水耕人为土磁性矿物的生成转化机制研究回顾与展望

随着环境问题的日益突出,人为活动对土壤的影响越来越深刻,需加强对"人为作用"的研究以便解释现代土壤磁性的过程和变化。水耕人为土在发育过程中人为作用的方式多种多样,明确其磁性矿物的生成和转化机制及其影响因素有利于理解人为活动对现代土壤磁性的作用。但目前水耕人为土磁学研究还比较零散,缺乏系统性,已有研究结果有待深入梳理。本文对已有的相关研究报道,包括水耕人为土磁性参数的演变特征、磁性矿物的生成转化机制以及对成土因素的响应等进行综合评述。最后,对当前研究的不足和存在问题进行总结,并对研究方向进行了展望,以期有助于环境磁学的发展。

Review and Prospect of Researches on Production and Transformation of Magnetic Minerals in Paddy Soils During Pedogenesis

With the problem of environmental deterioration becoming increasingly conspicuous and the impact of anthropic activities on soil formation getting more and more intense in recent decades, it is, therefore, essential to intensify the researches on the impact so as to explain processes of and changes in magnetism in modern soils. Hydragric Anthrosols (paddy soils) are defined as Anthrosols, and their formations are affected by human activities in various ways. Tillage and anthrostagnic moisture regimes are two major factors that control characteristics of the soil formation processes. However, so far only some scattered rather than systematic studies have been reported on how human activities induce changes in soil magnetism. Therefore, this paper is oriented to review or summarize all the findings of researches in this field, including characteristics of the evolution of parameters of magnetism in Hydragric Anthrosols, mechanisms of the formation and transformation of magnetic minerals and their responses to soil forming factors. Magnetic minerals in paddy soils, on one hand, inherit some of the features of their original soils and on the other, have undergone a series of apparent changes under the impacts of paddy cultivation. Water regime controlled the soil magnetic characteristics in the early stage of paddy soil formation, however, all different types of paddy soils could eventually develop into profiles similar in structure of magnetic susceptibility after long-term paddy cultivation. Most of the ferrimagnetic minerals and hematite in the anthrostagnic epipedon tended to reduce into goethite, lepidocrocite and/or their hydrated forms within a short term, while in the hydragric horizons (subsoils), the changes of magnetic minerals were more complicated and duration of artificial submergence and reduction degree were the major factors controlling changes of the ferrimagnetic minerals. In appropriate environment, Fe2 got oxidized slowly, thus forming ferrimagnetic minerals, which may represent one mechanism for enhancement of magnetism in the subsoil. Ferrimagnetic minerals in clays in the paddy soil were susceptible to breakage, while newly formed ferromagnetic minerals were concentrated in soil aggregates of the clay fraction. In paddy soils, periodic submergence made it difficult for the soil to develop drought-stressed environment that could dehydrate ferrihydrite into hematite, which was usually reduced first in contrast to goethite under reducive conditions. Goethite and lepidocrocite often coexisted in paddy soils and their relative contents depended mainly on soil environment. Human activities affected or governed the formation and transformation of magnetic minerals in the paddy soil mainly through their impacts on natural soil forming factors (i.e., climate, organism, parent material, relief, time). However, the impacts reduced in degree with paddy cultivation going on. In the end, the paper summarized shortages and problems existing in current studies and prospected for directions of future researches in hope to help development of environmental magnetism.