Background Sediment is one of the key hydrological factors in the watershed. In-depth exploration of its variation characteristics and influencing factors is of great significance to the comprehensive management of soil erosion in the watershed. Zhangshui watershed is the main sediment-producing area of Ganjiang river, and it is one of the regions with the longest time series of observation data in Yangtze River basin. In this paper, the Zhangshui watershed in the upper reaches of the Ganjiang river was taken as the study area to analyze the variation characteristics of sediment transport and the direct, indirect and comprehensive effects of hydrological and meteorological factors on sediment transport.

Methods Based on the measured hydrological and meteorological data from 1961 to 2018, the Mann-Kendall test method was used to analyze the trend change characteristics of sediment discharge, and the wavelet analysis method was used to analyze the periodic change law of sediment discharge. The significant influencing factors of sediment changes were screened by stepwise regression analysis. The direct and indirect path coefficients and decision coefficients of each factor on sediment discharge were calculated by path analysis, and then the direct, indirect and comprehensive effects were analyzed.

Results 1) The annual distribution of sediment was uneven, showing a single peak distribution, mainly concentrated in April to June; the annual sediment showed an extremely significant decreasing trend (P < 0.01). In terms of periodic variation, there were mainly three-fold scales of 3-7, 11-19 and 21-30 years, and the first to fourth main periods of sediment variation were 16, 6, 4 and 25 years. 2) The significant indigenous influencing factors of sediment reduction were runoff, wind speed and temperature, and their contribution rates were 52.5%, 28.8% and -18.7%, respectively. 3) The direct path coefficients of runoff, wind speed and temperature to the reduction of sediment transport were 0.73, 0.40 and -0.26; the direct impacts of runoff, wind speed and temperature on sediment reduction were ranked as follows: runoff > wind speed > temperature. The indirect path coefficients were: -0.03, 0.61 and -0.02; the indirect impacts were ranked as follows: wind speed > runoff > temperature. The decision coefficient was: 0.50, 0.14 and 0.17; the comprehensive impacts were ranked as follows: runoff > temperature > wind speed.

Conclusions Runoff, wind speed and temperature have an important influence on the change of sediment in Zhangshui watershed. The decrease of runoff, the decrease of air temperature and the increase of air temperature are the main reasons for the decrease of sediment in Zhangshui watershed. The research results can lay a theoretical foundation for watershed water and sediment regulation and comprehensive control of soil and water loss.