Abstract
The sedimentary sequence deposited in a depression provides good opportunity for karst watershed soil loss reconstruction. Extensive sediment dating and soil loss estimation in karst areas of Southwest China have been carried out in the past few decades. Unfortunately, most studies only revealed soil loss over the last 50–100 years by using 137Cs and/or 210Pb. This study attempts to reconstruct soil erosion in a watershed over the past millennium using sediment dating combined with palynological techniques. In this study, two karst watersheds with different degrees of rocky desertification were selected, and soil profile samples were collected from the depressions to determine pollen taxa, 137Cs and soil organic carbon, and then, the optically stimulated luminescence (OSL) and radiocarbon were used to date the sediments in the two profiles. The results showed that erosion rate characteristics in the Liaojiawodang (LJWD, severe rocky desertification) and Dajutang (DJT, mild rocky desertification) watersheds were markedly different over the last 1000 years. On average, the erosion rates of the LJWD and DJT watersheds were 0.13 Mg ha−1 yr−1 and 1.28 Mg ha−1 yr−1, respectively. Overall, the erosion rate in the areas with severe rocky desertification was obviously small in the past millennium, and there was no serious soil loss. This result indicated that rocky desertification developed at least 1000 years ago. Pollen analysis indicated that soil erosion changes in both watersheds over the past 1000 years were well correlated with the change in crop pollen indicating human farming activities. Based on changes in the content of different types of pollen in sediments, the change in soil erosion can be linked to the change in land use and vegetation landscape. Overall, this work improves our understanding of the relationship between soil erosion and agricultural activities and vegetation landscape change in karst watersheds.
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