Question

If you collect a jar of water from a stream, what part of its load will settle to the bottom of the jar? What portion will remain in the water indefinitely? What part of the stream's load would probably not be represented in your sample?

Short answer

Bed load settles, suspended load may remain indefinitely, and very large bed load particles might not be in the sample.

Step-by-step solution

Understand Stream Load Components

Stream loads consist of three main categories: bed load, suspended load, and dissolved load. The bed load consists of larger particles that roll or bounce along the stream's bottom. The suspended load includes finer particles like silt and clay that remain in suspension within the water column. The dissolved load is composed of soluble materials present in the water as ions.

Identify Components That Settle

In a jar of water taken from a stream, the portion of the load that is most likely to settle to the bottom is the bed load. This includes the larger particles that were originally rolling or sliding along the stream bed. Once the water becomes stationary in the jar, these particles will settle due to gravity.

Determine Components That Remain Suspended

The suspended load, primarily made of smaller particles like silt and clay, will remain in suspension for an extended period. In a jar of water, these particles take longer to settle compared to larger particles. In some cases, they can remain indefinitely due to their small size and the jar's limited depth and movement.

Analyze Components That Dissolve

The dissolved load will not be visible and will remain in the water as dissolved ions. These substances are part of the chemical load and will not settle but stay mixed in the water throughout.

Evaluate Missing Components

The portion of the load that might not be represented in your jar sample is the bed load that is too large to be picked up in your sample. Very large rocks and particles that are normally found at the streambed will not appear in a small jar of water.

Key concepts

Bed Load

Imagine a steady river flowing across a rocky bed. The bed load consists of the larger materials like sand, gravel, and small rocks that tumble or slide along the river bottom rather than suspending within the flowing water. These materials are driven by the water's current but are too heavy to be lifted off the bed entirely.

When you collect water from a stream and place it in a jar, the bed load tends to settle down quickly. Since the jar stops the flow, gravity takes over, causing these particles to drop to the bottom.

• Typically includes sand, gravel, and small rocks.
• Tumbles or rolls along the stream bed.
• Does not stay suspended when water flow stops.

Even if the water was once moving swiftly, in the jar, these larger particles rest at the bottom, making them easy to identify as they contrast against the clearer water above.

Suspended Load

Picture tiny specks swirling within the current of a lively stream. The suspended load in a stream is composed of finer particles such as silt and clay that float within the water rather than dragging along the bottom. These particles remain suspended thanks to the turbulence and energy of the moving water, which can carry them for long distances.

When the water is poured into a jar, these particles will stay afloat for a much longer time compared to the bed load. Sometimes, because of their small size and the reduced movement in the jar, they can stay dispersed indefinitely.

• Composed of small particles like silt and clay.
• Remains above the stream bed, carried by the water's energy.
• Settles slower than bed load once flow halts.

Over time, you may notice some settling, but they can remain suspended with even minor disturbances, like shaking the jar or slight movements.

Dissolved Load

Invisible to the naked eye, the dissolved load is the component of a stream's load made of dissolved materials, essentially turning the water into a mineral-rich solution. This load contains ions from soluble substances like salts and minerals that dissolve in the water.

When you fill a jar with stream water, these dissolved substances blend uniformly with the water. Unlike other load types, the dissolved load does not settle to the bottom or hang suspended in a visible form; it stays mixed within the water.

• Consists of dissolved ions and salts.
• Cannot be seen as separate particles.
• Remains entirely dissolved, much like sugar in tea.

Because it's distributed evenly, even as the water sits undisturbed, its presence is constant and pervasive, representing a chemical aspect of the stream that sampling for larger particles might overlook.