Fractal features of sandy soil particle-size distributions during the rangeland desertification process on the eastern Qinghai-Tibet Plateau

• Published in: Journal of soils and sediments Vol. 20; no. 1; pp. 472 - 485
• Main Authors: Feng, Xiao, Qu, Jianjun, Tan, Lihai, Fan, Qingbin, Niu, Qinghe
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 2020; Springer Nature B.V
• Subjects: Arithmetic; Biodegradation; Bulk density; Clay; Computer simulation; Correlation analysis; Data points; Deposition; Desertification; Dimensions; Drying; Drying ovens; Earth and Environmental Science; Ecological monitoring; Environment; Environmental degradation; Environmental Physics; Fractal geometry; Fractal models; Fractals; Lasers; Light; Nitrogen; Organic carbon; Organic soils; Oxidation; Parameters; Particle size; Potassium dichromate; Rangelands; Sand; Sandy soils; Sec 5 • Soil and Landscape Ecology • Research Article; Silt; Soil degradation; Soil density; Soil depth; Soil environment; Soil erosion; Soil moisture; Soil properties; Soil Science & Conservation; Soil testing; Soils; Sulfuric acid; Sulphuric acid; Variance analysis; Wind erosion; Wind tunnels; Tibet; Tibetan Plateau; Desertification process; Fractal dimension; Wind erosion and deposition; Soil properties; Soil particle-size distributions
• ISSN: 1439-0108; 1614-7480
• DOI: 10.1007/s11368-019-02392-6

Purpose Fractal theory has been frequently applied to quantify soil particle-size distributions (PSDs) and evaluate soil degradation. Eolian desertification occurring on the eastern Qinghai-Tibet Plateau is threatening the ecological environment. It is essential to investigate the desertification process by adopting the concept of space as a substitute for time. Here, the fractal features of soil PSDs and their relationships with selected soil properties and wind erosion and deposition were studied. Materials and methods The tested soil samples were collected from rangelands with four different degrees of desertification (light, medium, severe, and extremely severe). Soil particle sizes were measured by a laser diffraction particle-size analyzer. Soil moisture and soil bulk density were determined by the soil weight difference before and after oven-drying for 8 h. Soil organic carbon was determined by the K 2 Cr 2 O 7 -H 2 SO 4 oxidation method and soil total nitrogen was analyzed using the Kjeldahl digestion procedure. Wind tunnel experiments were conducted to simulate wind erosion and deposition during the desertification process. Values of the fractal dimension of soil PSDs were calculated using the volume-based fractal model. ANOVA with an LSD test and Pearson correlation analysis were used to analyze whether different parameters used in the fractal model influenced the results of the fractal dimensions and were reasonable to be applied. Results and discussion Different parameters, including the arithmetic mean size and the upper sieve size of two successive sieve sizes, values of R min , and the number of data points used in the fractal model, rarely influenced the results of the fractal dimensions ( p  > 0.05). The D values showed a significantly positive correlation with the clay and silt contents and a strong negative correlation with the sand contents. Along the degrees of desertification from light to extremely severe, the contents of clay, silt, and very fine sand decreased while the fine sand contents increased, and the D values decreased accordingly. Rangelands with heavier desertification and lower D values were more easily exposed to wind erosion, relating to the further loss of soil organic carbon, soil total nitrogen, and soil moisture and increased soil bulk density. The soil depth could affect soil PSDs and the selected soil properties of rangelands under light and medium degrees of desertification but rarely influenced those of severely and extremely severely desertified lands. Conclusions Different parameters, including the arithmetic mean size, the upper sieve size, values of R min , and the number of data points used in the fractal model, had no impacts on the results of the fractal dimensions, and were reasonable to be applied. We suggest the fractal dimension as an effective indicator to evaluate soil environment changes induced by desertification.