摘要
三峡水库是我国特大型水利枢纽工程,对其合理的开发利用、保护和治理具有至关重要的意义。2009年三峡大坝蓄水后形成落差为30米、面积达348.97km2的消落带,主要分布于库区周围海拔145m-175m之间。库区消落带每年5月末到6月初,水位保持在低水位145米,到10月份水位逐渐升高至175米并保持到12月,次年的1-4月降到156-160m,至5月底降到145 m。三峡库区消落带每年呈现出周期性的反季节性的涨落的特征。每年因周期性水位涨落、干湿交替,这可能使土壤结构体退化,抗蚀性能下降,使消落带水土流失加剧。
土壤退化与水土流失对人类社会生存和发展构成了严重威胁,引发了一系列的生态环境问题。本文以重庆小江流域典型消落带为研究对象,分析了消落带土壤的抗蚀性特征；进而研究了消落带土壤团聚体结构现状与稳定性特征,土壤团聚体组成的演变特征；探讨了消落带土壤团聚体与有机质之间的关系。研究结果如下：
(1)选用15项指标对研究区各地类土壤抗蚀性进行主成分分析,得到4个主成分因子。分别为水稳性团聚体因子；土壤无机胶粒因子；团聚类因子；有机质类因子。通过各主成分贡献率作为权重系数组成三峡库区消落带土壤抗蚀性综合指数计算方程Y=0.526Y1+0.277Y2+0.107 Y3+0.091Y4。通过相关分析表明,三峡库区消落带土壤的胶结物主要以<0.001 mm粘粒为主,而有机质对土壤胶结贡献较弱。>0.25mm水稳性团聚体含量、<0.001 mm粘粒含量是反映消落带土壤抗蚀性较好的评价指标。
(2)土壤团粒结构粒径分布的分形维数越小,水稳性大团聚体含量越高,水稳性团聚体破坏率越低,土壤结构稳定性越好,其中表层土壤团粒结构分形维数平均值为2.85。土壤颗粒的粒径分布分形维数受细颗粒物质含量影响,细颗粒物质越多,分形维数越大；细颗粒物质越少,分形维数越小,其中表层土壤颗粒组成分形维数平均值为2.62。土壤颗粒组成分形维数与水稳性团粒分形维数呈负相关性。
(3)消落带土壤有机质主要富集在团聚体0.25-0.5mm和0.5～1mm中。土壤粒级0.5～1mm和1～2mm团聚体保存几率与土壤有机质之间的相关性很好,相关系数极高,团聚体有机质对土壤粒级0.5～1mm和1～2mm的保存几率有直接影响。通过分析土壤有机质、水稳性指数、土壤团聚体的颗粒组成分形维数与团聚体稳定性指数在表层土壤中均呈正相关,而与土壤团聚体的水稳性团粒分形维数、>0.25mm土壤团聚体破坏率呈负相关。
(4)通过对库区消落带表层土壤有机质与>0.25mm水稳性团聚体含量、水稳性指数构成的变化趋势图反应,有机质含量、>0.25mm水稳性团聚体含量、水稳性指数变化具有变化趋势的一致性。A层土壤有机质对>0.25mm水稳性团聚体、水稳性指数具有正相关,土壤有机质含量越高,>0.25mm水稳性团聚体、水稳性指数就越高。但是通过对消落带土壤B层有机质与>0.25mm水稳性团聚体、水稳性指数变化的趋势图,反应出并没有变化趋势的一致性,说明B层土壤有机质含量对>0.25mm水稳性团聚体、与水稳性指数影响不明显。土壤中有机质含量变化并不是对所有土壤结构影响都有正相关的变化性。高程对其变化趋势的影响也并不很明显。
(5)通过测定不同粒级团聚体有机质表明,不同粒级团聚体有机质分布的最大值主要集中在0.25-0.5mm团聚体,在该粒级中最大值占到了13个近百分之五十。应用通径分析方法计算出的0.25-0.5mm团聚体保存几率对SOC决定系数为0.2344,其影响最大,有机质含量对保存几率有影响。这表明用通径分析计算出的结论与实际测的结果有一定的一致性。实际测的有机质数据也与理论数据有区别,理论分析结中认为1-2mm团聚体保存几率对SOC决定系数仅次于0.25-0.5mm团聚体保存几率对SOC决定系数,而实际测的结果为0.5-1mm团聚体有机质含量较高,其中有机质在各粒级中最大值出现9次。
Three Gorges Reservoir is the large Water Control Project in our country。It is vital importance for us to development、protection and management of Gorges Reservoir。Three Gorges Dam reservoir will formed the fall of 30 meters and the area of 300 km2 of the water-level-fluctuating zone in 2009, which is mainly located in the 145m-175m of the reservoir sea level. Each year in may and June, the water level of water-level-fluctuating zone remained at a low water level 145 meters, the water level gradually increased to 175 meters on October and maintained to 12 months, January to April of the following year dropped to 156～160m, by the end of May water level fell to 145 m. The water-level-fluctuating zone will show the cyclical and anti-seasonal features every year. The soil of the water-level-fluctuating zone will be soaked by the cyclical change of water level and the occurrence of alternating wet and dry, which may change the soil structure, resulting in soil erosion, so that the soil erosion increased in water-level-fluctuating zone.
Soil degradation and soil erosion produce serious threat on the survival and development of human society, triggering a series of ecological and environmental problems. The typical water-level-fluctuating zone in small river basin as the research object, the paper analyzes the soil corrosion resistance characteristic of water-level-fluctuating zone; and further study soil aggregate structure stability characteristics and the evolution of soil aggregates characteristic; discussed the relationship of soil aggregates and organic carbon. The results are as follows:
(1) The 15 indexes were used to analyze soil anti-erodibility by means of PCA and obtained the 4 categories of water-stable aggregate type, inorganic colloid type, aggregate type, and organic and index of soil water-stable type. PCA comprehensive exponent of anti-erodibility index can be calculated by offer rate of the four principal component factor. Through contribution rate of the principal component as the weight coefficient the can be composed. Soil erosion resistance index calculation equation of Three Gorges Reservoir (Y= 0.526Y1+0.277 Y2+0.107 Y3+0.091 Y4) Through correlation analysis showed that the soil organic matter content is very lower and not the main soil cement material, the main cement material is inorganic clay＜0.001 mm in The water level-fluctuating zone of the Three Gorges reservoir area.＞0.25mm water stable aggregate content,＜0.001mm clay content is good evaluation indexes of reflecting corrosion resistance.
(2) The fractal dimension of size distribution of soil aggregate structure is smaller, water stable aggregates content is in large higher, water stable aggregates is in the lower damage rate, the soil structure stability is the better. The mean value of fractal dimension of surface soil aggregate is 2.85. The fractal dimension of Soil particle size distribution is affected by the content of fine particulate matter, fine particulate matter is more, the fractal dimension is greater; fine particulate matter less, the fractal dimension smaller. The mean value of fractal dimension of surface soil particle is 2.62. Fractal dimension of soil particle was negative correlation with fractal dimension of water stable aggregates.
(3) Soil organic matter of the Fluctuating zone is mainly enriched in soil aggregates 0.25～0.5mm and 0.5～1mm. The ASI of soil aggregate 0.5～1mm and 1～2mm showed significant positive correlation with the content of soil organic matter, the correlation coefficient is extremely high. The content of organic matter of soil aggregates likely have a direct impact with the ASI of soil aggregates 0.5～1mm and 1～2mm. Through analysised, we discovered that soil organic matter, water stable index, fractal dimension of soil aggregate and aggregate stability index soil were positively correlation in each other,and with fractal dimension of soil water stable aggregates and＞0.25mm soil aggregate failure rate was a negative correlation in the surface.
(4) Through trend map which is constituted by the A layer soil organic matter and＞0.25mm water stable aggregates content, and water stability index in the surface soil, organic matter content and＞0.25mm water-stable aggregate content, and water stability refers to changing trends in consistency in Fluctuating zone of the reservoir. The A layer of soil organic matter has a positive correlation with＞0.25mm water stable aggregates and water stable index. The soil organic matter content is the higher,the＞0.25mm water stable aggregates and the water stability index is higher. However, through trend changing map which is constituted by the B layer soils organic matter and＞0.25mm water stable aggregates, and water stability index in the Fluctuating zone, there is no consistent trend. The B layer of soil organic matter has not obviously correlation with＞0.25mm water stable aggregates and water stable index. Changes of soil organic matter content does not have all the impact of soil structure. The impact of elevation change is not very obvious.
(5) By measuring organic matter content of the different size aggregates,it is showed that the maximum of organic matter content was distributed mainly in 0.25～0.5mm soil aggregate in the different size aggregates, the maximum value of the grain size aggregate is accounted for nearly 50 percent. The preservation probability of 0.25～0.5mm soil aggregate which was calculated by Path analysis has influence on decision coefficient of SOC, the decision coefficient is 0.2344. The content of organic matter has impact on preservation probability of soil aggregate. This indicates that the conclusions which was calculated by the Path analysis have a certain consistency with the actual measured results. Actual measured data and theoretical data of organic matter are different, the preservation probability of 1～2mm soil aggregate was smaller determination coefficient than the 0.25～0.5mm soil aggregate to SOC in theretical analysis. In actual measured results, content of organic matter of soil aggregate 0.5～1 mm is higher, the maximum value in content of soil aggregate(0.5～1mm)organic matter appear 9 times in various size.
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