dry deposition rate is 95 ng m−2 h−1 at Nahant and 9.3 ng m−2 h−1 at Wolf Neck. The large difference is attributed to the fact that Nahant is close to the urban-industrial metropolitan Boston area and Logan International Airport, whereas Wolf Neck has no major PAH-emitting sources nearby. Individual measurements have an error bracket of ±30%. The Chemical Mass Balance model was used to apportion the dry deposition to source categories. At Nahant, nine samples gave valid statistical attributes with a mean apportionment: jet exhaust 35%, gasoline fueled vehicles 32%, diesel fueled vehicles 17%, wood combustion 13%, others 3%. At Wolf Neck, six samples yielded a mean apportionment: jet exhaust 30%, gasoline vehicles 28%, diesel vehicles 18%, wood combustion 16%, others 8%. There is a considerable variation between the samples. The apportionment is greatly dependent on the quality and selection of the model inputs, i.e. source signatures, which for PAHs are questionable. 相似文献