Fractal expression of soil particle-size distribution at the basin scale

Soil structure at the basin scale affects the superficial moisture content, heat, salinity balance, and ecological balance of groundwater system. To study the soil particle size fractal characteristics at the basin scale, 188 groups of soil samples were collected over a distance of 258 km in the Ziya River basin of the North China Plain. Particle volume percent was measured using a laser particle size analyzer, and then analyzed by applying the fractal theory to reveal the spatial distribution of soil particle size and soil voids. The results showed that: (1) From the Taihang Mountain piedmont to the coastal area, soil particle-size volume percentages varied in a small range, with the fractal dimension D showing an overall decreasing trend; (2) D showed a significant spatial variation, ranging from 0.13 to 2.188. It was jointly determined by particle uniformity and particle size range; (3) When D <= 1, the characteristic fractal size was 30 mu m in the basin. When 1 < D <= 1.5, the characteristic fractal size was 20 mu m and D (a) was 1.37, and when D > 1.5, the two parameters were 10 mu m and 1.77, respectively. The research results indicated that D can effectively quantify the characteristics of soil structure at a large scale.