Spatiotemporal variation of the loose deposits in Baisha River Basin after the 2008 Wenchuan earthquake

Extensive landslides were triggered by the Wenchuan earthquake(in China)on 12 May 2008,causing a tremendous amount of loose material suspended on the hillslopes,likely to be eroded and transported by rain.It is of great significance to study the long-term variation of the quantity and spatiotemporal distribution of loose deposits after a great earthquake in order to understand the restoration process,to assess the risk of future soil erosion,including geological hazards,and to further develop ecological governance strategy.In this study,information about the multi-temporal loose deposits on the ranges of the Baisha River Basin,an alpine valley near the epicenter,was extracted by objectoriented remote sensing interpretation,and analysis on their spatiotemporal variation showed that the earthquake in 2008 resulted in loose deposits covering an additional area of 81.09 km2,with a volume estimated at 0.357 billion m3.Within five years after the earthquake,the vegetation had recovered rapidly,and the extent of the deposits was significantly less.From 5 to 13 years after the earthquake,the vegetation continued to recover but at a slower rate and a decreasing trend in newly formed deposits was evident.The total area,volume and quantity of the loose deposits gradually stabilized.The geometric mean center of the loose deposits gradually moved back towards the upstream area after the earthquake and,by 2021,the mean center was about 4 km away from its pre-earthquake position.Taking the mean center of the loose deposits in 2008 as the center,the deposits in the downstream area shrank significantly after the earthquake,but collapses and landslides of deposits persisted in the upstream area to the west-southwest,west-northwest and northnorthwest from the mean center,indicating future source areas of new loose deposits in the basin.

三峡水库消落带不同水位高程土壤碳氮磷生态化学计量学特征

明确周期性淹水-出露条件下消落带土壤碳(C)、氮(N)、磷(P)及其生态化学计量沿水位高程垂直分异特征,有利于该地区的土壤养分评估及管理。通过三峡水库典型土质消落带不同水位高程土壤的采样分析,探讨不同水位高程土壤C、N、P生态化学计量特征及其影响因素。结果表明:(1)消落带土壤有机碳(SOC)、全氮(TN)、全磷(TP)平均值分别为8.70、0.79、0.63 g/kg,均低于未淹水样地。随水位高程增加,土壤SOC、TN含量增加,TP含量减少。(2)土壤C/N、C/P、N/P平均值分别为11.67、15.37、1.47,其中C/N、C/P高于未淹水样地,N/P低于未淹水样地。随着水位高程增加,土壤C/N降低,C/P、N/P增加。土壤C、N、P之间存在较好的耦合关系,N可能是该地区的土壤限制性元素,存在硝酸盐淋溶风险。(3)Pearson相关性分析说明土壤理化性质会显著影响土壤C、N、P含量(P<0.05),进而调控其生态化学计量特征,其中土壤pH、容重、水稳性团聚体组成是主要影响因子,其次是土壤含水率和粒径组成。综上,周期性淹水过程影响消落带土壤C、N、P含量及其生态化学计量特征,今后应根据消落带土壤C、N、P生态化学计量特征的空间异质性,采取具有养分适应性的水土保持林草措施配置。