Spatio-temporal Distributions Of Suspended Sediment Load Of Global Rivers And Its Influencing Factors Analysis

The transport of sediment by rivers to the oceans is an important part of the biogeochemical cycle,a key component of the global erosion system,and an important measure of land degradation and global soil resource reduction.Studying the changes of global river sediment load is of great importance in studying the land surface processes and the material cycle of terrestrial ocean systems,like carbon cycling.Studying the distribution and timing of river sediment load and its influencing factors from global scale is also important to understand the general rule of river sediment load.And it is also important to understand the impact of human activities on river sediment transport.Over the past 50 years,many of the world’s rivers have experienced significant changes in the context of climate change and human activity.Reginal studies explained the trend and its influencing factors of river sediment load in the time scale.However,there are few studies on the sediment load of rivers from the global scale.The spatial distribution pattern of global river sediment load and its influencing factors have been just started in foreign countries.Based on 657 rivers sediment load data,this study employed mathematical statistics and spatial analysis method to analyze spatial distribution and influencing factors of suspended sediment load（SSL）of global rivers.Based on 8 representative rivers in different climate zone,this study employed mathematical statistics to analyze temporal distribution and influencing factors of SSL;On this basis,the future trend of global river sediment transport is forecasted based on the changing trend of each influencing factor.The results are as follows:（1）The total SSL of global rivers was estimated to be about 1.5-2.0×10¹⁰ t in recent years.Due to the non-stationary characteristics and spatial differences of suspended sediment,such values need to be carefully accepted.Overall,the mean annual SSL in Asia was the largest,accounting for more than half of the world’s total SSL,followed by Oceania,South America,North America,Africa and Europe.（2）There was no significant correlation between the precipitation and the sediment yield.Runoff was significantly linearly related to the sediment transport,especially after the drainage basins were divided into different climate zone by runoff.The correlation between runoff and SSL was 0.99 in humid climate zone.Generally,SSL increased with the increase of the basin area,but there was significant difference of SSL among the drainage basin with the same area.The drainage basins were classified according to terrain and geological conditions.The SSL of alpine rivers are one to three orders of magnitude higher than the lowland rivers.The annual sediment transport in the Cenozoic strata is higher than that in the Pre-Mesozoic drainage basin.（3）By using Mann-Kendall test and linear regression for trend test,the precipitation,runoff and SSL in eight representative drainage basin of each climate zone was studied.The results showed that the SSL of the Arctic and tropical representative river show an increasing trend while other rivers show decreasing trend.In addition to the two tropical rivers,the change trend of other rivers was extremely significant.There was no significant change in the runoff of the other rivers except the Yellow River and the Mississippi River.The river discharge of the Mississippi River showed a significant increase trend while the SSL showed a significant decrease trend.Therefore,the impact of climate change on SSL was not significant.In contrast,human activities,especially dam construction,had a greater impact on SSL.Preliminary estimates indicated that the SSL intercepted by the global dam is up to 4.4×10¹⁰ t,which is more than twice as much as the SSL to the coastal ocean.Dam should be taken as an important factor to analyze the causes of river SSL change.In developing countries,due to deforestation,mining or urbanization,the land use will still face a significant change and may cause a significant increase in SSL.（4）Compared with the trend change of precipitation,the extreme precipitation events caused by climate change had a greater impact on the SSL,and the researchers need to study the extreme precipitation events and their environmental effects furtherly.Land use change caused by land reclamation,mining and urbanization in local areas will lead to an increase in SSL,which is mainly concentrated in developing countries like Africa and South America.However,due to the large-scale construction of dams,the future global total SSL will continue to decrease.