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题名	土壤垦殖后<'210>Pbex平衡过程及农耕地侵蚀量计算模型的改进
作者	张云奇
学位类别	博士
答辩日期	2008
授予单位	中国科学院水利部成都山地灾害与环境研究所
授予地点	成都
导师	张信宝
关键词	210Pbex沉降 农耕地 土壤侵蚀 质量平衡模型 稳定态
其他题名	210Pbex Mass Balance Process after Cultivation and Improved Mass Balance Model for Erosion Estimation in Cultivated Land
学位专业	自然地理学
中文摘要	土壤210Pbex是环境中226Ra的衰变产物，被广泛应用于土壤侵蚀的示踪研究，对于当前210Pbex示踪的农耕地土壤侵蚀速率计算模型，研究者认为农耕地土壤全部210Pbex只匀分布于犁耕深度范围内，而未意识到由入渗所致210Pbex在犁耕层和犁底层之间再分配的深度分布变化规律。本研究深入讨论了210Pbex在土壤中入渗和衰变的物理机制，对土壤垦殖后210Pbex平衡过程进行理论推导，建立了农耕地210Pbex深度分布变化理论模型和稳定态的深度分布理论模型。210Pbex是天然核素，存在大气沉降的持续补充，土壤210Pbex最终会达到沉降补充与衰变、流失和入渗的平衡，实现稳定态深度分布，对于无侵蚀土壤而言，从初始垦殖到实现稳定态分布的时间为10.37a，与土壤扩散系数无关。比较而言，137Cs源于大气核试爆，没有持续沉降补充，由于衰变、流失和入渗，农耕地土壤137Cs的深度分布状态会持续变化。在深入讨论土壤垦殖后210Pbex平衡过程基础上，改进了农耕地侵蚀量计算的210Pbex稳定态质量平衡模型，并与当前模型的计算结果做了对比分析。与当前模型相比，改进模型的形式和操作稍显复杂，但理论基础更为完善，因此计算结果也更为准确。改进模型与当前模型计算结果的差值比即为扩散比，一般情况下210Pbex扩散比多在15％以上，也就意味着应用当前模型计算的结果，将比应用改进模型计算的结果低15％以上，故而当前模型计算结果与实际发生的侵蚀速率偏差较大，因此改进模型有广阔的应用前景。210Pbex法计算农耕地土壤侵蚀量的理论模型，无论是当前模型还是改进模型，均是以稳定态的假设为前提，即应用210Pbex稳定态质量平衡模型计算，计算结果所表征的可以是侵蚀速率发生某种变化后任一年以稳定态为假设的侵蚀速率，可以是稳定态的也可以是非稳定态的，而不是100年以来的平均侵蚀速率，因此不宜认为210Pbex法可用于计算100余年来的土壤侵蚀速率。理论上，如侵蚀农田长期以来一直处于稳定态（如>100年），210Pbex测定的侵蚀速率和137Cs测定的40余年来的侵蚀速率相等，前者的测定结果可以表征更长期的侵蚀速率。
英文摘要	Fallout 210Pbex measurements have been used in investigations of soil erosion in wide range of environments and many different areas of the world. However, the existing models for estimating soil erosion rates on cultivated land from 210Pbex measurements are similarly based on a hypothesis that the nuclide inventory is merely distributed in plough layer evenly while ignore the nuclide transport process between plough layer and plough pan layer which results in nuclide redistribution between the two layers. In this paper, the nuclide redistribution process between plough layer and plough pan layer has been developed mathematically on base of the nuclide transport process resulting from two physical mechanisms of diffusion and migration. 210Pb is naturally derived as a daughter of 226Ra existing in soils and rocks, whose redistribution in cultivated soils between the two layers will eventually achieve a steady state as result of a balance for constant fallout decay, loss, and transportation. The time of the process from initial cultivation to the steady state is about 10 years (y=10.37 a) for soils without erosion.An improved 210Pbex mass balance model for estimating soil erosion rates on cultivated land is developed in consideration of their redistribution processes between plough layer and plough pan layer. Comparing with the existing models, the improved models are based on more rational physical theory, and consequently may produce more accurate results despite of their comparatively complex forms. The deference values of estimated results between the improved model and existing model are proportional to diffusion ratio, consequently in practical, the improved model is more applicable than the existing model because the diffusion ratio is generally more than 15％.Using 210Pbex measurements to estimate soil erosion for cultivated land, practically, is based on the assumption of steady state, despite sometimes the fact is not so for the reason that the erosion rate is usually not constant. Consequently, the estimated result might actually reflect the erosion rate of the assumed steady state at any time after some change of erosion rate, either after the steady state or before. And with time, 210Pbex content of cultivated soil tend to be constant with the inventory and the depth distribution achieving new steady state, the estimated results are increasingly closing to the actual erosion rate. As a result, 100 a is the needed time for 210Pbex content of cultivated soil achieving steady state, not the timescale for 210Pbex measurements can quantify soil redistribution rates.
语种	中文
公开日期	2010-10-15
分类号	S15;TF1
内容类型	学位论文
源URL	[http://ir.imde.ac.cn/handle/131551/2209]
专题	成都山地灾害与环境研究所_成都山地所知识仓储（2009年以前）
推荐引用方式 GB/T 7714	张云奇. 土壤垦殖后<'210>Pbex平衡过程及农耕地侵蚀量计算模型的改进[D]. 成都. 中国科学院水利部成都山地灾害与环境研究所. 2008.

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