Comparative Studies Of Pedogenic Environment And Impact Of Human Activity During The Holocene In The Weihe And Fenhe River Basin

Abstract: The Loess Plateau is well known to the world for it's thickness of larger of loess. The Holocene layer of loess and palaesoil sequence in the Loess plateau consitutes excellent records of evolution of soil formation, change in monsoon, dust-sand storm accumulation and influence of human cultivating over 8500 year.In the study, four typical Holocene soil profiles in the Weihe and Fenhe River Basin were studied by field investigation and using high-resolution analysis of magnetic susceptibility, the content of CaCO3 and grain-size analysis. The results comparied study of these climatic substitute indexes reveal the relationship between the process of soil formation and the change in monsoon climate, and different physiognomy term in the region. The study provides new science basis to instruct human activities in this climatically sensitive semiarid zone. The main results are following by Comparative Studies :(1) The different progress of eluviation and illuviation of CaCO3 in the stratum of Holocene. Because of the impact of different physiognomy term, sediment of profile was eroded, conveyed and deposited in the low-lying place, which made the profiles have resemblingly character engender different kinds of eluviation and illuviation.(2) The different physiognomy term brought about surface erosion, which is the drive force that formed different eluviation and illuviation of CaCO3, different pedogenic environment, the immense differentia of profile stratum of soil formation in Holocene. The study shows the soil erosion has never benn interrupted, only but different intensity. Modern soil erosion is continuation and inheritance of historical soil erosion in the Loess Plateau. The intense soil erosion had occurred in the shift period of accumulation to pedogenesis. But soil erosion weakened in the transitional period of pedogenesis to accumulation, even though the impact of human acativitues.(3) The different variation progress of Pedogenic Environment were showed during the Holocene in the Weihe and Fenhe River Basin. 11500~8500 a B.P., summer monsoon was stronger and winter monsoon was weaker. Temperature went higher graduately, at the same time, precipitation got much, dust-sand storm weakened,but it was mainly still dry and cold. Pedological progress was becoming slowly strong, but there were corrasion and deposits in the dust sediments of late stage in the site of DXF-S profile. 8500-3100 a B.P., it was a period in which the temperature was the highest, the precipitation was the greatest, pedological progress was very strongest and summer monsoon reached its peak during the Holocene. There appeared human 's culture. Precipitation increased ramakably in this period, but pedological degree was different due to different precipitation, different physiognomy term and impact of human activities. The data of magnetic susceptibility and the content of CaCO3 reflect that the palesol So in the Weihe River basin was far more matured that that in the Fenhe River basin. 3100 a B.P. to now, the climate began to deteriorate around 3100 a B.P. and soil degradation is recorded in the profiles. Summer monsoon was weaker and winter monsoon stronger. The layer of loess L0 has been accumulated since 3100 a B.P.. The climate trended to become dry and cold, the sand-dust storm intensified. Pedological progress hardly stopped, but there were corrasion deposits in the dust sediments of the profiles.