Thursday, 13 July 2006

Anthropogenic Soil Changes of Different Time Scales : A Pedological Approach.

Gan-Lin Zhang and Zi-Tong Gong. Institute of Soil Science, Chinese Academy of Sciences, 71 Esat Beijing Road, Nanjing, 210008, China

Soils are subject to change naturally. Traditionally, pedogenesis represents the long-term soil changes taken place in natural environment, which involve mainly the changes of stable soil components rather than easily changeable characteristics. Therefore, pedogenesis is the central basis of virtually almost all current soil classification systems. However, human activity has brought in ever-increasing impacts on soil system, since the appearance of agricultural civilization about 7000-5000 years ago. Various human activities, including agriculturally important plough and deep working, artificial build-up, irrigation, manuring and fertilization etc. caused many human-induced changes, such as formation of deep soil horizon, increase of nutrient level, change of soil moisture regimes, formation of new morphological features, even the accelerated alteration of clay minerals. The rates of soil change caused by human activities vary among soil characteristics, as some of them change quicker while some much slower so the changes have different time scales. On the other hand, modern urban and industries cast more recent effects of human activities on soils, for instance, by direct and indirect pollution. Typical anthropogenic soils, like Cumuluc Anthrosols, Irragric Anthrosols and Hydragric Anthrosols, added by soils affected by modern industrial and urban activities, provide a good base for the study of anthropogenic soil changes of various time scales. As soils are recorder of environmental changes, anthropogenic soils thus are recorder of human activities. Classical pedological methods are based on horizon recognition and characterization. New modification such as more intensive soil sampling can yield much more detailed information of soil changes during use history. Studies about the horizontal changes of ancient Cumulic Anthrosols, Irragric Anthrosols and Hydragric Anthrosols revealed many soil changes in a time span of millennia, by comparison of surface and bottom layers with similar parent materials, such as mineralogical alteration, change of soil organic carbon isotope ratios, accumulation of secondary carbonates. Chornosequence study of Hydragric Anthrosols of different origins illustrated soil changes in centuries, which include human-induced soil particle change, loss and transformation of iron and manganese (oxides) s well as organic matter accumulation. Soil changes caused by modern human activities are widespread in the world, both in the area near to urban and that in the remote regions far from the vicinity of pollution source. Acidification and surface contamination are typical changes of soils occurred in some decades. Modern pedological investigation is an efficient tool in understanding soil changes caused by human activities in decades to millennia time span.

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