Abstract:
Background Ningxia Lingwu Baijitan National Nature Reserve (NLBNNR) is adjacent to the east coast of the middle and upper Yellow River in China, and the minimum distance from the Yellow River to it is only 5 km, while there are a large number of moving dunes in the Nature Reserve. Accurate analysis of the moving rate and its control factors of the dunes in Baijitan has a guiding role in the management measures to reduce the amount of quicksand into the Yellow River. However, the current qualitative analysis and one-to-one quantitative analysis methods limit the accurate determination of the control factors of dune moving.
Methods Three sample plots with triangular distribution and an area of 300 m×300 m were selected in the moving sandy land in Baijitan National Nature Reserve. Based on high-resolution remote sensing images, the geomorphological characteristic parameters and dune morphology parameters, and the moving rate of dunes in eight periods from 2008 to 2021 were analyzed. Based on Google Earth Engine(GEE), several environmental factors(resultant drift potential(RDP), fraction vegetation cover(FVC)、accumulation precipitation, average land surface temperature(LST), average air temperature) value in each period of the study area were obtained, and then redundancy analysis(RDA) was used to reveal the contribution rate of each environmental factor to the moving rate of dunes.
Results From 2008 to 2021, the ridge-line number of mobile dune gradually decreased, whereas the average length of ridge-line increased, which implied the dunes merged during the movement in NLBNNR. The moving rates of dunes steadily decreased in five stages, with 5.62 m/a in the first stage and 4.64 m/a in the last stage. The decreasing rate in each stage was 0.22 m/a to 0.28 m/a, with a total decrease of about 1 m/a in 13 a. The control factors of the moving rate of dunes were divided into internal factors and external factors. The height, width and defect density of the dunes were the internal control factors. The height and width of the dunes had extremely significant linear negative correlation with the moving rate, and the defect density was significant positively correlated with the moving rate (P < 0.01). The contribution rates of RDP, FVC, cumulative precipitation, average LST and average air temperature to dune movement were 78.7%, 6.7%, 3.9%, 2.7% and 2.6%, respectively, indicating that only RDP was the external control factor of dune movement.
Conclusions The number of moving dunes decreased, while the volume of single dune increased, and the moving rate of dunes dropped in five steps from 2008 to 2021 in the Nature Reserve. The main external factor controlling the moving rate of dunes was RDP in Baijitan in the past 13 years, but LST was found to be another key factor controlling dune moving during the seasonal freezing period.