Ting Hua

Nebkha (coppice dune) formation and significance to environmental change reconstructions in arid and semiarid areas

Environments in arid and semiarid regions are extremely sensitive to climate changes. High wind activity in these regions has resulted in an extensively developed arid geomorphology, but past environmental changes are poorly understood because of the absence of relatively high-resolution proxies. The accumulation characteristics of nebkhas, which have developed extensively in these regions, can be used as a method of reconstructing environmental changes. Here we summarized recent advances in research on the formation, development, and sediment characteristics of nebkhas and their significance to environmental changes in arid and semiarid regions. Based on the studies of our colleagues, we suggested that research on nebkha formation can provide distinct clues about environmental changes in arid and semiarid regions; however, continued studies are needed.

Key driving forces of desertification in the Mu Us Desert, China

The temporal trends and key driving forces of desertification in the Mu Us Desert are representatives of most arid regions of Asia with a high risk of desertification. We analyzed the significance of Aeolian transport on desertification in the Mu Us Desert by field investigations, sampling, wind tunnel experiments, particle size and nutrient measurements, and statistics on aeolian transport potentials. The results showed that high intensities of aeolian processes may result in low differences in aeolian transport despite differences in the underlying sediments. When high desertification occurred in the 1970s, the annual losses of the ammonium N, nitrate N, available K, and available P were approximately 116, 312, 46,436, and 1,251 kg km−2, respectively. After 2010, the losses were only 8, 20, 3,208, and 84 kg km−2, which were generally only 6.7% of those in the 1970s. The results showed that although human activity may trigger desertification, the dramatic decline of aeolian transport and low nutrient loss may be the key driving forces for the occurrence of rehabilitation in this region.

Modern dust aerosol availability in northwestern China

The sources of modern dust aerosols and their emission magnitudes are fundamental for linking dust with climate and environment. Using field sample data, wind tunnel experiments and statistical analysis, we determined the contributions of wadis, gobi (stony desert), lakebeds, riverbeds, and interdunes to modern dust aerosol availability in the three important potential dust sources including the Tarim Basin, Qaidam Basin, and Ala Shan Plateau of China. The results show that riverbeds are the dominant landscape for modern dust aerosol availabilities in the Qaidam Basin, while wadis, gobi, and interdunes are the main landscapes over the Ala Shan Plateau and Tarim Basin. The Ala Shan Plateau and Tarim Basin are potential dust sources in northwestern China, while the Qaidam Basin is not a major source of the modern dust aerosols nowadays, and it is not acting in a significant way to the Loess Plateau presently. Moreover, most of modern dust aerosol emissions from China originated from aeolian processes with low intensities rather than from major dust events.

Effects of aeolian processes on nutrient loss from surface soils and their significance for sandy desertification in Mu Us Desert, China: a wind tunnel approach

Mu Us Desert, a region with high aeolian activity, is at extremely high risk of sandy desertification. Using surface soil samples collected from Mu Us Desert of northern China, we evaluated the effects of aeolian processes on nutrient loss from surface soils by employing wind tunnel experiments. The experiments were conducted using free-stream wind velocities of 14, 16, 18 and 22 m/s. Our results showed that the fine particles (<50 μm in diameter; 12.28% of all transported materials) carrying large nutrient loadings were exported outside the study area by aeolian processes. After the erodible fine particles were transported away from the soil surfaces at low wind velocity (i.e. 14 m/s), the following relatively high wind velocity (i.e. 22 m/s) did not have any significant effect on nutrient export, because the coefficients of variation for soil organic matter, total phosphorus, total nitrogen and available potassium were usually <5%. Our experimental results confirmed that aeolian processes result in a large amount of nutrient export, and consequently increase the risk of sandy desertification in arid and semi-arid ecosystems.

The effects of sorting by aeolian processes on the geochemical characteristics of surface materials: a wind tunnel experiment

The geochemical characteristics of aeolian and surface materials in potential source areas of dust are frequently employed in environmental reconstructions as proxies of past climate and as source tracers of aeolian sediments deposited in downwind areas. However, variations in the geochemical characteristics of these aeolian deposits that result from near-surface winds are currently poorly understood. In this study, we collected surface samples from the Ala Shan Plateau (a major potential dust source area in Central Asia) to determine the influence of aeolian processes on the geochemical characteristics of aeolian transported materials. Correlation analyses show that compared with surface materials, the elements in transported materials (e.g., Cu, As, Pb, Mn, Zn, Al, Ca, Fe, Ga, K, Mg, P, Rb, Co, Cr, Na, Nb, Si, and Zr) were subjected to significant sorting by aeolian processes, and the sorting also varied among different particle size fractions and elements. Variations in wind velocity were significantly correlated with the contents of Cr, Ga, Sr, Ca, Y, Nd, Zr, Nb, Ba, and Al, and with the Zr/Al, Zr/Rb, K/Ca, Sr/Ca, Rb/Sr, and Ca/Al ratios. Given the great variation in the geochemical characteristics of materials transported under different aeolian processes relative to those of the source materials, these results indicate that considerable uncertainty may be introduced to analyses by using surface materials to trace the potential source areas of aeolian deposits that accumulate in downwind areas.

Variation in vegetation greenness along China’s land border

Fourteen countries share about 22000 km land border with China, but not much is known about the variation in vegetation in such a large diverse area. By employing the remotely-sensed vegetation indices the vegetation greenness along the border was discussed. Our results show that since the early 21st century, similar trends in vegetation greenness have occurred along most of China’s border, but differences occurred on either side of the border. Along the border with North Korea and South Asian nations, greater increasing trend in vegetation greenness occurred inside China’s border, suggesting that China’s vegetation protection programs have been successful. Spatial and temporal variations in vegetation greenness trends were observed along China’s border with Russia, Mongolia, and Central Asian nations. Vegetation variation was lower inside China, along the Russian border, and China’s eastern border with Mongolia. Along most borders with Central Asian nations, rates of vegetation change inside China’s border during the growing season were higher than the rates outside the border. The results suggest that social customs, resource exploitation patterns, and national environmental conservation programs may profoundly affect vegetation greenness.