[Dynamics of soil erosion at upper reaches of Minjiang River based on GIS]

Based on TM and ETM imagines, and employing GIS technique and empirical Revised Universal Soil Loss Equation (RUSLE) model, this paper studied the dynamics of soil erosion at the upper reaches of Minjiang River during three typical periods, with the main affecting factors analyzed. The results showed that the soil erosion area was increased by 1.28%, 1.84 % and 1.70% in 1986, 1995 and 2000, respectively. The average erosion modulus was increased from 832.64 t x km(-2) x yr(-1) in 1986 to 1048.74 t x km(-2) yr(-2) in 1995 and reached 1362.11 t x km(-2) yr(-1) in 2000, and soil loss was mainly of slight and light erosion, companying with a small quantity of middling erosion. The area of soil erosion was small, and the degree was light. There was a significant correlation between slope and soil loss, which mainly happened in the regions with a slope larger than 25 degrees, and accounted for 93.65%, 93.81% and 92.71% of the total erosion in 1986, 1995 and 2000, respectively. As for the altitude, middling, semi-high and high mountains and dry valley were liable to soil erosion, which accounted for 98.21%, 97.63% and 99.27% of the total erosion in 1986, 1995 and 2000, respectively. Different vegetation had a significant effect on soil erosion, and shrub and newly restored forest were the main erosion area. Excessive depasture not only resulted in the degradation of pasture, but also led to slight soil erosion. Land use type and soil type also contributed to soil loss, among which, dry-cinnamon soil and calcic gray-cinnamon soil were the most dangerous ones needing more protection. Soil loss was also linearly increased with increasing population and households, which suggested that the increase of population and households was the driving factor for soil loss increase in this area.