| The Three-River Headwaters region is the birthplace of the Yangtze River, Yellow River, Lancang rivers, located in the hinterland of qinghai-tibet plateau, is known as the "water tower" of China.the ecological environment of the Three Rivers region is one of the most sensitive and fragile regions in the world cause of its harsh natural conditions, simple structure of the ecological system community, slow material and energy flow in the system, and lower anti-jamming and self recover disabilities. Grassland area accounts for 65.37% of the Three Rivers region as a whole and Grassland ecological system is the main ecological system, which have a decisive effect to keep ecosystem service function of the area. But grassland degradation, At present, is the most foremost ecological environment problem of grassland ecosystem in the Three-River Headwaters region. After grassland degradated, the soil nutrient elements had different levels of loss. The differences of soil nutrient elements have been studied, which will be have a great significance on ecological restoration for scientific decision-making and ecological security of the country.The data of this study required is mainly from the second national soil survey in the 1980s. In addition, field investigation and soil sampling had been completed in the Three Rivers region of Qinghai in August 2009 and September 2010.100 sample points, 44 sample points in 2009,56 sample points in 2010, were digged from soil surface to soil parent material layer, soil samples were taken 100-500g in every 10 cm in each soil profile, total 479 soil samples were collected in the bulk bags, at the same time, the latitude and longitude of all the sample points were recorded by GPS. Soil organic matter, total nitrogen, total phosphorus, total potassium contents were measuremented by the Institute of Geographical Sciences and Natural Resources Institute of Ecosystem Network Observation and Modeling, State Key Laboratory of Physical and Chemical Analysis Center. Based on the data of the second soil survey and field sampling in 2009 and 2010, temporal-spatial variations of degraded grassland soil organic matter (SOM) contents, total nitrogen, total phosphorus, total potassium under the surface soil 0-10 cm,10-20 cm and 30-50 cm in Three～River Headwaters region in Qinghai Province for a 30-year period (1980-2010) were evaluated using geostatistics and geographic information system (GIS).The results are as follows:The results of the analysis of soil organic matter showed that:two periods of the mean SOM content showed a downward trend from the surface to the bottom after excluding the outliers. The average of SOM contents and coefficient of variation in 1980 was higher than that in 2010 in the same soil layer. SOM content of the two periods were log-normally distributed. By performing experimental semivariograms analysis, result showed that nugget effect in the same soil layer in 2010 was less than that in 1980, which indicated that spatial autocorrelation of SOM in Three-River Headwaters region in Qinghai Province were strengthening, structural factors had played a more and more important role on the spatial distribution of SOM. The range of organic matter content was becoming smaller from surface to 10 cm, instead, the range of 10-30 cm and 30-50 cm was becoming larger, which showed the distribution of surface organic matter content more complexity than the underlying. The results of ordinary kriging showed that there were regional differences in changes of soil organic matter content. Their spatial distributions were the central and eastern region decreased significantly, SOM content increased mainly in the parts of western, southern and northern region.The analysis results of total soil nitrogen showed that:The mean TN values of the two periods showed a downward trend from the surface to the bottom after excluding the outliers. The average TN contents and coefficient of variation in 1980 was higher than that in 2010 in the same soil layers. TN content of the two periods was log-normally distributed. By performing experimental semivariograms analysis, result show that nugget effect in the same soil layer in 2010 was less than that in 1980; indicated that spatial distribution autocorrelation of TN in Three-River Headwaters region in Qinghai Province were strengthening, structural factors had played a more and more important role on the spatial distribution of TN. The range of TN content was becoming smaller from surface to 10 cm, instead, the range of 10-30 cm and 30-50 cm was becoming larger, which showed the distribution of surface TN content more complexity than the underlying. The results of ordinary kriging showed that there are regional differences in changes of total nitrogen content. There are significant decreases in southern, central and eastern regions; while the increase mainly happened in western areas.The results of the analysis of TP showed that:the mean TP values of the two periods showed a downward trend from the surface to the bottom after excluding the outliers. The average TP contents and coefficient of variation in 1980 was higher than that in 2010 in the same soil layers. The coefficient of variation of total phosphorus content of 0～10cm layer increases and the coefficient of variation of 10-30cm, 30-50cm layer of the total phosphorus content decreases. TP content of the two periods were log-normally distributed. By performing experimental semivariograms analysis, results showed that nugget effect in the same soil layer in 2010 was less than that in 1980; indicated that spatial distribution autocorrelation of TP in Three-River Headwaters region in Qinghai Province were strengthen as structural factors on the spatial distribution of TP play an important role. The range of total phosphorus in the three layers in 2010 was smaller than that in 1980, which shows the distribution of total phosphorus content in the past 30 years in the three layered homogeneity weakened within a small range of variation to strengthen. The results of ordinary kriging showed that there are regional differences in changes of total phosphorus content. There are significant decreases in southern and central regions.The results of the analysis of TK showed that:After the processing of the specific value, the trend of the mean of the total potassium content in three layers first decreased, and then increases in 1980. The trend of the total potassium content in 2010 compared with 1980 is just the opposite. The average TK content in 2010 was higher than that in 1980 in the same soil layers. The coefficient of variation in 1980 was higher than that in 2010 in the same soil layers. TK content of the two periods was log-normally distributed. By performing experimental semivariograms analysis, results showed that the nugget effect of 0-10 cm was increasing, while nugget effect of 10～30 cm and 30～50 cm was reducing. This showed that spatial variation of the total potassium content of the surface were influenceed and controlled by the factors such as fertilization, tillage practices, cropping systems.the range of TK in the three layers in 2010 was smaller than that in 1980, which showed the distribution of total phosphorus content in the past 30 years in the three layered homogeneity were becoming weaken,but variation within a small range within becoming strengthen. The results of ordinary kriging showed that there were regional differences in changes of total nitrogen content. There are significant decreases in southern and central regions; while the increase mainly happened in eastern areas. |
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