Using four approaches to separate the effects of climate change and human activities on sediment discharge in karst watersheds.

[Display omitted] • Four methods were used to decomposed the effects of climate change and human activities effects on sediment discharge (SD). • Human activities had the larger influence on SD , especially dam construction. • Sediment identify factor analysis indicated that sediment concentration greatly influenced SD , accounting for 100% to 154%. • The four quantitative methods were compared and their relative merits were summarized. Quantifying the relative contributions of climate change and human activities to changes in sediment discharge is closely related to regional water resources, soil management, and healthy ecosystem function. However, few studies have used different methods to decompose influences of climatic variability and human activities on changes to sediment discharge, especially in karst regions of southwest China which are experiencing severe soil erosion. This study systematically reviewed four methods (simple linear regression, double mass curve, sediment identify factor analysis, and elastic coefficient method) to separate the contribution of climate change and human activities to sediment discharge variation in four karst watersheds of southwest China during 1955 to 2015. The trend and abrupt change year of sediment discharge in the four watersheds were obtained using a nonparametric Mann-Kendall trend test and sequential test method, respectively. Result showed that the sediment discharge in all four watersheds all decreased significantly (P < 0.05), and the abrupt change years were 2003 or 2004 for these watersheds. The simple linear regression method, double mass curve method, and elastic coefficient method all indicated that the sediment discharge was mainly influenced by human activities, which contributed more than 73% of the observed change. For the sediment identify factor analysis method, sediment concentration was the principal factor influencing sediment discharge variation. The results provide a reference for evaluating the influence of climate and human activities on sediment discharge, and can aid in preparing regional soil conservation policy in karst watersheds. [ABSTRACT FROM AUTHOR]