Final answer:
Sand and gravel are part of the river's bed load, as they are large enough to be rolled or bounced along the riverbed. Clay is carried in suspension rather than as bed load, and ions are dissolved in the water and do not constitute bed load.
Step-by-step explanation:
The bed load of a river primarily includes materials that are too heavy or too large to be held up by the turbulence of a river's current for an extended time. These materials roll, slide or bounce along the bottom of the streambed. Part of the bed load would include sand and gravel, as they are coarse enough to be moved in this way. On the other hand, clay, while present in the river's transport system, is typically fine-grained enough to be carried in suspension, rather than as part of the bed load. Ions would not be considered part of the bed load as they are dissolved in the water.
To clarify the sizes and modes of transport for sediments, pebbles and cobbles are also transported as bed load, but due to their larger size compared to sand and gravel, they move less frequently, usually during periods of higher water velocity. Silt and clay are much finer particles that are typically suspended in the water column or carried as part of the wash load, which is suspended material that does not settle out rapidly and is carried for extended distances.
Understanding these distinctions is crucial when studying sediment deposits and inferring past depositional environments and climates. Characteristics such as graded bedding and load casts can provide insights into the energy levels and transport mechanisms of sediments at the time of deposition.