Sediment Load Variation in Typical Watersheds of the North–South Transitional Zone, China

ABSTRACT The north–south transitional zone (NSTZ) is a key geographic and ecological transition zone in China. The runoff and sediment load (SL) of rivers in this zone have changed significantly, directly influencing the ecological restoration and exploitation of water resources in water basins. The previous studies have focused on one water basin; however, few studies have systematically investigated the spatiotemporal variation characteristics of SL and their driving factors in the rivers of the entire zone. Thus, this study attempted to probe the spatiotemporal variation of SL and its contributing factors in the Han River basin (HRB), Jialing River basin (JRB) and the mainstream of the Wei River basin (WRB) in the transitional zone, using observed data from 56 representative hydrological stations in this region from 1961 to 2019. The results indicated that the annual SL decreased significantly during 1961–2019 at each hydrological station ( p < 0.01). The SL of Xianyang, Huangzhuang and Beibei stations during 2010–2019 had decreased more than 83%, compared to that of the 1960s. The annual SL exhibited different abrupt change points, mainly occurred in the late 1960s and around the 1990s. The specific sediment yield (SSY) of the study area was lower in the east and higher in the west. Meanwhile, the SSY displayed a generally declining trend with time. Human activity was the leading contributing factor, accounting for greater than 94% of the total SL reduction. In summary, the SL reduction in the WRB was primarily affected by soil and water conservation practices, whereas it was related to ecological restoration projects and cascade reservoirs in the HRB and JRB. The results of this study are valuable for soil erosion control and comprehensive reclamation of river basins in different regions under complicated conditions worldwide.