201. The characteristics of gravelly soil physical properties and their effects on permafrost dynamics: A case study on the central Qinghai-Tibetan Plateau
- Author
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Yu Qin, Yujie He, Yongjian Ding, Jianjun Chen, Xinlei Guo, Shuhua Yi, and Qingbai Wu
- Subjects
Hydraulic conductivity ,Soil test ,Soil texture ,Soil water ,Erosion ,Environmental science ,Soil horizon ,Soil science ,Permafrost ,Active layer - Abstract
Soils on the Qinghai-Tibetan Plateau (QTP) have distinct physical properties from agricultural soils due to weak weathering and strong erosion. These properties might affect permafrost dynamics. However, few studies have investigated both quantitatively. In this study, we selected a permafrost site on the central region of the QTP and excavated soil samples from 20 cm to 200 cm. We measured soil porosity, thermal conductivity, saturated hydraulic conductivity and matric potential in the laboratory. Finally, we ran a simulation model replacing default sand or silty clay parameters with different combinations of these measured parameters. Results showed that gravel content (diameter > 2 mm) was ~ 55 % on average in soil profile; soil porosity was less than 0.3; saturated hydraulic conductivity ranged from 0.004–0.03 mm s−1; saturated matric potential ranged from −14 to −604 mm. When default sand or silty clay parameters were substituted with these measured values, the model errors of soil temperature, soil liquid water content, active layer depth and permafrost lower boundary were reduced. The root mean squared errors of active layer depths simulated using measured parameters, and the default sand and silty clay parameters were about 0.28, 1.06, 1.83 m, respectively. Among these measured parameters, porosities, which were much smaller than soil textures used in land surface models, played a dominant role in reducing model errors. We also demonstrated that soil water dynamic processes should be considered, rather than using static properties under frozen and unfrozen soil states as in most permafrost models. We concluded that it is necessary to consider the distinct physical properties of soil and water dynamics on the QTP when simulating dynamics of permafrost in this region. It is important to develop methods for systematic measuring physical properties of gravelly soil and to develop a spatial dataset for porosity because of its importance in simulating permafrost dynamics in this region.
- Published
- 2018