Friday, 14 July 2006

Using Data on Humic Acids of Paleosols Under Studying of the Ancient Cultural Landscapes.

Maria Dergacheva Sr., Institute of Soil Science and Agrochemistry SB RAS, Sovetskay, 18, Novosibirsk, Russia

Humic acids are memory of soils and ecosystems. They reflect and code the information about ecological conditions of their formation and functioning in the structure and properties. That is why they can be used as the reliable indicator for paleoenvironment reconstruction. As humic acids are sensory to environment, changes of environment are reflected in humic acids structure. In the case when changed conditions act for a long time, the humic acid compositions and structure can testify to environmental changes. If influence was not long term and did not exceed a threshold of stability of humic substances system, evidence of changes can't be preserved. The purpose of the report: to show possibilities, difficulties and limits of paleosol humic acids using as the ancient cultural landscapes indicator. Basic possibility of humic substances system as a whole and also humic acids – one of its components (subsystems) to reflect environment in its states and to support the structural state in varying conditions is considered on an example of humus properties change under chestnut soils irrigation of Kulunda steppe (Western Siberia). This example represents chronosequence of chestnut soils on the time of irrigation: a virgin soil and the irrigation soils of 0,5,10,13 and 20 years. Possibility and limits in use humic acids for revealing indicators of ancient irrigated agriculture in paleosols – on an example of the ancient presumably irrigated site 3800-3200 y. a. on the territory of archeological site "Arkaim" (Southern Ural)called “Vegetable garden of Arkaim”. Within this archaeological site there was dug a strip excavating soils of virgin and “irrigated” plots and also the deeper flute. From the soils of the virgin and “irrigated” plots there were extracted humic acids. They were investigated with the same method complex as humic acids of modern soils. Interpretation of research materials was occurred on the basis of the pedohumus method of paleoenvironment diagnostics (Dergacheva, 1997). Characteristics of modern soil humic acids served as the recent base for paleoreconstruction. The investigations have shown: Humic acids self-restoration in gradually varying conditions for the period of 20 years is real. Their characteristics changed by plowing up soils were restoring during an irrigation little by little. In 20 years the humic acids of irrigation soils on the majority of characteristics are close to virgin soils though are not yet identical. Soil humic acids of the virgin plot are characterized by a less content of C, H and N, by narrower H/C ratio than those of “irrigated” plot; this indirectly testifies to more arid conditions of virgin soil formation and functioning. Luminescence spectrum shift to longer waves of “irrigated” soil humic acids indicates a greater quota of integrated connections. Wider H/C ratios of old-irrigated soil humic acids comparing with those of paleosols excavated under the barrows and inside the settlement deposits can testify to the fact that irrigated agriculture took place (all compared objects are of the same age). Comparison of humic acids of virgin and “irrigated” plots allow to reveal differences in their composition, properties and structure peculiarities and to suggest old irrigation take place. However, these data aren't still sufficient to make an unequivocal conclusion about irrigated agriculture existence in the South Ural in the Arkaim epoch. All the soils excavated by sections on sites of irrigation and outside of them have different changes with depth of some humic acid features. They fix strengthening of aridity with depth on a virgin soil, and strengthening humidity on irrigated site. That is why it is possible to assume that the irrigation took place.*This investigation is supported by RFFI (project 04-04-49852).

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