Summary
Sediment particles finer than 60μm are not uniformly distributed in suspension in waters of the Amazon and Solimões Rivers. Concentrations of such tine particles at the river surface are only half as large as their concentrations in the full water column. Particles as small as 10μm are less concentrated near the river surface than at greater depths. Estimates of sediment yield and flux of suspended chemical constituents that are based only on surface samples are likely to contain significant errors.