Spatial Trends and Drivers of Bedload and Suspended Sediment Fluxes in Global Rivers

Bedload is notoriously challenging to measure and model; its dynamics, therefore, remains largely unknown in most fluvial systems worldwide. We present results from a global scale bedload flux model as part of the WBMsed modeling framework that well predict the distribution of water discharge, suspended sediment and bedload. The sensitivity of bedload predictions to river slope, particle size, discharge, river width, and suspended sediment were analyzed, showing the model to be most responsive to spatial dynamics in river discharge and slope. The relationship between bedload and total sediment flux is analyzed globally, and for representative longitudinal river profiles (Amazon, Mississippi, and Lena Rivers). The results show that while the proportion of bedload decreases from headwaters to the coasts, there is considerable variability between basins and along river corridors. The topographic and hydrological longitudinal profiles of rivers are shown to be the key drivers of bedload trends, with fluctuations in slope controlling its more local dynamics. Estimates of water and sediment fluxes to global oceans from 2,067 largest river outlets (draining 67% of the global continental area) are provided. Estimated water discharge at 30,579 km3/y corresponds well to past estimates; however, sediment flux is higher. Total global particulate load of 17.8 Gt/y is delivered to global oceans, 14.8 Gt/y as washload, 1.1 Gt/y as bedload, and 2.6 Gt/y as suspended bed material. The largest 25 rivers are predicted to transport more than half of the total sediment flux to global oceans. Plain Language Summary Sediment carried by rivers varies considerably in space and time as a function of hydrological and environmental characteristics, and human‐made modifications of river systems. Understanding and predicting the sediment dynamics within river systems are important, as they have direct impacts on the functioning of riverine and coastal ecosystems, water quality and use, and chemical dynamics of the Earth System as a whole (e.g., carbon fluxes). Sediment is transported in three modes: suspension for small particles, bedload for larger particles, and suspended bed material for medium particles. Bedload and suspended bed material are difficult to measure and model and thus remain largely unknown in most river systems. In this paper, we present new components to the WBMsed global hydro‐geomorphic modeling framework that estimate bedload and suspended bed material fluxes for