中国主要流域盆地风化剥蚀率的控制因素

利用中国40余条主要河流及其支流的沉积物和溶解质载荷分别去表征流域盆地的物理剥蚀率和化学风化率。研究发现,中国流域盆地的总剥蚀率明显高于世界平均值,且具有南北低中间高的地理分布特点,黄河中游的皇甫川机械和总剥蚀率是世界上已知的最高值。根据流域盆地的机械剥蚀率、化学风化率和总剥蚀率及其影响因子之间的相关分析,得出中国流域盆地中的机械剥蚀率在总剥蚀率中占主导地位,机械剥蚀率和总剥蚀率主要由流域的干旱指数和相对高差来控制,不同流域之间总剥蚀率72%的差异是由于这两个参数所造成的。而化学风化率在总剥蚀率中总是处于次要地位,它主要受到流域年均降水量和气温的影响(39%),且不受机械剥蚀率的控制。流域盆地自身属性、径流量、最高海拔和森林覆盖率对流域岩石的风化剥蚀率影响不大。构造活动提高了流域的机械剥蚀率和化学风化率,且对机械剥蚀率的影响更强烈。与世界流域盆地相比,中国流域盆地受到流域干旱指数的影响更为显著。

Natural Controls of Fluvial Denudation Rates in Major Drainage Basins of China

The chemical weathering and mechanical denudation play an important role in studying the sea-land matter balance and global climatic change. The rock weathering and erosion products, including the dissolved and solid yields which amount to 15Gt and 5Gt annually, are mainly transported through the rivers into the ocean. The dissolved and particulate loads of the river are used to estimate the physical erosion and chemical weathering rates over the world drainage basins, respectively. The total weathering rate is obviously higher than that of major world watersheds. It is found that the lower erosion rates are distributed in the northern and southern China, while the higher values are observed in the middle of China. The average physical denudationrate rate in Huangfuchuan (the Yellow River's tributary) is the highest value known in the world. The chemical weathering rate is always far less than the mechanical denudation rate in the same watershed, furthermore, the proportion of total denudation contributed by chemical weathering decreases as total denudation rate increases. Data demonstrates chemical weathering rate constitutes only a small proportion of the total denudation rate, while mechanical denudation rate is the most important denudation rate in most drainage basins in China. Moreover the chemical weathering rate is to a less extent controlled by the mechanical denudation rate in the same drainage basin.The environmental and basin property data are quantified and indicated by the annual mean precipitation and temperature, runoff, aridity index, relief ratio, highest altitude, vegetative ratio, river length and basin area in the past decades. Variables expressing basin relief characteristics and aridity indexes are found to be most strongly associated with mechanical and total denudation rates, with approximately 72% of the variance in the total denudation rates being accounted for by the basin relief ratios and aridity indexes. The annual mean precipitation and temperature are responsible for the 39% of the variance of the chemical weathering rates in the Chinese drainage basins. However, basin property, runoff, highest altitude and vegetative ratio are only weakly associated with the physical denudation and chemical weathering rates. The effect of vegetative ratio on increasing the chemical weathering rates and decreasing the physical denudation rates possibly shows clear on the small scale and usually faint on the large scale. The key factors identified as controlling denudation rates here are also applicable to the interaction between tectonic and denudation processes in the Chinese watersheds, although chemical weathering rates are more weakly associated with these topographic variables than mechanical denudation rates. In particular, compared to the world other watersheds, the aridity indexes play a major role in controlling the denudation rates of Chinese drainage basins.