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71.
碳酸盐岩的H2CO3溶蚀产生岩溶碳汇,占整个岩石风化碳汇的 94%。西南岩溶区硫酸型酸雨严重,硫酸型酸雨广泛参与碳酸盐岩的溶蚀。H2SO4参与的碳酸盐岩风化是一个大气CO2净释放过程,具有减汇作用巨大。另一方面,岩溶区石灰土壤和地下水具有较高的pH值及盐基饱和度,对H+有巨大的缓冲作用,大气酸沉降在碳酸盐岩地区可能并不会造成地下水的HCO3-和pH降低;相反,较高浓度的SO42-所产生的盐效应和SO2-4与各种阳离子形成的离子对会增大方解石、白云石溶解度,可增强H2CO3对碳酸盐的溶蚀,这可能会使岩溶作用产生更大的碳汇效应。因此,硫酸型酸雨参与碳酸盐岩风化的减汇效应不仅可能被高估,硫酸型酸雨还可能增强碳酸盐岩的H2CO3溶蚀,具有增加岩溶碳汇效应的作用。应结合石灰土壤对大气酸沉降的缓冲容量和阈值及大气酸沉降的H+与土壤中盐基离子的交换量,并综合考虑盐效应、离子对作用、同离子效应,客观评价硫酸型酸雨流经石灰土壤层后对碳酸盐岩溶蚀吸收大气/土壤CO2的影响 相似文献
72.
Peter R. Robichaud Edwin D. Bone Sarah A. Lewis Erin S. Brooks Robert E. Brown 《水文研究》2021,35(1):e13943
Active wildfire seasons in the western U.S. warrant the evaluation of post-fire forest management strategies. Ground-based salvage logging is often used to recover economic loss of burned timber. In unburned forests, ground-based logging often follows best management practices by leaving undisturbed areas near streams called stream buffers. However, the effectiveness of these buffers has not been tested in a post-wildfire setting. This experiment tested buffer width effectiveness with a novel field-simulated rill experiment using sediment-laden runoff (25 g/L) released over 40 min at evenly timed flow rates (50, 100 and 150 L/min) to measure surface runoff travel length and sediment concentration under unburned and high and low soil burn severity conditions at 2-, 10- and 22-month post-fire. High severity areas 2-month post-fire had rill lengths of up to 100 m. Rill length significantly decreased over time as vegetation regrowth provided ground cover. Sediment concentration and sediment dropout rate also varied significantly by soil burn severity. Sediment concentrations were 19 g/L for the highest flow 2-month post-fire and reduced to 6.9–14 g/L 10-month post-fire due to abundant vegetation recovery. The amount of sediment dropping out of the flow consistently increased over the study period with the low burn severity rate of 1.15 g L−1 m−1 approaching the unburned rate of 1.29 g L−1 m−1 by 2-year post-fire. These results suggest that an often-used standard, 15 m buffer, was sufficient to contain surface runoff and reduce sediment concentration on unburned sites, however buffers on high burn severity sites need to be eight times greater (120 m) immediately after wildfire and four times greater (60 m) 1-year post-fire. Low burn severity areas 1-year post-fire may need to be only twice the width of an unburned buffer (30 m), and 2-year post-fire these could return to unburned widths. 相似文献
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初始场估计共轭同化方法的精确化 总被引:2,自引:1,他引:1
通过例子,说明对偏微分方程模型使用共轭同化方法时,同周期性条件的重要性,提出尽可能精确地使用共轭同化方法于偏微分方程模型的办法及对有些方程不含e↓u/e↓项时,其相应差分方程模型精确共轭同化方法。 相似文献
76.
本文针对射线类偏移成像当中的速度模型光滑处理问题,借鉴数字图像处理当中的偏微分方程法,基于能量泛函,应用变分方法导出基于速度模型的偏微分方程实现射线类偏移成像当中的速度模型的光滑处理.由于偏微分方程法具有线性叠加特性、模型解的唯一性和局部特征保持性,因此,应用该算法可以实现基于原始速度模型空间结构的模型光滑处理.通过在原始速度模型以及光滑处理后的速度模型上计算速度的空间分布以及地震波走时、射线路径可以得出,偏微分方程法对速度模型的光滑处理能够很好地保持原始模型的空间结构,偏移成像结果也证明了该方法的实用性. 相似文献
77.
The paper describes the distinctive features of the pseudo‐dynamic test method as implemented at the ELSA reaction‐wall facility. Both hardware and software aspects are considered. Particular attention is devoted to the digital control system and to a coupled numerical–experimental substructuring technique allowing realistic earthquake testing of very large structures. Mathematical and implementation details corresponding to this testing technique are given for both synchronous and asynchronous input motion. Selected test results illustrate the advantages of the presented features. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
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引入PLSA模型的光学遥感图像舰船检测 总被引:2,自引:0,他引:2
提出一种基于概率潜在语义分析(Probabilistic Latent Semantic Analysis,PLSA)的检测算法,首先通过PLSA将目标表述为潜在成分的概率组合,然后利用统计模式识别方法对获取的潜在成分概率进行判别,从而完成最终的检测。其中,生成的潜在成分反映了目标与特征之间相互出现的频率关系,并以潜在成分在目标中概率差异的形式对上述不对应现象给出了直观描述。实验结果表明,所提出的算法对多种复杂情况下的光学图像舰船检测具有很好的准确性和鲁棒性。 相似文献
80.
H.F. Aristizábal 《水文科学杂志》2019,64(8):885-899
Wetlands are vulnerable to groundwater extraction, which has proven detrimental to aquatic ecosystems around the planet. As wetlands rank among the world’s most endangered ecosystems, versatile strategies are required to protect them. This paper provides a modelling-based method to delineate protection buffers in wetlands subject to groundwater extraction. The technique is sufficiently flexible to cater to a wide variety of conditions, and simple enough to underpin management decisions on a daily basis. A numerical model is used to obtain a map of the critical rate of groundwater abstraction, based on the distance between wetlands and suitable discharge thresholds. The outcomes determine the allowed pumping rate at any point under steady and transient-state conditions. A new iteration is developed every time a new pumping allowance is made. This procedure is demonstrated by means of hypothetical scenarios, as well as by a case study application in the Valle del Cauca region, Colombia. 相似文献