【作者】 张风宝；

【导师】 赵晓光； 杨明义；

【作者基本信息】 西北农林科技大学 ， 水土保持与荒漠化防治， 2006， 硕士

【摘要】 核素示踪技术在土壤侵蚀研究中越来越表现出鲜明的特点和优势,随着研究的深入,需要进一步拓宽核素示踪技术的应用的范围,提高核素示踪的精确性和准确性,为进一步深化坡面土壤侵蚀过程和建立土壤侵蚀预报模型提供有效的技术支撑。大气沉降核素⁷Be由于具有沉降连续性且半衰期较短而成为一种研究次降雨或较短时期（一个雨季）土壤侵蚀规律的核素,但已有的利用⁷Be研究土壤侵蚀规律的报道都是基于和¹³⁷Cs、²¹⁰Pbex具有相似的沉降-土壤吸附-运移的过程而加以利用,而对于⁷Be被土壤颗粒的吸附,沉降过程中植被截流和吸收等基础性的问题的系统研究尚未见报道。本文利用野外采样、布设试验,室内分析相结合的方法,对大气沉降核素⁷Be示踪土壤侵蚀的一些关键基础性问题进行了研究,得出以下主要结论:1.监测了⁷Be的沉降特征,分析了⁷Be沉降量与研究区降雨量的关系,初步探讨了黄土高原⁷Be的干沉降量通过分析研究区多次雨水中的⁷Be含量,发现雨水中⁷Be比活度在0.2～2.6Bq/L之间,平均值为0.88 Bq/L,雨水中⁷Be比活度与降雨量没有明显的相关关系。次降雨过程中降雨量与单位面积⁷Be湿沉降量相关性较好,相关系数为0.69,而单位体积雨水中的⁷Be含量对次降雨过程中单位面积的沉降量的影响较小。⁷Be的沉降量具有明显的季节性,雨季沉降量大,冬春季较少,月累计降雨量与⁷Be月沉降量呈明显正相关,相关系数为0.97。初步分析发现在黄土高原⁷Be月干沉降量为32～48 Bq/m2,占月沉降总量的14%～75%。2.研究了黄土高原地被物中⁷Be的分布规律春末地表不同层次的地被覆盖物中干枯植物中的⁷Be量最大,为224.9±5.5Bq/kg,是半分解覆盖物和活植物3倍之多。所研究的不同植物种中⁷Be含量的差异性很大,总体趋势为草本>半灌木及小灌木>种植作物,变异系数为0.6。在整个植物生长期,⁷Be含量逐渐增大,秋季达到最大,采样间隔期植物中⁷Be的增量在生长的中前期变化不大,到生长后期,增量突然增大,最后采样间隔期⁷Be的增量占整个生长期植物截留吸收⁷Be量的51%。坡面单位面积上植物截留⁷Be量随生长期增长和覆盖度的增大而增大,坡面⁷Be的植被截留率约为3 %～7%。更多还原

【Abstract】 Radionuclides tracing technique displays marked characteristics and advantages in soil erosion research. It was necessary to develop applying scope of the nuclides tracing technique with the research improvment, and to promote accuracy of tracing result, besides, it provides effective technical support for further understanding the soil erosion processes and establwashing soil erosion predict model.Atmospheric radionuclide ~7Be that has continuous deposition and short half-life was used as a soil erosion tracer to trace event rainfall or short period (a rainy season) soil erosion. At present, when ~7Be was used as a tracer to study soil erosion rule, we all think that ~7Be has the similar deposition - soil adsorption - migration process with 137Cs, 210Pbex. But in the worldwide, there are almost no concern on the critical basic questions that ~7Be adsorbed by the soil particle, intercepted and adsorbed by the vegetation in the depositional process, and ~7Be content in runoff and sediment.Combined methods of sampling and experimenting in field with detecting in the laboratory, we studied on the critical basic questions of the atmospheric radionuclides ~7Be tracing soil erosion, and drawn the main conclusions as follow:1. Measured the ~7Be depositional characteristic, analyzed the relationship between ~7Be depositional fluxes and rainfall, and discussed superficially ~7Be dry depositional fluxs on the Loess Plateau.The ~7Be concentration in the rainwater was from 0.2Bq/L to 2.6 Bq/L and the mean was 0.88 Bq/L by analyzing many rainfall events. There was no significant correlation between ~7Be concentration in the rainwater and the rainfall; however, in one rainfall event, the correlation between the rainfall and the ~7Be wet depositional fluxes was more significant, and correlation coefficient was 0.69. ~7Be concentration in the rainwater has less effect to the wet depositional fluxes, and the main impact factor was the precipitation. ~7Be fallout has the obvious seasonal change, the depositional fluxes was much more during the rainy season, and less during the spring and winter. The monthly accumulative rainfall and ~7Be depositional fluxes have significantly correlation, and the correlation coefficient was 0.97. The preliminary analysis indicated that the monthly ~7Be dry depositional fluxes was from 32 Bq/m2 to 48 Bq/m~2, the percentage was from 14% to 75% of the whole monthly deposition.更多还原