黄土高原河流悬沙粒径时空变异及驱动因素研究

Spatiotemporal variations and driving factors of grain size of suspended sediment in the Chinese Loess Plateau rivers

关键词:  悬沙粒径  时空变异  驱动因素  生态影响  黄土高原

Key words:  grain size of suspended sediment  spatiotemporal variations  driving factors  ecological impacts  the Chinese Loess Plateau

摘要:

悬沙粒径是研究水沙运动必不可少的参数，黄土高原作为世界上水土流失最严重的地区，每年向黄河及其众多支流输送的大量粗粒径泥沙，对泥沙输运和下游水环境产生了不可忽视的影响。关于该地区河流悬沙粒径变异特征的研究一直是学界关注的重点和热点。文章以黄土高原河流悬沙粒径时空变异为分析主体，采用30余年的悬沙粒径观测数据，分析阐述黄土高原河流悬沙粒径的时空变异特点，归纳水力、风力、下垫面条件和人为活动对河流悬沙粒径的影响和驱动机制，总结河流悬沙粒径变异对水生态系统的影响，并指出在全球气候变化和人类活动加剧的背景下，未来还需持续关注悬沙粒径时空变异特征及对全球变化的响应。主要结论如下：（1）黄土高原河流悬沙粒径在空间上的变化受各因素综合影响，整体上呈自西北至东南方向减小趋势，年平均降水量越低，风力作用越强，植被覆盖面积越小时， 悬沙粒径越粗；从时序角度来看，汛期悬沙中值粒径明显小于非汛期，且秋冬两季悬沙粒径变异情况最为显著；（2）悬沙粒径变异受气象水文、地质地貌及人为活动等因素综合影响，强烈的生产建设活动会导致悬沙粒径显著粗化；（3）关注悬沙粒径变异对水生生物的养护、河口生态系统保护等具有重要意义。

Abstract:

Background, aim, and scope Grain size of suspended sediment is a fundamental parameter in the study of sediment transport. As one of the most serious areas of soil erosion in the world, the Chinese Loess Plateau delivers a considerable amount of sediment to the main stem and tributaries of the Yellow River, exerting significant impacts on downstream sediment dynamics and aquatic environments. Research on the spatiotemporal variability of suspended sediment grain size in this region has long been a central focus. This study aims to synthesize findings on the spatiotemporal patterns of suspended sediment grain size in rivers of the Chinese Loess Plateau, analyze the driving mechanisms, summarize ecological impacts, and identify future research priorities in the context of global change. Materials and methods Suspended sediment grain size data from fifteen major hydrological stations along the main stem and tributaries of the Yellow River during 1987—2020 were used to analyze spatial variability. Temporal variability was examined by incorporating additional stations with relatively complete observation records based on data availability. Monthly mean grain size distribution data from the Toudaoguai, Longmen, and Huaxian stations in 1975, 1985, 1990, and 2010, as well as from the Wubu and Gaojiachuan stations during 2006—2016, were also included. One-way analysis of variance, linear trend analysis, and descriptive statistics were applied to investigate spatiotemporal variability in suspended sediment grain size. Results (1) From 1987 to 2020, grain size of suspended sediment in the Chinese Loess Plateau rivers exhibited significant spatial variability. Along the main stem, suspended sediment grain size increased markedly beginning at Toudaoguai on the middle reach, and thereafter showed a gradual decrease from north to south. For tributaries, the annual median grain size of suspended sediment generally decreased from the northwest toward the southeast, with the overall spatial pattern consistent with changes in surface material characteristics. (2) Grain size of suspended sediment in the Chinese Loess Plateau rivers showed pronounced intra-annual variation. During the non-flood season (December—May), suspended sediment was coarser, whereas during the flood season (June—October) grain size became significantly finer. At the seasonal scale, the pattern followed the order winter＞autumn＞spring＞summer, with the greatest variability occurring in summer and winter. (3) Interannual trends in suspended sediment grain size differed markedly among stations. Most stations exhibited weak correlations (with a maximum R² of 0.52), and only a few key main stem stations (Toudaoguai, Longmen, Xiaolangdi, and Huayuankou) showed an overall coarsening trend. The remaining stations displayed varying degrees of fining or abrupt changes. (4) The response of suspended sediment grain size to external driving factors was complex, with its characteristics being closely influenced by precipitation, wind action, and watershed geomorphology. Lower annual mean precipitation, higher frequency of extreme rainfall events, stronger wind forces, and lower vegetation cover all tended to increase suspended sediment grain size. Discussion When analyzing changes in suspended sediment grain size in rivers, it is essential to consider the integrated effects of hydrological and sediment regimes, basin geomorphology, regional climate, and anthropogenic activities. Relying on a single factor is inadequate, as sediment dynamics are governed by complex, often non-linear interactions among these drivers. Under ongoing ecological restoration and soil conservation measures, suspended sediment concentrations in rivers across the Chinese Loess Plateau are projected to decline further, accompanied by a continued fining of sediment grains. This trend reflects not only a reduction in erosive coarse sediment supply but also shifts in flow energy and sediment connectivity within the watershed. Conclusions The grain size of suspended sediment in the Chinese Loess Plateau rivers has significant temporal and spatial variability, which is driven by multiple factors. The study concerned about important value for ecological protection, environmental governance, planning, development, etc. Recommendations and perspectives There have been numerous studies on the relationship between variations in suspended sediment concentration and the health of aquatic ecosystems, but there have been relatively few on the impact of variations in suspended sediment grain size on aquatic ecosystems. This issue needs to be clarified as soon as possible in order to protect aquatic organisms.