Aeolian additions of podzolic soils on the high-altitude mountains in central Taiwan-sediment origin and pedological implications

Abstract

Abstract The podzolic soils with characteristic eluvial horizon are widely distributed in the mountainous area of Taiwan with a cold and humid climate, where the altitude is greater than 3000\xa0m above sea level. There are multiple sequence horizons along the soil profile in some of the places. These repeated patterns of the soil horizons have not been reported in the literature, which may indicate the cycles of climatic or environmental changes in the past. The puzzling origin of these soils may be answered by identifying the parent materials and their source areas through age dating and isotopic analyses. Four soil profiles were sampled from Hohuanshan (HHM and HWS), Nanhuashan (NH), and Battonguan (BTG) of the alpine area in central Taiwan. These soils, in general, show the characteristics of silt and silty loam in soil texture, high soil organic carbon, low cation exchange capacity, and low base saturation percentage. Soil classification in accordance with the US System (Soil Taxonomy) suggests all the soils in this study are Humicryepts. The index quantification from soil morphology also shows the extent of pedogenesis fairly between profiles, which is supported by the ages obtained from the charcoals or highly carbonized woods in various sizes found in the dark black soil horizons. It suggests that these soils began to develop approximately four thousand years ago, during the cool and dry period of the Holocene according to the paleoclimate records, and the cold and dry climate favors the preservation of charcoals. Despite the suspicions of aeolian deposits in Taiwan, the high mountain areas are far from the location of aeolian deposits. It was not until recent years that the researchers proposed the idea of aeolian addition to the soils in Hohuanshan. The characteristics of the multiple sequence soil horizons may offer an insight into the paleoenvironment of the high mountain areas. The bimodal pattern on the particle size distribution indicates an additional parental source for these soils. The evidence from the calculated strontium isotope ratios delivers an argument that these soils are developed by in-situ weathering with the addition of aeolian material. They are yellowish and subangular particles with sizes ranging from 7 to 10\xa0µm. The aeolian deposits of Hohuanshan reveal the geochemical characteristics of the river sediments of the Da-An, Da-Chia, Da-Du River, and Cho-Shui Rivers. This suggests that the source of the aeolian particles in the soils was supplied with materials connected with the river system of central Taiwan. In the same manner, the aeolian deposits of Nanhuashan and Battonguan were likely derived from the river sediments of eastern Taiwan. The example from the NH profile indicates a constant rate of aeolian addition, which rules out the influence of the fluctuations of climate change since the mid-Holocene. The findings of this study not only help validate previous studies on the paleoenvironment of Taiwan but also inspire further aspects of the Taiwanese paleoclimate researches.