Soil residence time and formation rate derived from meteoric 10Be in the Hemuqiao drainage basin, Zhejiang

Due to the complex physical and biogeochemical processes with the soil open system, the precise determination of soil formation rate is still a challenge. Meteoric cosmogenic radionuclide 10Be(MCN)is a nature tracer, which can quantitively estimate and trace the soil evolution process over 107 years. This study focuses on the H1 slope in the Hemuqiao watershed of Zhejiang Province, and samples the soil profiles weathering from bedrock of tuff at the top and middle ridge. We use the meteoric 10Be to date the soil residence time and evaluate the soil formation rate of these two profiles. The results suggest that the minimum age of soil profile with a depth of 20 cm at the ridge top is 1495±176 a, corresponding to a maximum soil formation rate of 134±16 mm/ka. Whereas, the minimum age of soil profile with a depth of 60 cm at the middle ridge is 8345±709 a, and the maximum soil formation rate yields 72±6 mm/ka. The soil formation rate shows a significant decrease trend with the increase of soil thickness, which is consistent with the law established based on the mass balance equation that the soil formation rate decreases with the increase of soil thickness. Compared with the soil formation rate estimated by terrestrial in-situ cosmogenic nuclides 10Be and 26Al(TCN)from bedrock in the global humid and semi humid regions(in the order of 10~102 mm/ka), the soil formation rate values estimated based on meteoric 10Be in this study is reasonable. On account of limitations of TCN method on bedrock lithology, this study uses MCN to determine soil age and soil formation rate, which is theoretically applicable to various types of bedrock and has the advantages of convenient sampling and simple pretreatment. The MCN method provides a new approach for evaluating soil age and formation rate, and the results can provide scientific guidance for the soil formation and evolution in the mountainous areas, soil resource protection, and research and practice in hydrology and ecology.