基于允许流失量和正负地形源汇理论的喀斯特关键带土壤侵蚀研究

喀斯特地区下垫面的特殊复杂性使得地表发生显著坡面径流需要达到更大的降水累积阈值,碳酸盐岩岩石成土速率的缓慢和空间异质性导致喀斯特地区的土壤存量被严重高估和均一化等,因此,传统经典的土壤侵蚀模型在喀斯特地区难以适用。本文依据喀斯特关键带岩性的差异,确定其有效降水侵蚀阈值,并对降雨侵蚀力进行重新测算;根据碳酸盐岩化学成分的差异,计算其成土速率并作为土壤允许流失量;通过地貌—水文分析法提取喀斯特洼地空间分布信息,对喀斯特关键带土壤侵蚀算法进行多次改进和创新。结果显示：① 传统算法忽视了喀斯特关键带下垫面的特殊性,致使其平均降雨侵蚀力被高估47.35%,且喀斯特区域的平均降雨侵蚀力仅相当于非喀斯特区域的59.91%;② 传统算法可能将一些无土或少土可流区计算为土壤的高侵蚀量区,而连续性碳酸盐岩、碳酸盐岩夹碎屑岩、碳酸盐岩与碎屑岩互层的土壤允许流失量仅分别为0.21 t ha^-1 yr^-1、1.2 t ha^-1 yr^-1、2.89 t ha^-1 yr^-1;③ 传统算法通常将有坡度和耕作的洼地视为土壤侵蚀的高发区,但其实际应是地表侵蚀的沉积区,喀斯特洼地在空间上的连续性与碳酸盐岩的分布区基本重合;④ 传统算法高估土壤侵蚀面积27.79%,土壤侵蚀量47.72%。总之,传统经典模型会大大高估喀斯特地区的土壤侵蚀量,因此,应该建立一种精确适用的模型。另外,由于喀斯特地区的成土速率慢而土层薄、总量少,土壤允许流失量远低于非喀斯特区域侵蚀标准,应制定适用于喀斯特地区的土壤侵蚀分类分级标准和风险评价方法。

Assessment of soil erosion in karst critical zone based on soil loss tolerance and source-sink theory of positive and negative terrains

Traditional classic soil erosion models are not applicable in karst areas. In this study, the effective rainfall erosion threshold was obtained and the rainfall erosivity was re-estimated, according to the lithologic difference of the karst critical zone. The soil formation rate was calculated and used as the soil loss tolerance, based on the chemical composition variation of carbonate rocks. The spatial distribution information of karst depression was extracted by geomorphologic-hydrologic analysis, and the soil erosion algorithm in the karst critical zone was modified and improved. The results showed that: (1) The traditional algorithm ignored the specificity of the underlying surface of the karst critical zone. The average rainfall erosivity was estimated to be 47.35%, and the average rainfall erosivity in the karst area is only 59.91% of the non-karst area. (2) The soilless or less soil areas could be miscalculated as the high erosion region by using the conventional algorithm. However, the soil loss tolerance by continuous carbonate, carbonate clastic, carbonate and clastic interbeds were about 0.21, 1.2 and 2.89 t ha^-1 yr^-1, respectively. (3) Sloping lands and croplands in the depressions are generally regarded as the high incidence area of soil erosion, but the depression of the karst should be the sediment area of surface erosion. The spatial distribution of karst depression was basically coincided with that of carbonate rocks. (4) The traditional algorithm overestimated the soil erosion area at about 27.79%, while the soil erosion amount at approximately 47.72%. Generally, the traditional classic model could greatly overestimate the soil erosion amount in the karst area, therefore, an accurate and applicable model should be established. In addition, due to the slow soil formation rate, the thin soil layer and the less total amount of soil in karst area, the soil loss tolerance was far lower than the erosion standard of non-karst area. The classifying and grading standard and risk assessment method of soil erosion applicable to karst area should be set and established.