Influences of human activities on sediment discharge from devastated weathered granite hills of southern China: effects of 4-year elimination of human activities

Sediment discharge is a serious problem in the weathered granite mountains of southern China. Human activities, such as the harvesting of ferns and litter for fuel, are the main source of sediment, but the details of the processes and mechanisms leading to sediment discharge are unclear. Data on sediment yields, percentages of peak storm runoff and fern undergrowth and litter cover extent in the two basins—one a control from which people have been excluded since 1997, and the other where normal harvesting practices are permitted—were used to evaluate how human activity affects sediment discharge. The annual sediment discharge decreased immediately after implementing control practice, despite no marked changes in the 4 years after 1997 in the percentages of peak storm turnoff and the fern and litter cover extent and density. The 4-year period of control practice was too short to affect the relationship between peak rainfall and peak storm runoff and the fern and litter covers and their amounts, but long enough to contribute to the reductions in sediment discharge in the control basin by decreasing erodibility. Thus, sediment discharge was probably reduced to some extent by the elimination of human impacts even though a well-developed vegetation layer did not develop.