基于GEE和Canoco的沙丘移动速率及其内外控制因子贡献率分析

Analysis of dune movement rate and contribution rates of internal and external factors based on Google Earth Engine and Canoco

环境因子控制沙丘移动速率的研究多集中于定性分析和一对一定量分析层面。基于高分辨率遥感影像分析2008—2021年间宁夏白芨滩流动沙丘在7个时段的移动速率,利用GEE获取研究区各时段的多个环境因子数值,再采用Canoco的冗余分析揭示各环境因子对沙丘移动速率的贡献率。结果表明:1)2008—2021年间,流动沙丘脊线数逐步减少而脊线平均长度递增,沙丘在移动中发生合并,沙丘移动速率分5个阶段稳步下降,每个阶段的降速在0.22~0.28 m/a间,13 a间共下降约1 m/a;2)内控因子沙丘高度和宽度与移动速率均呈极显著线性负相关关系,缺陷密度与其呈极显著线性正相关关系(P<0.01);外控因子合成输沙势(RDP)、植被覆盖度、累积降水量、平均地温(LST)、平均气温对沙丘移动的贡献率分别为78.7%、6.7%、3.9%、2.7%和2.6%,RDP是控制白芨滩流动沙丘近13年来移动速率的主要外因,但对比2个时段发现季节性冻结期内LST是控制沙丘移动的另一关键因子。

[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.